The role of food availability in regulating the feeding dynamics and reproductive cycles of bathyal benthopelagic fish in the northwest Mediterranean slope

Abstract

Trophic dynamics and reproductive cycles of fish from the middle slope of the northwest Mediterranean Sea were investigated seasonally from ~ 500 to 1000 m depth. Gut contents of seven species were analyzed, and weights of gonads and livers and C:N ratios of muscle were measured. Additionally, food availability was estimated through analyses of densities of potential prey and of indicators of organic matter sources. The trophic structure of the community was a function of the size of predators and of the height in the near‐bottom water column where megafauna fed. We established three trophic groups: benthic feeders, non‐migrator macroplankton feeders, and small‐sized fish, the latter feeding on macroplankton and hyperbenthos. Seasonal changes in fullness (F) were coupled to cycles of secondary production and to the availability of different food sources. The F of benthic feeders was related to total organic carbon percentage in the sediments, to surface production 2 months before the sampling, and to the abundance of benthic and hyperbenthic prey. For plankton consumers, lipids in the sediments and the abundance of Pasiphaea spp. explained trends in F. Temporal trends in gonadosomatic index (GSI) correlated to food derived from the winter bloom of surface production. Also, increased feeding intensity preceded increases in GSI, but different energy use strategies were deduced from the almost speciesspecific relationships between the GSI and different biological indices. Species from the same trophic guild reproduced at different times of the year, pointing to the existence of species‐specific life strategies that enhance reproductive success.