Feeding by larvae of the mussel Mytilus galloprovincialis on red-tide dinoflagellates

Abstract

To investigate feeding by the larvae of the mussel Mytilus galloprovincialis on red-tide dinoflagellates, we measured grazing rates of M. galloprovincialis larvae as function of larval age and prey concentration when feeding on several species of the red-tide dinoflagellates Alexandrium affine, Cochlodinium polykrikoides, Lingulodinium polyedrum, Prorocentrum minimum, Prorocentrum micans. and Scrippsiella trochoidea. as well as the flagellate Isochrysis galbana as I control species. The larvae were able to ingest all dinoflagellates offered in the current study; however, first feeding of the larvae on each species of the dinoflagellates occurred 9-13 days after fertilization. whereas that for I. galbana Occurred after 5 days. Ingestion rates of the larvae on unialgal diets of the dinoflagellates and I. galbana increased with increasing larval age up to 17-21 days, but were saturated or showed a Continuous increase thereafter. Ingestion rates of 25-day-old larvae feeding on unialgal diets of the dinoflagellates increased rapidly with increasing prey concentration up to 1000-2200 ng C mL(-1), but were saturated at higher prey concentrations. The harmful alga C. polykrikoides, which has been responsible for great losses in the aquaculture industry, was the optimal prey. Maximum ingestion and clearance rates of the larvae on these dinoflagellates were 14-69 ng C predator(-1) day(-1) and 1.5-11.4 muL predator(-1) h(-1), respectively. M. galloprovincialis larvae, one component of microzooplankters, exhibited higher maximum ingestion and clearance rates than previously reported for other microzooplankters, such as Fragilidium cf. mexicanum (mixotrophic dinoflagellate), Protoperidinium cf. divergens, Polykrikos kofoidii (heterotrophic dinoflagellates), or Tiarina fusus (small ciliate), but lower rates than Strombidinopsis sp. and Favella sp. (large ciliates). The results of the current study suggest that dinoflagellates sometimes can be primary prey for the Mytilus larvae. and the grazers compete with other microzooplankters for dinoflagellate prey. Also, red-tide dinoflagellates can be used for culturing the Mytilus larvae as prey in the aquaculture industry.