Mechanical disruption of seagrass in the digestive tract of the dugong

Mechanical disruption of seagrass in the digestive tract of 

the dugong 

J. M. Lanyon & G. D. Sanson 

School of Biological Sciences, Monash University, Clayton, Vic., Australia 

Journal of Zoology. Print ISSN 0952-8369 

Keywords 

dugong; mouthparts; diet; seagrass; 

digestion; mechanical breakdown. 

Correspondence 

Janet M. Lanyon. Current address: School 

of Integrative Biology, The University of 

Queensland, St Lucia, Qld 4072, Australia. 

Tel: (07) 3365 4416; Fax: (07) 3365 1655 

Email: j.lanyon@uq.edu.au 

Received 8 June 2005; accepted 

30 January 2006 

doi:10.1111/j.1469-7998.2006.00135.x 

Abstract 

The cheek teeth in dugongs are considered to be largely non-functional whereas 

the oral horny pads are important both in mechanical disruption of the diet and in 

conveying seagrass through the mouth. Particle size distributions of digesta from 

41 dead stranded dugongs were examined to investigate the relationship between 

degree of food breakdown, gut region and functional surface area of the 

mouthparts. The in vitro ease of fracture of major dietary seagrass species were 

compared. The rate of food breakdown through the gut appears to be more closely 

linked to fibre level of the diet than to size or age of the dugong and its mouthparts. 

Low fibre seagrass, for example Halophila ovalis, breaks down at a faster rate than 

high fibre seagrass, for example Zostera capricorni both in dugong guts and 

in vitro. Several structural characteristics of seagrass, including level and arrangement 

of fibre, and water content, make it particularly amenable to mechanical 

breakdown. The soft mouthparts of the dugong are highly modified so that the 

entire oral cavity functions to crush low fibre seagrasses. Thus, the dugong has 

developed an efficient method of food ingestion and mastication that is suited to 

processing large quantities of soft seagrass during short dive times. The potential 

cost to the dugong in having lost its hard dental surfaces is that it has become 

restricted to a low fibre diet. 

Introduction 

Dugongs are large marine herbivores that feed almost 

exclusively on a few species of seagrass (Wake, 1975; Marsh 

et al., 1982; Lanyon, Limpus & Marsh, 1989; Preen, 1993). 

Like their close relatives, the manatees, dugongs are hindgut 

fermenters, relying on symbiotic organisms in an expanded 

colon to ferment the fibrous portion of the diet (Murray 

et al., 1977; Goto et al., 2004). However, unlike the manatee 

and other hindgut-fermenting mammalian herbivores, the 

dugong does not show extreme dental development consistent 

with a strategy of maximizing cell content release 

(Lanyon & Sanson, 2006). Typically, hindgut fermenters 

have placed a premium on a functionally effective dentition, 

with adaptations that may include increased size of the 

cheek tooth row and/or diverse mechanisms for the maintenance 

of cutting edges or grinding surfaces (Vorontsov, 

1967; Fortelius, 1985). Although the three species of living 

manatee all have enamelled bilophodont teeth that are 

replaced sequentially throughout life via molar progression 

(Sanson, 1977; Domning, 1982), the dugong has a degenerate 

dentition (Lanyon & Sanson, 2006). The simple peglike 

cheek teeth of the dugong are relatively small for the 

body size compared with other hindgut-fermenting mammals, 

are simple in structure and are composed of soft 

dentine (Lanyon & Sanson, 2006). In contrast, the soft 

mouthparts of the dugong, including the opposing horny 

pads and the palate and tongue, are greatly developed 

(Marsh & Eisentraut, 1984; Marshall et al., 2003) and may 

function not only in disruption of seagrass but also 

in transporting seagrass through the mouth (Lanyon & 

Sanson, 2006). 

The high digestibility of the diet (Murray et al., 1977) and 

the finely ground nature of particulate matter in dugong 

stomach contents (Marsh, Heinsohn & Spain, 1977; Marsh, 

Beck & Vargo, 1999) indicate that some mechanical breakdown 

of seagrass probably occurs in the anterior part of the 

digestive tract, presumably by these mouthparts. Food 

particle breakdown, or the amount of new food surface area 

produced during mastication, is likely to be a function of the 

crushing surfaces of the functional mouthparts (Lanyon & 

Sanson, 1986). It may also be influenced by body size (Bae, 

Welch & Gilman, 1983), food intake (e.g. Santini et al., 

1983), as well as the nature of the food (Rensberger, 1973; 

Bailey et al., 1990), and processing time (i.e. amount of 

chewing). Occlusal efficiency may be defined in terms of the 

proportion of small particles relative to large particles that 

are produced by the mouthparts (Lanyon & Sanson, 1986), 

and can be described in terms of the particle size distribution 

of digesta in the stomach of a hindgut fermenter. Reduction 

of food particle size affects the capacity of the gut for 

enzymatic and fermentative digestion, and the overall 

digestibility of the diet (Spalinger, Robbins & Hanley, 

1986). 

Journal of Zoology 270 (2006) 277–289 c 2006 The Authors. Journal compilation c 2006 The Zoological Society of London 277

Mechanical disruption of seagrass by the dugong 

J. M. Lanyon and G. D. Sanson 

This paper investigates the degree of breakdown of 

seagrass digesta along the gut of dugongs and relates this to 

the functional surface area of the mouthparts and nature of 

the diet. We examine how dugongs cope with a fibrous plant 

diet in the absence of an effective hard dentition. 

Methods 

Digesta analysis 

Digesta samples were obtained from 41 dugongs. These 

samples included stomach samples in 10% neutral buffered 

formalin from 29 dugongs that had accidentally drowned in 

set nets in north Queensland, and now form part of the 

Museum of Tropical Queensland specimen collection. Skull 

and mouthparts measurements were possible for 28 specimens. 

Faecal samples were available from two captive and 

five wild animals. 

In addition, five fresh whole digestive tracts (four adults 

and one calf) were obtained from dugongs that had been 

accidentally drowned or hunted in northern Australia during 

the course of this study. These tracts were frozen soon 

after collection. Digesta samples (up to 250 g) were obtained 

from five regions along each complete adult digestive tract 

when available: (1) the anterior region of the stomach, 

(2) the anterior small intestine (duodenum), (3) the posterior 

small intestine, (4) the caecum and (5) the posterior colon 

(=faeces). In the calf, digesta samples were available from 

the stomach and colon only. Extracted gut contents were 

fixed in 10% neutral buffered formalin. 

Dietary composition 

The dietary composition of each digesta sample was determined 

to genus using a micro-stereological technique 

(Channells & Morrissey, 1981; Lanyon, 1986). In most 

cases, digesta could only be identified from leaf material of 

the largest particle size classes (41.6 mm) so that the bulk of 

each stomach sample could not be identified. Apparent 

dietary composition was expressed in terms of percentage 

volume of each identifiable genus of seagrass present. 

Particle size distribution 

Digesta samples were wet sieved into eight particle size 

classes using Endecott sieves with mesh sizes of 4 mm, 

1.6 mm, 1 mm, 500 mm, 250 mm, 125 mm and 75 mm. To 

alleviate the problem of particles being deformed and forced 

through the sieve, water pressure was minimized. Particles 

were separated on the basis of maximum dimension. The 

particulate content of each sieve was oven dried at 55 1C 

overnight to constant weight. Particulate matter from the 

washings of the finest sieve was collected through centrifuging 

and filtering. It was considered that the amount of 

matter filtered through paper with pore size 6 mm was 

negligible because the filtrate was clear. All particles from 

the largest sieve size, that is 44 mm, had maximum dimensions 

of o8 mm. 

Mouthparts 

The results of the investigation into the morphology and 

functional occlusion of the dentition of a total of 57 dugong 

specimens have been presented elsewhere (Lanyon & Sanson, 

2006). Crown surface areas of cheek teeth from these 

dead stranded dugongs from tropical north Queensland 

were measured. For 29 of these specimens, digesta contents 

were also available (see above). The surface area of each 

erupted cheek tooth was digitized in planar view from 

tracings made using a Nikon V12 profile projector at 5 

magnification under reflected light. These measurements 

were considered representative because dugong teeth wear 

relatively flat with age. Occlusal or functional surface area 

was estimated by subtracting non-functional tooth areas 

[i.e. those coated with calculus, partially erupted or nonoccluding 

teeth (Sanson, 1980)], from the total tooth surface 

area (Lanyon & Sanson, 2006). 

For each of 57 specimens, the surface area of the lower 

horny pad was measured through approximation to the 

surface area of the underlying bony attachment area on the 

symphysial part of the mandible (Lanyon & Sanson, 2006). 

The anterior edge of the horny pad was defined as running 

along the edge of the most anterior incisor socket, and the 

posterior edge along the dorsal margin of the deflected 

portion of the dentary, that is the posterior end of the lower 

incisor socket row (Fig. 1). The surface area of each traced 

lower pad was measured digitally on an image analyser. 

Because the upper and lower pads work in opposition, the 

lower pad was considered to be representative of the functional 

pad area. The surface area of mouthparts (dentition 

and horny pads) was expressed in terms of age across 

specimens from a wide age range (o1 to 46 years; animals 

of age o1 year were given an age of 0.5 years) for which 

intact skulls were available. The age of each dugong specimen 

had previously been estimated by counting the dentinal 

growth layer groups in the erupted and non-erupted tusks 

(Marsh, 1980). 

In vitro breakdown of seagrass 

Leaf samples of five seagrasses that form part of the 

dugong’s diet [Halophila ovalis, Halodule (narrow-leaf 

morph), Halodule uninervis (broad-leaf morph), Cymodocea 

serrulata and Zostera capricorni] and three common Australian 

terrestrial pasture grasses [Triticum aestivum 

(19-day-old wheat), Koeleria setacea and Erharta erecta] 

were subjected to in vitro mechanical damage to compare 

their susceptibility to fracture. Similar-sized samples of each 

of the fresh grasses were placed in 40 mL of 0.1 M phosphate 

buffer (pH 6.8) within individual lubricated, thin-walled, 

dot-ribbed, supersensitive latex balloons. Each sample was 

subjected to 60 min of grinding under constant pressure in a 

peristaltic pump fitted with metal rollers. Resultant plant 

breakdown was assessed visually and qualitatively. Further, 

278 

Journal of Zoology 270 (2006) 277–289 c 2006 The Authors. Journal compilation c 2006 The Zoological Society of London



weight of particles per size class was expressed as a percentage 

of the total dry weight of the sample. 

In order to examine the effects of plant cell lysis under 

acidic conditions that are likely to be experienced in a 

dugong’s stomach, the five species of seagrass were subjected 

to 2, 3 and 4 h periods in solutions of pH 7.8, 6.8, 5, 3 

and 1.5. These levels covered the range of pH conditions 

likely to be encountered within the anterior part of a 

dugong’s gut (Kenchington, 1972; Marsh et al., 1977) and 

included a control pH of 7.8 to mimic seawater (Dring, 

1982). The pH of a 0.1 M phosphate buffer was decreased by 

the dropwise addition of HCl. Equal blotted wet weights of 

fresh seagrass and equal volumes of buffer solution were 

used under each trial and pH treatment. Samples were 

examined for evidence of cell rupture. 

Fibre analysis 

Leaf samples (n=5) of each of five seagrass species were 

collected from intertidal seagrass meadows close to Townsville 

in north Queensland (Shelly Beach and Rowes Bay). 

These meadows are frequented by feeding dugongs 

(J. M. Lanyon, pers. obs.). These seagrasses along with leaf 

samples (n=1) from three terrestrial grasses (see above) 

were analysed for neutral detergent fibre (NDF) level, 

following the procedure of Van Soest & Wine (1967) using 

a Tecator Fibretec system. 

Figure 1 Anterior view of the downturned symphysial portion of the 

mandible showing the four pairs of vestigial incisor sockets, including 

one incisor in the third right socket (arrowed). The area within the 

dotted line is the area measured as horny pad surface area. Scale 

bar=5 cm. 

samples of each species were dried at 55 1C to constant 

weight to control for structural damage that may result as a 

function of cell turgidity due to water content, particularly 

in seagrasses. These dried whole samples were subjected to 

the same grinding treatment. 

Both terrestrial and marine grass species vary markedly in 

terms of overall size and shape, gross arrangement of 

vascular bundles (fibre) and water content, and each of these 

characters probably contributes to the ease of physical 

breakdown. To control for these variables, samples of each 

grass were dried at 55 1C overnight and then milled to pass 

through a 1 mm mesh sieve. Each sample was further 

ground 0, 100 and 500 times in a mortar and pestle under 

constant pressure to obtain a crude index of the physical 

damage caused by the grinding action of the mouthparts 

and the muscular action of the gut of the dugong, and as a 

measure of the differential resistance to mechanical action at 

a more cellular level. Ground samples were wet-sieved into 

seven particle size classes using Endecott sieves with mesh 

sizes 1.6 mm, 1 mm, 500 mm, 250 mm, 125 mm and 75 mm. 

Particulate matter from the last size class o75 mm was 

collected by centrifuging all water collected from the final 

sieve and drying and weighing the resultant pellet. The dry 

Statistical analysis 

The particle size distributions of digesta from various gut 

regions were plotted as frequency histograms, with particle 

size classes plotted as equal intervals along the x-axis. 

Because the distributions were often skewed, the median 

(M) particle size (mm) was considered to be a more valid 

measure of location of ‘average’ particle size per sample 

than the arithmetic mean (Sokal & Rohlf, 1969). 

The relationships between particle size of digesta and size 

of mouthparts were examined by multiple regression. Because 

particle size distribution in the stomach may be 

attributable to mechanical breakdown by the masticatory 

process, median particle size for each of the 30 stomachs was 

regressed against total surface areas of the cheek teeth and 

of the horny pad. The multiple regression model had median 

particle size (M) as the dependent variable, and total surface 

areas of the cheek teeth and the horny pad as the independent 

variables. The model was run as an interactive backwards 

stepwise multiple regression, with each factor 

removed on the basis of the least significant F-value until 

the most significant factor(s) or model remained. 

Particle size distributions produced by grinding leaf fractions 

of each of the eight grasses were plotted as histograms. 

For each particle size distribution, median particle size was 

calculated from the cumulative frequency curve of the 

weight of particulate matter against particle size, where the 

median (M) particle size corresponded to 50% cumulative 

frequency. The median values are likely to be more appropriate 

descriptors of the central tendencies of the 




distributions, especially if they are skewed. The change in 

median particle size between 0 and 500 grinds is indicative of 

the overall effects of grinding for each plant species. These 

values (=‘breakability index’) were compared. 

Results 

Size of mouthparts 

The occlusal surface area of cheek teeth ranged from 24 mm 2 

in a dugong aged o0.5 years to 485 mm 2 in an adult dugong 

aged 21 years, and was significantly regressed against skull 

length and age (F=32.12; d.f.=1, 51; Po0.0001; adj 

R 2 =0.36; n=52; Fig. 2). However, the coefficient of variation 

(CV) in occlusal surface area was high (CV=35.05), 

even when only adults were compared. 

The surface area of the lower horny pad ranged from 

901 mm 2 in dugongs aged 0.5 years to 6280 mm 2 in the 

largest adults, with a mean of 4933 109 for adult dugongs. 

Horny pad surface area was highly significantly regressed 

against body size (F=433.28; d.f.=1, 53; Po0.0001; adj 

R 2 =0.91; n=54) and followed an exponential growth 

curve against age (Fig. 2). The CV for the horny pad surface 

area of adult dugongs (CV=12.73) was considerably lower 

than that for the dental occlusal surface area of adults. The 

absolute surface area of the horny pads was up to nine times 

greater than the occlusal surface area of the cheek teeth. 

Digesta analysis 

Diet composition 

Twenty-seven of the 29 dugongs had fed on more than one 

seagrass genus and some on up to four or five. Seagrass 

genera recorded most frequently included Halophila, Halodule, 

Cymodocea, Thalassia and Zostera. One dugong had 

ingested some Enhalus. The most frequently ingested genera 

Surface area (mm ) 

7000 

6000 

5000 

4000 

3000 

2000 

1000 

0 

SA teeth 

Sa horny pad 

Satotal 

Log. (SA teeth) 

Log. (Sa horny pad) 

Log. (Satotal) 

y = 1102.9 Ln(x) + 1793.1 

R = 0.9309 

y = 1044.7 Ln(x) + 1674 

R = 0.9182 

y = 58.382 Ln(x) + 118.46 

R = 0.3648 

a 

0 5 10 15 20 25 30 35 40 45 50 

Age (years) 

Figure 2 Surface area (mm 2 ) of (a) functional cheek teeth, (b) lower 

horny pad and (c) total functional mouthparts (cheek teeth plus lower 

horny pad; all log-transformed) plotted against age (years). Lines of 

best fit included. 

c 

b 

recorded were Halophila and Halodule. Two dugongs had 

fed on only one seagrass genus, Halodule. Ten per cent of 

dugongs had identifiable algal fragments in their digesta. 

However, because digesta could only be identified from the 

largest particle size classes, seagrasses that were more amenable 

to breakdown during mastication (see below) would 

have been underestimated. Consequently, composition of 

diet could not be examined as a variable affecting particle 

size breakdown. 

Stomach contents 

In general, the stomach contents were well macerated. 

However, there was considerable variation in particle size 

distribution curves for the stomach contents of different 

dugongs. Figure 3 shows some representative stomach 

particle size distributions of dugongs of different ages. 

Median particle size ranged between 302.8 and 3454.3 mm, 

with a mean of 1241.8 141.98 mm (n=29; Table 1). The 

CV in median particle size (for stomachs pooled) was high 

at 62.6. 

The multiple regression model, with median particle size 

as the dependent variable, and total surface areas of the 

cheek teeth and the horny pad as independent variables, 

accounted for only 1% of the variation, R 2 =0.01, with 

none of the factors significantly regressed (P40.05). This 

suggests that particle size distributions in the stomachs of 

dugongs are not simply a function of the masticatory surface 

areas. 

Whole guts 

Particle size frequency histograms for each of five gut 

regions of three dugongs (for which the contents of each 

gut region were available) are shown in Fig. 4. Table 2 

compares the range, mean SE and CV for median particle 

size of each of five gut regions. Median particle size 

decreased progressively down the gut with a reduction 

in particle size distribution occurring at each gut region 

(Fig. 5), indicating significant post-oral particle size reduction. 

There was variation between specimens, both in 

particle size distributions within each gut region and differences 

in distributions between regions (Fig. 4). 

There was consistent particle reduction down each gut 

despite the fact that diet composition probably altered along 

each gut. Species composition of digesta was based on 

stomach digesta analysis only, because it was usually impossible 

to identify seagrass to generic level past the 

stomach, due to further particle reduction. However in the 

case of two of the three dugongs, Z. capricorni was identifiable 

in the hindgut. 

The amount of particle size reduction that was attributable 

to mastication by the mouthparts could not be quantified. 

However, based on the degree of mastication of digesta 

in the cardiac region of the stomach (i.e. all particles were 

less than 8 mm in maximum dimension), this was generally 

considerable. By examining the changes in median particle 

280 




(a) 

% of total 

dry weight 

(b) 


dry weight 

(c) 


dry weight 

mm 73 

30 

20 

10 

0 

mm 69 

30 

20 

10 

0 

mm 77 

30 

20 

10 

0 

(d) mm 148 

30 

20 

10 

0 


dry weight 

(e) mm 136 

30 

20 

10 

0 


dry weight 

(f) 


dry weight 

mm 102 

30 

20 

10 

0 

Particle size class 

Figure 3 Particle size distributions (% total dry weight) of the stomach 

contents of dugongs of different ages (years): (a) 5, (b) 9, (c) 14, (d) 19, 

(e) 21, (f) 34 years. 

Table 1 Median particle size (mm) of digesta in the stomachs and 

faeces of dugongs (mean SE; n=number of specimens) 

Median particle size (mm) 

Gut region n Mean SE Range 

CV 

Stomach 35 1241 141 302.8–3454.3 60.98 

Faeces 11 83 11 44.5–150.9 44.43 

With Zostera 3 138.6 8.4 122.5–150.9 10.49 

No Zostera 8 62.2 2.9 44.5–73 13.26 

Faecal samples have been divided into those in which seagrass was 

identifiable as Zostera capricorni, and faeces in which identifiable 

pieces of Z. capricorni were absent. CV, coefficient of variation. 

Stomach samples include 30 fixed samples plus five fresh samples 

from whole guts. 

(a) 311 

100 

% of total dry weight 

80 

60 

40 

20 

0 

(b) MB2 

100 


80 

60 

40 

20 

0 

(c) MB1 

100 


80 

60 

40 

20 

0 

Gut region 

> 4.0 mm 

> 1.6 mm 

> 1.0 mm 

> 500 μm 

> 250 μm 

> 125 μm 

> 75 μm 

< 75 μm 

Figure 4 Particle size distributions (% total dry weight) of digesta in 

five different gut regions (stomach, duodenum, small intestine, 

caecum, large intestine) of three dugongs. 

Table 2 Median particle size (mm) of digesta in different gut regions of 

dugongs (mean SE; n=number of specimens) 

Median particle size (mm) 

Gut region n Mean SE Range 

CV 

Stomach 5 1498.7 378.1 770.84–2837.6 56.42 

Duodenum 3 864.6 190.9 533.17–1194.73 38.26 

Small intestine 3 435.8 200.9 72.76–766.41 79.84 

Caecum 3 315.2 144.4 71.29–570.97 79.32 

Large intestine 4 57.91 4.65 44.49–64.38 16.05 

CV, coefficient of variation. 

size from one gut region to another, with a starting point of 

ingesta size in the anterior stomach, it was possible to 

roughly quantify the proportion of particle breakdown 

occurring within each part of the digestive tract. Between 

the anterior cardiac region of the stomach and the duodenum, 

a mean of 47% of total breakdown in the tract occurred 

(Table 3). A mean of 25% of particle reduction occurred in 




2000 

(a) mm 206 

100 

Median particle size 

(μm) (mean ± ) 

1000 


80 

60 

40 

20 

0 

Stomach Duodenum Small 

intestine 

Caecum 

Colon 

Figure 5 Change in median (M) particle size (mm) along the digestive 

tract of three dugongs. 

Table 3 Food particle breakdown (as a percentage of total breakdown 

occurring between the anterior stomach and posterior colon) within 

each of the principal gut regions 

Dugong Stomach Small intestine Caecum Large intestine 

mm 311 42.7 33.3 0.1 23.9 

MB1 70.8 15.1 0.00 14.1 

MB2 28.5 26.6 28.8 16.1 

Mean 47% 25% 10% 18% 

Mean, mean breakdown occurring in each gut region with the three 

specimens pooled. Dominant seagrass genera: mm 311, Halodule; 

MB1, Halophila/Zostera; MB2, Zostera. 

the small intestine, 10% in the caecum and 18% in the large 

intestine. 

There was considerable variation in the amounts of 

breakdown per gut region between specimens (Table 3). It 

is possible that these differences in particle breakdown may 

be attributable to composition of the diet or other factors. 

The diet of dugong MB2 was quite distinct from the other 

two specimens with a high proportion of Z. capricorni. The 

degree of digesta breakdown between the anterior stomach 

and duodenum for this dugong was less than for the others. 

Conversely, particle reduction in the caecum of this animal 

was greater than for the other two specimens. Despite the 

high variation in median particle size in the stomachs, 

duodena, small intestines and caeca (Table 2), the CV for 

the colonic samples (faeces) was relatively low (16.05). 

A comparison was made of the particle distributions of all 

sieved stomach (n=35)andfaecal(n=11) samples (Table 1). 

Representative particle distributions of stomachs and faeces 

are shown in Fig. 6. In all dugongs, except the calf mm 312 

(Fig. 6c), the median particle size of the faeces was significantly 

lower than that of the stomachs (e.g. Fig. 6a, b). The 

CV was high (60.98) for the stomach samples, and also quite 

high when the faecal samples were considered collectively. 

However, the faecal samples could be divided into two 

groups based on seagrass species composition (Table 1). In 

those cases where large particles of leaf and greater proportions 

of these were present (n=3), these were always 

identified as Z. capricorni; the mean particle size was 

138.6 8.4 mm (CV=10.49). Large pieces of Z. capricorni 

pass through the gut in a recognizable state. The other faecal 

0 

(b) mm 201 

100 


80 

60 

40 

20 

0 

(c) mm 312 

100 


80 

60 

40 

20 

0 

samples (n=8) had no recognizable leaf material and the 

mean particle size was lower at 62.24 2.92 mm (CV= 

13.26). This does not necessarily mean that Z. capricorni 

was absent, but that it was not apparent. Thus, despite the 

wide variation in stomach particle size distributions, variation 

among the faecal samples was low. In most of the faecal 

samples, particles caught on the 500 mm sieve consisted of fine 

fibres only. The dugong calf mm 312 (Fig. 6c) had markedly 

different particle size distributions because its stomach 

contained mainly milk, in addition to some fragments of 

Halophila ovalis and algae, and its faeces contained an 

undigested alga. 

In vitro breakdown of seagrass 

Fresh seagrass 

Stomach 

Stomach 

Faeces 

Faeces 

Stomach 

Faeces 

Gut region 

> 4.0 mm 

> 1.6 mm 

> 1.0 mm 

> 500 μm 

> 250 μm 

> 125 μm 

> 75 μm 

< 75 μm 

Figure 6 Comparison of the particle size distributions (% total weight) 

in the stomach contents and faeces of three dugongs. 

Each of the five seagrasses ruptured more easily than the 

terrestrial pasture grasses. Of the leaf fractions compared, 

the thin oval leaves of Halophila ovalis ruptured most easily. 

Next were C. serrulata, Halodule uninervis (n) and Halodule 

uninervis (b) with similar rupturing qualities. All of these 

282 




leaf fractions had the consistency of fresh lettuce leaves and 

were almost brittle, snapping when the leaf blade was bent. 

Sections of the leaf lamina remained joined along the fibrous 

vascular bundles. In contrast, the leaf fraction of Z. capricorni 

did not rupture as easily: sections of the lamina 

remained joined not only along the longitudinal vascular 

fibres but also along the numerous perpendicular crossveins. 

The rhizomes of Halophila ovalis and then C. serrulata 

were the easiest rhizomes to rupture. The rhizomes of 

Z. capricorni remained intact after grinding through the 

peristaltic pump. 

Dried seagrass 

Particle size distributions for each of the seagrasses and 

terrestrial grasses ground 0, 100 and 500 times after initial 

milling are shown in Fig. 7. There was an obvious difference 

in median particle size produced by differential grinding 

(Table 4). In all cases, more grinding resulted in a greater 

frequency of small particulate matter. 

There were marked differences between species with 

respect to particle size distributions produced by different 

amounts of grinding (Table 4, Fig. 7). The breakability 

index is defined as the median particle size resulting from 

milled+0 grinds minus the median particle size resulting 

from milled+500 grinds, that is the degree of shift in median 

particle size as a result of grinding. The breakability index 

and its associated rank in relation to decreasing breakability 

is given for each species (Table 4). Halophila ovalis was the 

most breakable, followed by Halodule uninervis (n) and 

Halodule uninervis (b): these were all more breakable than 

terrestrial grasses. Zostera capricorni was the least breakable 

seagrass and fell within the range measured for terrestrial 

grasses. The breakability index for seagrasses was significantly 

regressed against fibre (%NDF dm; F=56.74; 

d.f.=1, 24; Po0.001; adj R 2 =0.7; Fig. 8). Terrestrial 

grasses were not included as sample sizes were too small. 

Acid lysis 

For each of the five seagrasses and three terrestrial grasses, 

there was no discernible particle size reduction because of 

acid lysis. There was, however, increasing coloration of the 

acidic buffer solution containing seagrasses with decreasing 

pH, suggesting some pH-induced leaching of cellular 

(a) 

100 

80 

60 

% 

40 

20 

0 

Halophila ovalis (e) Zostera capricorni 

Zero 100 500 

100 

80 

60 

40 

20 

0 

Zero 100 500 

(b) 

100 

80 

60 

% 

40 

20 

0 

Halodule (n) 

(f) 

Triticum aestivum 

Zero 100 500 

100 

80 

60 

40 

20 

0 

Zero 100 500 

(c) 

100 

80 

60 

% 

40 

20 

0 

Halodule uninervis (b) (g) 

Koeleria setacea 

100 

80 

60 

40 

20 

Zero 100 500 

0 

Zero 100 500 

(d) 

100 

80 

60 

% 

40 

20 

0 

Cymodocea serrulata (h) 

Erharta erecta 

100 

80 

60 

40 

20 

0 

Zero 100 500 Zero 100 500 

Particle size 

category 

< 75 mm 

> 75 mm 

> 125 μm 

> 250 μm 

> 500 μm 

> 1.0 μm 

> 1.6 μm 

Figure 7 Distribution of particle sizes in five 

seagrass [(a) Halophila ovalis; (b) Halodule (n); 

(c) Halodule uninervis (b); (d) Cymodocea serrulata;(e)Zostera 

capricorni ] and three terrestrial 

grass species [(f) Triticum aestivum; 

(g) Koeleria setacea;(h)Erharta erecta]. X-axes 

refer to the number of grinds after milling. 

Legend indicates particle size class. 




Table 4 Effect of grinding on particle size distributions expressed as median (M) particle size (mm) of the leaf fraction of five dried seagrasses and 

three terrestrial grasses 

Median (M) particle size (mm) 

Breakability NDF (% dm) 

0 grinds 100 grinds 500 grinds Index Rank Mean SE 

Seagrass 

Halophila ovalis 287.6 164.7 55.9 231.1 1 42.6 0.9 (n=5) 

Halodule uninervis (n) 220.6 185.9 69.2 151.4 2 50.8 0.7 (n=5) 

Halodule uninervis (b) 230.1 190.1 104.4 125.7 3 54.2 1.1 (n=5) 

Cymodocea serrulata 161.5 114.4 70.9 90.6 5 52.5 0.9 (n=5) 

Zostera capricorni 155.5 131.6 73.9 81.6 6 62.6 1.7 (n=5) 

Terrestrial grass 

Triticum aestivum 214.5 166.2 93.8 120.7 4 42.0 (n=1) 

Koeleria setacea 193.7 148.4 146.1 47.6 8 57.0 (n=1) 

Erharta erecta 176.0 124.8 106.3 69.7 7 62.8 (n=1) 

Number of grinds refers to the number of grinds after milling. Grasses are assigned a breakability rank according to their breakability index, from 

most breakable (rank 1) through to least breakable (rank 8). NDF, neutral detergent fibre level expressed as a percentage of dry matter. 

Breakability index 

250 

200 

150 

100 

50 

0 

30 35 40 45 50 55 60 65 

Percentage NDF 

components. The nature of these leached materials was not 

investigated here. 

Fibre analysis 

There was a significant difference in fibre levels between 

seagrass species (F=1226.76; d.f.=1, 49; Po0.001). The 

NDF content of seagrass leaves ranged between 

42.64 0.9% dry matter in Halophila ovalis to 62.6 1.7% 

in Z. capricorni (Table 4). The NDF content of Halophila 

ovalis was comparable to that of young wheat T. aestivum. 

Zostera capricorni had NDF levels that were comparable to 

the two mature terrestrial grasses. 

Discussion 

Particle size reduction 

Masticatory efficiency 

H. ovalis 

C. serrulata 

H. uninervis (n) 

H. uninervis (b) 

Z. capricorni 

Figure 8 Relationship between breakability index and mean neutral 

detergent fibre (NDF) level (% dry matter; n=5) of the leaf fraction of 

each of five seagrass species. 

Seagrasses in the stomach of the dugong were well macerated, 

presumably by the mouthparts. The mean particle 

sizes of the stomach contents of dugongs in this study were 

comparable to those of dugongs from elsewhere (Marsh 

et al., 1999). Masticatory or occlusal efficiency (characterized 

by production of a greater number of small particles) 

does not appear to alter in a manner that is consistent with 

age nor with the occlusal surface area of the mouthparts of 

the dugong. Dugongs with greater occlusal surfaces did not 

have greater occlusal efficiency. Further, particle size distribution 

of the stomach contents did not appear to correlate 

with the composition of the diet in terms of seagrass 

species. However, determining the dietary composition for 

dugongs based on stomach contents was problematic because 

most of the ingesta were too finely ground to be 

identifiable. 

In contrast, variation in faecal particle size distributions 

could be attributed to species composition of the diet. The 

only seagrass species that could be consistently identified in 

the faeces was Z. capricorni. Preen (1993) also found 

identifiable Z. capricorni in the faeces but could not distinguish 

other species. Rather than indicate that Z. capricorni 

was more prevalent in the dugong’s diet, this result could 

equally indicate that Z. capricorni was less digestible. Zostera 

capricorni was present as larger particles so that the 

resultant particle distribution tended to have a greater 

median particle size than those faecal samples in which 

Z. capricorni was absent. Zostera capricorni is one 

of the seagrasses least preferred by dugongs (Preen, 

1993). 

In other faecal samples, the largest particle size class (i.e. 

41.6 mm) comprised vascular bundles only. These were 

also found in dugong faeces examined by Anderson & 

Birtles (1978). Otherwise, dugong faeces were uniformly 

very fine, which was unusual compared with the faeces of 

other herbivores that generally have a higher proportion 

of larger particulate matter. Bertram & Bertram (1968, 

p. 389) also remarked on the ‘smooth, greenish 

clay-like faeces’ of the dugong. The uniformity of the 

faeces may be accounted for by considerable postoral 

particle size reduction of seagrass ingesta. Interestingly, 

Bjorndal (1979) has remarked on the well-digested appearance 

of faeces of green turtles feeding on seagrasses. 

284 




Post-oral reduction 

The proportion of particle breakdown that is directly 

attributable to the mouthparts was not determined in the 

dugong. By the time seagrass reached the stomach, it was 

well macerated so that only between 18 and 30% of the dry 

matter of the digesta was particulate matter greater than 

1.6 mm long, and up to 10% of the digesta was small enough 

to pass through the 500 mm sieve. However, considerable 

particle size reduction occurred along the length of the 

digestive system, that is post-orally. 

Particle size was reduced post-orally, that is by about 

50% between the oesophagus and the pyloric region of the 

stomach of the dugong. Post-oral processing presumably 

includes detrition through friction of ingesta passage and/or 

by muscular action in the stomach. The well-packed nature 

of the stomach contents combined with strong muscular 

contractions may facilitate particle breakdown. Further, 

treatment with low pH, as occurs in the stomach, is known 

to soften plant tissue so that it is more amenable to physical 

(Wilson, McLeod & Minson, 1989) and fermentative breakdown 

(Parra, 1978). However, seagrasses do not appear to 

be susceptible to direct tissue lysis by low pH as would be 

found in the stomach. Further, particle reduction because of 

fermentation was probably negligible in the stomach, based 

on negligible volatile fatty acids (VFA) production in this 

organ (Murray et al., 1977). 

Considerable particle reduction also occurred in the small 

intestine. It is probable that this reduction occurred mainly 

through the processes of mechanical detrition and, perhaps, 

enzymatic digestion. The low fibre content and breakability 

of seagrasses probably account for a large part of the 

particle size reduction during passage through the digestive 

tract. Further particle reduction because of fermentation 

and detrition occurred in the hindgut region. Interestingly, 

particle reduction in the caecum was generally low, that is in 

two of the three dugongs examined, it contributed less than 

1% of the post-gastric breakdown. Presumably, this could 

be due to the extremely small size of the caecum, that is 

15 cm long in a hindgut of up to 30 m in length, suggesting 

that this organ may be functionally vestigial. Therefore, in 

the dugong, processes other than dental may contribute 

substantially to particle breakdown. Detrition may be a 

significant component, with fermentation more important 

further down the gut (Nocek & Kohn, 1988). The effectiveness 

of these processes may depend on the passage rate of 

particles through the digestive tract of the dugong. Digesta 

passage rates are slow, with mouth to anus retention times 

of 146–166 h (6–7 days) for particulate matter (Lanyon & 

Marsh, 1995). When feeding on a low fibre diet such as 

Halop. ovalis, apparent digestibility during this slow passage 

is high (Murray et al., 1977). 

Seagrass breakdown 

When subjected to mechanical pressures, seagrasses appear 

to rupture more readily than terrestrial grasses. One major 

difference between these two plant groups is the amount and 

distribution of the structural components of plant tissue, 

that is fibre. Fibre confers mechanical strength on plants and 

is a major obstacle to physical breakdown (Lees et al., 1981; 

Lees, Howarth & Goplen, 1982). The degree of particle size 

breakdown in herbivores has been directly linked to fibre 

levels (e.g. Parra, 1978; Lees et al., 1981, 1982; Spalinger 

et al., 1986). Although terrestrial grasses have supportive 

tissues throughout the plant body to resist gravity (Raven, 

Evert & Curti, 1976), seagrasses have conspicuously reduced 

supportive and protective tissues (Dawes & Lawrence, 1983; 

Lanyon et al., 1989). Leaf blades are thin and flattened 

(Phillips & Meñez, 1988), cell walls are thin, cuticle is 

reduced (Kuo, 1983) and there is a marked decrease in 

vascular tissue (Fahn, 1974). Seagrasses are supported by 

the water column and must be sufficiently flexible to 

accommodate the energy of water currents. Further, seagrasses 

are fully hydrated with water contents of 90–95% 

compared with 75–80% for terrestrial grasses (Best, 1981). 

These characteristics are among the most influential in 

providing mechanical support to the leaf blade (Tomlinson, 

1980). Large intercellular spaces or gas lacunae are also 

common in seagrasses (Tomlinson, 1980; Phillips & Menez, 

˜ 

1988), resulting in low tissue mass compared with terrestrial 

grasses. These features are reflected in the low NDF levels of 

seagrasses compared with terrestrial grasses and may account 

for the increased susceptibility of seagrass to physical 

rupture. 

In vitro comparisons indicated differences in breakability 

of seagrass species. This is not surprising given the taxonomic 

variation in morphology and anatomy within the 

seagrasses (Lanyon, 1986; Kuo & McComb, 1989). Both 

fresh and dried Z. capricorni leaf did not break as readily as 

the other seagrass species, having a lower breakability index 

that fell within the range of terrestrial grasses. The order of 

breakability of seagrasses based on this index roughly 

corresponded to their fibre levels and to the order of diet 

preference of the seagrasses by the dugong (Lanyon, 1991; 

Preen, 1993). Cymodocea serrulata was less breakable than 

its fibre level would suggest, indicating that not only fibre 

level but also the composition and distribution of fibre may 

affect breakability. Interestingly, C. serrulata is ranked as a 

less preferred species throughout most of the dugong’s range 

(Preen, 1993). 

We suggest that NDF levels may be reflected in the 

amount of vascular tissue and associated fibre bundles in 

each seagrass species, and that the distribution of these 

fibres may be reflected in breakability. Vascular bundles are 

highly visible in the leaf fraction of seagrasses and in some 

cases are used as taxonomic tools (Lanyon, 1986). Halophila 

ovalis has one prominent longitudinal vein with less prominent 

marginal vascular bundles running around the perimeter 

of the lamina and few well-spaced secondary veins 

(Lanyon, 1986). The number of longitudinal veins in other 

species ranges from three in Halodule spp. to 13–17 in 

C. serrulata: these species have no prominent cross-veins. 

In contrast, Z. capricorni has a significantly greater density 

of vascular fibres with numerous prominent and close crossveins 

running at right angles to five longitudinal veins. 




Further, Z. capricorni along with C. serrulata has fibre 

bundles associated with the vascular bundles (Kuo, 1983). 

According to Lees et al. (1982), a venation pattern with 

numerous secondary veins such as is found in Z. capricorni 

is likely to be more resistant to structural damage than other 

arrangements because secondary veins add structural 

strength. This type of venation may also be more effective 

in restricting digestion by gut microorganisms, while plants 

with a sparse network of secondary veins (Lees et al., 1982) 

such as Halophila ovalis will be easier to fracture. 

Factors other than leaf fibre may also affect breakability. 

Halophila ovalis has higher water content as a percentage of 

total weight than Z. capricorni (Lanyon, 1991), it lacks leaf 

sheaths which represent a highly fibrous plant fraction, its 

fibre is largely non-lignified (Lanyon, 1991), and its rhizomes 

have cell walls that consist of non-cellulosic polysaccharides 

(Baydoun & Brett, 1985). Halophila ovalis 

appears to more readily break down under mechanical 

pressure than Z. capricorni. We predict that the fibre of 

Halophila ovalis may also be more digestible because reducing 

particle size increases fibre digestibility (McLeod & 

Minson, 1969). In dugong faecal samples, identifiable fragments 

of Z. capricorni sometimes remain, while other 

seagrass species are indistinguishable. In fact, most dugong 

faeces are uniformly powder fine with only fibrous vascular 

strands and no discernible tissue. 

Mechanical processing of seagrass 

Little is known of the mechanism of seagrass ingestion, 

mainly through the difficulty of observing dugongs in the 

wild. However, observations suggest that unlike most herbivorous 

mammals, dugongs do not chew their food (Lanyon, 

1991). When feeding on morphologically small seagrasses 

such as their preferred genera Halophila and Halodule, 

dugongs uproot the entire plant, creating feeding trails 

through the substrate, with each feeding trail representing a 

single feeding bout. Feeding trails range in length from 1 to 

14 m (Heinsohn & Marsh, 1977; Anderson & Birtles, 1978) 

and are generally between 10 and 20 cm wide (J. M. Lanyon, 

pers. obs.). Dugongs remove an average of 63% of seagrass 

from trails (Wake, 1975; Preen, 1993), the equivalent of 

about 1 m 2 of seagrass from a conservatively sized trail, 

within a feeding dive of c. 1 min (Anderson & Birtles, 1978; 

Lanyon, 1991; Chivers et al., 2004). Thus, dugongs are 

capable of uprooting vast quantities of seagrass in a short 

period, and covering some distance at the same time. They 

do not remain on the surface, chewing, between successive 

feeding dives. In fact, the small gape and oral cavity of the 

dugong and the lack of cheek pouches suggest that they do 

not even have the capacity to retain food for chewing. Nor is 

there evidence that they regurgitate their food to re-chew in 

a manner similar to ruminants. Any mechanical processing 

by the mouthparts occurs continuously as the food is 

ingested. 

The dugong is a combination of a bottom feeder, a 

relatively poor diver and a herbivore feeding on low nutrient 

food so that a large amount of food must be processed to 

satisfy energetic requirements. It is quite likely that for the 

dugong, feeding is a protracted activity as it is with other 

grazing herbivores. On the basis of these considerations, we 

suggest that the masticatory apparatus of the dugong has 

developed to match a need for continuous cropping and 

processing which mitigates against chewing, so that the 

entire mouth cavity has been modified into a continuous 

masticatory organ. The continual forward movement of the 

dugong while feeding facilitates movement of seagrass into 

the mouth. Initially, anterior and orthal movement of the 

mandible (Lanyon & Sanson, 2006) secures seagrass between 

the pads. The backwardly directed bristles on the 

lower horny pad combined with mandibular retraction and 

orthal movement would move seagrass backwards in the 

mouth. The opposing pads are probably multifunctional so 

that not only do they move food up from the ventral mouth 

and back over the symphysial part of the mandible, but also 

food is masticated on the way by the cornified papillae and 

bristles on the pads and palate (Lanyon & Sanson, 2006), 

rather like a conveyer belt. 

However, this system can only work if the fracture 

properties of the diet are such that hard enamelled organs 

are not required. As described in this study, this is a peculiar 

property of low fibre seagrasses. It is interesting that other 

animals which utilize a seagrass food source can effectively 

macerate the diet without teeth: for example waterfowl 

(Thayer et al., 1984), which have a muscular gizzard; fish 

(Pollard, 1984), which have gill rakers, and the green turtle 

Chelonia mydas (Bjorndal, 1979, 1980). Each of these 

animals has a ‘beak’ with which to ingest seagrass but no 

tooth surfaces, and like other lower vertebrates lack a jaw 

system capable of translational mastication. However, despite 

the lack of teeth in the green turtle and the fact that it 

does not masticate its food (Bjorndal, Bolten & Moore, 

1990), the stomach contents are well macerated. Thus, 

breakdown of the food must occur within the soft parts of 

the digestive tract. In the green turtle, there are cornified 

papillae in the oesophagus whose function remains largely 

unknown, but it has been suggested that they may aid in 

crushing the food (Skoczylas, 1978). In fish, seagrass is 

macerated in the mouth, pharynx and stomach (Ogden, 

1980). Similarly in the dugong, apart from the oral cavity, 

breakdown could presumably occur in the muscular oesophagus 

(Owen, 1838) and in the thick-walled (Osman Hill, 

1945) and muscular small intestine (Owen, 1838) and stomach. 

In fact, the process of detrition or wearing away of 

the ingesta appears to account for a substantial proportion 

of the physical particle reduction during the digestive 

process of the dugong. Breakdown of seagrass during 

passage through the mouthparts and digestive tract appears 

to be facilitated by low fibre levels. 

The dugong does not fit the generally accepted paradigm 

of a mammalian hindgut fermenter in terms of development 

of dentition. In fact, the dugong appears to have abandoned 

a presumably ancestrally efficient dentition in favour of 

development of soft mouthparts, which may be better 

adapted for dealing with a seagrass diet that is low in fibre. 

However, great development of the horny pads and the 

286 




continuous mode of feeding may be advantageous for a 

bottom-feeding, air-breathing herbivore on a seagrass diet. 

The potential cost to the dugong in having lost hard dental 

surfaces is that it has become specialized to a low fibre diet 

of particular seagrasses that readily fracture. Certainly, it no 

longer appears well equipped to handle the fibre levels 

intrinsic to a seagrass species such as Z. capricorni. 

In terms of its dental adaptations and feeding strategy, 

the dugong appears to sit somewhere between the extant 

manatees (Trichechus) and its extinct dugongid relative, 

Hydrodamalis. All three species of manatee have dental 

adaptations in line with a hindgut-fermenting strategy, that 

is complex, molarized, enamelled cheek teeth (Domning, 

1982; Domning & Hayek, 1984), and are able to process a 

fibrous generalist diet (Best, 1981; Ledder, 1986; Colares & 

Colares, 2002). In stark contrast, the edentulous condition 

of the extinct giant Steller’s seacow Hydrodamalis (Domning, 

1978) and the degenerate dentition of the dugong 

(Lanyon & Sanson, 2006) suggest a case of convergent 

coevolution with low fibre diets of algae and seagrass, 

respectively. Both these animals appear to have developed 

a method of food ingestion and mastication that may be 

suited to processing large quantities of soft plant material 

during short dive times. Interestingly, despite its lack of hard 

dental surfaces, the dugong is able to masticate low fibre 

seagrasses to particle sizes that are smaller than those 

produced by the manatee (Marsh et al., 1999). However, 

the constraint to the dugong in maintaining this digestive 

efficiency is that it continue to select a diet low in fibre. 

Acknowledgements 

Dugong skulls were accessed from the collections of the 

James Cook University and the Museum of Tropical North 

Queensland, Townsville. We wish to thank Helene Marsh 

and Tony Preen for supplying some fresh dugong material. 

Early versions of this manuscript benefited greatly from 

comments by John Kirkwood, Helene Marsh and Daryl 

Domning. Two reviewers further improved the manuscript. 

Financial support was provided by a Great Barrier Reef 

Marine Park Authority Augmentative Research Grant, 

the MA Ingram Trust and a Monash Graduate Scholarship 

to J. M. L. 

References 

Anderson, P.K. & Birtles, A. (1978). Behaviour and ecology 

of the dugong, Dugong dugon (Sirenia): observations in 

Shoalwater and Cleveland Bays, Queensland. Aust. Wildl. 

Res. 5, 1–23. 

Bae, D.H., Welch, J.G. & Gilman, B.E. (1983). Mastication 

and rumination in relation to body size of cattle. J. Dairy 

Sci. 66, 2137–2151. 

Bailey, A.T., Erdman, R.A., Smith, L.W. & Sharma, B.K. 

(1990). Particle size reduction during initial mastication of 

forages by dairy cattle. J. Anim. Sci. 68, 2084–2094. 

Baydoun, E.A.H. & Brett, C.T. (1985). Comparison of cell 

wall compositions of the rhizomes of three seagrasses. 

Aquat. Bot. 23, 191–196. 

Bertram, C.K. & Bertram, G.C.L. (1968). The Sirenia as 

aquatic meat-producing herbivores. Symp. Zool. Soc. 

Lond. 21, 385–391. 

Best, R.C. (1981). Foods and feeding habits of wild and 

captive Sirenia. Mammal Rev. 11, 3–29. 

Bjorndal, K.A. (1979). Cellulose digestion and volatile fatty 

acid production in the green turtle, Chelonia mydas. Comp. 

Biochem. Physiol. 63A, 127–133. 

Bjorndal, K.A. (1980). Nutrition and grazing behaviour of the 

green turtle Chelonia mydas. Mar. Biol. 56, 147–154. 

Bjorndal, K.A., Bolten, A.B. & Moore, J.E. (1990). Digestive 

fermentation in herbivores: effect of food size. Physiol. 

Zool. 63, 710–721. 

Channells, P. & Morrissey, J. (1981). Technique for analysis 

of seagrass genera present in dugong stomachs, including 

a key to north Queensland seagrasses based on cell details. 

In The dugong: proceedings of a seminar-workshop: 

176–179. Marsh, H. (Ed.). Townsville: James Cook University. 

Chivers, B.L., Delean, S., Gales, N.J., Holley, D.K., Lawler, 

I.R., Marsh, H. & Preen, A.R. (2004). Diving behaviour of 

dugongs, Dugong dugon. J. Exp. Mar. Biol. Ecol. 304, 

203–224. 

Colares, I.G. & Colares, E.P. (2002). Food plants eaten by 

Amazonian manatees (Trichechus inunguis, Mammalia: 

Sirenia). Braz. Arch. Biol. Technol. 4, 67–72. 

Dawes, C.J. & Lawrence, J.M. (1983). Proximate composition 

and caloric content of seagrasses. MTS J. 17, 53–58. 

Domning, D.P. (1977). Observations on the myology of 

Dugong dugon (Muller). Smithsonian Contrib. Zool. 226, 

57 pp. 

Domning, D.P. (1978). Sirenian evolution in the north Pacific 

Ocean. Univ. Calif. Publ. Geol. Sci. 118, 176 pp. 

Domning, D.P. (1982). Evolution of manatees: a speculative 

history. J. Paleon. 56, 599–619. 

Domning, D.P. & Hayek, L.A.C. (1984). Horizontal tooth 

replacement in the Amazonian manatee (Trichechus inunguis). 

Mammalia 48, 105–127. 

Dring, M.J. (1982). The biology of marine plants. Contemporary 

Biology. London: Edward Arnold. 

Fahn, A. (1974). Plant anatomy. 2nd edn. UK: Pergamon 

Press. 

Fortelius, M. (1985). Ungulate cheek teeth: developmental, 

functional and evolutionary interactions. Acta Zool. Fennica 

180, 1–76. 

Goto, M., Ito, C., Yahaya, M.S., Wakai, Y., Asano, S., Oka, 

Y., Ogawa, S., Fruta, M. & Kataoka, T. (2004). Characteristics 

of microbial fermentation and potential digestibility 

of fiber in the hindgut of dugongs (Dugong dugon). 

Mar. Fresh. Behav. Physiol. 37, 99–107. 

Heinsohn, G.E. & Marsh, H. (1977). Sirens of tropical 

Australia. Aust. Nat. Hist. 19, 106–111. 




Kenchington, R.A. (1972). Observations on the digestive 

system of the dugong, Dugong dugon (Erxleben). J. Mamm. 

53, 884–887. 

Kuo, J. (1983). Notes on the biology of Australian seagrasses. 

Proc. Linn. Soc. NSW 106, 225–245. 

Kuo, J. & McComb, A.J. (1989). Seagrass taxonomy, structure 

and development. In Biology of seagrasses. A treatise 

on the biology of seagrasses with special reference to the 

Australian region. Aquatic plant studies, Vol. 2: 6–73. 

Larkum, A.W.D., McComb, A.J. & Shepherd, S.A. (Eds). 

Amsterdam: Elsevier. 

Lanyon, J.M. (1986). Guide to the identification of seagrasses 

in the Great Barrier Reef region. GBRMPA Special Publication 

Series 3 

Lanyon, J.M. (1991). The nutritional ecology of the dugong, 

Dugong dugon, in tropical north Queensland. PhD thesis, 

Monash University. 

Lanyon, J.M., Limpus, C.J. & Marsh, H. (1989). Dugongs 

and turtles: grazers in the seagrass system. In Biology of 

seagrasses. A treatise on the biology of seagrasses with 

special reference to the Australian region. Aquatic plant 

studies, Vol. 2: 610–634. Larkum, A.W.D., McComb, A.J. 

& Shepherd, S.A. (Eds). Amsterdam: Elsevier. 

Lanyon, J.M. & Marsh, H. (1995). Digesta passage times in 

the dugong. Aust. J. Zool. 43, 119–127. 

Lanyon, J.M. & Sanson, G.D. (1986). Koala (Phascolarctos 

cinereus) dentition and nutrition. 2. Implications of tooth 

wear in nutrition. J. Zool. (Lond.) 209, 169–181. 

Lanyon, J.M. & Sanson, G.D. (2006). Degenerate dentition of 

the dugong (Dugong dugon) or why a grazer does not need 

teeth: morphology, occlusion and wear of mouthparts. 

J. Zool. (Lond.) 268, 133–152. 

Ledder, D.A. (1986). Food habits of the West Indian Manatee, 

Trichechus manatus latirostris, in south Florida. MSc thesis, 

University of Miami, Florida. 

Lees, G.L., Howarth, R.E. & Goplen, B.P. (1982). Morphological 

characteristics of leaves from some legume forages: 

relation to digestion and mechanical strength. Can. J. Bot. 

60, 2126–2132. 

Lees, G.L., Howarth, R.E., Goplen, B.P. & Feeser, A.C. 

(1981). Mechanical disruption of leaf tissue and cells in 

some bloat-causing and bloat-safe forage legumes. Crop 

Sci. 21, 444–448. 

Marsh, H. (1980). Age determination in the dugong (Dugong 

dugon (Müller)) in northern Australia and its biological 

implications. Rep. Int. Whal. Comm. Spec. Issue 3, 

181–201. 

Marsh, H., Beck, C.A. & Vargo, T. (1999). Comparison of the 

capabilities of dugongs and West Indian manatees to 

masticate seagrasses. Mar. Mamm. Sci. 15, 250–255. 

Marsh, H., Channells, P., Heinsohn, G.E. & Morrissey, J. 

(1982). Analysis of stomach contents of dugongs from 

Queensland. Aust. Wildl. Res. 9, 55–67. 

Marsh, H. & Eisentraut, M. (1984). Die gaumenfalten des 

Dugong. Z. Saugetierkende. 49, 314–315. 

Marsh, H., Heinsohn, G.E. & Spain, A.V. (1977). The 

stomach and duodenal diverticula of the dugong (Dugong 

dugon). In Functional anatomy of marine mammals, 

Vol. 3: 271–294. Harrison, R.J. (Ed.). London: Academic 

Press. 

Marshall, C.D., Maeda, H., Iwata, M., Asano, S., Rosas, F. & 

Reep, R.L. (2003). Orofacial morphology and feeding 

behaviour of the dugong, Amazonian, West African and 

Antillean manatees (Mammalia Sirenia): functional morphology 

of the muscular-vibrissal complex. J. Zool. 

(Lond.) 259, 245–260. 

McLeod, M.N. & Minson, D.J. (1969). Sources of variation in 

the in vitro digestibility of tropical grasses. J. Brit. Grassl. 

Soc. 24, 244–249. 

Murray, R.M., Marsh, H., Heinsohn, G.E. & Spain, A.V. 

(1977). The role of the midgut caecum and large intestine in 

the digestion of sea grasses by the dugong (Mammalia: 

Sirenia). Comp. Biochem. Physiol. 56, 7–10. 

Nocek, J.E. & Kohn, R.A. (1988). In situ particle size reduction 

of alfalfa and timothy hay as influenced by form and 

particle size. J. Dairy Sci. 71, 932–945. 

Ogden, J.C. (1980). Faunal relationships in Caribbean seagrass 

beds. In A handbook of seagrass biology: an ecosystem 

approach: 173–198. Phillips, R.C. & McRoy, C.P. (Eds). 

New York: Garland Press. 

Osman Hill, W.C. (1945). Notes on the dissection of two 

dugongs. J. Mammal. 26, 153–175. 

Owen, R. (1838). On the anatomy of the dugong (Halicore). 

Proc. Zool. Soc. Lond. 6, 28–46. 

Parra, R. (1978). Comparison of foregut and hindgut fermentation 

in herbivores. In The ecology of arboreal folivores: 

205–230. Montgomery, G.G. (Ed.). Washington, DC: 

Smithsonian Institution Press. 

Phillips, R.C. & Menez, ˜ E.G. (1988). Seagrasses. Smithsonian 

Contrib. Mar. Sci. 34, 104. 

Pollard, D.A. (1984). A review of ecological studies on 

seagrass fish communities, with particular reference to 

recent studies in Australia. Aquat. Bot. 18, 3–42. 

Preen, A.R. (1993). Habitat selection and feeding ecology of 

the dugong in Moreton Bay. PhD thesis, James Cook 

University of North Queensland. 

Raven, P.H., Evert, R.F. & Curtis, H. (1976). Biology of 

plants. 2nd edn. New York: Worth. 

Rensberger, J.M. (1973). An occlusal model for mastication 

and dental wear in herbivorous mammals. J. Paleon. 47, 

515–528. 

Sanson, G.D. (1977). Studies on the evolution of mastication 

in the Macropodinae. PhD thesis, Monash University, 

Victoria. 

Sanson, G.D. (1980). The morphology and occlusion of the 

molariform cheek teeth in some Macropodinae (Marsupialia: 

Macropodidae). Aust. J. Zool. 28, 341–365. 

Santini, F.J., Hardie, A.R., Jørgenen, N.A. & Finner, M.F. 

(1983). Proposed use of adjusted intake based on forage 

particle length for calculation of roughage indexes. J. Dairy 

Sci. 66, 811–820. 

288 




Skoczylas, R. (1978). Physiology of the digestive tract. In 

Biology of the Reptilia, Vol. 8: 589–717. Gans, B.C. & 

Gans, K.A. (Eds). New York: Academic Press. 

Sokal, R.R. & Rohlf, F.J. (1969). Biometry. San Francisco: 

Freeman. 

Spalinger, D.E., Robbins, C.T. & Hanley, T.A. (1986). The 

assessment of handling time in ruminants: the effect of 

plant chemical and physical structure on the rate of breakdown 

of plant particles in the rumen of mule deer and elk. 

Can. J. Zool. 64, 312–321. 

Thayer, G.W., Bjorndal, K.A., Ogden, J.C., Williams, S.L. & 

Zieman, J.C. (1984). Role of larger herbivores in seagrass 

communities. Estuaries 7, 351–376. 

Tomlinson, P.B. (1980). Leaf morphology and anatomy in 

seagrasses. In A handbook of seagrass biology: an ecosystem 

approach: 7–28. Phillips, R.C. & McRoy, C.P. (Eds). New 

York: Garland Press. 

Van Soest, P.J. & Wine, R.H. (1967). Use of detergents in the 

analysis of fibrous feeds. IV. The determination of plant 

cell wall constituents. J. Assoc. Off. Agric. Chem. 50, 1–50. 

Vorontsov, N.N. (1967). Evolution of the alimentary canal of 

myomorph rodents. Novosibirsk: Nauka. 

Wake, J.A. (1975). A study of the habitat requirements and 

feeding biology of the dugong, Dugong dugon (Muller). 

Hons thesis, James Cook University of North Queensland, 

Townsville. 

Wilson, J.R., McLeod, M.N. & Minson, D.J. (1989). Particle 

size reduction of the leaves of a tropical and a temperate 

grass by cattle. I. Effect of chewing during eating and varying 

times of digestion. Grass and Forage Science 44, 55–63.

Mechanical disruption of seagrass in the digestive tract of the dugong

Create successful ePaper yourself

Delete template?

Save as template?