Juvenile flounder, Platichthys flesus (L.), under hypoxia: effects on tolerance, ventilation rate and predation efficiency

The flounder, Platichthys flesus, is the most abundant flatfish species in the northern Baltic Sea. Juvenile P. flesus are important epibenthic predat ors on shallow sandy bottoms in this area, and play an important role in st ructuring benthic infaunal communities by both lethal and sublethal predati on. These areas are affected by periodic oxygen deficiency during summer an d autumn when drifting algal mats are abundant, which causes changes in bot h structure and function of the zoobenthic community. Experiments were perf ormed to test for the effects of hypoxia on: (1) tolerance; (2) ventilation rate; (3) lethal predation efficiency; and (4) sublethal predation efficie ncy (siphon cropping) of P. flesus. In the lethal predation experiment, the amphipod Bathyporeia pilosa was used as prey, and in the siphon cropping e xperiment, the bivalve Macoma balthica was used. Recorded LT,, values of P. flesus exposed to hypoxia were 1835 +/- 87 (mean+/-SE) min at 20%, 149+/-8 min at 10% and 23+/-2 min at 5% oxygen saturation (13 degrees C, S 5 parts per thousand). In hypoxia, ventilation rate of P. flesus increased at 30% and 20%, and decreased at 10% and 5% oxygen saturation compared with normox ia. The predation efficiency of juvenile P. flesus was significantly lower at 20% and 30% compared with 40% and 100% oxygen saturation. In the subleth al predation experiment, the flounders cropped siphons most efficiently at moderate hypoxia (40% oxygen saturation) compared with normoxia. Our result s indicate that sublethal oxygen saturations (30-40%) cause changes in phys iology and predation behaviour of juvenile P. flesus. Such functional chang es in benthic communities, at sublethal oxygen saturations, may influence t he energy flow of benthic food webs in areas that are affected by periodic oxygen deficiency. (C) 1999 Elsevier Science Ev All rights reserved.