Factors influencing spatial patterns of molluscs in a eutrophic tropical bay

Abstract

Samples were collected from 10 stations distributed through three sectors in Guanabara Bay during two consecutive years, in order to determine factors that influence the spatial pattern of molluscs and to describe the structure and composition of this community in a eutrophic estuarine system on the Brazilian coast. Although only one species, the gastropodHeleobia australis, comprised 77% of mollusc abundance, 59 species were identified in the bay. In addition toH. australis, three other species were dominant: the gastropodAnachis isabelleiand the bivalvesAmericuna besnardiandErvilia concentrica. The mollusc communities were significantly influenced by the spatial gradient; the outermost sector has marine conditions, and the other sectors are typically estuarine, leading to differences in the composition and abundance of molluscs. The outermost sector showed the highest diversity, which gradually decreased towards the innermost sector where the dominance of a few opportunistic species is favoured by highly organic mud sediments. Sediment type was strongly correlated with mollusc occurrence in the bay. Guanabara Bay showed two indicator species: the bivalveE. concentricaof the outer sector, and the gastropodH. australisof the intermediate sector. Our results suggest that benthic molluscs in Guanabara Bay show characteristics related to levels of environmental impact. A monitoring programme based on this community is needed to evaluate the effects of human impacts on this community and to monitor changes in its biodiversity in Guanabara Bay.

The Relationship between Mollusks and Oxygen Concentrations in Todos Santos Bay, Baja California, Mexico

“…Differences in genera composition and abundances can be related to the method used to collect the mollusks (grab, trawl) and also depend on the sampling effort. We did not observe a clear relationship between sediment type and the genera composition of mollusks, which has been described in other malacological studies [41,42]; but we found that mollusks were related with dissolved oxygen (DO) concentrations near the seafloor (10% of total variance). The differences found could be due to the identification level (genus) while other studies have been done to species level.…”

“…A study performed in 2011 recorded 18 genera at 31 ∘ N which is the same latitude as TSB; in that study most stations were located at more than 200 m depth [27]. This genera abundance is low compared with the 36 genera collected in this study; however, it is low compared to tropical Guanabara Bay located in Brazil with 46 genera [41], but it is close to the subtropical Mersin Bay in Turkey with 35 genera [42].…”

“…Some research has described malacological fauna and DO; for example, Zamorano et al [26] described a segregation of mollusk species from the range of 0.04 to 2.20 mL L −1 DO concentrations in the Gulf of California, Mexico, where bivalves dominated in low DO concentrations and the scaphopod Dentalium agassizi was present in almost all the ranges of DO measured. Another work found two groups of species but only gastropods were related to a DO gradient in Guanabara Bay, Rio de Janeiro, Brazil; in this case, the first group was conformed by Natica pusilla, Acteocina bidentate, Olivella minuta, and Turbonilla sp., while the second group was conformed by Anachis isabellei, Heleobia australis, and Nassarius vibex [41]. Species inhabiting oxygen minimum zones (OMZ) require specific behavioral adaptations; for example, zooplankton migrates to well oxygenated waters and the pteropod Diacria quadridentata reduces oxygen consumption and ammonia excretion in OMZ [45,46].…”

“…The increase of human populations in coastal zones contributes to promoting sites with low levels of DO [9]. Other species belonging to families Naticidae and Acteocinidae, such as Natica pusilla and Acteocina bidentata, have been found in well oxygenated waters in Guanabara Bay, Rio de Janeiro, Brazil [41]. In our study, genera Natica and Acteocina were collected in high oxygen concentrations in the north and central sections of the bay (stations 1, 3, 9, 4, 13, 14, 19, and 21).…”

Spatial Patterns in Diversity and Distribution of Benthic Molluscs in a Weak Tidal Tropical Lagoon

“…Scale-dependent patterns of distribution may be particularly important in coastal areas, since they are characterized by variability in abiotic conditions (Neves et al, 2012). For benthic fauna, patterns of distribution are related to salinity (Atrill, 2002;Attrill and Rundle, 2002;Ysebaert et al, 2003), sediment characteristics (Teske and Wooldridge, 2003;Anderson et al, 2004) and other factors.…”