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Contributed Talk

Session: : Biodiversity: Effects Of Global Change 6

COS 119-6 - CANCELLED - Environment, shipping, and their interaction homogenize eukaryotic communities across commercial ports

Tuesday, August 8, 2023
4:45 PM – 5:00 PM PDT
Location: B114
Abstract: Spread of non-indigenous species by commercial shipping is a large and growing global problem that harms coastal ecosystems and economies. Despite decades of research to understand ship-borne species spread and mitigate its harms, the relative contributions of major abiotic and biotic drivers remain unresolved. Barriers to increased understanding of this global phenomenon include the high complexity of the global shipping network, wherein ships make millions of voyages between thousands of ports each year, and the broad diversity of coastal organisms and life stages that can be spread by ships from one port to another.

To begin to unravel the effects of the major drivers of ship-born species spread, we conducted a standardized environmental DNA (eDNA) metabarcoding survey across 21 ports spanning five continents from which we derived eukaryotic community dissimilarities (Jaccard and Unifrac) between 231 port pairs. We hypothesized that port pair dissimilarities would be driven by three factors: biogeography, environmental similarity, and shipping, with the first two factors having stronger effects than the third. Specifically, we anticipated that port pairs would have lower dissimilarities if both ports were in the same ecoregion (due to shared evolutionary history), had similar temperature and salinity profiles, and had high shipping traffic and ballast transport between them. To test our hypotheses we used dissimilarity regression models which rely on community dissimilarity metrics that were calculated from eDNA sequence data alone, thereby avoiding the need to identify taxa and their non-indigenous status at each port, which is a formidable barrier limiting traditional methods.

Consistent with some of our hypotheses, we found that environment, shipping, and their interaction explained a significant amount of variation in port pair dissimilarities. As expected, the environment was the largest driver, and its significant interaction with shipping suggests that high volume shipping routes connecting environmentally similar ports pose the highest risk for species spread. Surprisingly, dissimilarities between ports in the same ecoregion were only weakly or insignificantly different than those from ports in different ecoregions. We explored several non-exclusive hypotheses for this surprising result in our dataset. These results and their implications for management of ship-borne species spread under climate change will be discussed, along with recommendation for future studies using eDNA dissimilarities to answer large-scale ecological questions.