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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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2015 May

Contents

Beachgoers Bring Trophic Changes to Sandy Shores
Dwindling Nutrient Loads Sink Floating Macroalgae Problems
Mussel Strain
Ecological Impacts of Geoduck Aquaculture

Beachgoers Bring Trophic Changes to Sandy Shores

Effect of coastal development and tourism observed at site in Spain

More than just a place to play volleyball or build a sand castle, sandy beaches are dynamic transitional ecosystems with diverse and complex food webs. They also often attract droves of human visitors, accompanied by coastal development, which can affect the ecosystem in many ways. A recent study used trophic modeling to examine how developed and undeveloped sandy beaches might differ with respect to ecological function. Trophic models were developed for two sandy beaches on the Atlantic coast of Spain, one a highly-trafficked popular recreational beach and the other a protected beach with few human visitors. The Ecopath mass-balance models developed for each site tracked biomass flows among 27 (urbanized beach) and 28 (protected beach) compartments, including detritus, phytoplankton, zooplankton, invertebrates, fishes, and birds. Data on each were collected from the field or from the literature.

While the two beaches were found to have similar food web structures and trophic function, they differed in a number of ways. Species composition varied between sites: higher numbers of shore birds and piscivorous birds were found at the protected beach, for example. In addition, total respiration was higher at the unperturbed site, and total system throughput of energy was 25% higher at the protected beach than at the urbanized beach. Taken as a whole, the results indicate the protected beach was “more stable, more organized, and more highly developed [ecologically]” than the urbanized site. The authors state that one implication of this work is that it provides important information about the value of protecting habitats from human encroachment.

Source: Reyes-Martinez, M. J., D. Lercari, M. C. Ruíz-Delgado, J. E. Sánchez-Moyano, A. Jiménez-Rodríguez, A. Pérez-Hurtado, and F. J. García-García. 2014. Human pressure on sandy beaches: implications for trophic functioning. Estuaries and Coasts (November 2014). DOI: 10.1007/s12237-014-9910-6.

Dwindling Nutrient Loads Sink Floating Macroalgae Problem

Long-term monitoring reveals declines in floating algae parallel nutrient declines in Danish coastal areas

With the rise of nutrient enrichment in Scandinavian estuaries between the 1960s and 1990s came an increase in noxious, nuisance accumulations of drifting macroalgae, opportunistic species that thrived in the eutrophic conditions. In contrast, seagrasses, eelgrass in particular, did not fare well, experiencing serious declines throughout the twentieth century. In response to the degraded conditions, nutrient controls were implemented in the late 1980s, reducing nitrogen loadings by 50% and phosphorus loadings by 64% (as measured in 2010). Did these management approaches help address the macroalgae problem, and did the eelgrass rebound? Analysis of data from a long-term monitoring program provided some insight, and the news is generally good.

Researchers examined data on nutrient levels and percent cover of drifting macroalgae and eelgrass beds in more than 350 sites on the Danish coast. They found that the cover of drifting algae declined as nutrient levels decreased for all sites combined. In addition, drifting macroalgal abundance was found to be significantly correlated with total nitrogen concentrations, and with phosphorus concentrations in some areas. Regrowth of seagrass has lagged behind: the ratio of drifting algae cover to eelgrass cover showed no significant trend, because eelgrass coverage did not increase significantly over the time period covered by the data. The authors speculate that different mechanisms regulate growth of macroalgae and eelgrass, and that feedback mechanisms may be causing delays in eelgrass recovery. The good ecological news is that nutrient reduction steps worked in these systems to decrease the extent of drifting macroalgae, and perhaps recovery of eelgrass won’t be far behind.

Source: Rasumssen, J. R., K. M. Dromph, C. Göke, and D. Krause-Jensen. 2014. Reduced cover of drifting macroalgae following nutrient reduction in Danish coastal waters. Estuaries and Coasts (December 2014). DOI: 10.1007/s12237-014-9904-4.

Mussel Strain

Aquacultured mussels in Eastern Canada bay help with nutrient mitigation; production may be altered by climate change

Mussel aquaculture in eastern Canadian waters has exploded since the 1980s: nearly 21,000 metric tons were produced in 2011, representing over 70% of total Canadian mussel landings. During the same decades eutrophication of the embayments used for aquaculture generally increased, and the mussels were seen as a potential bioremediation tool as well as a harvestable commodity. A study of mussel aquaculture’s role in the ecosystem of a small Prince Edward Island bay, almost 40% of which is dedicated to mussel culture, used coupled hydrodynamic and biogeochemical models to examine mussel production and carrying capacity under different scenarios.

Parameterization of the model for current-day conditions, with and without mussels, indicated that the presence of mussels has a significant impact on phytoplankton and detritus levels in the bay, particularly in the mid-bay. The spring phytoplankton bloom is substantially reduced by the presence of mussels, and the fall bloom is nearly eradicated. Comparing 2011 and 1980 nutrient conditions revealed that increased nutrient loads over time provided more phytoplankton to support enhanced mussel production. Harvesting the mussels represents a net removal of nitrogen from the system, supporting the concept of cultured mussels as eutrophication mitigation. To simulate conditions in 2050, investigators took climate change into account by increasing temperatures and nutrient inputs (projected due to increased rainfall) in the model. These changes resulted in a 30% increase in mussel production, but also the potential for increased mussel mortality in the summertime.

These results indicate that cultured bivalves may play an important role in addressing the challenges of nutrient loading, with a bonus for humans of harvest of a delicious menu item. Climate change may increase production, as long as the cultivated species can tolerate warmer waters.

Source: Guyondet, T., L. A. Comeau, C. Bacher, J. Grant, R. Rosland, R. Sonier, and R. Filgueira. 2014. Climate change influences carrying capacity in a coastal embayment dedicated to shellfish aquaculture. Estuaries and Coasts (October 2014). DOI: 10.1007/s12237-014-9899-x.

Ecological Impacts of Geoduck Aquaculture

Farming the delicious bivalves is great for human diets, but does it impact food webs?

Aquaculture is on the rise world-wide, as are concerns about the impacts that industry practices could have on the marine environment. Research has revealed a range of effects of aquaculture, but few studies have examined potential impacts of aquaculture operations on ecological linkages or trophic interactions. A recent study sought to shed light on the question of whether Pacific geoduck clam aquaculture changes food web structure and function by comparing the diets of a common predatory fish, the Pacific staghorn sculpin, at aquaculture sites and nearby reference areas in Puget Sound, WA.

Gut content analysis revealed dietary differences between sculpins captured at aquaculture and reference sites: crabs and shrimp were consumed in higher proportions at aquaculture sites, while amphipods and isopods represented a larger part of the diet at reference plots. These differences likely reflect the fishes’ generalist feeding habits, as mark-recapture studies indicated that the fish exhibited high site fidelity, and previous studies have found differences between benthic communities at aquaculture and non-aquaculture sites. Despite the differences in diet, stable isotope analysis indicated that the trophic position of sculpins and the source of primary production in their food webs were not affected by aquaculture operations. Thus, the overall function and energy flow of the ecosystem remained intact. 

While this study found minimal effects of aquaculture operations on the trophic ecology of sculpin, the authors suggest that cumulative impacts of aquaculture could still place stress on the ecosystem and further studies are needed. In particular, specialist predators might be more affected than generalists if prey species composition is changed by aquaculture

Source: McPeek, K. C., P. S. McDonald, and G. R. Van Blaricom. 2014. Aquaculture disturbance impacts the diet but not ecological linkages of a ubiquitous predatory fish. Estuaries and Coasts (November 2014). DOI: 10.1007/s12237-014-9909-z.