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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 February


As Heat Rises, Some Disease Organisms May be Kept at Bay
Mexican Shrimp Farms Can Provide Foraging Habitat for Shorebirds
Nursery Ground Valuation: Time to Consider More Complexity

As Heat Rises, Some Disease Organisms May be Kept at Bay

Higher temps may mean lower incidence of wasting disease for Mediterranean seagrasses

One anticipated result of climate change, attributable to warming temperatures, is a change in rates of spread of infectious diseases affecting a wide range of organisms (including humans). But because temperature affects both pathogens and hosts in a range of ways, these changes will not always lead to monotonic increases in disease. Rising temperatures could exceed a pathogen’s maximum for growth, thereby decreasing disease, or increase pathogen growth while simultaneously increasing stress on the host organism, leading to a non-linear increase in disease. Teasing apart these effects will be critical for predicting, managing, and mitigating infection.

One study of a Mediterranean seagrass species and a seagrass wasting disease pathogen found that climate warming may actually alleviate pathogen pressure. The investigators infected shoots of the seagrass Posidonia oceanica with the pathogen Labyrinthula spp., the agent that causes a serious seagrass wasting disease. They incubated infected and uninfected shoots at a range of temperatures that included the maximum summer temperatures projected for the Mediterranean for the rest of the century. Results indicated that warming reduced the occurrence and severity of the disease, as temperatures greater than 28oC inhibited cell division and growth of the pathogen.

While this seagrass species may be vulnerable to other aspects of climate change, these results suggest that warming will reduce pathogen pressure and therefore reduce the risk of wasting disease, a reminder that the ultimate effects of global climate change are not always easy to predict.

Source: Olsen, Y. S., M. Potouroglou, N. Garcias-Bonet and C. M. Duarte. 2014. Warming reduces pathogen pressure on a climate-vulnerable seagrass species. Estuaries and Coasts (June 2014). DOI: 10.1007/s12237-014-9847-9.

Mexican Shrimp Farms Can Provide Foraging Habitat for Shorebirds

(No, the birds don’t eat scampi!)

Shrimp is currently the most-consumed seafood type in the U.S., and global demand for the shellfish appears to be insatiable. To satisfy that market, tropical nations have been farming shrimp for decades, destroying mangroves and other coastal wetland habitats to develop shrimp aquaculture facilities. While peel-and-eat fans might be happy, the losers in this development are the organisms that depend on those coastal habitats, including migratory shorebirds. But there is a ray of hope: the regular harvest cycle at many shrimp farms might allow for the farms to provide foraging habitat for birds when the water levels are drawn down in October/November, just when the birds start to arrive after long migratory flights from their breeding grounds, before the farms are reflooded and reseeded with the next year’s stock. A recent study in the Estero de Urías in the Mexican state of Sinaloa monitored shorebird use of one farm and the surrounding estuary during and after the shrimp harvest season.

Investigators found that all species of shorebirds they monitored were observed in the shrimp farm ponds during the harvest season when water levels were drawn down to expose a wet substrate, and most were actively feeding. Four species -- avocets, black-necked stilts, willets, and whimbrels -- were found to forage preferentially at the farms compared to nearby natural tidal flats. Once harvest was finished and the ponds dried up entirely, virtually no birds remained at the shrimp farm and there was also a great reduction in shorebird abundance associated to the Estero de Urías.

The authors conclude that the shrimp farm could provide an important foraging area for these shorebirds, helping to maintain overall populations in the estuary. Proper management of the farms throughout Sinaloa could therefore counteract some of the habitat loss the farms have precipitated.

Source: Navedo, J. G., G. Fernández, J. Fonseca, and M. C. Drever. 2014. A potential role of shrimp farms for the conservation of Nearctic shorebird populations. Estuaries and Coasts (July 2014). DOI: 10.1007/s12237-014-9851-0.

Nursery Ground Valuation: Time to Consider More Complexity

Export of juveniles is necessary but not sufficient for valuation

Coastal nursery grounds are recognized as vital for their contributions to adult fish stocks. Assigning value to these habitats usually involves determining the biomass of juveniles that move from the coastal nursery to offshore areas via ontogenetic migrations, where they join adult populations. While this approach represents a step in the right direction, a recent paper argues that it must be broadened to incorporate more complexity if the true value of coastal nurseries is to be determined.

The authors provide a new framework for assessing the complexity of nurseries. They propose ten components of nursery habitat value that should be considered, grouped into three areas: 1) connectivity and population dynamics (including connectivity, ontogenetic migration, and seascape migration), 2) ecological and ecophysiological factors (ecotone effects, food/predation tradeoffs, food webs, physiological effects) and 3) resource dynamics (resource availability, ontogenetic diet shifts, allocthonous inputs). Ideally, all of these factors should be considered when valuing nursery areas. While this type of calculation may seem daunting, the authors point out that already well-developed techniques can be combined, refocused, and extended to collect the kinds of data needed. For example, connectivity studies using natural and artificial biomarkers can be used not only to determine biomass contributions from particular nurseries to adult stocks, but when combined with other techniques (such as habitat or dietary studies) they can also shed light on ontogenetic migration, connectivity, and ecotone effects.

The paper provides a range of possible approaches for collecting data relevant to the components of nursery value, and stresses the need for further data collection to support understanding  of these processes. At the same time, the authors urge managers to go beyond coastal nursery valuation based simply on export of biomass based on information we have now.

Source: Sheaves, M., R. Baker, I. Nagelkerken, and R. M. Connolly. 2014. True value of estuarine and coastal nurseries for fish: incorporating complexity and dynamics. Estuaries and Coasts (June 2014). DOI: 10.1007/s12237-014-9846-x