Impact of coelenterate predation on larval plaice Pleuronectes platessa and flounder Platichthys flesus stock in the western Wadden Sea

Abstract

During the seasonal immigration of plaice and flounder larvae into the Dutch Wadden Sea in spring, the coelenterates Pleurobrachia pileus L. and Aurelia aurita L. have been positively identified as predators of both flatfish species. Evidence for a causal relation between outbursts of the predatory coelenterates and the observed abrupt termination of larval flatfish immigration is found in (1) the coincidence of increases in coelenterate numbers and decreases in larval densities, (2) positive observations of larval flatfish in coelenterate stomach contents, (3) a comparison between food demand of the coelenterate population and standing stock of the pelagic food resource at that time. Impact of this predation on plaice recruitment is expected to be small, since most larvae have already completed their immigration into the Wadden Sea when the coelenterate outburst starts. Although the coelenterate outburst occurs at about the same time every year, their predation may have a density-dependent component, since the timing of plaice immigration seems to be related to abundance, with larger yearclasses arriving later than smaller ones. For flounder larvae the impact will be greater, because of the shorter period of immigration and the coincidence between coelenterate outburst and maximum flounder abundance.

Prey selection and dietary overlap among zooplanktivorous jellyfish and juvenile fishes in Prince William Sound, Alaska

“…Möller 1980, van der Veer 1985, Arai 1988, Bailey & Houde 1989, Shiganova 1998, virtually no direct comparisons of diet and co-occurrence have been made. Although 2 recent studies reached different conclusions, any results probably would be specific to a particular situation.…”

“…Species in the gelatinous genera Aurelia, Pleurobrachia, Cyanea, and Aequorea often occur in great abundance in the world's oceans (e.g. Hirota 1974, van der Veer 1985, Fancett 1988, Purcell & Grover 1990, Båmstedt et al 1997, Dawson & Martin 2001, Purcell et al 2001, Sparks et al 2001. Walleye pollock, Pacific herring and pink salmon are highly abundant fish species that support important commercial fisheries in various areas of the North Pacific Ocean; similarly, species of sandlance and herring are fished in several northern oceans (FAO 1999a,b, National Marine Fisheries Service 1999.…”

Clearance rates of jellyfish and their potential predation impact on zooplankton and fish larvae in a neritic ecosystem (Limfjorden, Denmark)

“…The scyphomedusa Aurelia aurita or the hydromedusae Rathkea octopunctata and Sarsia tubulosa are dominant jellyfish species in several neritic ecosystems (van der Veer 1985, Matsakis & Conover 1991, Kopacz 1994, including Limfjorden, and were therefore selected for clearance measurements. A single measurement of the clearance rate of Bougainvillia superciliaris was also made.…”

The recovery of the Barents Sea capelin (Mallotus villosus) from a larval point of view

“…They spawn at night (Ferraro 1980), thus maximizing the dispersal of the spawning products before visual predators can recognize the egg patches. There also seems to be a tendency towards spawning and hatching before the blooms of gelatinous plankton (van der Veer 1985;Bailey and Houde 1989). However, this is probably not an adaptive reproductive strategy, but rather an indication that other planktonic zooplankton organisms occurring later in the season are the main prey organisms of gelatinous predators.…”

“…However, this is probably not an adaptive reproductive strategy, but rather an indication that other planktonic zooplankton organisms occurring later in the season are the main prey organisms of gelatinous predators. Spatial separation of fish eggs and larvae and their predators also seems to be important (Bailey and Yen 1983;Frank and Leggett 1985;van der Veer 1985). Mass hatching in capelin was studied by Frank and Leggett (1982) and they concluded that this could be another strategy and have a positive effect due to "swamping" and satiation of predators.…”