A trophic analysis of target species of macrobenthos in a subtropical coast community: a taxa relationship essay

– Studies on the feeding habits of aquatic organisms are a requirement for the management and sustainable use of marine ecosystems. The aim of the present research was to analyze the habits and trophic similarities of decapods, starfish and fish in order to propose trophic relationships between taxa, using Hennigian methods of phylogenetic systematics. This new grouping hypothesis, based on shared and exclusive food items and food types, corresponds to the broad taxonomic groups used in the analysis. Our results indicate that algae, Mollusca, Polychaeta, Crustacea, Echinodermata and Actinopterygii are the most exploited common resources among the species studied. Starfish were differentiated from other organisms for being stenophagic, and were grouped for feeding on bivalve mollusks. A larger group of fish and crustaceans shares algae and mainly crustaceans as food items. A third group united all eight species of Actinopterygii. This largest subgroup of fish is typically carnivorous, feeding on Anthozoa and a great quantity of Crustacea. synodus foetens has a special position among fishes, due to its unique feeding on nematodes. A Euclidean distance dendrogram obtained in a previous publication grouped s. foetens with starfish. That result was based on a few non-exclusive shared similarities in feeding modes, as well as on shared absences of items, which are not an adequate grouping factor. Starfish are stenophagic, eating bivalves almost exclusively. synodus foetens and isopisthus parvipinnis have restricted food items, and are thus intermediary in relation to starfish, decapods, and other fish, which are euryphagous. The trophic cladogram displays details of food items, whether or not shared by all species. The resulting trophic analysis is consistent with known historical relationships. CLADOGRAM COMMOn FOOD ITEMS TROPHIC RELATIOnS 36 M. E. DE ARAÚJO, M. J. LunARDOn-BRAnCO, J. R. VERAnI et al. Vie milieu, 2014, 64 understanding of food webs. Knowledge about mean path length is important as it quantifies the average number of links necessary for an effect to propagate from one species to another (Froese et al. 2005). nearly half of the world’s commercial salt-water fisheries, both marine and estuarine, consist of shellfish and demersal fishes whose main food is benthic (Joydas & Damodaran 2009). The fish species studied herein were only one trophic level away from each other. In contrast, Mediterranean fishes are, on average, two trophic links (corresponding to levels 2-4) away from each other (Froese et al. 2004). Benthos represents the main food items of demersal fish (Longhurst & Pauly 1987). Thus fishes which feed on the benthos contribute to energy transfers for higher trophic levels. They thus play a significant role in transferring energy from detritus and other benthic macroand microvegetation organisms, suspended particulate matter, bacteria, protists, and primary consumers to higher trophic levels (Manickchand-Heileman et al. 1998). A theoretical overview of recent studies of trophic ecology has identified the application of phylogenetic methods as one of the recent breakthroughs in the study of community ecology (Christoffersen et al. 2011). In this paper we propose a new analysis based on the food items of 15 target species (Lunardon-Branco et al. 2006), and discuss some of the implications of these results for phylogenetic and ecological concepts. Material and MetHodS Information on food content for the 15 target species, representing the most common species captured in commercial trawling activities in the chosen study site, are presented in Appendix I. All references used to analyze the data base are listed in this same appendix. Monthly collections were carried out at Armação do Itapocoroy (26°40’-26°47’S, 48°36’-48°38’W) in three traditional artisanal shrimp fishing areas: Ponta da Vigia; in the proximity of Feia Island; and between this island and the Itacolomis Islands (Lunardon-Branco et al. 2006). These areas have a predominantly silt-clay sediment. Dredgings were carried out between January and December 1995 on the bottom at depths of 8 to 15 meters between 8:00 and 14:00, during 30 minutes. Two seine nets were dragged by a 10.5 m boat powered by a 40 hp engine that kept a mean constant speed of two knots (Branco et al. 2002). The Point Method and Frequency of Occurrence (see Hynes 1950, Berg 1979, Williams 1981) was used in the qualitativequantitative analysis of diets. Food items were used to construct a data matrix and a trophic analysis for 15 target species selected among the most common asteroids, decapods, and fishes from the macrobenthos community in Itapocoroy, southern Brazil (Lunardon-Branco et al. 2006). The stomach contents were identified to the lowest possible taxonomic level with the aid of appropriate taxonomic guides (see Appendix I). The food items were united in categories that represent organisms at several hierarchical levels. Besides the different analyses of Crustacea items, we grouped all taxa of this subphylum as a special item, because the frequencies of occurrence between the 15 species showed high variation. Whenever the range of frequency variation is very wide, we created another category, indicating the minimum frequency percentual of occurrence of the food item. We considered a species as euryphagous or omnivorous when the stomach items of both vegetal and animal origin are found in significant amounts. In this context, a species is considered stenophagous when it eats practically a single item and only a small percentage of the other