Effect of habitat complexity and predatory style on the capture success of fish feeding on aggregated prey

Abstract

When offered a choice between open water and a ‘vegetated’ area of an aquarium (artificial sea grass), mysid (Paramesopodopsis rufa) swarms always selected open water. In contrast, juvenile and adult sea horses, Hippocampus abdominalis, which feed by ambush predation, always selected vegetated areas even when their mysid prey occurred in the adjacent clear water. Lunging predators, Australian salmon (Arripis trutta), always preferred open water to vegetated regions of the tank. Increasing vegetation density, i.e. from low to medium habitat complexity had a positive effect on capture success of juvenile and adult sea horses feeding on mysid swarms. However, number of attacks by juvenile sea horses, but not adults, was significantly reduced in higher density vegetation. Number of attacks by Australian salmon decreased as vegetation density increased but capture success, nonetheless, increased. Density of vegetation did not significantly affect the number of unsuccessful attacks by adult sea horses. Whereas proportion of unsuccessful attacks increased with vegetation density for juvenile sea horses, it decreased for juvenile salmon. This result is thought to be due to the fact that high vegetation densities disrupt structure of the prey swarm, itself a defensive formation, leaving a large number of more vulnerable small groups. Cohesive escape responses of a large swarm are likely to be a more effective defence against a lunging predator than against an ambush predator whose strategy is to use stealth to avoid provoking escape responses. Dense vegetation will militate against this strategy.

Assessing diet composition of seahorses in the wild using a non destructive method: Hippocampus reidi (Teleostei: Syngnathidae) as a study-case

“…With swimming capabilities more suited to maneuverability than speed, and with a strongly prehensile tail (Hale, 1996;Consi et al, 2001), the seahorse body form is adapted to inhabiting relatively complex habitats and these fishes rarely venture into open water when feeding (Flynn & Ritz, 1999).…”

Habitat Preference and Population Structure of Two Data Deficient Seahorse (Syngnathidae) Species

“…Seahorse distribution was correlated with the presence of seagrass, especially E. acoroides and C. serrulata. Seagrasses may increase prey density, capture efficiency and predator avoidance (Bell and Westoby, 1986;Flynn and Ritz, 1999) and are known as an important habitat for seahorses Vincent et al, 2011). H. fuscus has been reported from shallow protected bays with calm water, algal reefs and seagrass beds up to a maximum depth of 10m (Lourie et al, 2004).…”

Spatial and temporal patterns of habitat use by three estuarine species of mysid shrimp

“…Complex habitats are not principally chosen as a refuge from predation in mysid species, with aggregation or swarming a preferred anti-predator strategy (Flynn and Ritz 1999). Swarming in open water may not protect sympatric mysid species from predation by larger conspecifics or other carnivorous mysid species, as observed for Rhopalophthalmus terranatalis (Jerling and Wooldridge 1995); however, this may be overcome by partitioning habitat between mysid prey and potential mysid predators during periods of feeding.…”