BIOTURBATION AND TACTILE INTERACTIONS: INSIGHTS INTO A COMPLEX RELATIONSHIP BETWEEN REEF FORMING CORALS AND SEA CUCUMBERS

Abstract

Coral reefs are increasingly threatened by many anthropogenic stressors. It has been argued that the more stressful an environment a coral is living in, the fewer resources it has at its disposal to defend itself against pathogenic bacteria. While there are many factors in the ocean that dictate the stress experienced by a given reef, the removal of key organisms, specifically sea cucumbers, that reside in reef’s benthic substrates are important and overlooked elements with large scale impacts on an ecosystem’s structure and resilience. Aimed at elucidating how the presence or absence of sea cucumbers in adjacent sediments could impact the health and resilience of resident coral fragments, our manipulative experiment isolated the interaction between sea cucumbers and coral fragments and our bioassays enabled us to assess the resulting differences in coral’s pathogen suppression capacity. Our bioassays used samples of Vibrio coralliilyticus, a common pathogenic bacterium of coral, inoculated with mucus from coral fragments (coral water) from our manipulative experiment to assess differences in coral health and immune response as varied with different sediment community conditions. From these assays and our in-situ observations, we concluded that sea cucumbers significantly altered their local sediment communities which in turn impacted the residing coral fragments; coral water from coral fragments residing in the sea cucumber occupied sediments had stronger capacities for suppressing an ecologically relevant coral pathogen. Our experiment sets up the framework to look into the mechanisms involved in determining the capacity of coral across different environments to regulate Vibrio abundancies.