Award: OCE-2049225

Marine diseases influence the structure of coastal ecosystems. Through mortality of susceptible hosts, they drive nutrient cycling and enrich biodiversity, but can also lead to environmental degradation and losses to aquaculture. In this project, we examined the diversity and dynamics of echinoderm parasites to address three questions. We focused on a recently discovered aquatic flavivirus (aiFV) in the California sea cucumber Apostichopus (formerly Parastichopus) californicus (PcaFV) in southeast Alaska. We hypothesized (1) that the enigmatic group of viruses to which PcaFV belongs was widespread amongst echinoderms and that (2) under typical conditions they do not cause any disease, but when they experience low oxygen stress the viruses grow rapidly and cause the animals to become sick. We further hypothesized that (3) periodic increases in algae and higher temperatures exacerbate low oxygen conditions around echinoderms which may make worse their impacts on hosts.

We started our investigation by performing a survey of aiFVs amongst Apostichopus californicus collected in Washington State, British Columbia (Canada) and found that these viruses were only present in southeast Alaska. We then performed a survey of other sea cucumbers in Florida and the United States Virgin Islands, but found no evidence of any aiFV in their tissues. Finally, we examined other echinoderm taxa including sea urchins and sea stars but did not detect any aiFVs amongst their tissues. We therefore rejected our hypothesis that PcaFV, nor aiFVs were widespread amongst echinoderms.

Next, we focused efforts on understanding how hypoxic stress influences the number of PcaFV viral particles in tissues by performing an experiment in southeast Alaska. We incubated Apostichopus californicus in seawater tanks in which we added several sugars and depleted oxygen, then monitored the types of microbes that were on their surfaces and PcaFV loads in their tissues. This experiment yielded the opposite result to our expectation: PcaFV decreased over time in animals which had more anaerobic conditions at their surfaces, and was inversely correlated to their health (i.e. the healthier the animals were, the less they had this virus). The proportion of bacterial taxa which only grow when there is no oxygen available (anaerobes) increased in incubations where oxygen was removed as well as in sugar additions, suggesting that our approach yielded low oxygen conditions on the surfaces of sea cucumbers. Based on this result, we rejected our hypothesis that suboxic conditions exacerbated animal health due to viral infection, since these results suggested that it was favored only when animals were healthy. PcaFV appears to be unrelated to animal health, is restricted in geographic range to southeast Alaska and only in Apostichopus californicus, precluding our work looking at how temperature and productivity influence viral dynamics as they relate to animal health.

In order to address the broader question of how environmental productivity and temperature affect echinoderm pathogen loads, we focused on the Diadema antillarum (sea urchin) scuticociliatosis Philaster ciliate (DaScPc), which causes mass mortality of these herbivorous sea urchins in tropical ecosystems. This taxon also occurs on the surfaces of corals. We discovered that this pathogen increases in abundance through time in concert with macroalgal abundance, suggesting that it is responsive to changes in primary production. However, its abundance does not correlate with periodic increases in temperature.

Finally, we sought to further investigate what types of microorganisms thrive on organic matter originating from the tissues of echinoderms through a series of experiments employing sea stars, a sea urchin, and a sea cucumber, as well as their provenance. Our work showed that bacteria that are well known to thrive in environmental conditions that normally occur in highly productive environments (e.g. during algal blooms) thrive on decaying echinoderm tissues, including the ubiquitous Vibrio spp. This bacterial group has received recent attention as a putative parasite of sea stars and members of this genus can cause diseases in both aquatic wildlife and humans. However, our work demonstrates that many species of Vibrio spp., including those reported as pathogenic agents in other echinoderms, may instead represent microbes that consume dead or decaying tissues (called saprobes), and that these may also be some of the bacteria that drive oxygen depletion around animals in the wild.

The project has generated considerable opportunities for undergraduate students to engage in research opportunities both in the lab and as part of a class in marine disease ecology. The results of this project have also been communicated to students and faculty at the University of Alaska Southeast, and other institutions. More widely, the results of this project have been communicated to the public through outreach events including public seminars and two webinars, and adult-focused and child-focused activities on the topic of marine diseases in the Caribbean. Finally, the results of this work have been used in popular and social media appearances talking about echinoderm mass mortalities.

 

Last Modified: 01/29/2026
Modified by: Ian Hewson