Role as consumers

Abstract

Cephalopods are voracious, versatile predators. They generally have a short life span and a single spawning event followed by death. Populations are subject to dramatic fluctuations and their impact on prey populations is equally variable. The prehensile arms and tentacles of cephalopods, coupled with a highly evolved sensory system, allow them to occupy a broad trophic niche and migrations enable populations to exploit the temporal and spatial variability of production systems and populations of prey. Shoaling is a common behavioural feature of many species which facilitates prey capture and contributes to the impact of cephalopods on prey populations. Research on cephalopod stomach contents is hampered because the beak is used to bite the prey into small pieces so hard parts, which are usually needed for identification of prey species, are often rejected causing potential bias in estimation of diet. Cephalopods may also feed unnaturally in the presence of sampling gear. Despite these problems there is a growing body of data on cephalopod predation collected using direct observations, conventional visual analysis of stomach contents and serological methods. Most species feed on small crustaceans as juveniles and shift the diet to larger fish and other cephalopods during growth. This shift is accompanied by ontogenetic changes in the allometry of the brachial crown. There is increasing evidence that myctophid fishes are an important food resource for oceanic squid. The diet and stock size of some commercially exploited squid populations is sufficiently well known to quantify the impact of a single generation on the prey community. Where there is predation on commercial stocks of fish and crustaceans, the effect of cephalopod feeding on recruitment may be significant. Cephalopods are trophic opportunists in marine food webs from polar to equatorial seas.

Stable isotopes, beaks and predators: a new tool to study the trophic ecology of cephalopods, including giant and colossal squids

“…In the few cephalopods so far investigated, most species feed on small crustaceans as juveniles and shift the diet to larger fishes and other cephalopods during growth (Rodhouse & Nigmatullin 1996). We observed a 1.9‰ difference (about half a trophic level) in d 15 N between medium and large beaks of M. ingens; a value that corresponds well with the known feeding ecology of the species with smaller squids feeding on both crustaceans and fishes, while larger squids prey mainly upon mesopelagic fishes (Cherel & Duhamel 2003;Phillips et al 2003).…”

“…Determining and quantifying their trophic relationships is therefore a key issue in understanding the structure and functioning of marine ecosystems. Cephalopods are voracious, versatile and fast-growing predators but, except for some fast swimming and muscular species, knowledge of their feeding habits is limited by lack of data (Rodhouse & Nigmatullin 1996). Detailed information on the biology of cephalopods is restricted to a few commercially exploited species, mainly belonging to shelf-living families, and much less is known about oceanic and more prolific forms.…”

“…Second, we hypothesized that the d 15 N signature increases with beak size. In cephalopods feeding shifts occur from small, lower trophic level prey of juveniles to large, higher trophic level prey eaten by adults (Rodhouse & Nigmatullin 1996). Finally, we investigated for the first time the trophic structure of a community of cephalopods because the stable isotopic approach is a powerful method of providing new insights into trophic segregation between closely related species (Hobson et al 1994).…”

Vampire squid: detritivores in the oxygen minimum zone

“…They have evolved a wide variety of strategies to pursue living prey like fish, crustaceans and other cephalopods [1]. Benthic octopuses use their extensive repertoire of camouflage patterns to sneak up on or ambush prey [2].…”

Productivity and linkages of the food web of the southern region of the western Antarctic Peninsula continental shelf

“…Cephalopods are opportunistic feeders (Rodhouse and Nigmatullin, 1996) and feed on 432 crustaceans and fish (Collins and Rodhouse, 2006). The diet specified for this group was 433 equally divided between fish and zooplankton, with most of the zooplankton being Antarctic 434 krill (Table 2).…”