Rise ofRuppiain Chesapeake Bay: Climate change–driven turnover of foundation species creates new threats and management opportunities

Abstract

Global change has converted many structurally complex and ecologically and economically valuable coastlines to bare substrate. In the structural habitats that remain, climate-tolerant and opportunistic species are increasing in response to environmental extremes and variability. The shifting of dominant foundation species identity with climate change poses a unique conservation challenge because species vary in their responses to environmental stressors and to management. Here, we combine 35 y of watershed modeling and biogeochemical water quality data with species comprehensive aerial surveys to describe causes and consequences of turnover in seagrass foundation species across 26,000 ha of habitat in the Chesapeake Bay. Repeated marine heatwaves have caused 54% retraction of the formerly dominant eelgrass ( Zostera marina ) since 1991, allowing 171% expansion of the temperature-tolerant widgeongrass ( Ruppia maritima ) that has likewise benefited from large-scale nutrient reductions. However, this phase shift in dominant seagrass identity now presents two significant shifts for management: Widgeongrass meadows are not only responsible for rapid, extensive recoveries but also for the largest crashes over the last four decades; and, while adapted to high temperatures, are much more susceptible than eelgrass to nutrient pulses driven by springtime runoff. Thus, by selecting for rapid post-disturbance recolonization but low resistance to punctuated freshwater flow disturbance, climate change could threaten the Chesapeake Bay seagrass’ ability to provide consistent fishery habitat and sustain functioning over time. We demonstrate that understanding the dynamics of the next generation of foundation species is a critical management priority, because shifts from relatively stable habitat to high interannual variability can have far-reaching consequences across marine and terrestrial ecosystems.

Assessment of treatment-specific tethering survival bias for the juvenile blue crab Callinectes sapidus in a simulated salt marsh

“…Moreover, the dominant seagrass species of the southern Chesapeake Bay, eelgrass Z. marina , is threatened due to increasing temperatures and poor water quality [ 56 – 58 ]. Although recent reductions in nutrient loads have led to recoveries in seagrass beds [ 59 ], future projections depict long term declines in Z. marina beds due to thermal stress, while projections of widgeon grass Ruppia maritima distributions remain uncertain and likely depend on further nutrient reduction [ 60 ]. Mounting evidence suggests salt marshes and certain unstructured sand habitats may be as valuable or more so at the population level due to their extensive areal cover [ 27 , 30 , 31 ].…”

Quantifying Seagrass Density Using Sentinel-2 Data and Machine Learning

“…Finally, seagrasses also provide food and shelter to many aquatic organisms in coastal ecosystems, from tiny invertebrates to large fish, crabs, turtles, marine mammals, and birds. A change in seagrass density and types impacts sea creature habitats and the population of these sea creatures [7]. For example, in the last decade, the Chesapeake Bay has experienced a shift in seagrass species from eelgrass to widgeon grass due to anthropogenic impacts.…”

“…This shift results in a seagrass emergence time shift from eelgrass emergence in early spring to widgeon grass emergence in summer. This emergence time shift impacts the population density of species such as blue crabs and black sea bass, which need seagrass habitats when they migrate into the bay during the spring months [7].…”

Hot and fresh: evidence of climate-related suboptimal conditions for seagrass in a large Gulf coast estuary

“…These changes will profoundly alter physicochemical habitats, creating suboptimal or uninhabitable conditions for many species (Madeira et Species shifts are also expected to occur as changing physical conditions decrease the competitive advantages of historically abundant species. In Chesapeake Bay, the abundance of widgeongrass (Ruppia maritima) has responded positively to nutrient reduction and is replacing the formerly dominant but now heat-stressed (Z. marina, Hensel et al 2023). Changing frequency and severity of precipitation patterns may further alter salinity regimes and with it the distribution and abundance of seagrasses throughout the estuary (Rasheed and Unsworth 2011; Webster et al 2021).…”