Bivalves of the São Sebastião Channel , north coast of the São Paulo State , Brazil

The north coast of the Sao Paulo State, Brazil, presents great bivalve diversity, but knowledge about these organisms, especially species living subtidally, remains scarce. Based on collections made between 2010 and 2012, the present work provides a species list of bivalves inhabiting the intertidal and subtidal zones of the Sao Sebastiao Channel. Altogether, 388 living specimens were collected, belonging to 52 species of 34 genera, grouped in 18 families. Tellinidae, Veneridae, Semelidae, Ungulinidae, Mactridae, Solecurtidae, Corbulidae, Cardiidae, Lucinidae, Cooperellidae, Nuculidae, Psammobiidae, Donacidae, Solenidae, Periplomatidae, Thraciidae and Arcidae were the most representative families in this collection. Among the identified species, Caryocorbula caribaea , Codakia pectinella and Diplodonta punctata were intertidally abundant, while Macoma uruguayensis and Pitar fulminata were subtidally abundant.


Introduction
The municipalities of São Sebastião and Ilhabela are within an area of important biodiversity along northern coast of São Paulo State.Between the continent and Ilhabela island is the São Sebastião Channel (Figure 1).In this area, marine communities have been irreversibly altered because of exponential urban growth and anthropogenic influence in coastal zones.The commercial harbor at São Sebastião, an oil terminal (Dutos e Terminais Centro Sul -DTCS) (Zanardi et al. 1999), and two submarine outfalls (one on the mainland, near the harbor at the Araçá Bay, and another at Saco da Capela, in Ilhabela municipality) have increasingly contributed to local contamination by chemical compounds.Furthermore, much attention has been given to this area due to an expansion of the harbor at São Sebastião, which requires information about environmental impact to marine ecosystems at the region (Teodoro et al. 2010).
In this context, all knowledge on ecological dynamics of coastal and oceanic areas represents important contributions to the evaluation and monitoring of environmental quality.New information is essential to planning and can draw attention to the preservation and sustainability of this delicate natural heritage in São Paulo State (Arasaki et al. 2004;Amaral et al. 2010;Teodoro et al. 2010).
São Sebastião Channel has been an important hub for scientific research due to its variety of habitats and biodiversity.Mollusks are conspicuous among the invertebrate groups found in this region (Amaral et al. 2010).Bivalves contribute to the conduction of nutrients from the pelagic to the benthonic zone, are considered key Abstract: The north coast of the São Paulo State, Brazil, presents great bivalve diversity, but knowledge about these organisms, especially species living subtidally, remains scarce.Based on collections made between 2010 and 2012, the present work provides a species list of bivalves inhabiting the intertidal and subtidal zones of the São Sebastião Channel.Altogether, 388 living specimens were collected, belonging to 52 species of 34 genera, grouped in 18 families.Tellinidae, Veneridae, Semelidae, Ungulinidae, Mactridae, Solecurtidae, Corbulidae, Cardiidae, Lucinidae, Cooperellidae, Nuculidae, Psammobiidae, Donacidae, Solenidae, Periplomatidae, Thraciidae and Arcidae were the most representative families in this collection.Among the identified species, Caryocorbula caribaea, Codakia pectinella and Diplodonta punctata were intertidally abundant, while Macoma uruguayensis and Pitar fulminata were subtidally abundant.Anomalocardia brasiliana, a species with great ecological and socioeconomic importance, was not included in this study, despite the huge biomass and conspicuous populations in certain sampling localities such as Araçá Bay.This species has a high nutritional value and supplies food for local fishermen and tourists (Amaral et al. 2010).Anomalocardia brasiliana was excluded from the present study because it has been investigated in other studies (Narchi 1974;Arruda-Soares et al. 1982;Boehs 2000;Arruda and Amaral 2003;Amaral 2010;Boehs et al. 2010).
All specimens were immediately submersed in seawater and kept alive for transport to the Marine Biology Center, São Paulo University (CEBIMar-USP), where they were dissected for other purposes.Foot and adductor muscle tissues were fixed in 95% alcohol for molecular analyses and gonads were prepared for electron/light microscopy.The remaining soft parts and shells of the voucher specimens were deposited in the Museum of Zoology "Prof.Dr. Adão José Cardoso" (ZUEC), in the State University of Campinas (Table 1).Species identifications were based on Rios (1994Rios ( , 2009)), Mikkelsen and Bieler (2008), Quast (2003), Arruda (2005), Amaral et al. (2006), andDenadai et al. (2006), while suprageneric nomenclature and taxonomic order follow Bieler et al. (2010).
Images of shells were made using a stereomicroscope (Stereo Discovery V8, Carl Zeiss Microscopy) and a Canon digital camera (Figures 2-4).Some specimens were slightly damaged during dissection and other, well-preserved specimens from the teaching collection of State University of Campinas were photographed instead.However, all rare specimens collected as part of this study were all photographed.

Results
Altogether 388 living individuals and 52 species of bivalves were collected.They belong to 34 genera, grouped in 18 families and five orders (Table 1, Figures 2-4).
A few species were exclusively found in the subtidal zone: Anadara chemnitzi (Figure 2. Araçá Bay is formed by sand and mud sediments and is one of the last remaining mangrove locations in the region.The bay has a high number of species.In six collections 93 individuals belonging to 22 species were found. The collections from Engenho D'água Beach (one station) and Velho Barreiro Beach (two stations) show a large number of species.At Engenho D'água Beach, 108 specimens belonging to 19 species were found.At Velho Barreiro Beach, 72 specimens belonging to 15 species were collected.
Due to possibly insufficient search effort at some sites, species previously reported in other studies were not found.The absence of such species in our data does not necessarily show that they are no longer extant in the area.Thus, we cannot state that the absence of certain species in our survey represents a reduction in biodiversity.Willig et al. (2003) and Ricklefs (2004) suggest a pluralistic approach to study biodiversity, considering that there is not a universal criterion to measure it within a specified geographic area.Factors that influence biodiversity are not fully understood, although weather, climate stability, spatial heterogeneity, physical disturbances of the environment, sediment type, competition, predation and productivity are likely important.More heterogeneous environments are related to higher species richness (Soares-Gomez and Pires-Vanin 2003).
Water current and sediment type may contribute to the distribution of bivalve species in São Sebastião Channel.Seasonal dynamics of water masses in the channel greatly influences the marine biota (Migotto et al. 2001).Some localities contain a wide range of sediment sizes from sand and gravel grain classes to silt or clay, and this heterogeneity has been related to abundance of bivalves (Denadai et al. 2005).Araçá Bay, Engenho D'água and Velho Barreiro beaches have these heterogeneous sediments and favorable water currents.

Figure 5 .
Figure 5. (A) Total of species per family collected in the intertidal zones of the São Sebastião and Ilhabela beaches, between 2010 and 2012.(B) Total of species per family of bivalves collected in 2012 in locations within the São Sebastião Channel.