Variation in purple sea urchin (Strongylocentrotus purpuratus) morphological traits in relation to resource availability

Flexible resource investment is a risk-sensitive reproductive strategy
where individuals trade resources spent on reproduction for basic
metabolic maintenance and survival. This study examined morphological
variation in herbivorous sea urchin grazers across a mosaic landscape of
macroalgae-dominated habitats interspersed with patches of sea urchin
barrens to determine whether sea urchins shift energy allocation in
response to food limitation. Extensive underwater surveys of habitat
attributes (e.g., sea urchin density, algae cover) were paired with
detailed laboratory assays (e.g., sea urchin dissections) to determine how
resource abundance affects energy allocation between reproductive capacity
and body structure in the purple sea urchin, Strongylocentrotus
purpuratus. We found that: (1) sea urchins had a more elongate jaw
structure relative to body size in habitats void of macroalgae (i.e.,
barrens), (2) sea urchin reproductive capacity (i.e., gonad index) was
lower in barrens and the barrens habitat was primarily comprised of
encrusting algae, and (3) sea urchin jaw morphology (i.e., lantern index)
and reproductive capacity (i.e., gonad index) were inversely related.
These results suggest that sea urchins respond to macroalgae limited
environments by shifting energy allocation between reproductive capacity
and modifications of the foraging apparatus, which may explain the ability
of sea urchins to persist in low resource
environments.