The Ecology of the Seagrasses of South Florida - USGS National ...

Taylor and Sa1 oqan (1968) contrasted the roots, a moderate arloifnt of enrich!i:e~t.
uodjsturbed areas of the bay, where iuxu- nay actuatly enhance productivity, urrder
rfant grass grew in sedialentr; averaging certain conditions where ~aters are wcl l-
94% sand and lit~cll, with the kott~itl of mixed, as observed I?y this author in tbe
dredge canals, where unvegetated sedirvents rich growt? of turtle grass and associated
averaged 32% silt and clay. Hhile several epiphytes in the vicinity (within 1 krrl or
studies of Boca Ciegai Ray collectively
described nearly 700 species of plants and
(1.6 mi)
plant.
of Pdiaami's Vir~inia Key swage
This discharge is on the side of
animals occurring there, Taylor and Saloman
(1968) falrnd only 2CZ of those same
the key open to the ocean. In tbe in~ediate
area where these wdstes are disspecies
in the canals.. FIost of those were
ffsh that are highly motil~ and thus not
charged, however, water qua1 ity is so
reduced that seagrasses cannot grow. Stinrestricted
to the canal s durirlg extreri~c ul ation of excess epiphytic production iy!ay
conditions. Tntcrestingly, whi le species adversely affect the seagrasses by persi s-
numbers were higher in undfsturbed areas, tent light reduction, Qften the effects
30% ilrore fish were found in the canals, of sewage discharge in such areas are cornthe
most abundant of which wer-e the bay pounded by turbidity from dredging. In
itnckovy, thc Cubart anchovy, and the scaled Christiansttld Harbor, St, Croix, where
sardine, The authors noted that in the turtle grass beds were subjected to both
fey4 ycars since the in1 tial disturbance, foralis of pollution, the seaarasses decl incnlnnizatican
was rtegll'gihle at tire botturn ed and were replaced by the green aloa,
of thc: canals and concluded that thc sedi- acerornor_pf&. In a 17-year period, the
rnents there were unsul'tiable For most of grasms in the crrlha ment were reduced by
the bayg$ benthic invertebrates. Light 662 (Don:! et a1 . 19723.
tranrfl~fssian values were highest in the
open bay away froctx landfills, lowest near Phytoplankton productivity increased
the fir led areas, and increasctd somewhat in i-lillsborough Bay, near Tarnpa hecause of
4rs the quie~eettt waters of the canals, nutrient enrichment for domestic sewaae
Because of the doytt~ of the canals, how- and phosphate mining discharges (Taylor
ever, 1 ight dt the battoirr gas insufffcient et al. 1973). Phytoplankton blooms con-
Par seagrass grawttt, Taylor and Salemarl trihuted to the prohle~ of turbidity,
{f9C@), using canservlatiue and incomplete whlch was increased to such a level that
figures, astilitated that fi 1 'I operations in scagrasses persisted only in small sparse
the bny resul tetl in an annual lass of 1.4 patches. The only irnportant nacrophyte
mfl'l ion r!ollars for ff sherles and recrea- found in the hay wds the red alga, Craciltfan.
- laria, Soft sediments in combinalti~~?~
low oxygen levels 1 iirrited diversity and
IP seagrasses are only 1 igt\tly abundance of benthic invertebrates,
covered and the rhizotire systalr is not
changed, regrowtt.~ through the scditnent is Few seagrasses grow in waters of
stltretfmes possltslc?, Thorhatrg et a1. Dl'scayne Ray that were pol luted hy sewage
(1973) found tht coflstructian of a canal discharge in 1956 (McNul ty 1470). Only
In Card Sound tetnporarily ceverod turtle shoal grass and Halophilal grew sporadi-
Z km (Q.6
gras5 Jn nn area of 2 ta 3 ha (5 to 7 cally in small patches w~thin
acres) w-i th up to 10 cm (4 inches) of ini) of the outfall. Post-abaterent studsedirqerrt,
killfrzg the leaves, hut not: thc ies Jn 1960 sfro~ed seagrasses in the area
ri1iz01"r system, Regt-owth occurred when had actual ly decl ined, probably because of
the drcdglng operations ceased and cur- the persistent resuspension of dredge
rents carriePl the sedlnlent away,
materials resulting fron the construction
of a causeway.
6,2 EUTKQPH ICAJ ION AEC SEgAGE Physiological studies reveal that
seagrasses are not only affected by low
S~agrass ~0wif"~ltnities arc sensitive to levels of light, but also suffer %!hen disadd1
tions of ntatrients from sewage out- solved oxygen levels are persistently low,
falls or industrial wastes. Because a situation encountered where sewage addiseagsasscs
have the ability to take up tions cause increased microbial respiranutrfents
throtrgh thc leaves as well as tion, Hammer (1968a) compared the effects
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