Abundance and ingestion rate of the sea hare, Dolabella auricularia (Lightfoot, 1786) in a shallow embayment (eastern Mactan Is., Cebu central Philippines)

The hypothesis that the sea hare, Dolabella auricularia (Gastropoda: Aplysiidae) is capable of regulating the biomass of the dominant macroalga, Cladophora sp. and thus restructure the algal assemblage in a small shallow water embayment eastern Mactan Is., central Philippines was explored. A mark and recapture technique was employed to quantify the overall population of Dolabella in the area. A feeding experiment was also conducted to determine if algal type (food preference among the green alga, Cladophora sp., the brown alga, Sargassum cristaefolium and the seagrass Cymodocea rotundata), time of day (daytime vs nighttime) and size (small vs large specimens) could significantly affect the feeding rate of D. auricularia. The estimated population of D. auricularia ranged from 4,163 – 14,288 individuals. Assuming only 2 hectares of the 15-hectare embayment are inhabited by the sea hare, the population density would ranged from 2-7 individuals/10 m. The ingestion rate by food type showed the following order of preference: Cladophora sp. > C. rotundata > S. cristaefolium. Time of day did not significantly affect overall ingestion rate of the sea hare. However, smaller individuals ( 100 g) whether it is during the day or night. The daily ration of D. auricularia for the green alga, Cladophora is about 47 g FW *Corresponding author’s email address: dydt_up@yahoo.com The Philippine Scientist, Volume 42 (2005) 68 for sea hare 100 g. Considering the population size of the Dolabella and its ingestion rate with particular preference for Cladophora, it can be deduced that the D. auricularia population should be an important structuring force in regulating the growth of Cladophora in the shallow embayment.