Heat stress does not induce wasting symptoms in the giant California sea cucumber (Apostichopus californicus)

Abstract

Oceanic heat waves have significant impacts on disease dynamics in marine ecosystems. A severe sea cucumber wasting event occurred in Nanoose Bay, British Columbia, Canada, following an extreme heat wave, resulting in mass mortality of Apostichopus californicus. Here, we sought to determine if heat stress in isolation could trigger wasting symptoms in A. californicus. We exposed sea cucumbers to i) a simulated marine heat wave (22{o}C), ii) an elevated temperature treatment (17{o}C), or iii) control conditions (12{o}C). We measured the presence of skin ulcers, mortality, posture maintenance, antipredator defences, spawning, and organ evisceration during the 79-hour thermal exposure, as well as 7-days post-exposure. Both the 22{degrees}C and 17{degrees}C treatments elicited stress responses where individuals exhibited a reduced ability to maintain posture and an increase in stress spawning. The 22{o}C heat wave was particularly stressful, as it was the only treatment where mortality was observed. However, none of the treatments induced wasting symptoms as observed in the Nanoose Bay event. This study provides evidence that sea cucumber wasting is not triggered by heat stress in isolation, leaving the cause of the mass mortality event observed in Nanoose unknown.