Effects of exposure to toxic and non-toxic dinoflagellates on oxygen consumption and locomotion in stage 1 larvae of the crabs Cancer oregonensis and C. magister

Abstract

Sublethal effects on larval crabs upon exposure to toxic dinoflagellates were examined in the laboratory in early 1999. Specifically, oxygen consumption rates and geotaxis responses were determined for stage 1 larvae of the crabs Canceroregonensis (Dana) and C. magister Dana that were exposed to non-toxic (Alexandriumtamarense, strain 115) or toxic (A. fundyense, strain 1719) dinoflagellates or to freshly hatched nauplii of the brine shrimp Artemia sp. In C. oregonensis, larvae exposed to the toxic dinoflagellate showed reduced rates of oxygen consumption compared to those exposed to non-toxic dinoflagellates or brine shrimp nauplii. Larvae exposed to a filtrate of the non-toxic dinoflagellate showed no change in oxygen consumption, but a reduced rate when exposed to filtrate from the toxic alga at densities >5×102 cells ml–1. In C. magister, larvae exposed to the non-toxic A. tamarense or the toxic A. fundyense had reduced oxygen consumption rates. Larvae exposed to filtrates of non-toxic and toxic dinoflagellates had no change in oxygen consumption. In geotaxis tests, C. oregonensis larvae exposed for 1 day to the toxic A. fundyense reduced their level of locomotion compared to those exposed to non-toxic A. tamarense or to brine shrimp nauplii. C. magister larvae showed no change in activity after a 1-day exposure to the toxic A. fundyense. After a 4-day exposure to A. fundyense, C. magister larvae had much reduced locomotion. Reduced locomotory activity in larvae exposed to toxic algae is consistent with the changes in oxygen consumption rates. Responding to exposure to toxic algae by reducing locomotion may affect vertical migration in these negatively buoyant crab larvae, resulting in sinking below a toxic alga bloom, at least temporarily.