A study of some sublittoral populations of Asterias Rubens (1.) and their prey
This study investigated the biology and predatory behaviour of
Asterias rubens (L ), as a potential predator ofcommmeroial scallopst
Pecten maximus (L. ý
and quejen scallops Chlamys opercularis (L. ).
A population of A. rubens was monitored in a sub-littoral area by
divers. The density of A. rubens varied little, annually, but lower
densities were associated with an increase in sub-sea swell or with
darkness. Parallel studies on activity were carried out in the field
and in the laboratory.
A high recovery rate but little net movement of tagged starfish
was found within the area. This contrasted strongly with estimates
of daily distance travelled and led to the suggestion of a "home range"
in A. rubens.
Different sized starfish spent equal time foraging and feeding,
while "substrate" feeding was the most common form of feeding. Smallstarfish
fed on sedentary items such as barnacles, while larger starfish
fed on a greater variety of larger and more mobile prey e. g.
prosobranchs* The importance in the diet of calorifically rich9rare
food items, such as bivalves and carrion was noted,
Five other asteroid species were commonly found and details of
their biology noted. In particular# Stichastrella rosea fed, exclusivelyt
on sedentary prey, while Marthas
terias glaciatis-and Henricia
oculata showed broadly similar diets to large A. rubens.
Sampling of two separate populations of A. rubens led to the development
of reliable techniques for weighing and measuring starfisho
The (armlength/armwidth) ratio (LW) was proposed as a condition factor
The trophic conditions of the two populations were indirectly
assessed from bionomic factors. Mean weight for size, LW ratios and
organ indices were combined with results from feeding experiments to
demonstrate differences in trophic condition between the two populations.
The differences were also reflected in bodywall, pyloric caecum
and gonad indices, Improved trophic conditions, however, did not necessarily
lead to a great Increase In reproductive output,
The benthic populations of two sampling sites were examined to
assess the relationship between scallop and starfish speciesq their
relations to substrate type and the effect of fishing pressure. Little
correlation between density of scallop species and A. rubens was found.
An aggregated pattern of dispersion was found for (P. scallop species maximust C.
and C. tigerina)9 while A. rubens displayed a
more random dispersion* The aggregated nature of scallop stocks was
discussed in terms of spat settlement and active movement.
The shell orientation and the numbers of recessed or byssally
attached scallops was studied in relation to patterns of tidal flow
and substrate type.
The importance of physical availability of prey9 compared with density estimates was revealed In field and laboratory work. Observations
on starfish behaviour and evidence of predation led to the
suggestion that infaunal bivalves and Chlamys tigerina, were of greater
significance in the diet of A. rubens than commercial scallop species.