TROPHIC ECOLOGY IN SYMPATRIC ASTEROIDS FROM COASTAL PATAGONIA.

ZAVATTIERI, V.; PENCHASZADEH, P. E.

Banyuls-Sur-Mer

Conferencia; 6th European Conference on Echinoderms; 2001

The diet ofthree Asteriinae, the broodingAnasterias minuta, the fissiparous Allostichaster inaequalis, and the broadcast-spawnerCosmasterias lurida, was studied in northern Patagonia (64°S ; 42°W), from November 1998 to March 2001. Sea stars weresampled in intertidal and subtidal environments to determine proportion of foragers and diet composition. Foraging occurs bystomach eversion in the three studied species. A. inaequalis (radius = 3.5 cm, range 0.5-6.7; n = 208) was found manly in subtidalhabitats, A. minuta (radius = 3.3 cm, range 0.2-7.2; n = 1,125) in intertidal and subtidal areas, and e lurida (radius = 10.7 cm,range 3.6-19.4; n = 424) was exclusively subtidal. Foraging iodividuals made 20-40% of the sample. A. inaequalis fed mostlypelecypods (89% ofthe prey items). Individuals of all sizes preyed on the rnytilid Aulaeomya atra atra; the burrowing bivalveLithophaga patagonica was preyed by the largest sea stars. Other prey were gastropods and c1ams. A. minuta in subtidal stationspreyed mainly 00 the snail Tegula patagonica (75%), on small bivalves (A. atra atra) and, rarely, on chitons. Intertidal individualshad a broader diet. The largest of the studied species, e lurida, fed mostly A. atra atra (51%), with a positive and significantcorrelation between predator and prey sizes (R = 0.65). The smaller sizes preyed upon T. patagonica (36%) while medium sizestarfish forage on L. patagonica. Prey iterns found at lower levels of predation were sea urchins, clams and polychetes.