Canopy Functions of R. maritima and Z. marina in the Chesapeake Bay

Abstract

Shoots in seagrass beds form canopies: structurally complex habitats that provide refuge for fauna and trap sediment particles by dampening water movement. Unfortunately, seagrasses are faced with continuing negative impacts to survival, including climate change and poor water quality. In areas where several seagrass species coexist, changing conditions may influence composition of beds so one species is favored over another. Two species found worldwide, Zostera marina and Ruppia maritima, are undergoing this shift: as Z. marina dies back, in some locations it is replaced by R. maritima, a smaller-form seagrass with shorter, thinner shoots. This process is occurring in Virginia, United States in the southern Chesapeake Bay, at intermediate depths where the species co-occur. Although changes in seagrass species abundance have previously been documented, few studies have measured the resulting effects on ecosystem functioning. We evaluated three sites to determine whether canopies of the two species displayed similar small epifaunal invertebrate animal assemblages and sediment properties, and found that Z. marina beds exhibited a greater amount of fine surface sediment than those of R. maritima, but found no effect of seagrass species on invertebrate assemblages. Epifaunal invertebrates were, however, more abundant and speciose with greater biomass, and more abundant with greater shoot density. This study provides baseline information from one summer for areas where the two seagrass species coexist. Although more research is needed, this study suggests in mixed beds, decline of Z. marina could result in coarsening of sediment, but dense R. maritima canopies could harbor similar small invertebrate assemblages.

Sensitivity of Photosynthesis to Warming in Two Similar Species of the Aquatic Angiosperm Ruppia from Tropical and Temperate Habitats

“…From an ecological point of view, a dominance shift from Zostera to Ruppia had no effects on canopy invertebrate assemblages, suggesting that the two seagrasses could harbor similar function for marine fauna. However, Ruppia had a lower sediment retention due to coarsening of the bottom substrate [79]. Hence, some ecosystem services provided by one seagrass species may not be lost due to a shift in dominance, while some may vanish.…”

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

“…While the consequences of shifts in seagrass identity in the Chesapeake Bay to food webs are unknown, examples from other regions suggest that the long-term response of fisheries to shifting seagrasses is linked to habitat consistency; after large-scale Z. marina die-off in Portugal, temperature-tolerant dwarf eelgrass ( Z. noltii ) is now dominant but supports lower long-term fish diversity and abundance because of interannual cover fluctuations ( 62 ). In the Chesapeake Bay, widegongrass’ short leaf height and size require higher shoot densities to provide comparable canopy structure and prey refuge to eelgrass ( 30 , 31 ), but temporal differences in emergence time [i.e., early spring eelgrass emergence vs. summer widgeongrass emergence ( 37 )] could result in lack of habitat altogether for important transient or juvenile species like blue crabs ( Callinectes sapidus ), spot ( Leiostomus xanthurus ), mysids ( Neomysis spp. ), or Black Sea Bass ( Centropristis striata ) that immigrate into the bay during the spring months.…”

“…First, widgeongrass meadows have undergone dramatic fluctuations in area that far exceed anything observed for eelgrass [e.g., reported 70 to 80% meadow loss in 1 to 3 y, 600 to 900% meadow recovery over 3 y ( 29 )]. Second, their shorter, thinner blades and shallower root depths provide different habitat structure that may alter the flow of nearshore goods and services ( 30 , 31 ). These differences challenge both scientists and managers seeking to restore the Chesapeake Bay ecosystems and enhance human well-being.…”

The Abundance and Persistence of Temperate and Tropical Seagrasses at Their Edge-of-Range in the Western Atlantic Ocean

“…This transition, effectively shuffling the landscape of the seagrass ecosystem, could have important implications for ecological functions and services as well as resilience (Micheli et al, 2008). For example, if there were a lag time replacing Z. marina cover with H. wrightii many of the positive feedbacks in the temporarily unvegetated habitat (e.g., sediment stabilization, nutrient cycling, and sequestration) would be lost, and in the worst case permanently impaired should H. wrightii not colonize those areas (Moore, 2004;Lefcheck et al, 2017;French and Moore, 2018). Likewise, shifts in the timing of the dominant seagrass abundance may affect faunal recruitment and utilization of these critical fishery and wildlife habitats (Micheli et al, 2008).…”