The dominant seagrass species in Chesapeake Bay has been replaced by widgeongrass, as per a recent study.

Mangroves grow in areas that were historically dominated by salt marshes and oyster reefs. Invasive Pacific oysters replace the native blue mussels of the Wadden Sea. Macroalgae show their dominance on scleral coral reefs in the Caribbean, Indian and Pacific oceans. Climate change-driven shifts in the dominant species that make up habitats like this one could have major conservation implications, and this is a phenomenon that appears to be particularly prevalent in seagrass systems worldwide.

In research published today in Proceedings of the National Academy of SciencesVIMS researchers and collaborators assess the causes and consequences of the emergence of a new dominant seagrass species in the Chesapeake Bay, demonstrating new threats and management opportunities.

In this study, the authors combined 38 years of data on nutrient and sediment contamination from runoff, temperature, plankton blooms, and river flow with aerial surveys of seagrass to describe the causes and consequences of shifting core seagrass species across 26,000 ha of habitat in the Chesapeake Bay. .

The shifts shown in seagrasses lead to faster recovery but greater mortality across the Chesapeake Bay

Marine heat waves and poor water clarity in the Chesapeake Bay over the past few decades have halved the area occupied by the once dominant seaweed, the eelgrass. At the same time, dietary reductions that have been successfully implemented throughout the Gulf have encouraged the rapid expansion of another seagrass, the global wedgong.

Confined to a fringing area of ​​shallow, brackish water until the mid-1990s, widgeongrass has now replaced eelgrass as the most abundant seagrass in the Chesapeake Bay by expanding by more than 150% due to both its tolerance to high temperatures and long-lasting seeds that allow for rapid recovery after disturbance.

“The ability of widgeongrass to recover and expand is very strong,” explains lead author Hensel, “Perfect widgeongrass conditions have resulted in two record peaks of seagrass cover in the Chesapeake Bay. The mid-1990s was an expansion of wedgegrass into areas vacated by eelgrass.”

However, some of the negative consequences of this shift have worried habitat managers.

“We’ve seen periods of rapid expansion and decline of grass eels for decades now, far beyond what we’ve documented for eelgrass,” says Landry, co-author and leader of the Chesapeake Bay Program’s Submerged Aquatic Vegetation (SAV) Working Group.

“But now that widgeongrass is so widespread in the Gulf, the abundance of volatile can have a significant impact on our overall acreage trends and on achievement of the Gulf-wide restoration goal. on widgeongrass as a habitat in the absence of eelgrass.”

Understanding the reasons for these fluctuations has been difficult because wedgong and eelgrass seem to respond differently to climate change and nutrient pollution stressors.

However, when the authors examined long-term and large-scale data on climate stressors and watershed pollution from agriculture and development along with year-to-year aerial survey images of seagrass meadows, they recognized an important shift in climate stresses prevailing in the Chesapeake. Bay seagrass: While wedgegrass is resistant to heat waves and high temperatures, it is highly susceptible to spring periods when heavy rains can bring massive flows of nutrient- and sediment-laden water into the bay, reducing the water’s clarity.

“This study is an important step forward in building our knowledge of human-ecosystem interactions along the coast and how they change over time,” says author Lefcheck.

“Our previous work showed record emergence of underwater weeds in response to nutrient management, but we now see that the story is considerably more complex and, in fact, still being written. Understanding, adapting and communicating this changing narrative is a challenge, but not one that cannot be overcome by any means.” Anyway.”

Keeping species with different needs simultaneously is both necessary and complex

The team’s modeling contributes to a greater understanding of both anthropogenic and climatic factors of annual changes in widgeongrass and highlights a critical difference in management compared to eelgrass-dominated bays.

Patrick, director of the SAV Monitoring Program at VIMS, explains, “Heat wave stress cannot be controlled at the local or regional level, but managing the amount of nutrients entering the bay from the watershed during the rainy spring is something we can actually control.”

This study confirms that because species differ in their traits and stress sensitivities, living habitat conservation management requires more research, monitoring, and community- or species-focused actions under climate change. Climate change is altering the landscape of species formation, creating new winners in these new environments, and management must switch sides.

Detailed monitoring data allows agencies to focus on each species and encourages them to manage community or individual habitat requirements, and to adapt strategies as species composition changes. This study also demonstrates the pitfalls that can occur if habitat-forming species are grouped together into individual “stocks”, such as “hectares of seagrass” or “acres of marsh”.

Indeed, the differences between seagrass species in this study explain many of the shifts in seagrass meadow dynamics in the Chesapeake Bay. “Widgeongrass has shorter, thinner blades than eelgrass,” Hensel says, making it more vulnerable to spring run-off events because sunlight cannot reach the short blades through cloudy, nutrient-laden water. Also, the widgeongrass’ shallow root system may not sequester carbon as well, and its tendency to have high fluctuations in cover means it may not provide a consistent habitat for major seagrass-dependent species such as Blue Crabs and Black Sea Bass. ”

The authors call for a parallel shift in coastal monitoring and assessment of management successes and failures, using the Chesapeake Bay as an example. They noted the need for long-term monitoring programs with coordinated, standardized, detail-oriented on-land surveys, as well as the importance of community or species-specific recovery targets across coasts where multiple seagrass species are present and responding. climate differently.

“This is a compelling example of how climate change is evolving around the world,” said Patrick. “With regional climate change, the emergence of new ecosystems is intrinsically challenging everything we think we know from analyzing historical data. The rules governing the dynamics of the world’s ecosystems are changing and we need to step up our monitoring efforts, assess changes in real time, and adapt our strategies over time. Along the way. ”

“What worked 10 years ago may not work five years in the future, or even today. This example challenges the conventional wisdom that the winners of climate change will be new species migrating north and invading a new habitat. At least in the short term, native species that have always been present may step up.” and redefine their role in ecological communities.”

“By fully understanding climate-driven changes in seagrass species, policymakers and practitioners are better equipped to make evidence-based decisions about short- and long-term conservation strategies in coastal ecosystems. This specific study focuses on about 100 square miles in the Chesapeake Bay, but Its effects extend far beyond the Gulf, to seagrass ecosystems in the Mediterranean, Caribbean, Atlantic, and Pacific oceans.”