<b> Natural diet of <i> Ligia exotica </i> (Crustacea, Isopoda, Ligiidae) in two estuarine regions of Patos Lagoon, Rio Grande do Sul, Brazil </b>

Abstract

Isopods are examples of the evolutive transition of the crustaceans from sea to land, inhabiting aquatic and terrestrial environments. Ligia exotica is dominant in the intertidal region of the of Patos Lagoon estuary, playing an important role in recycling nutrients and in the trophic web as a whole. The study area was the West Breakwater of Rio Grande Channel and Leonideo Island. The natural diet was analyzed through standardized one hour manual sampling performed in October/2003, January, April and July/2004. After collected, individuals were immediately fixed in 4% formalin during 24 hours and conserved in 70% ethanol. The guts were weighted and repletion degree was estimated. Each gut content was diluted in 1 ml of distilled water. To quantify the items, content was placed in a graduated slide for counting. Each identified item was quantified by the number of occurrences in the slide squares. To test significant differences between the frequencies of items consumed by males and females, a chi-square test was used. Qualiquantitative analysis was performed following the method of relative frequency of occurrence and relative frequency of points. A total of 912 guts was analyzed: 426 individuals from the West Breakwater and 485 individuals from the Leonideo Island. Six food items were identified and significant differences were observed in the items consumed by males and females of both populations. The most important food items in the natural diet of Ligia exotica were: vegetal detritus, sand and the seaweed Polysiphonia sp. Thus, in both regions of the Estuary, the species can be considered generalist.