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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.

January 2005


Getting Warmer: An Exercise in Extrapolation Elucidates Effects of Global Warming
More Work Needed on Increasing Light Availability Under Piers for SAV, Study Finds
Sometimes Seagrass Declines are Not Our Fault!
Better, Faster, Cheaper Benthic Sampling

Getting Warmer: An Exercise in Extrapolation Elucidates Effects of Global Warming

Speculation abounds as to the potential ecological effects of global climate change. What will a small change in sea surface temperature mean for primary productivity, fisheries production, or ecological function of estuaries? One way to predict these consequences, as demonstrated in a recent Estuaries paper, is to examine recorded differences in such parameters as they've already varied with climate changes on a smaller scale. This analysis requires reliable long-term temperature records and the relevant ecological data, which, fortuitously, are available for Narragansett Bay, Rhode Island. These data were compared to similar information also available for western Europe. This study reveals that relatively small winter temperature increases may have led to fairly significant ecological shifts, perhaps indicative of permanent and larger-scale changes that will result from global warming.

The data indicate that 1926-1938 and 1983-1999 were relatively warm periods, in which winter water temperatures averaged 1.5 oC higher than the 1880-2000 mean. The 1959-1968 period was slightly cooler than the long-term mean. The corresponding ecological data reveal that during the warmer periods, northern species declined, southern species increased, and eelgrass declined on both sides of the Atlantic. Chlorophyll was lower in the winter in the warm as compared to the cool years, representing a minimized winter-spring diatom bloom in those years. The reduced bloom, perhaps attributable to continued zooplankton and benthic filter feeder grazing in the warm winters, may have lead to another observed difference in the warmer years: an increase in ctenophores in early summer. Maximum abundance of ctenophores - small filter-feeding jellies - was shifted earlier in the spring/summer in warmer years, which may have lead to reduced summer zooplankton levels as the jellies grazed on them. Another observed difference was a decrease in boreal demersal fish species abundances and a replacement increase in pelagic fish and decapod crustaceans.

Source: Oviatt, C. A. 2004. The changing ecology of temperate coastal waters during a warming trend. Estuaries 27(6): 895-904. (View Abstract)

More Work Needed on Increasing Light Availability Under Piers for SAV, Study Finds

It is clear that one factor influencing submerged aquatic vegetation (SAV) growth and abundance is light availability, which can be severely curtailed by over-water structures such as docks. As coastal areas become more developed, shading of SAV beds becomes an increasing environmental concern. A recent study evaluated the utility of a 19th-century technology in addressing this 21st-century problem.

The investigators explored whether docks constructed with embedded hexagonal glass prisms like those used to provide light below-decks in wooden whaling vessels would allow SAV to thrive underneath. Light penetration, water quality and SAV cover were measured under experimental docks with prisms, docks without prisms, and in control areas without docks in the St. Johns River, Florida. Unfortunately, this clever solution did not work as expected: There was no difference in SAV growth under the two dock types. SAV declined in all areas due to water quality problems, but declined most rapidly under all docks (compared to open water control areas). SAV recovery did not occur under either type of dock, leading to the conclusion that the additional light penetration allowed by the prisms was not sufficient to promote SAV growth.

The authors note that reduced light magnifies the susceptibility of SAV to environmental stressors. They add that dock placement should be considered carefully to minimize impacts on SAV, and that other alternate dock designs allowing greater light penetration should continue to be pursued.

Source: Steinmetz, A. M., M. M. Jeansonne, E. S. Gordon and J. W. Burns, Jr. 2004. An evaluation of glass prisms in boat docks to reduce shading of submerged aquatic vegetation in the lower St. Johns River, Florida. Estuaries 27(6): 938-944. (View Abstract)

Sometimes Seagrass Declines are Not Our Fault!

Anthropogenic impacts on coastal habitats such as seagrass beds are extensively documented, and the subject of countless monitoring and management programs. However, a recent incident in Florida's Indian River Lagoon reminds us that sometimes changes in estuarine habitats are due not to human influences, but to natural cycles that we do not yet completely understand.

Extensive seagrass monitoring in the Indian River Lagoon using both aerial photographic surveys and field monitoring along fixed transects allowed documentation of a complete die-off of seagrass beds in a relatively pristine embayment, followed by a total recovery of the beds within three years. The aerial monitoring showed a decline bay-wide from 124 ha in 1989 to 34 ha in 1999, with a particularly sharp decline in 1996-1999. The transect monitoring (along a single transect in the bay) revealed more details: first, species composition changed from Halodule wrightii to Ruppia maritima, and macroalgae cover increased. By 1997, all seagrass along the transect had disappeared and a hard, sandy substrate and large numbers of molluscs were observed. The recovery was rapid and occurred in reverse species order: R. marina returned, followed by recolonization by H. wrightii. By 2000, coverage of H. wrightii was greater than it had been before the die-off.

Extensive concurrent water quality and light attenuation monitoring did not detect any changes in these parameters that would have caused the die-off. The authors hypothesize that the seagrass changes were due to a natural cycle of decline and recovery operating in this restricted-circulation bay, in which accumulation of dead seagrass leaves and mats of drift algae create a poor substrate for growth of seagrass, and a mass die-off would ensue. Once the organic matter is flushed from the site, perhaps by a storm, recolonization could begin on a largely mineral sediment, as observed here.

Of course, appropriate monitoring is required in order to detect such trends. If only infrequent large-scale mapping is used, it would be impossible to discern the causes for this type of cycle. The approach of the St. Johns River Water Management District, using both aerial and field transect protocols, can help discriminate short and long term patterns.

Source: Morris, L. J. and R. W. Virnstein. 2004. The demise and recovery of seagrass in the northern Indian River Lagoon, Florida. Estuaries 27(6): 915-922. (View Abstract)

Better, Faster, Cheaper Benthic Sampling

Coastal resource managers want the information they need about ecological resources without going overboard and wasting time, effort, and money. On the other hand, they can not afford to skimp and make poor decisions based on inaccurate or insufficient information. A recent Estuaries paper can help managers confronted with the problem of how best to balance data needs and costs to accurately estimate habitat values with respect to benthic macrofaunal communities in Pacific Northwest (USA) estuaries.

The study, conducted in Willapa Bay, Washington, investigated four endpoints (number of species, numerical abundance, total biomass, and fish and crab prey abundance) in four habitat types created by the system's major "ecosystem engineers" - eelgrass, Atlantic cordgrass, mud shrimp, and ghost shrimp. Endpoint values associated with each habitat provide useful information for prioritizing habitats for protection and assessing effects of habitat alterations. The sampling variables were number of replicate samples per habitat, sample unit area, sample unit depth, sieve mesh size, and cost. Cost/benefit analysis showed that the optimal (effective and least costly) benthic macrofaunal sampling protocol was to collect 15 to 20, 0.01 m2 x 5 cm deep, 0.5-mm mesh samples per habitat.

The authors urge managers not to rely on old, untested methods; rather, conduct a pilot study when necessary (i.e., when data for designing a cost effective study are absent or insufficient) to determine the optimal sampling protocol for the purpose of your study. While pilot studies and cost/benefit analyses incur some additional upfront costs, the authors suggest that in the end these costs are much better than continuing to rely on potentially inefficient or ineffective ways to collect and process environmental samples.

Source: Ferraro, S. P. and F. A. Cole. 2004. Optimal benthic macrofaunal sampling protocol for detecting differences among four habitats in Willapa Bay, Washington, USA. Estuaries 27(6): 1014-1025. (View Abstract)