Waterborne cues from crabs induce thicker skeletons, smaller gonads and size-specific changes in growth rate in sea urchins

Abstract

Indirect predator-induced effects on growth, morphology and reproduction have been extensively studied in marine invertebrates but usually without consideration of size-specific effects and not at all in post-metamorphic echinoids. Urchins are an unusually good system, in which, to study size effects because individuals of various ages within one species span four orders of magnitude in weight while retaining a nearly isometric morphology. We tracked growth of urchins, Strongylocentrotus droebachiensis (0.013–161.385 g), in the presence or absence of waterborne cues from predatory Jonah crabs, Cancer borealis. We ran experiments at ambient temperatures, once for 4 weeks during summer and again, with a second set of urchins, for 22 weeks over winter. We used a scaled, cube-root transformation of weight for measuring size more precisely and for equalizing variance across sizes. Growth rate of the smallest urchins (summer: <17 mm diameter; winter: <7 mm diameter) decreased by 40–42% in response to crab cues. In contrast, growth rate of larger urchins was unaffected in the summer and increased in response to crab scent by 7% in the winter. At the end of the 22-week experiment, additional gonadal and skeletal variables were measured. Cue-exposed urchins developed heavier, thicker skeletons and smaller gonads, but no differences in spine length or jaw size. The differences depended on urchin size, suggesting that there are size-specific shifts in gonadal and somatic investment in urchins.

Long-term and trans-life-cycle effects of exposure to ocean acidification in the green sea urchin Strongylocentrotus droebachiensis

“…This suggests that adults were fully acclimated to their new environmental conditions and were able to replenish their energy stores for successful reproduction. Sea urchins are well known to exhibit a high degree of plasticity toward a great range of stressors (e.g., Levitan 1991, Lau et al 2009, Selden et al 2009, Hernandez and Russell 2010 and required up to 20 weeks to fully exhibit new morphological and physiological changes (Hernandez and Russell 2010). These changes also require energy with accompanying potential negative effects on energy stores.…”

Substratum cavities affect growth-plasticity, allometry, movement and feeding rates in the sea urchinStrongylocentrotus purpuratus

“…Previous studies have highlighted the importance of small-scale variation in sea urchin growth (Russell, 1987;Russell et al, 1998;Meidel and Scheibling, 1999;Russell, 2001), and food availability has been identified as important in controlling growth and allometry (Ebert, 1980;Black et al, 1982;Levitan, 1988;Fernandez and Bouderesque, 1997). Recently, Selden and colleagues (Selden et al, 2009) have determined that predator cues induce changes in growth, morphology and reproduction.…”

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

“…Mann et al 1984, Vadas & Elner 2003, Matassa 2010. Juvenile Strongylocentrotus droebachiensis tend not to move (Nishizaki & Ackerman 2006) and have less growth in the presence of predator cues (Selden et al 2009). …”