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2017 August

Contents

Shade from Docks Can Slow Down Spartina
Good News for the Everglades is Bad News for Lobsters
Nesting Terns Caught in the Middle
Scarring, Then Recovery, for Chesapeake Bay's Seagrass

Shade from Docks Can Slow Down Spartina

Building taller docks reduces negative impacts on salt marsh vegetation

Editor’s note: Estuaries and Coasts has a new “Management Applications” article type for papers that address real-world problems in estuarine/coastal management. The paper by Logan et al. that is highlighted here is the first one published in this new category. We expect that these articles will be of particular interest to our readers and anticipate that they will be featured in future issues of CESN.
The number of docks constructed in coastal areas is increasing, thanks to people’s desire to access the water, but they can have negative effects on ecologically important salt marsh vegetation. Some states have guidelines for dock construction intended to minimize the impacts on vegetation, but do these rules actually work? To assess this, a group of researchers installed 24 experimental docks in a coastal salt marsh in Massachusetts and monitored their effects on the temperature, light, and plant growth underneath for three years.

Massachusetts, New Hampshire, Maine, and Connecticut recommend a height to width ratio of 1:1 for new docks and the study compared this with docks with lower and higher height to width ratios. Both temperature and light were lower under docks than in control areas, with lower temperatures and less light under docks with lower height to width ratios. Both stem density and plant biomass generally increased with increasing height to width ratio, though the effects were delayed in the Spartina patens-dominated high marsh. Docks in the high marsh also appeared to facilitate the expansion of Spartina alterniflora from the low marsh toward land.

These results suggest that plants perform better under docks with a greater height to width ratio. The current guidance of 1:1 used in much of New England, while better than a dock with a ratio of 0.5:1, has a negative effect on salt marsh productivity, and the results of this study should be useful for improving best management practices for dock structures.

Source: Logan, J.M., S. Voss, A. Davis, and K.H. Ford. 2017. An experimental evaluation of dock shading impacts on salt marsh vegetation in a New England estuary. Estuaries and Coasts. DOI: 10.1007/s12237-017-0268-4

Good News for the Everglades is Bad News for Lobsters

Declining salinity from Everglades restoration may cause spiny lobster declines

The Comprehensive Everglades Restoration Plan (CERP) aims to increase freshwater flow through the famous wetlands—but the resulting declines in salinity downstream in Florida Bay may have a detrimental effect on the region’s commercially important spiny lobsters. Spiny lobsters are marine organisms and do not tolerate low salinity. Additionally, reduced salinity, both directly and through algal blooms triggered by the combination of unusually low salinity and pulses of limiting nutrients, can cause die-offs of sponges that provide crucial shelter for juvenile lobsters.
Researchers simulated the effects of decreased salinity alone and in combination with harmful algae blooms. The model predicted a 6-24% decline in lobster abundance in the future, depending on the conditions. However, only one-third of this decline was the direct effect of decreased salinity on lobster mortality—the rest was from the impact of decreased salinity and algal blooms on sponges and the resulting loss of habitat.
Spiny lobsters are thought to have expanded into Florida Bay following the re-engineering of the Everglades in the late 1800s and early 1900s and the resulting declines in salinity. Because of the commercial importance of the spiny lobster fishery, restoring the Everglades may conflict with the interests of some stakeholder groups. While some may perceive Florida Bay’s lobster population as “natural,” this is an example of the shifting baseline phenomenon, a perception of what’s normal that changes over time.

Source: Butler, M.J., IV, T.W. Dolan III. 2017. Potential impacts of Everglades restoration on lobster and hard bottom communities. Estuaries and Coasts. DOI: 10.1007/s12237-017-0256-8

Nesting Terns Caught in the Middle

Both top-down and bottom-up interactions harm Caspian tern fledging success

The battle between “top-down” and “bottom-up” controls of ecosystem dynamics is a classic conflict in the field of ecology, but the reality is more complex than a simple either-or question. To demonstrate this, a recent study investigated the factors involved in declining fledging success at North America’s largest Caspian tern breeding colony, East Sand Island at the mouth of the Columbia River, which has dropped dramatically from about 1.2 young fledged per nest in 2001 to 0 in 2011.

The researchers used a combination of aerial photography and ground-based counts to monitor terns’ fledging success, looking for correlations with prey availability (bottom-up) and predator dynamics (top-down). Average May and June river discharge increased over the course of the study, which was correlated with a decline in the availability of marine forage fish. This meant there was less food available for nesting terns. However, it also meant there were fewer fish to feed other birds such as gulls and bald eagles, which then turned to terns as an alternative food source. Both bald eagle disturbance and gull kleptoparasitism (stealing food from terns) increased over the course of the study, and tern fledging success was inversely correlated with gull kleptoparasitism rates.

Although predator control is often an important element of managing seabird nesting colonies, this study shows that when feasible, managing for the availability of prey could also be beneficial.

Source: Collar, S., D.D. Roby, and D.E. Lyons. 2017. Top-down and bottom-up interactions influence fledging success at North America’s largest colony of Caspian terns. Estuaries and Coasts. DOI: 10.1007/s12237-017-0238-x

Scarring, Then Recovery, for Chesapeake Bay’s Seagrass

New regulations reduce seagrass bed scarring by fishing activity in the Chesapeake Bay

Seagrass beds provide a variety of ecosystem services, but they’re vulnerable to disturbance by human activity thanks to their close proximity to shorelines. A new study documents the realization that commercial fishing activities were causing scarring of Chesapeake Bay’s seagrass beds, the regulations that were put in place to protect them, and the effectiveness of those regulations.

Since 1987, the region’s seagrass beds have been monitored using aerial imagery. Scarring of the beds, generally attributed to boat propellers, began to increase in many areas in the late 1990s, which led the Virginia Marine Resources Commission (VMRC) to seek more information on the problem. Scarring was most intense in two areas of the lower Chesapeake Bay, the Browns Bay and Poquoson Flats areas, which are located along the bay’s western shore. The location and nature of the scarring suggested that two types of fishing activities were the culprits—crab scraping on the eastern shore, and haul seining for fishes on the more heavily impacted western shore. However, individual scars typically recovered in less than three years, thanks to the fact that the two seagrass species in the area can regenerate quickly via both sexual and asexual reproduction.

During the course of the study, VMRC conducted meetings with stakeholders and ultimately introduced regulations requiring changes to haul seining practices to reduce sea grass damage. Subsequent aerial monitoring from 2003 through 2015 revealed 90% and 43% reductions in scarring in Browns Bay and Poquoson Flats, respectively, making this a conservation success story that demonstrates the effectiveness of swift management action in coordination with science.

Source: Orth, R.J., J.S. Lefcheck, and D.J. Wilcox. 2017. Boat propeller scarring of seagrass beds in lower Chesapeake Bay, USA: Patterns, causes, recovery, and management. Estuaries and Coasts. DOI: 10.1007/s12237-017-0239-9