Gumboot Chiton Cryptochiton stelleri Die-off

Observation by Ryan Brubaker:

We were walking on the beach at Point Partridge and noticed a huge amount of kelp and many dead gumboots, which I took to be giant western fiery chiton. We saw over 100 on a 1/2 mile stretch of beach. There were also a lot of waves that day. There were people out surfing and there was a boat that had ran ashore. Apparently the kelp had clogged the water intakes and caused the outboards to overheat. Maybe because of all the loose kelp in the water?? Anyway, I am wondering if the chiton die-off is related to the stormy conditions or something else?

Comment by LEO Editors:

This is the first observation in LEO Network about the giant western fiery chiton. There are however, background articles that reference a Pacific Coast marine die-off in 2011 that included gum boot chitons, along with sea urchins and sea stars. A UC Davis study attributed the event to a harmful algae bloom (see Washington Post article). The giant western fiery chiton Cryptochiton stelleri are found on the Pacific coast from Northern California to Southern Alaska across the Aleutians to Kamchatka and as far south as Japan. They are nocturnal and feed largely on algae and kelp. According to the article in Wikipedia, they are vulnerable to becoming unattached from their substrate during strong waves and washing up on the beach. Given the ocean conditions and the large amount of kelp reported by the observer, this may be the cause of the October chiton die-off. This post has been shared with the Snohomish County, Department of Parks, Recreation and Tourism and the Washington Department of Fish and Wildlife.

Tom Okey with the Broughton Aquaculture Transition Initiative writes:

Yes, storms are a source of natural disturbance in nearshore subtidal and intertidal habitats. Pacific coastal marine biological communities are shaped and regulated in part by these disturbances. Unusual storm events in terms of intensity or frequency can cause unusually severe perturbations to these biological communities. Shifting storm disturbance regimes along a coastline, such as due to global environmental change, could shift these systems to novel or degraded states. These stranded chitons are likely 'strongly interacting grazers' (sensu Solomon et al 2007), and so such physical disturbances potentially cause trophic cascades that lead to disproportionately large ecological effects.

https://esajournals.onlinelibrary.wiley.com/doi/10.1890/06-1369.1

Salomon, A.K., Tanape Sr, N.M. and Huntington, H.P., 2007. Serial depletion of marine invertebrates leads to the decline of a strongly interacting grazer. Ecological Applications, 17(6), pp.1752-1770.