Hyposalinity reduces coordination and adhesion of sea urchin tube feet

Abstract

Climate change will increase the frequency and intensity of low-salinity (hyposalinity) events in coastal marine habitats. Sea urchins are dominant herbivores in these habitats and are generally intolerant of salinity fluctuations. Their adhesive tube feet are essential for survival, effecting secure attachment and locomotion in high wave energy habitats, yet little is known about how hyposalinity impacts their function. We exposed green sea urchins (Strongylocentrotus droebachiensis) to salinities ranging from ambient (32‰) to severe (14‰) and assessed tube feet coordination (righting response, locomotion) and adhesion [disc tenacity (force per unit area)]. Righting response, locomotion and disc tenacity decreased in response to hyposalinity. Severe reductions in coordinated tube foot activities occurred at higher salinities than those that affected adhesion. The results of this study suggest moderate hyposalinities (24-28‰) have little effect on S. droebachiensis dislodgement risk and survival post-dislodgment, while severe hyposalinity (below 24‰) likely reduces movement and prevents recovery from dislodgment.

Keywords: Climate change; Echinoderms; Extreme climatic events; Muscular hydrostats; Precipitation.

Fig. 1.

Sea urchin tube foot adhesion and coordination with decreasing salinity. Estimated smooths and scatter plots for (A) activity coefficient, (B) maximum locomotor speed and (C) disc tenacity of sea urchins kept in salinities from 32‰ (ambient) to 14‰ seawater for 24 h. The solid black lines represent the estimate of the smooth and dashed lines represent two standard errors above and below the smooth.

Fig. 2.

Performance with decreasing salinity. Mean percentage of maximum performance for (A) activity coefficient, (B) maximum locomotor speed and (C) disc tenacity for sea urchins kept in salinities from 32‰ (ambient) to 14‰ seawater for 24 h. Data are means±1 s.e.m.