Food preferences of four aspidochirotid holothurians species (Holothuroidea: Echinodermata) inhabiting the Posidonia oceanica meadow of Mostaganem area (Algeria)

Abstract

Analysis of the digestive contents of four aspidochirotid holothurians species (Holothuria poli, H. tubulosa, H. forskali and H. sanctori) sampled in two localities in the Mostaganem area (Stidia, Salamandre) were carried out in order to overview the different food sources appreciated by these animals. Our results show that holothurians feeds on diatoms, cyanophytes, macrophytes algae, Posidonia oceanica leaves (alive and dead), foraminifera, crustaceans, molluscs bivalve shells, sponge ossicles and nematodes. Diatoms were mostly consumed by holothurians at both sites. The greatest rates of ingested diatoms are recorded for H. poli (38.66% and 34.44% respectively at Stidia and Salamandre). The Posidonia oceanica leaves (alive and dead) are also consumed, but with low rates. Holothuria forskali feeds in a preferential way on the Posidonia oceanica leaves (3.33% dead leaves, 14% live leaves at Stidia and 9% live leaves at Salamandre). Foraminifera are consumed mostly by H. forskali (13.33% and 15% respectively at Stidia and Salamandre), even if that food source is not appreciated very much (Ivlev index: -0.3 and -0.06 respectively at Stidia and Salamandre). At both sites, most holothurian species consume large amounts of sponge ossicles and this is their preference. Crustaceans and nematodes are less consumed, regardless of their significant electivity index (Ivlev index = 1 for nematodes, in most holothurians species of Stidia area).