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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.

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2016 June


Some SAV Can Save Itself
Crustacean Perturbation
Plumbing a Carbon Sink
Disappearing Wetlands

Some SAV Can Save Itself

Healthy SAV beds exhibit resilience to storms, and can even contribute to their own recovery

Perhaps because the effects of climate change are increasingly obvious, the concept of resilience is receiving a lot of research and management attention. Can coastal ecosystems absorb or recover from climate change-related stressors such as sea level rise and major storms? The answer for some submerged aquatic vegetation (SAV) beds might be that they help themselves, if they’re large and robust enough, according to a recent study of a large, healthy SAV bed in the upper Chesapeake Bay.

Chlorophyll a and turbidity tend to be lower in SAV beds compared to outside the bed. When back-to-back storms hit the Chesapeake region in late summer 2011, chlorophyll a and turbidity rose within the beds due to sediment resuspension and plants were lost at the margins. However, the integrity of the bed's interior was preserved, and shortly after the storms chl a and turbidity once again declined. At ebb tide, this clear water appeared to “spill over” into immediately adjacent areas, improving conditions for additional plant growth at the margins of the bed. Plant production increased between 2012 and 2013/14 concurrently with improved water quality.

These positive feedback mechanisms not only protected the beds from destruction by the storms, they contributed to its recovery. The authors note that larger plant beds will generally exhibit higher resilience to storm events because their inner core is protected, allowing the flow attenuation mechanism to kick in during and after the storm.

Source: Gurbisz, C., W. M. Kemp, L. P. Sanford, and R. J. Orth. 2016. Mechanisms of storm-related loss and resilience in a large submersed plant bed. Estuaries and Coasts (February 2016). DOI: 10.1007/s12237-016-0074-4.

Crustacean Perturbation

Impacts of Deepwater Horizon oil spill on marsh fiddler crabs may linger 

The world watched in horror in April of 2010 as the Deepwater Horizon oil rig spewed alarming volumes of oil into the depths of the Gulf of Mexico. The spill was the largest ever in U.S. marine waters, ultimately releasing more than three million barrels of crude oil into the gulf and oiling over 1700 km of shoreline. While the effect of the oil on marsh vegetation has been fairly well documented, marsh invertebrates did not receive as much attention, despite their important roles in coastal ecosystems. Because they serve as both ecosystem engineers and prey for a range of other species, fiddler crabs are particularly deserving of attention. A recent meta-analysis of post-spill studies of fiddler crabs in the gulf using published and recent Natural Resources Damage Assessment data revealed that the oiling appears to have had a negative effect even years after the oil stopped flowing into the gulf.

Three metrics were examined at oiled and unoiled sites: burrow density (a proxy for crab abundance), burrow diameter (crab size), and crab species composition. A negative effect of oiling was observed for all three, although the timing and magnitude of the effects varied. Crab burrow density decreased at some of the oiled sites for as long as four years after the spill. Burrow diameters were reduced initially, but recovered to pre-spill sizes at all sites after two years. Fiddler crab species composition shifted: a higher proportion of Uca spinicarpa, a species usually found in sparsely vegetated areas, was observed at oiled sites, compared to the normally more abundant U. longisignalis. This shift persisted through at least 2013, and only returned to reference conditions where marsh grass recovered (via restoration planting in one case).

Studies such as this one are a good reminder that oil spill effects can linger long after the television cameras have left, the oiled birds have disappeared, and there is no longer visible oil on the shore.

Source: Zengel, S., S. C. Pennings, B. Silliman, C. Montague, J. Weaver, D. R. Deis, M. O. Krasnec, N. Rutherford, and Z. Nixon. 2016. Deepwater Horizon oil spill impacts on salt marsh fiddler crabs (Uca spp.). Estuaries and Coasts (February 2016). DOI: 10.1007/s12237-016-0072-6

Plumbing a Carbon Sink

Does fertilization affect a seagrass bed's ability to lock up carbon? 

In order to understand, and possibly mitigate, global climate change, we need to understand organic carbon dynamics. Where does it come from? Where does it go? Where does it tend to get locked away? One significant place it gets sequestered is in seagrass beds, particularly in the soil in which the plants grow. One recent study of seagrass beds in east-central Florida Bay took advantage of an accidental experiment to examine the impact of nutrient enrichment on carbon storage in the beds’ soils. As part of an unrelated long-term project, bird perches had been placed at some of the sites, resulting in substantial fertilization of those sites by bird feces. Investigators examined whether this nutrient enrichment, as well as seagrass species composition and biomass, influenced carbon storage in the soils.

Despite major differences in nutrient availability, net primary production, and seagrass community structure between fertilized and control sites, there was no difference in carbon storage in the top 15 cm of underlying soil. This somewhat surprising finding was attributed to the fact that the high-flow environment in which all the beds were situated did not allow for much sedimentation at all, and so soil carbon storage differences were, in effect, washed out. The results are summarized very well by the paper's title "Fertilization changes seagrass community structure but not blue carbon storage," and suggest an important role for local environmental factors in carbon storage dynamics.

Source: Howard, J. L., A. Perez, C. Lopes, and J. W. Fourqurean. 2016. Fertilization changes seagrass community structure but not blue carbon storage: results from a 30-year field experiment. Estuaries and Coasts (March 2016). DOI: 10.1007/s12237-016-0085-1.

Disappearing Wetlands

Study shows high rates of coastal wetland loss in New England, with more likely

Tidal wetlands are both an excellent natural line of defense against sea level rise and very vulnerable to its effects. As water levels rise, wetlands are often drowned, particularly where they have no inland space into which to migrate. In New England, where marsh loss has been significant over the past few decades, scientists and managers are interested in determining the causes of that loss in order to project, and possibly prevent, future losses. One recent study of tidal wetlands in Rhode Island linked marsh loss to sea level rise and explored likely future loss scenarios.

Using historic and modern aerial photos, the researchers found that rates of marsh loss in RI over the past 40 years have ranged from <2% to >40%. Marsh loss mechanisms included shoreline erosion and landward retreat of fringing marshes, widening of tidal creeks, increased marsh interior ponding, and inlet widening, among others. Using mesocosm experiments, the study also found that increased inundation leads to decreased plant productivity, suggesting that sea level rise destabilizes these marshes by limiting above- and below-ground plant productivity and peat formation. Taken together with projections of future sea level rise, these results suggest that New England marshes are more vulnerable to sea level rise than previously thought. The authors also point out that the dominant paradigm of marsh response to sea level rise – that marshes can keep up with rising seas if coastal submergence matches or is exceeded by sediment deposition – might not hold here. Instead, sudden inundation from storms, inlet erosion, or barrier breaches may lead to marsh drowning. One suggested “life preserver” for drowning marshes could be rigorous remote sensing programs to detect localized changes and drive conservation strategies.

Source: Watson, E. B., C. Wigand, E. W. Davey, H. M. Andrews, J. Bishop, and K. B. Raposa. 2016. Wetland loss patterns and inundation-productivity relationships prognosticate widespread salt marsh loss for Southern New England. Estuaries and Coasts (February 2016). DOI: 10.1007/s12237-016-0069-1