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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 bi-monthly basis.

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2017 July


Terrapin Territory Terminated?
A “Red Light” for Blue Crabs
Effects of Land Use and Shoreline Hardening on Estuarine Species
National Estuarine Research Reserves: The Gold Standard?

Terrapin Territory Terminated?

Sea level rise in the Chesapeake could lead to significant impacts on diamondback terrapin habitats

Diamondback terrapins are the Maryland state reptile, known to many as the beloved mascot of the University of Maryland sports teams. While the Terps may win basketball games, their namesake may lose serious ground as sea level rise floods the fringing habitats of low-lying coastal areas they use throughout their life histories. A recent study examined how moderate projections of sea level rise in the Chesapeake might affect known terrapin nesting sites and other habitats. The investigators conducted shoreline surveys to identify active nesting sites, and then used a model to map regional inundation and erosion under a range of sea level rise scenarios projected out to future dates ranging from 2025 to 2100. Results suggest that numbers of historical nesting sites on beaches could be reduced by as much as 80% by 2100, and the bay will likely experience significant losses of brackish marshes (up to 94% by area, under some scenarios), used by the terrapins for foraging. Female terrapins exhibit high site fidelity, often returning to the same nesting areas each year, so moving to another suitable habitat might pose challenges. Even if “new” beaches are formed as sea levels rise, the authors say, they will not necessarily be equivalent in habitat value to the historical sites. Management and conservation efforts for this species, and others that use similar fringing habitats, should consider the potential impacts of sea level rise.

Source: Woodland, R. J., C. L. Rowe, and P. F. P. Henry. 2017. Changes in habitat availability for multiple life stages of diamondback terrapins (Malaclemys terrapin) in Chesapeake Bay in response to sea level rise. Estuaries and Coasts (January 2017). DOI:10.1007/s12237-017-0209-2.

A “Red Light” for Blue Crabs

Color of bycatch reduction devices on crab traps affects both terrapin entry and blue crab retention

Bycatch reduction devices (BRDs) have been used in a variety of fisheries to exclude or release unwanted species from fishing gear. In nearshore blue crab fisheries in the mid-Atlantic, terrapin BRDs (wire or plastic devices that narrow the funnel-like openings into crab pots) are sometimes used to block terrapins from entering the crab traps. Concern remains over whether the BRDs affect crab catch. One recent study used a combination of lab and field experiments to examine whether changing the color of the BRD or imbuing it with a weak magnetic field (a deterrent for sea turtles) might simultaneously protect terrapins while retaining crabs.

Although the magnetic field did not deter terrapins from entering traps, traps outfitted with red BRDs caught fewer terrapins compared to black or any other color. While red seems to mean “stop” to the terrapins, green meant “go”: they entered the traps outfitted with green BRDs most readily. As for the crabs, although they entered traps with BRDs less frequently than those without BRDs, they remained in the BRD traps for longer, so the net crab catch was no different with or without red BRDs. Overall, use of red BRDs seems to be the best solution for retaining blue crab catch while excluding terrapins. However, the authors caution that the color may become less relevant if obscured by biofouling or if traps are used at deeper depths, where red wavelengths of light are filtered out.

Source: Corso, A. D., J. C. Huettenmoser, O. R. Trani, K. Angstadt, D. M. Bilkovic, K. J. Havens, T. M. Russell, D. Stanhope, and R. M. Chambers. 2017. Experiments with by-catch reduction devices to exclude diamondback terrapins and retain blue crabs. Estuaries and Coasts (February 2017). DOI: 10.1007/s12237-017-0223-4.

Effects of Land Use and Shoreline Hardening on Estuarine Species

Largest study of its kind evaluated 587 sites, 39 sub-estuaries, 15 fish and crustacean taxa

Answering big questions sometimes requires big data sets. A team of researchers recently decided to “go big” to address questions of the effects of land use and shoreline hardening on estuarine species at a landscape scale in the Chesapeake and Delaware Estuaries. A variety of statistical techniques were used to relate abundance patterns of 15 common taxa to gradients of urban and agricultural land cover and to shoreline use (wetland vs. hardened) at 587 sites spanning 39 sub-estuaries. The results provided support to many smaller-scale studies conducted over the past few decades that have suggested shoreline hardening affects nearby estuarine species. The study also went a step further: using these extensive data sets the authors demonstrated empirically that more agricultural land in a watershed and more hardened shoreline along a coast are associated with lower abundances of many important species.

In this study, shoreline hardening at a local level and at a cumulative watershed level had largely negative effects on most of the examined taxa. Local and landscape-scale wetland coverage was associated with higher abundances of 12 of the 15 study species. Cropland coverage in a given watershed was also an important driver of species abundance: Agricultural land use was negatively related to abundance of several bottom-oriented taxa like blue crab and Atlantic croaker, likely because of impacts such as eutrophication and wetland loss, but positively related to planktivorous fish like Atlantic menhaden, perhaps because enhanced nutrient runoff stimulates phytoplankton growth. Results of this study provide long-sought-after, solid evidence of linkages between fish and crustacean abundance, watershed land cover, and cumulative shoreline condition. Growing populations on the coast may lead to increased shoreline hardening, especially as people seek to protect coastal property from sea level rise, so coordinated management efforts will be necessary to address this threat.

Source: Kornis, M. S., D. Breitburg, R. Balouskus, D. M. Bilkovic, L. A. Davias, S. Giordano, K. Heggie, A. H. Hines, J. M. Jacobs, T. E. Jordan, R. King, C. J. Patrick, R. D. Seitz, H. Soulen, T. E. Targett, D. E. Weller, D. F. Whigham, and J. Uphoff, Jr. 2017. Linking the abundance of estuarine fish and crustaceans in nearshore waters to shoreline hardening and land cover. Estuaries and Coasts (February 2017). DOI:10.1007/s12237-017-0213-6.

National Estuarine Research Reserves: The Gold Standard?

Can wetland restoration success be evaluated by comparing restored sites to National Estuarine Research Reserve sites?

Evaluating success of wetland restoration projects is challenging because the appropriate reference sites and monitoring parameters to gauge change are not always clear. In a perfect world, “before” data describing the restored site in its pre-degradation state would be available, so restoration progress could be measured against a baseline of the restored site itself. Without these baseline data, the next best approach is to compare the site to a similar, unimpacted site using standardized methods. Researchers at some of the NOAA National Estuarine Research Reserves (NERRs) and the NOAA Restoration Center recently partnered to examine the progress of 17 tidal wetland restoration projects by comparing them to nine reference sites in or near five NERRs. The study used an RPI (restoration performance index) scoring approach which compares changes in parameters over time between reference and restoration sites to determine the level of restoration achieved. Because the RPI compares the restoration trajectory of a given site to a paired reference site, pre-restoration data is useful but not required.

This approach worked well for these sites: the restoration sites consistently exhibited an intermediate level of restoration when compared to the reference sites, consistent with similar assessments described in the literature. This study provides strong evidence that the NERR network can be used as reference sites and in setting restoration goals. These sites, found in diverse biogeographic regions, are permanently protected and already monitored, reducing the effort and cost required to start such a comparison from scratch.

Source: Raposa, K. B., S. Lerberg, C. Cornu, J. Fear, N. Garfield, C. Peter, R. L. J. Weber, G. Moore, D. Burdick, and M. Dionne. 2017. Evaluating tidal wetland restoration performance using National Estuarine Research Reserve system reference sites and the restoration performance index (RPI). Estuaries and Coasts (March 2017). DOI:10.1007/s12237-017-0220-7.