Gray whale foraging in Puget Sound influences spatial and temporal shifts in ghost shrimp population dynamics

Ecological disturbance is an essential aspect of climate change research as ecosystems around the globe encounter diverse and numerous shifts in environmental conditions. The intensification of climate change necessitates a better understanding of the impacts of disturbance on predator-prey interactions because of the importance of these interactions to ecosystem structure. The predator-prey relationship between bay ghost shrimp (Neotrypaea californiensis) and one of their major predators, gray whales (Eschrictius robustus), which forage in the shallow intertidal of the Northern Puget Sound (NPS), exemplifies the role of disturbance in foraging predation. Gray whales create large “feeding pits” as they excavate sediment to feed on ghost shrimp, creating ecological “destruction and opportunity” on the seafloor. Previous studies describe ghost shrimp populations in the NPS, but less is known about whether gray whale foraging impacts the distribution, individual size, and population dynamics of ghost shrimp. Further, an increasing gray whale population over the last 30 years necessitates an investigation into potential dynamic shifts within the ghost shrimp population. This study analyzed ghost shrimp collected from recently created feeding pits and “undisturbed” areas within the same sites to determine whether the increasing gray whale population is driving shifts in ghost shrimp density and distribution. We anticipated to observe differences in the size structures and densities of shrimp collected in foraged and unforaged areas, as well as temporal impacts of foraging (i.e. decreasing density) over the course of the three month gray whale stopover in the NPS. Ghost shrimp (n = 1553) were collected from five gray whale feeding sites in the NPS between the years of 2023 and 2024. Overall shrimp density did not appear to change between 1990 and 2024, despite the increase in foraging gray whales in the NPS. However, average shrimp size differed between sites where whale feeding has been observed for either decades or only several years, with larger shrimp located at “newer” sites (i.e. those foraged for less than a decade). Shrimp density inside pits was significantly lower than density outside pits at all sites, but average shrimp size did not significantly differ between samples collected inside and outside of pits. This study suggests that repeated disturbance may influence prey distribution and size in complex ways across different temporal and spatial scales. The findings also signal that this prey population is resilient in the short term (months to years), but that long-term disturbances (multiple decades) may leave lasting impacts on size distribution and population density.