Abstract
Based on a set of intermittent and seasonal data, covering a discontinuous 21-year period (1995 to 2016) and using a standard beach seine with replicates at several collection points inside the Tramandai River estuary (TRE) and outside in the marine adjacent coastal area (MACA), we evaluated connectivity between TRE and MACA and the spatiotemporal variations of fish associations. In the TRE (405 samples; 42,987 individuals) 55 species were captured. In the MACA (297 samples; 54,295 individuals) 41 species were captured. After data standardization the expected richness of the TRE [E(S) = 18.2] was significantly greater (p <0.05) than that of the MACA [E(S) = 14.4]. The fish association structure and distribution patterns in TRE and MACA are dynamic and interconnected but quite different in terms of species composition, especially due to the influence of local salinity. The TRE association is richer in a number of species but numerically dominated by marine estuarine-dependent juveniles. Freshwater species may eventually be carried in by heavy rains, bringing pulses of species richness. The MACA association is represented by a few typical marine species in addition to a couple of estuarine-related transient species who uses the surf-zone as a passageway to enter the estuaries. Even if there is a higher percentage of common species reported (30 out of 66), the monthly average Jaccard Index of similarity (JI = 28%) and the monthly average Percent Similarity Index (PSI=30%) was low, suggesting that the shallow water functional connectivity between MACA and TRE are represented by few species that occur equally in abundance in both environments. Juvenile of two species of mullets (Mugil liza and Mugil curema) add up to more than 70% of the total catches in both environments. The hypothesized signal of decadal diversity and abundance reduction seems to be muffled by seasonal environmental fluctuation revealing that fish assemblage of MACA and TRE are highly resilient through the years. The only observed interdecadal trend was the reduction in abundance of juvenile M. liza that seems to parallel the reduction in abundance of the adults fishing stocks in southern Brazil.
Highlights
Estuaries, and coastal areas are environments with high biological productivity, and are considered important nursery areas for juvenile of many coastal fish species, including those of economic interest (Beck et al, 2001; Barletta et al, 2010)
Based on a set of intermittent and seasonal data collections, covering a period of 21 years (1995 to 2016), the present study investigated the connectivity between the shallow water of the Tramandal River estuary (TRE) and the adjacent coast (AC)
Understanding the level of connectivity between estuarine and marine environments is essential for the appropriate management of taxa associated with coastal zones
Summary
Estuaries, and coastal areas are environments with high biological productivity, and are considered important nursery areas for juvenile of many coastal fish species, including those of economic interest (Beck et al, 2001; Barletta et al, 2010). Freshwater species are much less frequent in the coastal region adjacent to estuaries (Ramos and Vieira, 2001; Monteiro-Neto et al, 2003; Lima and Vieira, 2009; Rodrigues et al, 2014), but the general abundance and diversity of the fish fauna in the marine coastal region are affected by freshwater runoff coming from the estuary (Martins et al, 2015)
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