Short-Term Responses of Some Planktonic Crustacea Exposed to Enhanced UV-B Radiation

Abstract

With shrimp and crab larvae, several-day exposures to UV-B radiation below lethal threshold levels of dose-rate and total dose had no significant effects on either activity or development (molting). Above those UV levels, activity, development, and survival rapidly declined. The specimens in those experiments were held in flow-through seawater containers of 8 cm depth. Perhaps these near-surface zooplankton in nature could increase their depth slightly, if they could sense fatal dose-rates or doses of UV-B. With such a short-term response they might completely avoid damaging solar UV.

Experiments in paired 2-liter glass cylinders (38 cm water depth) suggested that there is no difference in behavior between irradiated and non-irradiated shrimp larvae (Pandalus platyceros) or copepods (Epilabidocera longipedata). The irradiated specimens maintained their near-surface positions (as did the controls) until the time of decreased activity and death at about 4 days. The progress and outcome were similar in experiments using a 44-liter plastic cylinder (140 cm water depth).

The zoea stage of the shore crab Hemigrapsus nudus is extremely attracted to strong visible light. No differences in response-time (seconds) was noted between control larvae and larvae receiving lethal UV-B doses until decreased activity and death of the irradiated larvae at about 10 days. There was no apparent reluctance of the crab larvae to swim toward and to hold themselves within lethal doses of UV-B.