MEPS 268:93-103 (2004)  -  doi:10.3354/meps268093

Juvenile-adult associations in sea urchins Strongylocentrotus franciscanus and S. droebachiensis: Is nutrition involved?

Michael T. Nishizaki1, Josef Daniel Ackerman1,2,*

1Physical Ecology Laboratory, University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada and Bamfield Marine Sciences Centre, Bamfield, British Columbia V0R 1B0, Canada
2Present address: Departments of Zoology & Botany, University of Guelph, Guelph, Ontario N1G 2W1, Canada
*Corresponding author. Email:

ABSTRACT: Juvenile-adult associations (i.e. juvenile sheltering) in sea urchins of the genus Strongylocentrotus provide an example of an important post-settlement behaviour in benthic invertebrates. It has been suggested that these associations provide a nutritional advantage to juveniles by facilitating access to kelp. We examined this hypothesis in a series of growth experiments involving 2 sea urchin species, Strongylocentrotus franciscanus and S. droebachiensis, which show high and low levels of juvenile sheltering, respectively. Juvenile sea urchins (7.73 ± 0.09 mm [mean ± SE] test diameter) of both species had lower growth rates in the presence versus absence of adults, regardless of food type, though the effect was more pronounced in S. franciscanus (0.2 ± 0.1 vs 1.2 ± 0.3 mm mo-1) than in S. droebachiensis (0.8 ± 0.5 vs 1.2 ± 0.7 mm mo-1). This relationship was not evident in the absence of food, which leads us to conclude that the reduction in growth is due to intercohort competition. Hence, other post-settlement factors (e.g. predation and hydrodynamic disturbance) are likely responsible for maintaining the juvenile-adult associations observed in S. franciscanus. Species-specific strategies in juvenile sheltering indicate that behavioural processes are important for the recruitment of benthic invertebrates with mobile juvenile stages.


KEY WORDS: Strongylocentrotus ·Intercohort competition · Post-settlement · Sea urchin · Juvenile strategies


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