The feeding habits of the amphipods Lembos websteri Bate and Corophium bonnellii Milne Edwards

Abstract

The gut contents of both Lembos websteri Bate and Corophium bonnellii Milne Edwards include detritus and sand grains. Lembos websteri collected from Laminaria holdfasts also contain strands of filamentous algae although Corophium bonnellii do not. In addition, macroalgal fragments and naviculoid diatoms are present, more often in Lembos websteri than in the guts of Corophium bonnellii. Occasionally, in animals collected from a sheltered algal turf, arthropod appendages may also be observed in the gut of Lembos websteri. The size of particles consumed by Lembos websteri is larger than in Corophium bonnellii. Feeding in both species is primarily by filtration but a variety of other methods may be used, including deposit-feeding, consumption of food of animal origin (including the species' own eggs), and consumption of tube material. These alternative techniques are brought to bear increasingly in poor feeding conditions. The behavioural sequences involved in these activities are described in detail and food preferenda related to the nutritional state of the animals. Defaecation in Lembos websteri (males and females) is normally followed by immediate refection of the faecal pellet but again is more noticeable when food is scarce. Gut-residence time in both species is ≈ 2 h at 13–15 °C. The proposition is made that Corophium bonnellii is a more efficient small-particle filter-feeder than Lembos websteri and that as such, it has met no evolutionary requirement to recycle its faeces (large particles) in the manner of L. websteri. Lembos, on the other hand, having a very “plastic” feeding repertoire appears to be better adapted to withstand periods of low food availability. The larger particles on which L. websteri feeds will be scarcer and will require more turbulence to keep them in suspension and even at exposed localities where L.websteri is more common, periods of calm occur, so flexibility in food-gathering technique is clearly advantageous. The more efficient small particle filter-feeding technique of Corophium bonnellii is well suited to a life in sheltered waters, where only the smallest particles remain in suspension for long periods, which is so typical of the genus.