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.
April 2007
Contents
Fallout from Sewage Outfall Relocation: Changes in Water Quality and Productivity in Boston Harbor
Altered Ecosystem, Altered Fish Assemblage in the Sacramento-San Joaquin Delta
Goodbye to Terrapin Bycatch: A Florida Solution
Can Natural Reseeding Contribute to Marsh Restoration?
Fallout from Sewage Outfall Relocation: Changes in Water Quality and Productivity in Boston Harbor
After nearly 300 years of serving as the receiving waters for regional discharges of 1.5 to 2.7 million m3 of sewage per day, Boston Harbor’s water quality was in pretty bad shape. To address serious concerns about the health of the Harbor, a court order required that the sewage outfall located in mouth of the Harbor be moved 15 km into Massachusetts Bay. Data collected by an ongoing monitoring program initiated well before the move is allowing for comparisons of water quality parameters before and after outfall relocation.
The data indicate that, as expected, Harbor nutrient concentrations decreased after outfall relocation, and chlorophyll a concentrations increased at the new outfall. However, there were a few unanticipated results. In the Harbor, primary productivity and zooplankton abundance remained the same after the move, and at the new outfall primary productivity remained the same and zooplankton concentrations decreased.
Why the unexpected results? A major complicating factor may be the significant variability of parameters such as wind direction and speed and water column mixing. These factors may dampen the effect of the change in nutrient loadings, at least in the short term. Another explanation, particularly for the decrease in zooplankton in the Bay, may be the increased abundance of ctenophore predators in recent years. Increased ctenophore grazing may have reduced the zooplankton crop, which in turn relieved grazing pressure on phytoplankton, allowing increased concentrations of chlorophyll a in the Bay. The significant annual meteorological and biological variation in this system probably necessitates at least a decadal post-relocation monitoring data set before firm conclusions can be drawn about the environmental impacts of outfall relocation.
Source: Oviatt, C. A., K. J. W. Hyde, A. A. Keller, and J. T. Turner. 2007. Production patterns in Massachusetts Bay with Outfall Relocation. Estuaries and Coasts 30(1): 35-46. (View Abstract)
Altered Ecosystem, Altered Fish Assemblage in the Sacramento-San Joaquin Delta
For 150 years the Sacramento-San Joaquin Delta of the San Francisco Estuary has been diked for agriculture and channelized for navigation and water diversion. It comes as no surprise that such alterations impact native faunal communities. In the case of the Sacramento-San Joaquin Delta, the impacts of ecosystem alteration are exemplified by the fish community, which has been dominated by non-native species for decades.
A delta-wide electrofishing survey took stock of fish communities and characterized habitat availability in 1980-83 and again in 2001-03. These surveys were undertaken to provide information and guidance relevant to water management and resource protection in the system. During the 20-year period between studies, the overall catch of all species increased. However, catches of native fish declined and alien fish increased in the second survey compared to the first, such that introduced fish species, already prevalent in the 1980s survey, came to dominate the fish community even more strongly. Alien fishes particularly dominated in the central, south, and east portions of the delta, the same regions in which a significant increase in cover of the introduced aquatic plant, Egeria densa, was observed. The spread of E. densa is likely responsible for the overall increase in catches of all species, as it seems to be providing habitat for the invasive fish species in particular.
Past restoration efforts aimed at native fish populations assumed that restoration should focus on providing more tidal wetland habitat. The results of this study suggest that a more nuanced approach may be necessary: native fish restoration efforts will most likely be successful in the northern and western portions of the delta, since tidal wetland restoration elsewhere might actually provide additional E. densa habitat, and in turn, refuge for even more alien fishes.
Source: Brown, L. R., and D. Michniuk. 2007. Littoral fish assemblages of the alien-dominated Sacramento-San Joaquin Delta, California, 1980-1983 and 2001-2003. Estuaries and Coasts 30(1): 186-200. (View Abstract)
Goodbye to Terrapin Bycatch: A Florida Solution
Occasionally, a relatively simple, inexpensive solution to an ecological problem presents itself. The case of bycatch reduction devices (BRDs) designed to prevent diamondback terrapins from entering and drowning in crab traps may be one example, as outlined in a recent study. Brackish-water diamondback terrapins share habitat with the blue crab throughout their range, and are often unfortunate victims of traps designed to harvest the crustaceans (eel traps have also been shown to be a problem for the turtles, as discussed in CESN 28(4)). One study in the Chesapeake Bay estimated that 15-78% of the terrapin population was captured in crab traps annually. A simple BRD tested at a number of sites throughout Florida consists of a 4.5x12 cm rectangle fabricated of 12-gauge wire affixed to the entrance of the trap, thereby preventing turtles from entering.
Results indicated that the BRDs were highly effective: 37 terrapins were captured in control traps without BRDs, while only 4 were captured in the experimental BRD-equipped traps. Capture rates of crabs did not differ significantly between experimental and control traps, and trap treatment had no effect on captured crab sex or size. The authors conclude that BRDs would decrease terrapin bycatch by 73% with no significant effect on blue crab catch. They urge managers to require that the devices be used in Florida waters as soon as possible, and suggest that the Florida Fish and Wildlife Conservation Commission should make the devices available free of charge to retrofit existing gear.
Source: Butler, J. A., and G. L. Heinrich. 2007. The effectiveness of bycatch reduction devices on crab pots at reducing capture and mortality of diamondback terrapins (Malaclemys terrapin) in Florida. Estuaries and Coasts 30(1): 179-185. (View Abstract)
Can Natural Reseeding Contribute to Marsh Restoration?
Salt marsh restoration is clearly worth the effort, considering the valuable ecosystem services provided by these wetlands. But wouldn’t it be great if Mother Nature could assist in the labor-intensive undertaking of transplanting marsh vegetation in the service of restoration? A recent study in the Tijuana River National Estuarine Research Reserve in Southern California examined the potential for natural reseeding of restoration sites by comparing the seed bank (seeds stored in the sediment) of a natural marsh to that in two restored marshes. They also looked at the presence, abundance, and types of seeds in tidal waters flowing in and out of the marshes, in wrack deposits on the marsh surface, and in rabbit fecal pellets (one potential vector for seed dispersal).
Results indicated that seed dispersal was limited for most marsh species. “Rabbit dispersal” was ruled out: the only seed species found in fecal pellets were terrestrial invasives. The dominant plant species growing in the natural marsh site were not well represented in the seed bank of the restored area, and the newly restored marsh (< 3 years old) was particularly low in number and species of seed bank seeds.
The species most common in the canopy of the natural marsh, Sarcocornia pacifica (formerly known as Salicornia virginica), was also well represented in the marsh tidal waters and wrack, so its seeds should be readily available to colonize nearby restoration sites. So, at least one species might reseed naturally if restoration is planned for early winter when seed abundance in tidal waters and wrack is highest. Another way to maximize recruitment from seeds is to place restoration sites near existing marshes. Species other than the abundant S. pacifica may need some extra help in the form of actual transplantation.
Source: Morzaria-Luna, H., and J. B. Zedler. 2007. Does seed availability limit plant establishment during salt marsh restoration? Estuaries and Coasts 30(1): 12-25. (View Abstract)
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