Vital role of drift algae in the life history of the pelagic harpacticoid Parathalestris croni in the northern North Atlantic

Abstract

The harpacticoid copepod Parathalestris croni, a widespread pelagic species of the northern North Atlantic, was found to be closely associated with seaweed originating in the intertidal zone floating on the surface of the sea around Iceland. The abundance of the copepod increased with distance from the shore and it showed a special affinity for the brown alga Ascophyllum nodosum. The copepods in the macroalgal clumps were mostly ovigerous females, and the seaweed clearly serves a nest function. The eggs were deposited on the seaweed where the nauplii, which are unable to swim, crawl on the algae until they metamorphose into the first copepodite stage (CI). The CI copepodites leave the floating weed, and the juvenile stages may eventually disperse widely in the water column until floating weed is colonized, probably by adults or juveniles in the lest one or two copepodite stages. Parathalestris croni is one of a group of very few species known or suspected to be dependent for survival on the extremely unpredictable habitat of floating weed in the northern North Atlantic.