23
of prey may indicate how the octopus handled the food item ( E� dofleini: Dodge
and Scheel 1999). Octopuses are known to apply strength alone to pull open prey
(McQuaid 1994; Steer and Semmens 2003; Anderson and Mather 2007) so that not
all remains from prey eaten by octopuses will be marked. Pulling may be the method of choice for some prey, especially bivalves (Steer and Semmens 2003), but pulling is not always successful. Octopuses are also well known for drilling through the
shell of their prey, using salivary enzymes, papilla, and radula (Nixon and Maconnachie 1988). Drilling forms a small ovoid depression in the outer layer of the shell
that penetrates the inner layer with holes 1.5–3.0 mm long and 0.25–2.0 mm wide
(inner and outer width dimensions, respectively; Nixon and Maconnachie 1988;
Dodge and Scheel 1999). Octopuses are known to drill hard shells and carapaces, as
well as puncture softer tissue such as eyes ( Eledone cirrhosa: Grisley et al. 1996).
In some species of octopuses attacking bivalves, drill attempts consistently may be
made in a location where the prey is vulnerable (Wodinsky 1969; Cortez et al. 1998;
Anderson et al. 2008a). However, this does not appear universal and some octopusdrilled locations are variable or may be a function of prey type or size ( E� dofleini:
Dodge and Scheel 1999; Scheel et al. 2007). Alternatively, octopuses may chip prey
with their beaks (Anderson 1994; Dodge and Scheel 1999) leaving characteristic
marks on the edges of bivalves or breakage patterns on crab carapaces, chelae, or
legs.
According to foraging theory (Pulliam 1974; Sih 1984; Stephens and Krebs
1986), diet selection by rate-maximizing foragers among spatially mixed prey types
will be determined by prey energy content, handling time, and encounter rates. Spatial segregation of prey types may result in habitat selection influencing encounter
rates and prey selection (Vincent et al. 1996). Alternatively, octopuses may act as
risk-minimizing or time-minimizing foragers (Scheel et al. 2007; Leite et al. 2009).
If so, this could result in a preference for larger prey (greater energy content) without regard for handling time. This seems particularly likely given the octopuses
often consume food at a den or other shelter (Mather 1991a), and spend the majority
of their time hiding (e.g. O� vulgaris: Mather 1988, E� dofleini: Scheel and Bisson
2012), which allows time to drill, chip, or pull open prey in safety (see Sect. 2.2).
Scheel et al. (2007) and Scheel and Anderson (2012) found that E� dofleini exhibit a
preference for larger prey individuals within a species, and for larger species among
similar prey types (crustaceans). Preferences by this octopus species may further be
influenced by detectability of the prey, possibly itself a function of prey camouflage
behaviour, epiphytes, or escape responses. There is now a growing interest in examining the constraints octopuses may face in nutrient trade-offs (e.g. Lee 1994; Rigby
and Sakurai 2004; Onthank and Cowles 2011) and their effects on diet, but research
in this area is only beginning.
Few studies examine how octopuses choose where to forage or how they find
food. O� cyanea conducts tactile, speculative, and saltatory foraging on shallowwater reefs (Yarnall 1969, Forsythe and Hanlon 1997), similar to speculative webover foraging described for E� dofleini in shallow water (Johnson 1942, Cosgrove
2002). In both species, as well as O� vulgaris, foraging excursions may follow along
habitat edges such as reef edges or cliff faces preferentially in habitats containing
2 Behaviour
of prey may indicate how the octopus handled the food item ( E� dofleini: Dodge
and Scheel 1999). Octopuses are known to apply strength alone to pull open prey
(McQuaid 1994; Steer and Semmens 2003; Anderson and Mather 2007) so that not
all remains from prey eaten by octopuses will be marked. Pulling may be the method of choice for some prey, especially bivalves (Steer and Semmens 2003), but pulling is not always successful. Octopuses are also well known for drilling through the
shell of their prey, using salivary enzymes, papilla, and radula (Nixon and Maconnachie 1988). Drilling forms a small ovoid depression in the outer layer of the shell
that penetrates the inner layer with holes 1.5–3.0 mm long and 0.25–2.0 mm wide
(inner and outer width dimensions, respectively; Nixon and Maconnachie 1988;
Dodge and Scheel 1999). Octopuses are known to drill hard shells and carapaces, as
well as puncture softer tissue such as eyes ( Eledone cirrhosa: Grisley et al. 1996).
In some species of octopuses attacking bivalves, drill attempts consistently may be
made in a location where the prey is vulnerable (Wodinsky 1969; Cortez et al. 1998;
Anderson et al. 2008a). However, this does not appear universal and some octopusdrilled locations are variable or may be a function of prey type or size ( E� dofleini:
Dodge and Scheel 1999; Scheel et al. 2007). Alternatively, octopuses may chip prey
with their beaks (Anderson 1994; Dodge and Scheel 1999) leaving characteristic
marks on the edges of bivalves or breakage patterns on crab carapaces, chelae, or
legs.
According to foraging theory (Pulliam 1974; Sih 1984; Stephens and Krebs
1986), diet selection by rate-maximizing foragers among spatially mixed prey types
will be determined by prey energy content, handling time, and encounter rates. Spatial segregation of prey types may result in habitat selection influencing encounter
rates and prey selection (Vincent et al. 1996). Alternatively, octopuses may act as
risk-minimizing or time-minimizing foragers (Scheel et al. 2007; Leite et al. 2009).
If so, this could result in a preference for larger prey (greater energy content) without regard for handling time. This seems particularly likely given the octopuses
often consume food at a den or other shelter (Mather 1991a), and spend the majority
of their time hiding (e.g. O� vulgaris: Mather 1988, E� dofleini: Scheel and Bisson
2012), which allows time to drill, chip, or pull open prey in safety (see Sect. 2.2).
Scheel et al. (2007) and Scheel and Anderson (2012) found that E� dofleini exhibit a
preference for larger prey individuals within a species, and for larger species among
similar prey types (crustaceans). Preferences by this octopus species may further be
influenced by detectability of the prey, possibly itself a function of prey camouflage
behaviour, epiphytes, or escape responses. There is now a growing interest in examining the constraints octopuses may face in nutrient trade-offs (e.g. Lee 1994; Rigby
and Sakurai 2004; Onthank and Cowles 2011) and their effects on diet, but research
in this area is only beginning.
Few studies examine how octopuses choose where to forage or how they find
food. O� cyanea conducts tactile, speculative, and saltatory foraging on shallowwater reefs (Yarnall 1969, Forsythe and Hanlon 1997), similar to speculative webover foraging described for E� dofleini in shallow water (Johnson 1942, Cosgrove
2002). In both species, as well as O� vulgaris, foraging excursions may follow along
habitat edges such as reef edges or cliff faces preferentially in habitats containing
2 Behaviour