Frontiers in Marine Science (Nov 2015)
Using fish larvae as indicators of estuarine ecosystem condition in Rio de Janeiro State, Brazil
Abstract
Estuaries enhance growth and maximize the survivorship of initial development stages of fish species, functioning as nursery grounds for many species. However, estuaries throughout the world host a wide variety of human activities, and fish communities can be severely impacted. Protection of aquatic biodiversity and proper management of these coastal systems require robust tools to assess habitat integrity and ecological quality status. Thus, the present study investigated the use of fish larvae as indicators of estuarine ecosystem condition in Brazil, testing the hypothesis that estuaries with different human impacts and environmental conditions carry distinct larval fish assemblages. For this, four estuaries were analysed with: similar environmental conditions (the same water mass surveyed), similar pool of species (the same geographical region) and no seasonal influences (different periods analysed separately). Surveys were conducted in Macaé, São João, Bracuí and Perequê-Açu estuaries located in Rio de Janeiro State, Brazil. Sampling surveys were conducted every two months between May 2013 and March 2015. All samples were taken in the estuary middle region (salinity 15-25) during nightly ebb tides. At each estuary, ichthyoplankton subsurface tows were perfomed using a Bongo net. Water parameters were measured by a multiparameter probe and surface water samples collected for further analytical analyses. Fish larvae were identified and species were assigned into functional guilds. The water conditions were assessed based on water temperature, pH, chlorophyll a, dissolved oxygen and total particulate matter. Faecal coliforms, nutrient load (NO3, NO2, NH3, PO4, SiO3) and presence/absence of dams, dredging and mangroves were used as anthropogenic pressure descriptors. The species composition and ecological guilds of Macaé and Perequê-Açu differed significantly of São João and Bracuí, separating the impacted versus non-impacted estuaries. Furthermore, the lower nutrient load and faecal contamination associated with the presence of mangroves, high number of species and guilds were indicative of a better ecological condition in São João and Bracuí. The results supported the hypothesis that estuaries with different human impacts and consequently different environmental conditions carry distinct larval fish assemblages.
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