Can the Continuous Plankton Recorder (CPR) be used to infer sardine diet?

Knowledge on the impact of climate variability in the diet of planktivorous fish is limited by the laborious work involved in stomach content analysis, impractical for large scale studies. Routine measurements of plankton such as the Continuous Plankton Recorder (CPR) survey provide valuable information of the temporal variation of phyto- and zooplankton prey availability for higher trophic levels. Sardines are a world-wide distributed and commercially important planktivorous fish, at the basis of the pelagic marine food web. Being predominantly non-selective filter-feeders, their diets closely correspond to the water plankton species and a significant relationship was recently found between Sardina pilchardus feeding intensity and remotely sensed chlorophyll alpha . Data of sardine stomach prey composition and CPR were obtained during 2003 for the same location off the west coast of Portugal, an area characterised by strong seasonality of plankton abundance and composition, mainly governed by upwelling events. Phyto- and zooplankton prey in sardine stomachs were identified to the lowest possible taxa and their numerical and volumetric abundance was registered, as well as their contribution to the prey carbon content. The seasonal variation of the abundance and composition of sardine diet was then compared to the abundance and composition of the water plankton obtained with the CPR at the same time and for the same area where the fish were collected, in order to evaluate if CPR data can be used to proxy sardine prey availability and diet composition at large temporal scales.

Strong preference for decapod prey by the western rock lobster Panulirus cygnus

Western rock lobsters, Panulirus cygnus are an abundant benthic consumer distributed along the temperate west coast of Australia and constitute the largest single species fishery in Australia. As a dominant consumer, it is important to understand their predator-prey interactions as they can potentially exert strong trophic effects, and may influence ecosystem function as seen in other spiny lobster species. While previous field studies have focused on the diet composition of P. cygnus, this study investigated their preference for various benthic invertebrate prey to better understand the likely predator-prey interactions of P. cygnus. Prey preferences of small sub-legal juvenile lobsters, as well as medium and large legal-sized mature lobsters were investigated using laboratory feeding trials to identify size-associated differences in lobster prey preference. Handling time and diet quality were investigated to estimate energetic cost and gain from consuming different prey which may explain prey choice by lobsters. It was found that large lobsters preferred crabs and mussels while medium and small lobsters preferred crabs over mussels, gastropods, and sea urchins. This suggests that strong predator-prey interactions between P. cygnus and crabs may occur in the wild.