EFFECTS OF SOLAR AND ARTIFICIAL ULTRAVIOLET‐B RADIATION ON LARVAL NORTHERN ANCHOVY, <i>ENGRAULIS MORDAX</i>*

Abstract

Abstract— Northern anchovy larvae were exposed to various amounts of both natural (global solar) and artificial (sunlamps filtered by cellulose triacetate) UV‐B energy over a 12‐day period. Dosage was determined on the basis of a weighting function for biological effectiveness. The action spectrum on which this biologically effective dose for anchovy mortality is based was developed using broad‐band spectroscopy. These experiments indicated that biologically adverse conditions exist near the sea surface. Larvae exposed in shallow containers to global solar UV for 12 days suffered significant UV mortality from February to October. Larvae surviving all solar and artificial UV doses were smaller than those not exposed to UV. [Lowest dosage = 398 J·m −2 (bio.eff.) .] Fifty percent of the larvae survived a cumulative dose of 605 J·m −2 (bio.eff.) , or 50 J·m −2 ·day −1 (bio.eff) . Dose reciprocity did not hold; when a similar cumulative dose was given in the first 4 days of 12, there were about one‐half as many survivors. One meter below the sea surface the daily solar UV dose (corrected for average cloud cover) is equal to or greater than 50 J·m −2 (bio.eff.) (33°N, 118°W), the daily equivalent of the LD 50 , for 7 months of the year (March to September) at moderate chlorophyll‐a concentrations (0.5 mg‐m −3 ). These data suggest that larvae in the sea may be subject to some UV‐B stress at present. Owing to their seasonality of spawning and vertical distribution, anchovy populations may not be gravely endangered by moderate degree of stratospheric ozone diminution.