UVR-induce mortality of zoea I larvae from five crab species of the Patagonian coast

HERNÁNDEZ MORESINO R. D & HELBLING E. W.

Düsseldorf

Congreso; 15th International Congress in Photobiology; 2009

International Union of Photobiology

Decapod crustaceans have a planktonic larval period during which approximately 90% of the mortality occurs.  The 39 species of decapod that were described for the temperate-cold waters from SW Atlantic represent a large part of the benthic biomass and they are part of the diet for higher trophic level.  Most of these curstacean larvae have small cromathophores and a thin quasi-translucid carapace, so harmful solar radiation can reach the larvae and thus have detrimental effects.  In this work we assess the UVR effects in crabs larval survival of the Patagonean coasts.  Adults of five species (Leucippa pentagona, Libinia spinosa, Pilumnoides hassleri, Cyrthograpsus angulatus and Cyrthograpsus altimanus) were collected from rock intertidal zones, using nets (bottom traps) and scuba diving, during spring and summer.  The adults were transported to the lab and newly hatched zoea (< 24 hs) were used in short-term exposition experiments under a solar simulator (Hönle, Sol 1200, Germany).  Each experiment was carried out in a temperate chamber (15°C) and the zoea used belonged to one female.  Healthy zoea were separated (when swimming to a light source) and carefully pipetted in 12 open glass dishes (100 ml), 20 zoea per container.  Three radiation treatments and dark (in triplicates) were set up using cut-off filters: (1) PAB treatment, larvae were exposed to radiation >280nm (UV-B, UV-A and PAR), (2) PA treatment, exposed to radiation >320nm (UV-A and PAR), (3) P treatment or control, radiation >395nm (PAR); and (4) Dark treatment.  The experiments were done at three irradiances controlling the distance to the solar simulator, for UV-B the irradiances were: 0.76, 1.22 and 2.19W/m2.  Larval survival was registered at several times during each experiments that lasted less than 10 hous.  Sigmoidal curves were used to fit the data and from them we obtained the threshold for inhibition (ThP) and the lethal dose at 50% (LD50). The ThP and LD50 were compared among irradiances and species using ANOVA. Our results indicated that: (1) only UV-B induced 100% mortality for all the studied species, while for other wavelengths (i.e., the other treatments) the mortality did not exceeded 10%, (2) in all experiments total mortality (100%) was reached at a UV-B dose between 20-30 kJ/m2; and these lethal doses were lower than the daily doses in summer (ca. 50 kJ/m2), (3) the sensitivity of the studied species was different (based on ThP and LD50) with C. altimanus and C. angulatus been less sensitive than L. pentagona, L. spinosa and P. hassleri. The threshold values in the first group were deberia haber sido 17-23 kJ/m2 and the LD50 were 21-26 kJ/m2.  These values were significantly higher than the respective values for the other group that were 11-18 kJ/m2 and 13-22 kJ/m2, for the ThP and LD50, respectively.  It is interesting to note that the adults of the two less sensitive species of the genus Cyrthograpsus can be found not only in shallow subtidal but in the intertidal zone too, while adults of the other three species normally had deeper distribution in the subtidal zone. Our data suggest that the sensitivity of the zoea might be related to the depth distribution of the adults and/or the presence of UV absorbing compounds that the adults can accumulate through the diet and potentially pass to the eggs.