Food web of a SW Atlantic shallow coastal lagoon: spatial environmental variability does not impose substantial changes in the trophic structure

Abstract

We performed a detailed analysis of the food web structure of Laguna de Rocha, a temporally open coastal lagoon in the Southwest Atlantic, characterised by spatial gradients in salinity, nutrient levels and trophic status. Carbon and nitrogen stable isotopes of main producers, invertebrate and vertebrate consumers, and stomach contents of ichthyofauna were analysed seasonally at freshwater (north) and marine-influenced (south) sites to determine whether environmental differences induced changes in food web structure. Contribution of primary and secondary food sources and trophic linkages were assessed with the multisource-partitioning model IsoSource and an index that quantifies the contribution of each organism as food for the ecosystem. Isotopic analyses were performed for 10 primary organic matter sources (OM), 13 invertebrates and 9 fish species. Suspended and sediment OM constituted the most important primary sources, while direct consumption of macrophytes and macroalgae was marginal. The small invertebrates Neomysis americana, Nephtys fluviatilis, Pseudodiaptomus richardii and an amphipod were the most important intermediate consumers at both sites (except P. richardii, which was present only in the north). Top predators were the fish species Micropogonias furnieri, Paralichthys orbygnianus and Hoplias malabaricus, and the maximum estimated trophic level (between 3.4 and 4.8) varied seasonally, but not between sites. Fish stomach content analyses largely confirmed results from the IsoSource mixing model. Overall results indicated that, despite environmental differences between sites, the structure of the biological assemblages and general trophic patterns were similar at both sites.KEY WORDS: Food web structure · Coastal lagoon · Estuaries · Benthic-pelagic coupling · Isotopic mixing models Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 362: [69][70][71][72][73][74][75][76][77][78][79][80][81][82][83] 2008 organic matter (OM) sources, energy pathways supporting consumers, and the processes modulating their spatial and temporal variability (Chanton & Lewis 2002, Froneman 2004. Most studies in shallow estuaries have focused on identifying OM sources that sustain specific consumer groups. Traditional views of macrophyte detritus as a fuel for secondary production (Odum & Heald 1975) have received only partial support (Deegan & Garrit 1997, Kwak & Zedler 1997, Chanton & Lewis 2002, Kibirige et al. 2002, Perissinotto et al. 2003, Vizzini & Mazzola 2003, Bouillon et al. 2004. Microphytobenthic algae, phytoplankton, macrophytes and detritus can all be important sources, and relative contributions differ between systems according to environmental characteristics (Kanaya et al. 2007).Less effort has been devoted to identifying the most significant secondary-level food sources (i.e. heterotrophic OM sources for secondary and higher consumers). The structure of the assemblage of intermediate consumers that link basal OM sources and higher predators can be...

The trophic position of the Atlantic blue crab Callinectes sapidus Rathbun 1896 in the food web of Parila Lagoon (South Eastern Adriatic, Croatia): a first assessment using stable isotopes.

“…The TP estimation is consistent with that of other investigations performed using stable isotopes, ranging from 2.8 to 4.3 (Moncreiff & Sullivan, 2001;Abreu et al, 2006;Rooker et al, 2006;Rodriguez-Graña et al, 2008;Winemiller et al, 2007;Carrozzo et al, 2014). Most importantly, this study indicated that a considerable size-related variation occurs in the trophic position of C. sapidus, increasing from values as low as 3.34 for juveniles to values in the 3.7 -4.11 range for the largest individuals.…”

Effect of different protein supply on growth of three populations of a crab adapted to low energy diets

“…Intermolt periods of N. granulata were always longer, increasing gradually up to double the values of C. angulatus at stages 5 or 6, while increment per molt was half that observed in C. angulatus. This result indicates that N. granulata growth can be considered slow (both in time and size increment per molt), even when fed with high quality diets, compared to a more carnivorous aquatic species as C. angulatus [23]. Additionally, the similarity of intermolt periods of crabs fed with 18 and 24 % protein in this study suggest that N. granulata fed with diets above 18 % protein molt as frequently as possible for a certain size and temperature, and growth cannot be substantially accelerated by higher quality diets.…”

Life history traits influence in gonad composition of two sympatric species of flatfish

“…Such selective retention of HUFA has been associated with a limited availability of this FA in the food web and also clearly shows an efficient ability to retain FA (KOUSSOROPLIS et al, 2011). P. orbignyanus is a high trophic level predator in coastal lagoons (RODRÍGUEZ-GRAÑA et al, 2008), so the accumulation of certain FA which are found in low proportion in their estuarine diet, such as n-3HUFA, is to be expected. Additionally we could consider the possibility of a greater ability of P. orbignyanus to elongate and desaturate LNA to DHA and EPA.…”