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

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.

A secondary chemical cue facilitates juvenile-adult postsettlement associations in red sea urchins

“…As indicated above, juvenile sea urchins aggregate and shelter under adults in response to predators, but in so doing they decrease foraging opportunity due to competition with adults (Nishizaki and Ackerman 2004). Balancing these risks against opportunities requires that juveniles detect aggregation cues (i.e., in the presence of a predator) simultaneously with being able to locate adult urchins under which to shelter.…”

“…Conversely, postsettlement processes (i.e., nutrition, predation, fluid dynamics) are likely to be important in recruitment dynamics. In the case of S. franciscanus, there does not appear to be a nutritional advantage for juveniles in the aforementioned juvenile-adult associations (Nishizaki and Ackerman 2004); however, protection from predation and fluid dynamics have not been examined. Consequently, an investigation of postsettlement processes for sea urchins, as representative mobile organisms, is warranted.…”

“…Such strategies, however, may incur a cost in the form of lower access/use of resources (Sih 1980), which in S. franciscanus has been attributed to increased competition for food between sheltering juveniles and adults (Nishizaki and Ackerman 2004). Thus, it would be a selective advantage for juvenile sea urchins to assess the need to shelter in an expeditious and accurate manner that optimally balances potential risks (i.e., predation) against potential gains (i.e., growth) (Sih 1980).…”

Small macrobenthic invertebrates affect the mortality and growth of early post-settlement sea urchins and sea stars in subtidal cobble habitat

“…biofilms), regardless of the addition of kelp. Nishizaki & Ackerman (2004) Mar Ecol Prog Ser 431: [173][174][175][176][177][178][179][180][181][182] 2011 conspecific adults were present, suggesting intercohort competition, although generally sea urchins grow better when fed kelp than coralline algae or bare rocks (e.g. Briscoe & Sebens 1988, Rowley 1990, Jennings 2011.…”

Effect of macrophyte diet and initial size on the survival and somatic growth of sub-adult Strongylocentrotus purpuratus: a laboratory experimental approach

“…Furthermore, their growth and future reproduction could be time-lagged and become variable across relatively small spatial and/or short temporal scales as a consequence of the quantity and quality of available food (Lawrence and Lane 1982;Meidel and Scheibling 1999;Nishizaki and Ackerman 2004).…”