22
1973; Dickel et al. 2000; Darmaillacq et al. 2004; Cole and Adamo 2005; Agin
et al. 2006; Guibé et al. 2012). Within 24–48 h after hatching, cuttlefish strike at
small suitable prey (Messenger 1973); attack latency, success rates, and suitability
of potential prey items can be influenced by learning (e.g. Hanlon and Messenger
1996; Darmaillacq et al. 2004; Cole and Adamo 2005). Ontogenetic changes in prey
selection also occur in squid, where adults may occupy a higher trophic level than
smaller juveniles (e.g. Hunsicker et al. 2010; Ibáñez and Keyl 2010).
Squid depend on movement of prey items and contrast with the background to
locate potential prey and elicit attack (Hanlon et al. 1983). Lacking these stimuli,
especially motion, squid and cuttlefish will not attack and will starve to death. Prey
size range does not appear critical, with both large and small squid taking prey
ranging in size from macroplanktonic to nearly the same length as the squid itself
(Hanlon et al. 1983). Squid orient visually towards their prey (Hanlon and Messenger 1996), as do cuttlefish, although cuttlefish also exhibit searching behaviour for
partially buried prey in the substrate, which they uncover by expelling a jet of water
over the substrate which can blow away cover (Hanlon and Messenger 1996). All
squid are cannibalistic, a tendency enhanced under food shortage and in the presence of smaller or injured conspecifics. Further, mating behaviours such as male
courtship of females and male–male aggression can disrupt feeding and may lead
to injuries to fins or other areas that contribute to cannibalism (Hanlon 1990). Thus,
feeding in captivity can be promoted and cannibalism reduced by keeping squid in
tanks containing all individuals of the same size and sex.
2.3.2 Octopuses
The diets of a few species of octopuses are well known. Many species use dens in
shallow water and discard hard remains of prey, including shells, carapaces, and
bones, in midden piles outside the dens. The diet of shallow-water benthic octopuses is dominated by crustaceans (e.g. Mather et al. 2012) and molluscs such as
bivalves (e.g. Vincent et al. 1998) and snails (Ambrose 1984). Diets typically are
dominated by one to a handful of prey species, but diverse other prey occur occasionally in diets (e.g. Ambrose 1984; Scheel and Anderson 2012). Such occasional
items may include alternative crustaceans or bivalves, but also almost any other
prey group characterized by hard parts such as gastropods, chitons, cephalopods,
echinoderms, fish, and even birds (Sazima and de Almeida 2006; Nightingail 2012;
Scheel and Anderson 2012). Soft items (e.g. worms) may also be eaten but are less
likely to be detected in the diet. In some populations, individual octopuses appear to
exhibit prey specificity (Anderson et al. 2008b), although diet composition across
the population is broad; in other populations, individual specialization appears not
to be the rule (Mather 2011; Mather et al. 2012; Scheel and Anderson 2012; Leite
et al. in sub).
Hard shells protecting crabs, bivalves, and other prey represent a challenge to
octopuses’ intent on feeding on the soft tissue inside, and octopuses have several methods to surmount this challenge. Marks left by octopuses on hard remains
J. Mather and D. Scheel
1973; Dickel et al. 2000; Darmaillacq et al. 2004; Cole and Adamo 2005; Agin
et al. 2006; Guibé et al. 2012). Within 24–48 h after hatching, cuttlefish strike at
small suitable prey (Messenger 1973); attack latency, success rates, and suitability
of potential prey items can be influenced by learning (e.g. Hanlon and Messenger
1996; Darmaillacq et al. 2004; Cole and Adamo 2005). Ontogenetic changes in prey
selection also occur in squid, where adults may occupy a higher trophic level than
smaller juveniles (e.g. Hunsicker et al. 2010; Ibáñez and Keyl 2010).
Squid depend on movement of prey items and contrast with the background to
locate potential prey and elicit attack (Hanlon et al. 1983). Lacking these stimuli,
especially motion, squid and cuttlefish will not attack and will starve to death. Prey
size range does not appear critical, with both large and small squid taking prey
ranging in size from macroplanktonic to nearly the same length as the squid itself
(Hanlon et al. 1983). Squid orient visually towards their prey (Hanlon and Messenger 1996), as do cuttlefish, although cuttlefish also exhibit searching behaviour for
partially buried prey in the substrate, which they uncover by expelling a jet of water
over the substrate which can blow away cover (Hanlon and Messenger 1996). All
squid are cannibalistic, a tendency enhanced under food shortage and in the presence of smaller or injured conspecifics. Further, mating behaviours such as male
courtship of females and male–male aggression can disrupt feeding and may lead
to injuries to fins or other areas that contribute to cannibalism (Hanlon 1990). Thus,
feeding in captivity can be promoted and cannibalism reduced by keeping squid in
tanks containing all individuals of the same size and sex.
2.3.2 Octopuses
The diets of a few species of octopuses are well known. Many species use dens in
shallow water and discard hard remains of prey, including shells, carapaces, and
bones, in midden piles outside the dens. The diet of shallow-water benthic octopuses is dominated by crustaceans (e.g. Mather et al. 2012) and molluscs such as
bivalves (e.g. Vincent et al. 1998) and snails (Ambrose 1984). Diets typically are
dominated by one to a handful of prey species, but diverse other prey occur occasionally in diets (e.g. Ambrose 1984; Scheel and Anderson 2012). Such occasional
items may include alternative crustaceans or bivalves, but also almost any other
prey group characterized by hard parts such as gastropods, chitons, cephalopods,
echinoderms, fish, and even birds (Sazima and de Almeida 2006; Nightingail 2012;
Scheel and Anderson 2012). Soft items (e.g. worms) may also be eaten but are less
likely to be detected in the diet. In some populations, individual octopuses appear to
exhibit prey specificity (Anderson et al. 2008b), although diet composition across
the population is broad; in other populations, individual specialization appears not
to be the rule (Mather 2011; Mather et al. 2012; Scheel and Anderson 2012; Leite
et al. in sub).
Hard shells protecting crabs, bivalves, and other prey represent a challenge to
octopuses’ intent on feeding on the soft tissue inside, and octopuses have several methods to surmount this challenge. Marks left by octopuses on hard remains
J. Mather and D. Scheel