CONTRIBUTION OF THE POLYCHAETOUS ANNELIDS TO THE DIET OF THE FISH CALLIONYMUS LYRA AND LESUEURIGOBIUS FRIESII IN AN ESTUARINE SYSTEM ALTERED BY MUSSEL RAFT CULTURE
Parapar, J. & Fernández, L.
Departamento de Bioloxia Animal e Bioloxia Vexetal, Faculdade de Ciencias Bioloxicas, Universidade de A Corua, E-15071 A Corua, Spain
The Ría de Arousa (Galicia, NW Spain) is an estuary characterized by an intensive mussel (Mytilus galloprovincialis) raft culture, which has altered the nature of the bottom (granulometry and organic material) and the food contribution to the megafauna (the great raft epifauna community). Callionymus lyra and Lesueurigobius friesii are two of the most abundant species of demersal fish in this area, and the polychaetous annelids constitute one of their most important feeding resources. A total of 738 C. lyra and 1542 L. friesii stomachs with food were analyzed in order to evaluate the polychaetes'contribution to their diet. The fish were collected at four stations (raft: B1, B5, B6; nonraft: M2) representing different environmental conditions in the Ría de Arousa (Galicia, NW Spain). The polychaetes (23 families and approximately 50 prey items identified) represented more than 30% of the stomach contents of both species (30.5% in C. lyra and 37.7% in L. friesii), as the sessile surface and sub-surface deposit feeders are more abundant than the mobile ones. In C. lyra, Ampharete acutifrons was the dominant polychaete item (24%PSC), specially in the inner raft station, B1 (88%PSC), where C. lyra was the principal prey (26.3% of the total diet, 64% frequency of appearance). Ampharetids (26%PSC) were also dominant in the diet of L. friesii in stations B1 (41.6% PSC) and M2 (28%PSC), while in B5 the principal prey item was the dorvilleid Ophryotrocha labronica (36.2%PSC). This species was consumed preferentially by the smaller size classes, while the larger individuals showed preference for bigger prey belonging to the families Cirratulidae and Spionidae. L. friesii also showed differences in prey selection between size classes, as the species belonging to the families Nereidae and Polynoidae were only found in stomach contents of the larger individuals. In both species, temporal variations in dominant prey items were also found, although a clear pattern was hard to recognize.