COS 232-5 - After an outbreak: variable host population response over space, species and time

Background/Question/Methods

Disease can have strong negative effects on populations, and novel outbreaks can lead to loss of individuals over a relatively short time frame. Many factors can influence the host-disease relationship; host-disease traits (e.g. susceptibility, disease induced mortality) can vary by host species, and environmental context could alter host-disease traits. Host-population responses following a disease outbreak can provide insight into these potential drivers of disease dynamics. We monitor a diverse population of sea stars associated with a range of subtidal habitats (seagrass, rocky reefs and kelp forests) in central British Columbia, Canada, from 2013-2022, starting a few years before sea star wasting disease (SSWD) reached the region in 2015. With expert diver belt transects we monitor the size and distribution 20 species of sea star.

Results/Conclusions

For all habitat types that we monitored we saw a marked decrease in many sea star species, most notably a large decline in P. helianthoides, both in density and biomass biomass density. We also saw declines in density for Solaster, Evasterias troscheli and Orthasterias koehleri. At the same sites, there was no change in mean density of D. imbricata, Mediaster aequalis, or Henricia sp. In the years since there have been repeated surges of SSWD in the region between 2015-2022, with 14 different species showing signs of disease. P. helianthoides juveniles have recruited to several habitats, however the biomass density from 2018-2022 remains drastically reduced. Within several Fjords in the region P. helianthoides biomass density remains relatively high and representative of pre-wasting size distributions found within the region. This disparate response over 10’s of kilometers suggests that some aspect of the Fjord protects the populations from the costs of SSWD, and future work within this region will evaluate this question.