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

Abstract

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 acquire food in resource-limited environments.

Consequences of kelp forest ecosystem shifts and predictors of persistence through multiple stressors

“…Moreover, Smith et al . [ 23 , 30 ] demonstrated the role of sea otters in maintaining remnant patches of kelp forests in this study system. Therefore, although kelp persistence is associated with preexisting environmental conditions, grazer suppression by sea otters can further facilitate the longevity of patch resistance, ultimately contributing to enhanced ecosystem resilience through the maintenance of kelp spore production sources.…”

“…Sea urchin barrens are characterized by an abundance of exposed actively foraging sea urchins, are primarily dominated by encrusting red and coralline algae, and are devoid of macroalgae [19]. Barrens are generally highly unproductive and can persist for several years because of the ability of sea urchins to survive with minimal resources and consume newly recruited algae [21][22][23]. As such, sea urchin barrens are often considered a stable alternative ecosystem state because of intrinsic feedback mechanisms (e.g.…”

Alternations in the foraging behaviour of a primary consumer drive patch transition dynamics in a temperate rocky reef ecosystem

“…The results presented in this study highlight the role of behaviorally mediated effects in structuring ecological communities. One of the most unusual aspects of this system is the ability of sea urchins to persist in low‐resource environments for extended periods of time (Ebert, 1967; Ebert, 1982; Smith & Garcia, 2021), which may contribute to the longevity of the alternative barrens state of the ecosystem. Therefore, the behaviour of grazers, especially ecosystem engineers, is fundamental to community and ecosystem dynamics.…”