Status, Trends, and Conservation of Eelgrass in the Northeast

Workshop invitation. The objective of the workshop was the timely dissemination of information regarding the science and conservation of eelgrass among federal, state, and provincial agencies and environmental organizations. Invited presentations and discussions highlighted status and trends in eelgrass distribution and abundance, factors controlling ecosystem change, current management issues, and regional examples of eelgrass conservation efforts. Participants were invited from all sectors of eelgrass science and management throughout eastern Canada and the northeastern United States. This event was hosted by Gulf of Maine Council on the Marine Environment, Friends of Casco Bay, Casco Bay Estuary Partnership, and Bay of Fundy Ecosystem Partnership. Additional sponsors included James W. Sewall Co., Maine Coastal Program, and U.S. Geological Survey

Eelgrass Habitat in Casco Bay: Past, Present, and Future? (2015 State of the Bay Presentation)

https://digitalcommons.usm.maine.edu/cbep-presentations/1018/thumbnail.jp

Detecting and Understanding Threats to Eelgrass in the Gulf of Maine: The Times, They Are A-Changin’

Eelgrass forms extensive meadows in coastal and estuarine waters throughout northern New England and Atlantic Canada. Threats to ecosystem stability include indirect impacts of watershed development and direct physical alterations associated with coastal construction, boating operations, and commercial fishing. Effects of human activities are exacerbated by natural disturbances such as severe weather events and biotic, geomorphic, and climatic processes. Spatial simulation models have shown even small scale disturbances in eelgrass meadows to require decades for full recovery. However, lack of consistent trend data of sufficient duration, spatial extent, and resolution often impedes anticipating threats before management solutions become cost prohibitive. Development and implementation of a hierarchical monitoring framework has provided an efficient and feasible way to detect and predict change. In recent years, new threats from invasive species have risen to prominence. Bioturbation from invasive European green crabs has caused extensive eelgrass loss from bays in the region: for example, over 1800 ha of eelgrass disappeared from Casco Bay, Maine, in about a six-month period from 2012 – 2013. In addition, invasive species of colonial tunicates are expanding their distribution from hard substrates onto eelgrass throughout the Gulf of Maine. These new threats appear related directly or indirectly to increases in regional seawater temperatures, and demand new approaches to ensure long-term sustainability of eelgrass ecosystems

Relative effects of nutrient enrichment and grazing on epiphyton-macrophyte (Zostera marina L.) dynamics

Dissolved nutrient concentrations and invertebrate grazing activity regulate epiphytic biomass. Because epiphyton may limit light and carbon at leaf surfaces and the consequent productivity of submerged macrophytes, factors which influence epiphytic biomass may indirectly affect macrophyte abundance. I measured the simultaneous effects of water column nutrients (ambient or 3x ambient concentrations of nitrogen and phosphorus) and grazing (presence or absence of epifaunal community) on epiphyton and macrophytes seasonally in eelgrass (Zostera marina L.) microcosms on lower Chesapeake Bay. Grazing was more important than nutrients in controlling accrual of total epiphytic biomass, although effects on epiphytic components varied; numbers of diatoms responded to grazing, whereas numbers of cyanobacteria responded to nutrients. Numbers of heterotrophic microflagellates mimicked those of bacteria. The indirect effects of nutrients and grazing on macrophytes depended upon the relative magnitude of each factor and the physiological demands of the macrophyte. Under low grazer densities of early summer, macrophyte production (g m&\sp{lcub}-2{rcub}& d&\sp{lcub}-1{rcub}&) was reduced with grazer removal and nutrient enrichment independently. In contrast, under high densities of late summer, production was reduced by enrichment with grazers absent only. There were no macrophyte responses to treatment during the spring and fall, regardless of differences in epiphytic biomass; this may have been related to comparatively low light requirements of eelgrass at low temperatures. I used a simulation model to extrapolate microcosm results to predictions for community persistence. The model included ranges of environmental variables specific to lower Chesapeake Bay, where declines in eelgrass abundance in recent decades were correlated with nutrient enrichment, reduced grazer populations, and increased turbidity. Simulations indicated that neither nutrient enrichment nor loss of grazers alone would limit eelgrass survival, but together would cause community instability. Simulations indicated further that with grazers present, nutrient enrichment with a slight decrease in submarine irradiance would cause macrophyte loss. Measured rates of epiphytic accrual on artificial substrata in situ suggested that with grazers present, light reduction actually reduced the absolute rates of biomass accumulation despite nutrient enrichment. Predictions for macrophyte community stability must thus consider the relative effects of both direct (acting on macrophytes) and indirect (acting via epiphyton) environmental controls

Zostera marina (eelgrass) growth and survival along a gradient of nutrients and turbidity in the lower Chesapeake Bay

Survival of transplanted Zostera marina L. (eelgrass), Z. marina growth, and environmental conditions were studied concurrently at a number of sites in a southwestern tributary of the Chesapeake Bay to elucidate the factors limiting macrophyte distribution in this region. Consistent differences in survival of the transplants were observed, with no long-term survival at any of the sites that were formerly vegetated with this species but that currently remain unvegetated. Therefore, the current distribution of Z. marina likely represents the extent of suitable environmental conditions in the region, and the lack of recovery into historically vegetated sites is not solely due to lack of propagules. Poor long-term survival was related to seasonally high levels of water column light attenuation. Fall transplants died by the end of summer following exposure to levels of high spring turbidity (K-d \u3e 3.0) Accumulation of an epiphyte matrix during the late spring (0.36 to 1.14 g g(-1) dry wt) may also have contributed to this stress. Differences in water column nutrient levels among sites during the fall and winter (10 to 15 mu M dissolved inorganic nitrogen and 1 mu M dissolved inorganic phosphates) had no observable effect on epiphyte accumulation or macrophyte growth. Salinity effects were minor and there were no symptoms of disease. Although summertime conditions resulted in depressions in growth, they did not alone limit long-term survival. It is suggested that water quality conditions enhancing adequate seagrass growth during the spring may be key to long-term Z. marina survival and successful recolonization in this region

Status, Trends, and Conservation of Eelgrass in Atlantic Canada and the Northeastern United States: Workshop Report

Eelgrass (Zostera marina L) is the dominant seagrass occurring in eastern Canada and the northeastern United States, where it often forms extensive meadows in coastal and estuarine areas. Eelgrass beds are extremely productive and provide many valuable ecological functions and ecosystem services. They serve as critical feeding and nursery habitat for a wide variety of commercially and recreationally important fish and shellfish and as feeding areas for waterfowl and other waterbirds. Eelgrass detritus is also transported considerable distances to fuel offshore food webs. In addition, eelgrass beds stabilize bottom sediments, dampen wave energy, absorb nutrients from surrounding waters, and retain carbon through burial

Neonatal Subventricular Zone Neural Stem Cells Release Extracellular Vesicles that Act as a Microglial Morphogen

Subventricular zone (SVZ) neural stem cells (NSCs) are the cornerstone of the perinatal neurogenic niche. Microglia are immune cells of the nervous system that are enriched in the neonatal SVZ. Although microglia regulate NSCs, the extent to which this interaction is bi-directional is unclear. Extracellular vesicles (EVs) are cell-derived particles that encase miRNA and proteins. Here, we demonstrate that SVZ NSCs generate and release EVs. Neonatal electroporated fluorescent EV fusion proteins were released by NSCs and subsequently cleared from the SVZ. EVs were preferentially targeted to microglia. Small RNA sequencing identified miRNAs within the EVs that regulate microglia physiology and morphology. EVs induced a transition to a CD11b/Iba1 non-stellate microglial morphology. The transition accompanied a microglial transcriptional state characterized by Let-7-regulated cytokine release and a negative feedback loop that controlled NSC proliferation. These findings implicate an NSC-EV-microglia axis and provide insight to normal and pathophysiological brain development

Update on a Continuing Saga: Eelgrass and Green Crabs in Casco Bay, Maine (Poster)

https://digitalcommons.usm.maine.edu/cbep-graphics-maps-posters/1035/thumbnail.jp