Escape responses in four epibenthic brittle stars (Ophiuroidea: Echinodermata)

Abstract

Escape reactions to simulated sub-lethal predation were investigated in field and laboratory experiments in four epibenthic brittle stars, Ophiura albida (Forbes), Ophiura ophiura (L.), Ophiothrix fragilis (Abildgaard) and Ophiocomina nigra (Abildgaard) from the Swedish West Coast. Predation attacks were simulated in three ways: by (1) momentarily approaching an individual with the palm of the hand, simulating an attack attempt without contact, (2) pinching an arm with forceps simulating a failed attack, and (3) amputating an arm using scissors and thus simulating a sub-lethal attack causing an injury. All brittle star species responded to predation attempts by escaping in a direction away from the site of attack, and a more rapid response was elicited when an arm was amputated (3) than if the arm was pinched (2). However, O. albida showed little or no reaction at all when attacked. O. ophiura was the only species that responded when momentarily approached by the palm of the hand (I). O. ophiura also showed a possibly intimidating (deimatic) behaviour by twisting up towards the point of attack, followed by a rapid escape response when pinched by forceps. In O. fragilis, observations also indicated that the thrashing of amputated arms may act as an efficient decoy pre-occupying a predator such as O. nigra and allowing O. fragilis to escape. The escaping behaviour of O. fragilis and O. nigra in the field varied depending on the proximity to a potential shelter such as a holdfast or aggregate of conspecifics. If a specimen was found close to a shelter it only withdrew its arms or took a single step. Crypsis was also the main defensive behaviour in aquarium experiments with O. nigra in the presence of sustained predation by a fish, Labrus bergylta. The diverse reactions to predation encounter events found in this study suggest that the initial response to predation events by active flight may be followed by a cryptic behaviour to reduce the probability of detection and recognition if the predation pressure remains high.

Published in

Ophelia
1998, volume: 49, number: 3, pages: 163-179
Publisher: OPHELIA PUBLICATIONS

SLU Authors

• Sköld, Mattias

  • County Administrative Board of Västra Götaland
  • University of Gothenburg

UKÄ Subject classification

Ecology

Publication identifier

• DOI: https://doi.org/10.1080/00785326.1998.10409380

Permanent link to this page (URI)

https://res.slu.se/id/publ/42486