The effects of climate-induced elevated seawater temperature on the covering behavior, righting response, and Aristotle's lantern reflex of the sea urchin Lytechinus variegatus

Abstract

Anthropogenic climate change is causing a global increase in sea-surface temperatures with some of the largest increases expected in the subtropical regions of the Northern Hemisphere. Populations of the sea urchin Lytechinus variegatus in the Gulf of Mexico are especially vulnerable as they are already living near the upper limit of their thermal tolerance and cannot migrate further north to escape rising seawater temperatures. In regular echinoids, neuromuscular-mediated behaviors including the covering and righting responses, and the Aristotle's lantern reflex can be employed as organismal level “indicators” of well-being under these near-future conditions. Individuals of the regular sea urchin L. variegatus were collected in Eagle Harbor, FL and held in the laboratory under a 12L:12D light cycle at both 28°C (current summer seawater temperature) and 32°C (predicted near-future summer seawater temperature) for acute (one day) and chronic (ten day) exposures. Covering and righting responses and Aristotle's lantern reflexes were measured. Individuals chronically exposed to 32°C covered themselves with less material than did individuals acutely exposed to either 28°C or 32°C. They also righted less frequently and had lantern reflexes less often than individuals in the other acute or chronic temperature treatments. Moreover, although individuals acutely exposed to 28°C and 32°C covered their tests more during daylight periods, individuals chronically exposed to these temperatures did not, indicating that these individuals had an impaired ability to cover in response to increased light levels. Our results suggest that near-future elevated seawater temperatures may impair important neuromuscular-mediated behaviors that could negatively impact population and community dynamics.