Beneath the tranquil waters of Chesapeake Bay, a profound ecological transformation is quietly unfolding. Researchers at William & Mary’s Batten School of Coastal & Marine Sciences and the Virginia Institute of Marine Science (VIMS) have unveiled findings that highlight a significant shift in the region’s foundational seagrass species. This shift involves the gradual replacement of eelgrass (Zostera marina), a species long dominant in the Bay’s submerged aquatic vegetation, by its warmer-water counterpart, widgeon grass (Ruppia maritima). The study, soon to be published in Marine Ecology Progress Series, reveals that this botanical interchange could reverberate throughout the Bay’s complex food webs, fisheries, and overall ecosystem functionality.
Seagrasses in coastal ecosystems like Chesapeake Bay serve as the backbone for biodiversity, offering essential habitat, food resources, and nursery grounds for a plethora of marine organisms. While both eelgrass and widgeon grass provide vital habitat services, this research delineates a crucial distinction between their ecological roles. The results indicate that as eelgrass meadows succumb to environmental stressors and give way to widgeon grass, there will be a noticeable decline in the total invertebrate biomass these habitats support. The team projects a staggering 63% reduction in invertebrate biomass by 2060 should current trends persist without intervention.
Eelgrass, renowned for its broad leaves and structured canopies, creates a complex physical habitat that accommodates larger invertebrates such as pipefish, blue crabs, and isopods. These broader leaves facilitate a dense canopy that not only provides shelter but also influences sediment stability and nutrient cycling. Conversely, widgeon grass, characterized by its narrower, more delicate leaves, offers a higher surface area-to-biomass ratio. This trait permits a greater abundance of smaller invertebrates to attach and flourish. However, despite this numerical abundance, the ecological value and biomass contribution of these smaller organisms do not equate to the ecosystem functions delivered by eelgrass-associated fauna.
The research spearheaded by Lauren Alvaro, a recent master’s graduate from William & Mary’s Batten School, encompassed meticulous fieldwork in Mobjack Bay. Her team performed comprehensive surveys on distinct seagrass beds—pure eelgrass, pure widgeon grass, and mixed species meadows—to quantify both plant biomass and the assemblage of invertebrate communities within these habitats. Their findings underscore that while widgeon grass supports more individual invertebrates per gram of plant mass, the total biomass of animal life supported by eelgrass beds remains significantly higher. This discrepancy underlines the critical role of seagrass structural traits in shaping faunal communities.
Central to this shift are the multifaceted environmental pressures reshaping the Bay’s underwater landscapes. Increasing water temperatures, nutrient loading from agricultural and urban runoff, and habitat fragmentation from coastal development have heightened stress on eelgrass populations. Unlike eelgrass, widgeon grass exhibits a robust tolerance for warmer temperatures and fluctuating salinities, enabling it to thrive where eelgrass declines. However, this resilience comes with ecological trade-offs, especially in terms of habitat quality and food resource availability for higher trophic levels, which rely on the size and biomass of the invertebrates within these meadows.
Projected ecological consequences extend well beyond invertebrate communities. The term “secondary production”—a measure of biomass available to predators such as commercially valuable fish and blue crabs—could be drastically diminished. Current estimates attribute approximately 66,139 tons of invertebrate biomass living within Chesapeake Bay’s seagrass beds, with 35,274 tons of new animal biomass generated each growth season. A decline in meadow quality as eelgrass is overtaken by widgeon grass threatens this crucial energy source for the food web, potentially cascading up to affect fisheries, ecosystem stability, and even coastal economies dependent on these resources.
The intricate relationship between seagrass structure and faunal assemblages also influences predator-prey dynamics. The larger, more structurally complex eelgrass beds foster higher abundances of larger prey species, which are inherently more valuable to predators than the smaller invertebrates supported by widgeon grass. This shift in prey community size distribution may render food webs more fragmented and less efficient, with potential reductions in fishery yields and biodiversity. Although quantifying exact impacts at the fishery scale remains challenging, the researchers warn of likely declines in both commercial and recreational species across the Bay.
This seagrass succession illuminates broader themes in marine ecology regarding the influence of climate change and anthropogenic stressors on foundational species worldwide. The replacement of sensitive, slow-growing species by more tolerant, opportunistic ones is mirrored in other ecosystems, such as the shift from Florida’s mangroves to salt marshes or the global transition from coral-dominated reefs to algae-covered seascapes. Understanding the ecological ramifications of these shifts is imperative, as foundation species underpin the resilience and productivity of entire habitats.
From a management perspective, these insights underscore an urgent need to prioritize the preservation and restoration of eelgrass meadows within Chesapeake Bay. Strategies to improve water quality through nutrient reduction, combined with protection against habitat degradation, could help maintain eelgrass populations and their invaluable ecosystem services. Simultaneously, research into the ecological nuances of widgeon grass may reveal opportunities to mitigate the negative impacts of this transition, potentially through habitat enhancement or species-specific fisheries management.
The study’s lead and senior authors emphasize that this seagrass dynamic is not an isolated event but a symptom of broader environmental changes challenging coastal ecosystems. They advocate for integrated approaches combining ecological monitoring, modeling, and targeted restoration to safeguard the Bay’s biological integrity. Moreover, the work illuminates the necessity of maintaining diverse habitat structures that support a range of species sizes and functional roles within marine communities.
This research also advances our conceptual understanding of how foundational species govern ecosystem processes and biological communities. By unveiling how slight morphological differences between seagrass species propagate substantial changes in food web architecture, the findings invite further exploration into seagrass ecosystem functioning under future climate scenarios. The study serves as a clarion call for scientists and coastal managers alike to anticipate and address the ecological consequences of species shifts driven by a warming planet.
As stewardship of the Chesapeake Bay continues amid increasing environmental pressures, the integration of scientific insights such as those from this seagrass study will be pivotal. By illuminating hidden connections between plant structure and animal communities, and their implications for ecosystem productivity, this research charts a path towards sustainable management of one of the United States’ most important estuarine habitats.
The full study can be accessed through the Marine Ecology Progress Series and offers an indispensable resource for ecologists, marine biologists, and conservationists committed to understanding and preserving seagrass ecosystems in the face of unprecedented environmental change.
Subject of Research: Impact of shifting foundation seagrass species on faunal communities and ecosystem functions in Chesapeake Bay
Article Title: Changing foundation species in Chesapeake Bay (USA): implications for faunal communities of two dominant seagrass species
News Publication Date: 4-Sep-2025
Web References:
- SAV Monitoring and Restoration Program: https://www.vims.edu/research/units/programs/sav/
- DOI: http://dx.doi.org/10.3354/meps14901
Image Credits: Frederick Corey Holbert
Keywords: Marine ecosystems, Marine food webs, Marine conservation, Fisheries
