Sea-surface temperature anomalies mediate changes in fish richness and abundance in Western North Atlantic and Gulf of Mexico estuaries

Aim: Anthropogenic-driven warming of marine systems has resulted in a series of biological and physiological responses that are fundamentally altering ecosystem structure. Because estuaries exist at the land-ocean interface, they are particularly vulnerable to the effects of ocean warming as they can undergo rapid biogeochemical and hydrological shifts due to climate and land-use change. We explored how fish diversity structures—turnover, richness and abundance—have changed in the western North Atlantic and Gulf of Mexico estuaries through space and time and the drivers of change.

Location: North Atlantic and Northern Gulf of Mexico

Taxa: Fish

Results: We found that species richness and abundance, turnover have increased in North Atlantic and northern Gulf of Mexico estuaries in the last 3 decades. These changes were mediated largely by sea-surface temperature anomalies, especially in more northern estuaries where warming has been relatively pronounced. There is also an indication that urbanization, perhaps through habitat fragmentation and/or fisheries activities may be contributing to the increase in fish richness in many of these estuaries.

Main Conclusion: The increasing trajectory of turnover in many of the estuaries suggests that the fish communities have changed fundamentally from the baselines. A fundamental change in community composition can lead to an irreversible trophic imbalance or alternative stable states among other outcomes. Thus, predicting how shifting community structures might influence food webs, ecosystem stability and human resource use remains a pertinent task.

Methods
We compiled long-term (>30 years), continent-wide fisheries independent trawl surveys conducted in estuaries—from the Gulf of Maine to the Gulf of Mexico (U.S. waters)—and combined these with climate and land-use-land-cover data to examine trends and ecological drivers of fish richness, abundance, and turnover using mixed-effect models.