Benthic fauna of macrotidal sandy beaches along a small-scale morphodynamic gradient on the Amazon coast (Algodoal Island, Brazil).

Journal of Coastal Research SI 64 435-439 ICS2011 (Proceedings) Poland ISSN 0749-0208 Benthic fauna of macrotidal sandy beaches along a small-scale morphodynamic gradient on the Amazon coast (Algodoal Island, Brazil). J.S. Rosa Filho, T.P. Gomes, M.F. Almeida* and R.F. Silva Lab. Oceanografia Biológica FAOC/IG Universidade Federal do Pará, Belém, Brazil jsouto@ufpa.br Lab. Oceanografia Biológica FAOC/IG Universidade Federal do do Pará, Belém, Brazil tatiannepgomes@yahoo.com.br * Lab. Oceanografia Biológica FAOC/IG Universidade Federal do Pará, Belém, Brazil mayk@ufpa.br Lab. Oceanografia Biológica FAOC/IG Universidade Federal do Para, do Pará, Belém, Brazil roseanne_figueira@yahoo.com.br Abstract Rosa Filho, J.S., Gomes, T.P., Almeida, M.F. and Silva, R.F., 2011. Benthic fauna of macrotidal sandy beaches along a small-scale morphodynamic gradient on the Amazon coast (Algodoal Island, Brazil). Journal of Coastal Research, SI 64 (Proceedings of the 11th International Coastal Symposium), 435 439. Szczecin, Poland, ISSN 0749-0208 The general aim of this study was to describe the macrobenthos and meiobenthos along a small-scale morphodynamic gradient on Algodoal Island in northern Brazil. Samples were collected using cylindrical cores (3.14 cm 2 for meiofauna and 0.08 m 2 for macrofauna) in the high intertidal (HT), middle intertidal (MT), and low intertidal (LT) zones. For each sample, richness and density were calculated. Univariate (ANOVA, Spearman correlation analysis) and multivariate (MDS, ANOSIM) techniques were used for data analysis. The meiofauna was composed mainly of Nematoda (56%), Tardigrada (29%), and Turbellaria (14%). was composed of 37 taxa with dominance of annelids. As a rule, density and richness significantly increased from Princesa to Caixa d Água. Across-shore, meiofauna maximum numbers were always recorded in the middle intertidal zone, whereas macrofauna abundance and richness increased from the high- to low-tide line. Two groups of samples were identified for macrofauna and meiofauna: one of them composed of samples from Princesa (all zones) and the high intertidal zone of Farol and Caixa d`água, and the other with the remaining samples (middle and low intertidal zones of Farol and Caixa d`água). Mean particle diameter and percentage of fine sediments were the environmental characteristics most related to richness and abundance of the benthic fauna. The information from this study indicates that the morphodynamic state, along with its related environmental characteristics including sediment type, wave climate, and beach face slope, plays a central role in structuring benthic communities in Amazon sandy beaches. Aditional index words:, meiofauna, intertidal zone INTRODUCTION The physical structure of sandy beaches can be defined in terms of sediment, wave climate, and tides. Beach morphology reflects the continuous adjustment of topography and fluid dynamics, evolving sediment transport (Short, 1999). McLachlan (1980) proposed the first scheme of beach classification according to the exposure, creating three categories: protected, semi-exposed and exposed. Based on Dean parameter (Ω - dimensionless fall velocity), Wright and Short (1984) classified microtidal ocean sandy beaches along a continuum from reflective to dissipative beaches. Considering the role of tidal range on beach morphodynamics, Masselink and Short (1993) created an eight categories classification, covering beaches of all tide ranges. Sandy beaches harbor a diverse and abundant meiofauna and macrofauna. Nematoda, Copepoda Harpacticoida, Turbellaria, Tardigrada, and Oligochaeta are among the most common meiofauna taxa; whereas Polychaeta, Crustacea, and Mollusca dominate the macrofauna. The patterns of occurrence and abundance of benthic fauna in sandy beaches at a small scale (across the shore) and medium scale (between beaches in the same geographical region) are determined by beach morphodynamics, wave exposure, and species interactions (Mclachlan and Brown, 2006, Giere, 2009). As a general rule, macrotidal dissipative beaches have higher diversity, abundance and biomass than microtidal reflective beaches (McLachlan and Dorvlo 2005). Across shore, richness and density of macrofauna increase from high to low tide line (Degraer et al. 2003), while the meiofauna is most abundant and rich at mid tidal level (Armonies and Reise 2000). In the Amazon coast, the macrotidal regime, the large amount of sediments carried by rivers to the coast, and the high hydrodynamic in shallow water favor the occurrence of ocean beaches with different characteristics (sediment type and exposure). Following changes in beach characteristics, median and small-scale morphodynamic and associated benthic gradients are expected to occur. At present, the benthos in the Amazon sandy beaches has been surveyed in Ajuruteua by Gomes and Rosa Filho (2009) and Rosa Filho et al. (2009), who described the spatial and temporal changes in macrofauna and meiofauna communities. 435

Benthic fauna of macrotidal sandy beaches o 47 34 W 5 km o 0 36 S Table 1: General characteristics of the beaches studied in Algodoal Island. P Princesa beach, F Farol beach, CD Caixa d`água beach, HT high tidal zone. MT Middle tidal zone, LT Low tidal zone, MPD Mean particle diameter, % G Percentage of gravel, %S Percentage of sand, % Percentage of silt + clay. Beach Zone Lenght MPD % % % Slope (m) (Φ) G S F HT 40 1º 40 2.36 0 100 0 P MT 145 0 o 58 2.40 0 100 0 LT 47 3º19 2.39 0 100 0 HT 60 2º17 2.12 0 100 0 F MT 160 1º43 2.66 0 100 0 LT 100 1º8 2.61 0 100 0 HT 58 2 o 03 1.07 17 83 0 CD MT 168 0 o 17 3.11 0 99 1 LT 63 0 o 11 3.27 0 98 2 Figure 1: Map of study sites (Algodoal island). The general aim of this study was to describe the macrobenthos and meiobenthos along a small-scale morphodynamic gradient on Algodoal Island, emphasizing: 1. the variability of beach characteristics at the study sites; 2. the biodiversity of meiobenthos and macrobenthos; 3. the patterns of faunal zonation; and 4. the relationship between morphodynamic state and the benthic fauna. METHODS The beaches studied are on Algodoal Island on the Brazilian Amazon coast. The island possesses 35 km of beaches with different levels of exposure to wave action, slope, width, and sediment ranging from sand to mud. A natural small-scale morphodynamic gradient exists between Princesa (dissipative beach, exposed), Farol (intermediate low-tide terrace, semiexposed), and Caixa d`água (intermediate low-tide terrace, sheltered) (Figure 1). The climate is tropical humid (annual rainfall 3,000 mm) and tides are semidiurnal with mean spring tide range of 4.5 m (Souza Filho et al., 2009). Samples were collected in December 2005 (dry season), using cylindrical cores (3.14 cm 2 for meiofauna and 0.08 m 2 for macrofauna) in the high intertidal (HT), middle intertidal (MT), and low intertidal (LT) zones. After collection, the macrofauna samples were passed through a 0.3 mm-mesh screen and the meiofauna samples were fixed in 4% saline formalin. At each station, a sediment sample was taken for textural analysis. In the laboratory, meiofauna was extracted from sediments using manual elutriation and sieved through meshes of 0.045 and 0.5 mm. For each biological sample density, richness, diversity, and evenness were calculated and compared among beaches and intertidal zones using one-way ANOVA (data log (x+1) transformed). Ordination analysis (MDS) was employed to describe spatial and temporal patterns of sample distribution. These analyses were based on similarity matrices calculated from Bray-Curtis similarity, with the data 4 th root transformed. To compare communities between beach zones and seasons, Analysis of Similarity (ANOSIM) was applied. Spearman correlation analysis was applied for describing the relationship between biotic and abiotic variables. The significance level of 5% was used for all analysis. RESULTS Physical parameters Princesa was the narrowest beach (± 200m) and Caixa d`água the widest one (± 500 m). The beach face slope varied from 1/50 in Princesa to 1/125 in Caixa d`água (1/75 in Farol). The beach profile in Farol and Caixa d`água is very steep in the higher intertidal zone and plain downward (Figure 2). Fine sand is the dominant sediment in Princesa and Farol, whereas very fine sand dominates in Caixa d água. In the former beach, median sand poorly sorted is the main sediment on the high intertidal zone (Table 1). Benthic fauna The meiofauna was composed mainly of Nematoda (56%), Tardigrada (29%), and Turbellaria (14%). was composed of 37 taxa belonging to Nemertea, Annelida, Mollusca, and Arthropoda (mainly Crustacea), with annelids dominating in all beaches and intertidal zones. Polychaeta represented always more than 85% of total organisms, particularly Orbinia sp., Nephtys simoni and Scolelepis squamata. Figure 2: Beach profiles of the beaches studied. 436 436

Rosa Filho et al. Figure 3: Density and richness of meiofauna and macrofauna across shore in the studied beaches in Northern Brazil. HT High intertidal zone, MT Middle intertidal zone, LT Low intertidal zone. Vertical bars are confidence interval (95%). As a rule, density and richness significantly increased in all zones from Princesa to Caixa d Água (Table 2). Across-shore, meiofauna maximum density and number of taxa were always recorded in the middle intertidal zone, whereas macrofauna abundance and richness increased from the high- to the lowintertidal line (Figure 3). Two groups of samples were identified for macrofauna and meiofauna: one of them composed of samples from Princesa (all zones) and the high intertidal zone of Farol and Caixa d`água, and the other with the remaining samples (middle and low intertidal zones of Farol and Caixa d`água) (Figure 4). Mean particle diameter and percentage of fine sediments were positive and significantly relater to meiofauna and macrofauna richness and abundance. The amount of sand was negative and significantly related to the number of meiofauna taxa and to the macrofauna densities (Table 3). DISCUSSION A natural small-scale morphodynamic gradient exists between Princesa and Caixa d`água. According to Masselink and Short (1993), the beaches studied are classified as barred dissipative (Princesa) and low tide terrace (Farol and Caixa d`água), rflecting the level of exposition to wave action of these beaches, since Princesa is the most exposed and Caixa d`água the most sheltered. The taxonomic composition, richness, and abundance of meiofauna and macrofauna in Algodoal are similar to other open ocean beaches (Rodríguez et al., 2003; Pinto & Santos, 2006). The dominance of nematodes and annelids result of three main factors: the shape of the organisms body (long, thin and as a fuse), which facilitate the burrowing activities; the well know high tolerance to environmental stress, allowing them to survive in harsh environment like sandy beaches; and the diversity of feeding habits, leading them to use all food resources available (Bowman, 1983, Giere, 2009; Rosa Filho et al., 2009). Among beaches, even though Nematoda and Polychaeta were dominant, there were significant differences in the relative abundance of other taxa. In the upper intertidal zone of Caixa d`água Turbellaria and Tardigrada increased their abundance. In this zone we observed the highest percentage of median sand, and it is known the preference of these groups for well oxigenated substrata (Giere, 2009), like median and coarse sands. Conversely, Rodriguez et al. (2001) found that the meiofauna biomass and number of major taxa increase from exposed to very exposed beaches. The increase of meiofauna toward more exposed beaches is related to the fact that the grater the grain size and the exposure rate, the higher flushed and oxygenated will be the interstitial space (McLachlan, 1989). Therefore, while the meiofauna in fine grain size beaches are confined to the oxygenated upper few centimeters, in or coarse grain size beaches the meiofauna can reach deep into the sediment (Rodrigues et al., 2003). 437

Benthic fauna of macrotidal sandy beaches Table 2: Summary of ANOVA used to compare density and richness among beaches and intertidal zones. P Princess beach, F- Farol beach, C Caixa d`água beach, HT High intertidal zone, MT Middle intertidal zone, LT Low intertidal zone * - (p<0,05), ** - (p<0,01), ns not significant. Density Richness Density Richness Beach P-F ns ns * ns F-C ** ** ** ** F-C ** ** ** ** Zone P F C P F C P F C P F C HI-MI ns ** ** ns ** * * ** ns ns ** ** HI-LI ns ** ns * ** ns ns ** ns ns ** ns MI-LI ns ns * ns ns ns ns ns ns ns ns ns Richness and abundance of meiofauna and macrofauna increased from Princesa to Caixa d`água. It is know that the morphodynamic state and the physical variables are the principal factors controlling the intertidal benthic fauna on exposed sandy beaches (Huz and Lastra, 2008). Biotic variables of macrofauna increase from microtidal reflective (steep beaches and coarse sand) to macrotidal dissipative (flatter slope and fine sand) (McLachlan and Dorvlo, 2005). Exclusion of species toward the reflective end of the beach gradient resulting of both harsh swash and coarse sand (McLachlan, 2001). Across-shore we observed significant differences in meiofauna and macrofauna communities among intertidal zones. The number of major taxa and abundance of macrofauna increase toward the sea, whereas the meiofauna is most abundant and rich at the midtidal level. These results agree with many other surveys of benthic fauna in ocean sandy beaches reviewed by McLachlan and Brown (2006). The increase in the biotic values of macrofauna toward the sea can be explained by the risk of dissecation (in the upper intertidal zone) and the dependence of feeding activities in most macrofaunal species on tidal submergence (McLachlan and jaramillo, 1995, Armonies and Reise, 2000). For the meiofauna, the mid-intetidal presents environmental characteristics more favoring due to the balance between water content, interstitial oxygen, stability and food availability (Pennak, 1951, McLachlan and Turner 1994). CONCLUSION In conclusion it can be stated that in Algodoal island there is a natural small-scale morphodynamic gradient exists between Princesa and Caixa d`água. The beaches are classified as barred dissipative (Princesa) and low tide terrace (Farol and Caixa d`água). The taxonomic composition, richness and abundance of meiofauna and macrofauna in Algodoal are similar to other open ocean beaches. Nematodes dominate the meiofauna and annelids are the most abundant taxa of macrofauna. Richness and abundance of meiofauna and macrofauna increased toward the most protected beach. The number of major taxa and abundance of macrofauna increase toward the sea, whereas the meiofauna is most abundant and rich at the mid-tidal level. Morphodynamic state and sediment grain size are the main factors structuring benthic fauna and more studies have to be undertaken covering a large number of morphodynamic state in order to understand the factors controlling the spatial and the temporal changes in benthic fauna in Amazon beaches. Figure 4: MDS plots of macrobenthic community data performed with Bray Curtis similarity. Abundance data had been fourth root transformed. HI Upper intertidal zone, MI Middle intertidal zone, LI Low intertidal zone. 438 438

Rosa Filho et al. Table 3: Pearson s correlations among benthic fauna (Aabundance, R- richness) and sediment characteristics (MPD Mean particle diameter, % G Percentage of gravel, %S Percentage of sand, % Percentage of silt + clay). Asterisks indicate significant result. A R A R MPD 0,54 * 0,77 * 0,83 * 0,79 * % G -0,26-0,12-0,06-0,16 % S -0,15-0,39 * -0,44 * -0,31 % F 0,46 * 0,64 * 0,67 * 0,60 * LITERATURE CITED Armonies, W. and Reise, K., 2000. Faunal diversity across a sandy shore. Marine Ecology Progress Series, 196, 49-57. Bouwman, L.A., 1983. A survey of nematodes from the Sem estuary. Part II. Species assemblages and associations. Zoologische Jahrbuecher Systematik, 110, 345-376. Croker, R.A., 1977. Macro-infauna of northern New England marine sand: long-term intertidal community structure. In: Coull, B.C. (ed.). Ecology of marine benthos. Columbia: University of South Carolina Press, pp. 439-450. Defeo, O, Jaramillo, E. and Lyonnet, A., 1992. 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We are very grateful to Afonso Quaresma de Lima, who assisted in the field work and to Dr. Janet Reid for the English revision of the original manuscript. 439