Combined effects of radiation and food on vertical migration of crab larvae Cyrtograpsus altimanus

HERNÁNDEZ MORESINO, R.D.; VALIÑAS, M.S.; FIORDA GIORDANINO, M.V.; GONCALVES, R.J.

Mar del Plata

Conferencia; CERF 2012: The Changing Coastal and Estuarine Environment: A Comparative Approach; 2012

Estuarine Research Federation - Universidad Nacional de Mar del Plata

Many studies have documented the negative effects of the increased ultraviolet radiation (UVR, 280-400 nm), especially ultraviolet-B (UV-B, 280-315 nm), in aquatic ecosystems. To cope with this potential threat, organisms may respond either behaviorally, developing repair systems, and/or accumulating photoprotective compounds. Many species of zooplankton seem to be adapted to high UVR levels altering their depth into the water column by diel vertical migration (DVM). DVM may be caused by biotic (predation, food) and abiotic (solar radiation, temperature) factors as well. Planktonic crab larvae are able to actively swim to perform DVM, so our goal is to determine the response of the first larval stage (Zoea I) of the crab Cyrtograpsus altimanus under different conditions of radiation and food. Three experiments were performed using a solar simulator in presence and absence of UVR (i.e., visible light + UVR or visible light only), combining these two radiation treatments with or without food supply (ie, dinoflagellate Alexandrium tamarensis). Adult crabs of C. altimanus are a transient component along the Patagonian coast, while A. tamarensis is found in high concentrations in these waters and could be an important food item for their crab larvae during the early developmental stages. Our results show that the presence of UVR inhibits the tendency of larvae of C. altimanus to swim towards the surface (i.e., compared to larvae exposed to visible light only). In this treatment, vertical distribution shifted downwards. This helps explaining why larvae are not concentrated in the surface even when they swim actively towards the light in the laboratory. On the other hand, food presence didn?t have a significant effect on the vertical distribution of larvae. Thus, diel vertical migration appears to be a very important strategy of C. altimanus to cope with high UVR irradiances in Patagonia during the hatching seasons (spring-summer).