High survival of neustonic zoea I larvae of American lobster Homarus americanus following short-term exposure to ultraviolet radiation (280 to 400 nm)

Ultraviolet radiation (W-B = 280 to 320 nm; UV-A = 320 to 400 nm) is harmfu l to the planktonic early life stages of some marine organisms. In the Gulf of St. Lawrence, Canada, measurements of the diffuse attenuation coefficie nts have indicated that the maximum depth to which 10% of the surface energ y penetrates at 310 nm is 3 m. Thus, organisms residing in this surface lay er are exposed to UV radiation. During the summer spawning season (May to S eptember), the first zoeal larval stages of the American lobster Homarus am ericanus are present in the first 2 m of the water column during the day. T hus, H. americanus larvae are exposed to UV radiation. We incubated stage I larvae of H, americanus under an artificial Light source that simulated th e irradiance conditions measured at a depth of 1 m in the Gulf of St. Lawre nce waters near solar noon. Three spectral exposure treatments were used: ( 1) UV-B+UV-A+PAR; (2) UV-A+PAR; (3) PAR only. Larvae were irradiated for 4 d (2 h d(-1)) and maintained thereafter under a natural photoperiod (fluore scent lamps) until first molt. Mortality was monitored daily throughout the experiment. There were no differences in mortality amongst the 3 spectral treatments. Larvae began dying at the same time and at the same rate indepe ndently of the spectral irradiation that they received. Thus, lobster larva e appear to be tolerant of short (2 h) exposures to UV radiation.