Wetlands as stepping stones for transients
In this article: How oyster reefs help transient species leave wetlands and how scientists feel about carbon offsets.
Like the dense South Korean capital city of Seoul, where vertical living supports the presence of approximately 10 million people on 605 square kilometers of land, oyster reefs provide surplus habitat with their three-dimensional structures. Natural and restored oyster reefs foster biodiversity and support more individuals than adjacent mud bottom environments with their added vertical space. Mobile aquatic organisms including toadfishes, grass shrimp, and mud crabs, otherwise known as nekton, use the vertical buildup of old shells and other hard surfaces in restored oyster reefs and sanctuaries for shelter, food, and substrate.
Reefs are crucial intermediate ecosystems between salt marshes and open ocean. Wildlife struggle with the harsh conditions in tidal wetlands where fluctuating tides, temperatures, and saltwater inundation make it difficult for organisms to permanently settle. Therefore, land and aquatic species will only occasionally inhabit marsh soils or surface waters before departing for reefs or the open sea. Researchers have contested the contributions of salt marshes to the growth and survival of transient aquatic species, which suggests that their hydrologic or soil dynamics offer more important ecosystem services.
Newly hatched oysters use existing reefs to expand upwards, where abundant algae, phytoplankton, and higher flow create the ideal conditions to filter-feed and grow. Harvested oyster beds are flat in comparison. Oyster hatchlings, or spat, are nearly impossible to track due to their miniscule size and free-flowing nature. However, computer models can estimate the paths of drifting larvae in their first 2-3 weeks of life before they attach to hard surfaces, become immobile, and develop into adults. Predictors include tides, river flow, salinity, and temperature, among other factors. Model results have shown that at least two-thirds of oysters may settle outside of their home reef. Deliberately restoring or positioning engineered reefs in predicted flow paths can help to catch drifting larvae and provide ideal environments for growth.
Intertidal oyster reefs located at the edges of salt marsh habitat feature lower nekton population density than expected because of redundancy. Salt marsh fringes, like oyster reefs, are believed to provide space for reproduction, enhanced feeding, environmental and predator refuge, and habitat enrichment. Ecosystem edges are especially important because although they can provide fish and crab habitat, species seldom rely only on salt marsh habitat, instead using various terrains that will meet their needs. One review article ranked underwater seagrass meadows as the best fish nursery areas, followed by mangrove forests, salt marshes, then reed beds. Mainland salt marshes have been found to serve salt marsh-dependent nekton (e.g., mummichog), whereas island environments with higher perimeter to area ratios are ideal for aquatic predators (e.g., smooth dogfish, butterfish).
Research suggests that oyster reefs located 25 to 50 meters from the nearest structured habitat (i.e., salt marsh, seagrass, or other reef) best enhance recruitment of nekton species, namely pinfish. Furthermore, low-lying subtidal reefs successfully recruit new individuals when their height does not surpass one meter. This information, acquired through coastal field ecology, can be used to inform environmental management decisions and maximize the effectiveness of future restoration projects.
“[Salt marshes are] a complex of vegetated and non-vegetated ecological habitats that includes the intertidal vegetated marsh surface, marsh pools and ponds, intertidal creeks, subtidal creeks, marsh coves and the marsh-bay fringe (adapted from Minello et al. 2003). In tidal systems, ecological habitats may also be defined on frequency of flooding, such as the high marsh (irregularly flooded), low marsh (regularly flooded), intertidal creeks and subtidal creeks.”
Aquatic Ecology, 2007
Shallow subtidal oyster reefs are expected to replace drowning coastal marshlands of Louisiana as sea level rises. Freshly established and growing reefs will slow the erosion of the wetlands that are left by boosting biological diversity and storm surge protection. The result would still involve a shrunken shoreline and a panorama of open ocean, but expansive oyster reef would sprawl over former emergent wetlands under the surface.
Peatlands in the News
A British wetland was the site of a historical precedent. Two bright-feathered azure kingfishers were spotted building a nest for breeding at a wildlife reserve in Gloucestershire, a rural county in Southwest England. Bird experts at Slimbridge Wetland Center noted that the swamp-dwelling pair started digging a riverbank nest in February rather than the typical March timeframe, potentially because of the mild winter. Although their numbers are decreasing, these avians are of least concern for endangerment. Outside of vegetated creek banks and swamps, they can also be found near lakes, tidal estuaries, and mangroves.
Pennsylvanian peat lovers are protecting a wetland from development. Old Crow Wetland was originally restored by the state’s Department of Transportation to compensate for damages from highway construction elsewhere, but now faces potential conversion to a 7-acre paved truck stop. It is a valuable stopover in an area otherwise devoid of large continuous wetland habitat that attracts birders, herpetologists, entomologists, and more. Consequently, a local citizens’ group appealed the Department of Environmental Protection’s decision to grant a building permit to the same company that committed water quality violations and failed to implement erosion and sedimentation controls at another site.
Hanshiqiao Wetland Park in Beijing, China is open for the spring season. Visitors are encouraged to tent camp, fish, pedal boat, or bike around to take in the sights. Migrating or rare bird species which can be spotted there include herring gulls, large swans, and white-rumped sandpipers.
Science Highlights
Mangrove forests, salt marshes, and seagrass meadows trap plastic pollution. Plastics in blue carbon ecosystems are largely damaging to aquatic species, but bolster microbial populations and decrease the amount of particles delivered to the open ocean. “Plastic Paradox in Blue Carbon Ecosystems” published last month in Environmental Science and Technology provides more details.
Researchers at the University of New Hampshire measure CO2 in moving water. By integrating a low-cost sensor with other components, the scientists share a simple way to measure stream and river gas emissions.
A long term analysis shows growing CH4 emissions in Boreal–Arctic wetlands. The study involved scientists from Lawrence Berkeley National Laboratory, University of Wisconsin–Madison College of Agricultural and Life Sciences and the Department of Forest and Wildlife Ecology, University of Illinois Chicago, and other institutions. Research was funded by NASA Carbon Monitoring System.
Read, Listen, or Watch All About It
Professor and oceanographer David Ho from the University of Hawaiʻi at Mānoa stresses the importance of attitude shifts that must accompany emerging carbon sequestration technologies on Sea Change Radio. In the episode, the scientist explains why carbon dioxide removal methods must become more efficient, or humans must produce less greenhouse gas emissions, to significantly undo damages to the climate. Behavioral and systemic changes, like driving less, and curtailing CH4 leaks during fossil fuel exploration, production, and transportation are equally as important as promoting verifiable, durable carbon removal strategies.
“… If you remove 4,000 tons of CO2 from the atmosphere every year, that’s … going back in time by three seconds compared to current emissions. … While 4,000 sounds really impressive, when you put that into context … it’s not as impressive. [The time machine analogy] … helps us contextualize what these big numbers mean, but it also gives you a sense of the challenge that we face.”
David Ho on Carbon Offsets: Much Ado About Nothing?
Ecologist and earth system scientist Dr. Robert W. Howarth opposes carbon capture and storage as a climate solution that relies on underdeveloped technologies. Criticisms of the method shared in an opinion piece for The Hill highlight its low efficiency and high cost relative to embracing renewable energy. Relying on uncertain technological remedies to the climate crisis could also continue reliance upon fossil fuels and even increase climate pollution during the process of “enhanced oil recovery”. Similar concerns have been voiced by experts in other fields, including the Vice President of Taxpayers for Common Sense and the founder of For a Better Bayou.
“…Shute Creek in the U.S. underperformed its carbon capture capacity by around 36% over its lifetime, Boundary Dam in Canada by about 50%, and the Gorgon project off the coast of Western Australia by about 50% over its first five-year period.”
Ireland’s peat bogs occupy desired space for wind turbines, aquaculture, large-scale data centers, sheep grazing, and small-scale fuel harvest. Dublin resident and media scholar Patrick Brodie informs readers of the challenges in protecting these valuable habitats in a nation with growing electricity use, expanding digital infrastructure, and an upcoming energy transition. Sustainable food production and renewable energy farming must be balanced with careful site selection, accountability for negative downstream impacts, and well-funded household energy solutions.
“In places where peat is still widely depended upon as a household fuel source, and in the midst of extortionately high imported solid fuel prices, the contradictions of climate action amidst widespread fuel poverty and lack of direct state investment in initiatives such as household retrofitting are stark.”
Fish Farming in the Digital Cloud