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Fernandes & Soares-Gomes Community structure of macrobenthos in two tropical sandy beaches Table 2. The dominant species of the beaches studied in winter and summer. winter % summer % Pontal beach species Scolelepis squamata (Muller, 1806) 41.08 63.65 Emerita brasiliensis (Schmitt, 1935) 21.40 17.37 Excirolana armata (Dana, 1853) 32.37 13.37 Excirolana braziliensis (Richardson, 1912) 4.25 4.62 Donax hanleyanus (Philippi, 1842) 0.07 0.70 Pseudorchestoidea brasiliensis (Dana, 1853) 0.55 0.28 Phaleria testacea (Say, 1824) 0.27 – Costa Azul beach species Pisionides indica (Aiyar & Alikunhi, 1940) 8.40 0.82 Emerita brasiliensis (Schmitt, 1935) 20.15 30.23 Donax hanleyanus (Philippi, 1842) 27.50 19.15 Hemipodus olivieri (Orensanz & – 1.40 Gianuca, 1974) Excirolana braziliensis (Richardson, 1912) 38.10 44.87 Pseudorchestoidea brasiliensis (Dana, 1853) 5.30 3.56 Olivancillaria vesica vesica (Gmelin, 1791) 0.36 – Table 4. Density of species [ind.Æm )2 ] and total number of individuals per beach, in winter (W) and summer (S). species PO, W PO, S C.A, W C.A, S Scolelepis squamata 3337.6 4602.5 – – Pisionides indica – – 192.3 21.36 Hemipodus olivieri – – – 29.91 Emerita brasiliensis – – 192.3 200.85 Donax hanleyanus – – 363.24 213.67 Olivancillaria vesica vesica – – 68.37 – total faunal density 3337.6 4602.5 816.23 465.81 total number of ind. 781 1077 191 109 PO, Pontal Beach; CA, Costa Azul Beach. co-dominated in summer (Table 2). At Pontal Beach, the higher density of intertidal individuals was found in the winter survey, and at Costa Azul the higher density was found in summer. However, at the breaking zone, the opposite pattern was observed with the higher density occurring in summer at Pontal Beach, and in winter at Costa Azul (Tables 3 and 4). According to the cluster and MDS analyses (Figs 2 and 3) there were three groups of stations at Pontal and two at Costa Azul. On the other hand, when applying the ANOSIM test, only two of these groups were statistically significant for both the beaches (global R ¼ 1.0). Comparing the intertidal zones, the Pontal Beach showed a higher species richness than Costa Azul. However, species richness at the breaking zone at the Costa Azul Beach Fig. 2. Cluster analysis and n-MDS ordinations. Above: Pontal Beach winter; Below: Pontal Beach summer. Table 3. Density of species [ind.Æm )2 ], and total number of individuals per beach, in winter (W) and summer (S). species PO, W [m )1 ] PO, W [m )2 ] PO, S [m )1 ] PO, S [m )2 ] C.A, W [m )1 ] C.A, W [m )2 ] C.A, S [m )1 ] C.A, S [m )2 ] Scolelepis squamata 1636.6 3140 2651.2 4545 – – – – Pisionides indica – – – – 1150 230 150 30 Hemipodus olivieri – – – – 200 40 250 50 Emerita brasiliensis 1150.6 1315 1446.6 1240 2550 550 5300 1105 Excirolana braziliensis 259 370 288.7 330 4920 1040 795 1640 Excirolana armata 2030 2400 1114.1 955 – – – – Pseudorchestoidea brasiliensis 70 40 87.5 50 500 115 416.6 130 Ocypode quadrada – – – – 25 5 – – Donax hanleyanus 323.7 5 – – 3325 750 2950 700 Olivancillaria vesica vesica – – – – 50 10 – – Phaleria testacea 35 20 70 20 – – – – total density 5504.9 7290 5658.1 7140 12720 2740 9861.6 3655 total number of ind. 1458 1428 548 731 PO, Pontal Beach; C.A, Costa Azul Beach. Marine Ecology 27 (2006) 160–169 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 163
Community structure of macrobenthos in two tropical sandy beaches Fernandes & Soares-Gomes stratum 8, at about 40 m from the water line. According to the ANOVA results, the density of E. braziliensis did not differ significantly between the sectors or periods (P > 0.05) (Fig. 4). According to the results from the Student’s t-test, the abundance of macrobenthic fauna was significantly different in the sublittoral zone between Pontal and Costa Azul (P < 0.05). At Pontal Beach, the macrobenthic fauna were more abundant in summer, whereas at Costa Azul they were more abundant in winter. The Spearman rank correlation analyses revealed a significant positive relationship between mean grain size and beach slope (P < 0.005), and between omega (X) and macrofaunal density (P < 0.005). Conversely, significant negative correlations were found between mean grain size and macrofaunal density (P < 0.005), and between beach slope and macrofauna density (P < 0.005) (Table 5). Discussion Fig. 3. Cluster analysis and n-MDS ordinations. Above: Costa Azul beach winter. Below: Costa Azul Beach summer. was higher than at Pontal. At Costa Azul the species richness increased from the higher to the lower intertidal zone, while at Pontal, the higher species richness occurred at the intermediate levels (c. 23 m from the water line). On both beaches the total macrobenthic fauna did not differ significantly between intra-sector transects (S1 – T1 · T2 · T3 · T4 · T5; P > 0.05) and (S2 – T1 · T2 · T3 · T4 · T5; P > 0.05). Also, no significant differences were found between inter-sectors (S1 · S2; P > 0.05) as well as between the two sampling periods (P > 0.05). At Pontal Beach, S. squamata occurred from the sublittoral zone to stratum 7, at approximately 24 m distance from the water line. The distribution of E. brasiliensis ranged from the sublittoral to stratum 5, peaking at stratum 4 (c. 14 m distance from the water line). Excirolana armata and E. braziliensis occurred from stratum 4 to stratum 7, and from stratum 5 to 10, respectively. According to the results from the ANOVA, the density of S. squamata, E. brasiliensis and E. braziliensis did not differ between sectors or periods (Two-Way ANOVA factors sector and periods P > 0.05). The density of E. armata was higher in the winter (P < 0.05) but did not differ between sectors (P > 0.05). At Costa Azul, the highest density of E. brasiliensis occurred in stratum 1, at about 5 m distance from the water line. Donax hanleyanus ranged from strata 1 to 5, about 15 m above the water line. Its density was statistically different between the two sectors but did not differ between the seasons. Excirolana braziliensis occurred from stratum 2, at about 10-m distance from the water line, to Grain size and swash period are the physical factors that control community structure. Grain size often tends to be coarser at reflective rather than at dissipative beaches, as a result of intense wave action in the former (McLachlan 1990; Defeo et al. 1992; McArdle & McLachlan 1992; Borzone et al. 1996). The physical features of both beaches studied in this work are in accordance with these statements; the Pontal Beach has a slight slope and fine grains, while the Costa Azul Beach has a steeper slope and coarser grains. Dexter (1983) and Borzone et al. (1996) showed that the density of the macrofauna was negatively correlated to mean grain size. In addition, Defeo et al. (1992) found a negative correlation between beach slope and macrofaunal density, concluding that both slope and grain size are factors determining beach macrofaunal structure. According to McLachlan (1990), the abundance of macrofauna is best correlated with Dean’s parameter. On the other hand, Jaramillo & McLachlan (1993) observed that grain size was the sediment factor that best correlated with variations of macrofaunal abundance in Chilean beaches. For those beaches, slope, grain size, and the Dean parameter were positively correlated with macrofaunal density. Some authors, when comparing morphodynamic types, found an increase in the abundance of macrofauna, from reflective to dissipative beaches (Brown & McLachlan 1990; Defeo et al. 1992; Borzone et al. 1996; Brazeiro 1999). Jaramillo et al. (2001) however, stated that the morphodynamics was not always a useful predictor of sandy beach community structure. McArdle & McLachlan (1992) observed that variations in swash, a factor that is related to slope, lead to changes in the distribution of macrofauna. According to Bowman 164 Marine Ecology 27 (2006) 160–169 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
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Community structure of macrobenthos in two tropical sandy ... - UFF

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