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Coastal & Estuarine Science News (CESN)

Coastal & Estuarine Science News (CESN) is an electronic publication providing brief summaries of select articles from the journal Estuaries & Coasts that emphasize management applications of scientific findings. It is a free electronic newsletter delivered to subscribers on a bimonthly basis.

May 2011


Plastic Litters Developed and Undeveloped Beaches in NE Brazil
Nutrient Management and Shellfish Restoration Should Go Together, Study Shows
Wetland Site Types Vary in Their Ability to Keep Their Heads above Water as Sea Level Rises
Modeling Forecasts Outcomes of Freshwater Flow Restoration in the Everglades: Management Goals Can be Achieved

Plastic Litters Developed and Undeveloped Beaches in NE Brazil

Plastic and other debris litters beaches worldwide, threatening wildlife and degrading the aesthetic values of beautiful coastlines. Both land and offshore sources (boats, oil platforms) of debris have been shown to contribute to the problem, sometimes varying seasonally or with the level of development of a given beach. One study of debris and its sources on the beaches of NE Brazil found that while the amount of debris was about the same, the types and sources differed on developed and undeveloped beaches.

Investigators looked at anthropogenic debris on transects along a nearly 100-km long stretch of beach that includes both developed and undeveloped areas. They found everything from cigarette butts to fishing gear to unidentifiable pieces of plastic. Of the more than 6,000 pieces of debris catalogued during the course of the study, plastic items were the most common. There was no statistical difference in average number of items found in summer vs. winter or on developed vs. undeveloped beaches. However, sources varied: on developed beaches, 70% of the debris came from local tourist sources (items used while on the beach), while on undeveloped beaches local sources accounted for only 9% of the debris; 46% of the non-local debris came from domestic sources (items disposed of locally but not by beach-goers) and 24% from fishing activity offshore.

Plastic debris is a serious concern at these particular beaches, which serve as significant sea turtle nesting grounds. Ingestion of plastic by sea turtles has been reported worldwide. Plastics remain in the environment for a very long time, and are not easily removed by municipal beach-cleaning programs. The investigators urge reduction of land-based litter and enforcement of MARPOL regulations to address boat-based waste sources.

Source: Ivar du Sul, J. A., I. R. Santos, A. C. Friedrich, A. Matthiensen, and G. Fillmann. 2011. Plastic pollution at a sea turtle conservation area in NE Brazil: contrasting developed and undeveloped beaches. Estuaries and Coasts 34(May 2011). DOI: 10.1007/s12237-011-9392-8.

Nutrient Management and Shellfish Restoration Should Go Together, Study Shows

Thanks to active nutrient management initiatives to address issues such as eutrophication and dissolved oxygen depletion, nutrient loadings have been declining in some coastal systems. However, important species like seagrasses and bivalves have not, in many cases, rebounded. To explore these dynamics, mesocosm studies conducted in a Long Island embayment simultaneously examined the effects of nutrient loading and presence of adult suspension-feeding bivalves on the growth of eelgrass, juvenile bivalves, and juvenile planktivorous fish. Mesocosm treatments included high or low nutrient loadings with or without adult bivalves.

The body of results contributes to a conceptual model, which posits that nutrient loading and suspension-feeding bivalves act in opposite directions on phytoplankton biomass. High-nutrient treatments led to higher phytoplankton concentrations, increased juvenile bivalve growth, and decreased eelgrass growth. Adding adult suspension-feeding bivalves to the mesocosms generally led to decreased phytoplankton levels, increased light penetration and growth of eelgrass, and decreased growth of juvenile bivalves and fish. Ultimately, according to the model, more nutrients leads to increased growth of bivalves and fish, but decreased seagrass growth, while more adult bivalves means less food for juvenile bivalves and planktivorous fish, and increased light availability for seagrasses.

These results provide evidence that ecosystem-based management in estuaries needs to consider both nutrient management and shellfish restoration jointly because of their separate effects on ecosystem health. These results could also have implications for shellfish aquaculture operations: if shellfish stocking densities increase, aquaculture operations may limit each other or adjacent natural shellfish populations.

Source: Wall, C. C., B. J. Peterson, and C. J. Gobler. 2011. The growth of estuarine resources (Zostera marina, Mercenaria mercenaria, Crassostrea virginica, Argopecten irradians, Cyprinodon variegatus) in response to nutrient loading and enhanced suspension feeding by adult shellfish. Estuaries and Coasts 34(May 2011). DOI: 10.1007/s12237-011-9377-7.

Wetland Site Types Vary in Their Ability to Keep Their Heads above Water as Sea Level Rises

One of the many ecological casualties of sea level rise is likely to be coastal marshes, especially ones that have been altered by the construction of dams, impoundments, and dikes, and extraction of subsurface resources like natural gas. As marshes subside and sediment sources are reduced via these anthropogenic impacts, marshes are at risk of “drowning.” To survive, coastal wetlands will have to increase rates of accretion and vertical elevation gain to keep pace with accelerated sea level rise. Results of a study of 55 Mediterranean deltaic and lagoon wetlands suggest that some types of marshes will fare better as sea level rises than others.

The researchers examined the relationship between vertical accretion and surface elevation change in 1992-2002 at riverine, marine, and impounded marsh sites and compared those values to literature estimates of sea level rise and subsidence. The highest rates of elevation gain occurred at riverine sites where vertical accretion was highest, because of high rates of fluvial sediment input and high levels of above and belowground biomass production. Predictive models generated using projections of future sea level rise indicate that only the riverine wetlands will be able to keep up with accelerated rates of sea level rise. Impounded marshes with no or restricted riverine input had very low accretion rates and are already not keeping pace with sea level rise, let alone the predicted accelerated rates. “Rescue” of these sites will require measures that increase sediment flow to the coastal zone and restoring natural hydrology in impounded areas.

Source: Day, J.W., C. Ibáñez, F. Scarton, D. Pont, P. Hensel, J.N. Day, and R. Lane. 2011. Sustainability of Mediterranean deltaic and lagoon wetlands with sea-level rise: the importance of river input. Estuaries and Coasts 34(May 2011). DOI: 10.1007/s12237-011-9390-x.

Modeling Forecasts Outcomes of Freshwater Flow Restoration in the Everglades: Management Goals Can be Achieved

The world’s largest ecosystem restoration project is now underway in the Florida Everglades, in which coastal managers are attempting to redress more than a century of anthropogenic impacts in the region. Freshwater flow diversions to drain the Everglades have led to both increases in average salinity and decreases in salinity variability in Florida Bay, and in response dense beds of turtle grass (Thalassia testudinum) have replaced shoal grass (Halodule wrightii) in large stretches of the bay. Restoration is focusing on reestablishing natural freshwater flows in order to return the salinity regime of Florida Bay to more estuarine conditions, which is expected to lead in turn to restoration of natural vegetative communities.

While there’s no crystal ball that can predict for sure what the outcomes of restoration efforts will be, scientists have used a two-stage modeling approach to assess the potential for reaching the restoration project’s goals. FATHOM, a hydrological box model, was used to predict salinity changes in bay sub-basins under various Everglades flow increase scenarios. These salinity results were used as input to a statistical model that associates extent of eight seagrass community types with a range of water quality variables. Results varied widely by sub-basin: in the western sub-basins bordering the Gulf of Mexico even a five-fold increase in freshwater flow from the Everglades had no effect on salinity, but other areas responded to relatively small changes in flow with the desired salinity changes and projected increases in H. wrightii and decreases in T. testudinum. The analyses suggest that the desired bay-wide restoration goals can be achieved with a three-fold increase in freshwater inflow.

Source: Herbert, D. A., W. B. Perry, B. J. Cosby, and J. W. Fourqurean. 2011. Projected reorganization of Florida Bay seagrass communities in response to the increased freshwater inflow of Everglades restoration. Estuaries and Coasts 34(May 2011). DOI: 10.1007/s12237-011-9388-4.