Spatial variability in the icthyoplankton structure of a subtropicalhypersaline lagoon

Abstract

The Lagoa de Araruama is a hypersaline ecosystem inhabited by distinct fish species, either permanently or during their reproductive season. Over recent years, some significant environmental changes have been observed in this ecosystem related to the sewage runoff, as salinity decrease (from 64 to 41 psu during the last 40 years) and nutrients increase. As both changes are thought to affect the ichthyoplankton assemblage, the present study aimed to evaluate all the potential relationships between salinity disruption and fish larvae distribution. Ichtyoplankton samples were collected monthly from January 2010 to March 2011 at eight sites in Araruama Lagoon by means of a WP2 plankton net equipped with a flowmeter. During this period, low egg densities were coincident with high salinity regions, suggesting that adults are avoiding to release their eggs under less favorable environmental conditions to the larvae. The uneven distribution of eggs and larvae inside the lagoon, as revealed by both spatial and temporal analyses lead us to suggest that changes in salinity have influenced the reproductive rhythms of those fish species that depend upon the Lagoa de Araruama.

Spatial and temporal variability of the zooplankton community at Araruama Lagoon

“…In the present study, O. hebes was poorly abundant and A. lilljeborgi was found only in station 12, close to the seawater entrance. This variation in species may be related to the changes in salinity over the years, which decreased the average from 64‰ to 41‰ over the last 40 years (ROSA et al, 2016a).…”

“…The entry of freshwater into the lagoon causes a decrease in salinity. The change in salinity affects the composition of plankton (RODRIGUES, 1998;ROSA et al, 2016a;2016b). In addition to sewage pollution, the lagoon also suffers from invasive species such as the copepoda Temora turbinata and the cladocera Pleopis schmackeri (CARVALHO et al, 2014).…”

Tracking of spatial changes in the structure of the zooplankton community according to multiple abiotic factors along a hypersaline lagoon

“…After many years of sewage discharge, Araruama is now considered as an eutrophic lagoon (Carvalho et al, 2014). Moreover, its average salinity is currently 41‰, which is higher than that of the sea of Cabo Frio where the lagoon water exchange occurs (Rosa et al, 2016a).…”

“…Since the 1980s, the Araruama lagoon has been subjected to sewage contamination (Pereira, 2007) due to an increased number of summer tourists and growth of the resident populations of Araruama and neighboring towns (Coutinho et al, 1999;Pereira, 2007;Carvalho et al, 2014). The continuous discharge of sewage in the lagoon has decreased the salinity and increased the nutrient loading (Souza et al, 2003;Rosa et al, 2016a). After many years of sewage discharge, Araruama is now considered as an eutrophic lagoon (Carvalho et al, 2014).…”

“…In 2010, samples were taken monthly from January to June, October to December, and in 2011, from January to March. During the data sampling, the state of the tide (ebb or flood) could not be standardized at the time of sampling, but previous data reveal that the tide has no significant influence on salinity from the Boqueirão sampling site (station 1) to Ponta dos Excursionistas (station 8) (Rosa et al, 2016a). However, the general scenario of tidal trends ranged between ebb and flood ( January 2010 ebb; February 2010 ebb; March 2010 ebb; May 2010 flood; October 2010 ebb; November 2010 ebb; December 2010 flood; January 2011 ebb; February 2011 ebb; March 2011 flood).…”