Behavioral mechanisms underlying the refuge value of benthic habitat structure for two flatfishes with differing anti-predator strategies

Abstract

Juvenile flatfish habitat is usually modeled on the basis of sediment grain-size, depth and temperature. Recent evidence indicates that some juvenile flatfishes associate with emergent structures such as sponge, shell and other biogenic and bed-form features of otherwise low-relief shelf habitats. In laboratory experiments we examined the habitat preference and effects of habitat structure upon predation vulnerability of sub-yearling (Age-0) Pacific halibut Hippoglossus stenolepis and northern rock sole Lepidopsetta polyxystra. When given the choice between bare sand or sand with 16% sponge coverage, halibut demonstrated strong preference for sponge, while rock sole showed no preference. Larger Age-2 halibut (used as predators in the subsequent experiment) also preferred sponge, but this preference declined with increasing hunger. When allowed to forage for Age-0 flatfishes in either bare sand or sponge, predators consumed more prey in sand and consumed more Age-0 halibut than rock sole. We were able to determine which behavioral processes in the predator-prey interaction were modified by the presence of habitat structure. Predator-prey encounter rates decreased in the sponge habitat as predator search was impeded: predators paused more frequently and swam more slowly to maneuver through the sponges. Sponges also tended to hinder the pursuit of prey. Rock sole utilized stereotypic flatfish defense-mechanisms, relying upon immobility, burial and crypsis, and were less likely to flush at a predator's approach than halibut. Halibut have a less developed ability to mimic sediments, but a deeper/narrower body that confers greater swimming speed, and were more likely to flush as a predator approached. Once they had flushed and were pursued by a predator, halibut were more likely to escape than were rock sole. These experiments support an accumulating body of evidence that emergent structure, in otherwise low-relief benthic habitats, may play an important role in the ecology of some juvenile flatfishes. Removal of emergent structure by towed fishing gear and other anthropogenic and/or natural disturbance may influence patterns of distribution for juvenile halibut, as fish redistribute to less preferred habitat, and may decrease survival rates through increased losses to predation.

Compensatory growth, energy storage and behavior of juvenile Pacific halibut Hippoglossus stenolepis following thermally induced growth reduction

“…Even with the ability to compensate for periods of reduced growth, delayed halibut face considerable obstacles to survival and recruitment, as the estimated time to complete compensation was at least 3 times the duration of the growth reduction. Further, the increased foraging activity during the growth compensation period may result in additional predation risk (Ryer et al 2004). Finally, the diversion of assimilated energy from lipid storage to growth may increase vulnerability to starvation during subsequent periods of prey scarcity.…”

Density-dependent habitat selection in marine flatfish: the dynamic role of ontogeny and temperature

“…Juvenile flatfish often demonstrate avoidance response to other approaching fish (Ryer et al 2004), and it is possible that the flatfish observed in this study move in order to simply avoid such interactions. In no instances did we observe territoriality or other agonistic behavior (e.g.…”

“…To date there have been few explicit tests of DDHS in marine fish species (juvenile pollock Pollachius virens, Rangley & Kramer 1998; juvenile cod Gadus morhua and G. ogac, Laurel et al 2004; gag Mycteroperca microlepsis, Lindberg et al 2006) despite the multitude of studies describing area-abundance relationships in marine environments (see Shepherd & Litvak 2004 for review). In flatfish, fine grained sand substrates are preferred over relatively coarser grained substrates (Stoner & Ottmar 2003), most likely because flatfish are more capable of burying in such habitats as a means of reducing predation (Ryer et al 2004; although see Manderson et al 2000) or finding food (Livingston 1987). The increased use of coarse grained habitats at higher densities suggests the fitness benefits of sand (e.g.…”

Cuttlefish dynamic camouflage: responses to substrate choice and integration of multiple visual cues

“…Camouflage is also a primary reason for substrate choice in many animals that have fixed, or slowly changing, body patterns across the animal kingdom (Cott 1940), from insects to arachnids and crustaceans to vertebrates (e.g. mayfly larvae, Tikkanen et al 2000;spiders, Heiling et al 2005; tiger prawns, Kenyon et al 2003;sculpin, Brown 1991;weedy seadragons, Sanchez-Camara et al 2006;flatfish, Moles & Norcross 1995;Stoner & Ottmar 2003;Stoner & Titgen 2003;Ryer et al 2004Ryer et al , 2008. Moving to the wrong substrate may render an animal with a fixed body pattern conspicuous (Merilaita et al 1999).…”