black dot
   
  Predators & defenses
  black dot
 

Tube-feet anchoring

 

Defenses of asteroids include tube-feet anchoring, considered here, and SPINES & OSSICLES, PEDICELLARIAE, ESCAPE BY CRAWLING, RIGHTING RESPONSE, DISTASTEFUL CHEMICALS, MUCUS, AUTOTOMY, and CAMOUFLAGE, considered in other sections. 

 
Research study 1
 

histogram comparing sizes of sea stars Evasterias troschelii and Pisaster ochraceus eaten by gulls Larus spp. in Puget Sound, Washingtongraph showing attachment strengths of sea stars Evasterias troschelii and Pisaster ochraceus for different body sizesAs part of a general survey of habitats occupied by Pisaster ochraceus and Evasterias troschelii in Puget Sound, Washington researchers from Friday Harbor Laboratories document incidences of predation on both species by gulls Larus spp.  Smaller sizes of both prey species are generally preferred, likely explained by the fact that the gulls find pecking bits from a sea star less preferable to swallowing them whole (see histogram on Left). Note on the graph that only small-sized Pisaster are eaten and no large individuals of either species are eaten.  The gulls prefer Evasterias over Pisaster (88 vs. 12%, respectively) possibly owing to its generally less bulky shape and to the fact that Evasterias anchors by its tube feet significantly less securely than Pisaster (see graph on Right).  The data show that Pisaster attaches with 1.3 times greater strength than Evasterias.  With respect to habitats occupied, there is an ontogenetic shift in preference, with the smaller more vulnerable sizes of both species favouring crevice microhabitats possibly as a predation refuge.  As the sea stars become larger and enter size refuge (from gull predation?), they tend to move out into open areas such as rocks or pilings and docks,with less structural complexity, but more abundant and larger food resources in the form of barnacles and mussels.  Rogers & Elliott 2013 Mar Biol 160: 853. Photograph of sea gull eating P. ochraceus courtesy Jeff Masters, Michigan myvalleylll; photograph of sea gull eating E. troschelii courtesy Bob Armstrong and Juneau Empire, Alaska.

NOTE glaucous-wing Larus glaucescens and possible hybrids with western gulls Larus occidentalis

NOTE assessed using a cable tie attached at the base of one arm and spring balance. The data in the graph upper Right are presented as antilog equivalents of the natural log values used originally by the authors, for visual clarity (thus explaining why they are not whole numbers)

 
photograph of sea gull Larus glaucescens eating a sea star Pisaster ochraceus In areas of Puget-Sound, sea stars appear to be the primary prey of sea gulls. Small- to medium-sized sea stars, such as shown here, are generally swallowed whole. Time to ingestion varies from seconds to hours depending on size of prey photograph of a sea gull Larus sp. eating a sea star Evasterias troschelii
 
Glaucous-wing gull Larus glaucescens eating an ochre star Pisaster ochraceus

Larus sp. eating a mottled
star Evasterias troschelii

 
  RETURN TO TOP