Pipefish foraging: effects of fish size, prey size and altered habitat complexity

Abstract

Laboratory experiments determined the effects of 2 levels of habitat complexity upon pipefish Syngnathus fuscus foraging for amphipods. Habitats were composed of equal densities of either narrow (low complexity) or wide (high complexity) leafed artificial seagrass. Response to habitatas measured by rate of encounter with amphipods, probability of attack after encounter, probability of success after attack, and overall rate of amphipod consumption -was determined for combinations of 2 fish size classes and 3 amphlpod size classes. Small fish did not respond to changes in habitat complexity, while large fish &d. Large fish encountered fewer amphipods in the high than in the low complexity habitat. In general encounter rate increased with amphipod size. Large fish attack probability was negatively related to amphipod size in the narrow leaf habitat, but positively related to amphipod size in the wide leaf habitat. Small fish attack probability was negatively related to amphipod size in both habitats. Success was negatively related to prey size and greater for large than for small fish. and showed no overall effect of habitat. The position that amphipods occupy in the structure of vegetation in part determines their vulnerability to predation, a criterion by which pipefish appear to select prey. In this respect pipefish behavior is flexible, allowing adjustment of foraging tactics to match habitat constraints. Results suggest that relative sizes of predator and prey are important factors in determining the effect of structural complexity upon predator-prey dynamics.

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

“…In H. zosterae, for example, male metabolic rates increases from 10 to 52% over pregravid levels (Masonjones, 2001), as these animals are responsible by osmotic regulation and oxygen and perhaps provide nutrition to the embryos (Strawn, 1958;Masonjones, 2001;Foster & Vincent, 2004). According to Lyons & Dunne (2004), the male seahorse pregnancy may produce a behavioral response that limits the movements of males, reducing energetic expenditure on chasing larger vagile prey (Ryer, 1988;Lyons & Dunne, 2004) and risk of capture by predators (Lyons & Dunne, 2004;Oliveira et al, 2007). Thus, it is possible that the greater consumption of harpacticoid copepods and reduced consumption of caridean shrimps and gobiid fishes by the adult males in the present study is related to reproduction, as found in another species of Syngnathidae (Ryer, 1988;Lyons & Dunne, 2004;Oliveira et al, 2007).…”

The eelgrass canopy an above-bottom refuge from benthic predators for juvenile bay scallops Argopecten irradians

“…Similar mimics have been successfully used in previous studies (Heck & Thoman 1981, Blundon & Kennedy 1982, Virnstein & Curran 1986, Ryer 1988. Argopecten irradians larvae have been shown to readily settle on a variety of artificial substrates, including polypropylene, and settlement appears to be controlled primarily by availabil-ity of surface area (Eckman 1987, Ambrose & Lin in press).…”

New dimensionless indices of structural habitat complexity: predicted and actual effects on a predator's foraging success

“…Complex habitats provide refuges for prey by limiting a predator's ability to move throughout a habitat in search of prey, by interfering with a predator's ability to detect prey within the habitat, and by interfering with a predator's ability to catch prey, once detected (Ryer 1988, James & Heck 1994. We propose 2 new structural habitat indices that directly measure these interference mechanisms: (1) the total amount of crosssectional area (total cover) within a given habitat area for prey to hide behind, and (2) the sizes of the interstructural spaces or gaps that the predator must maneuver through relative to the size of the predator itself.…”