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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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2017 January

Contents

Ocean Acidification at the "Fattening Line"
For Northern Spartina, Global Climate Change May Mimic a Move South
Better than Ever
Learning While Doing

Ocean Acidification at the “Fattening Line”

A confluence of factors affects oyster larvae growth in Willapa Bay, WA

Willapa Bay, WA is home to a major oyster aquaculture industry as well as naturalized populations of Pacific oysters, but there has not been a commercially viable natural set of oysters in the bay since 2005. This failure coincided with significant oyster larvae production failures at most of the oyster hatcheries in the Pacific Northwest which were attributed to ocean acidification, thus introducing a relatively new climate change-related threat into the public consciousness. However, the role of ocean acidification in the settlement failure in Willapa Bay is far from straightforward.

A recent study measured carbonate chemistry, with an emphasis on aragonite (a carbonate mineral essential to shell formation) saturation state, at the “Fattening Line,” a location in the bay that has been observed to be optimal for larval oyster retention and growth. The investigators found that optimal aragonite saturation and temperatures for spawning and early larval oyster growth now overlap for only a few weeks each year, in contrast to the several months of overlap that seemed to have occurred in the pre-industrial era.

The authors note that the variable conditions in the bay may have always led to erratic settlement there, but climate change has exacerbated the variability. Rising CO₂ levels have lowered aragonite saturation overall, but with a disproportionate effect in the early part of the season when bay waters are fresher and cooler and CO₂ solubility is greater. This early season impact plays a large role in driving the modern-day mismatch between thermal and carbonate-chemistry optima.  Taken together, all of this variability could result in a decline in successful oyster sets in Willapa Bay and elsewhere.

Source: Hales, B., A. Suhrbier, G. G. Waldbusser, R. A. Feely, and J. A. Newton. 2016. The carbonate chemistry of the “Fattening Line,” Willapa Bay, 2011-2014. Estuaries and Coasts (August 2016). DOI: 10.1007/s12237-016-0136-7.

For Northern Spartina, Global Climate Change May Mimic a Move South

Northern plants may behave more like southern plants as temperatures rise – if they survive at all

Spartina alterniflora, the major salt marsh plant on the U.S. Atlantic coast, generally maintains salt marsh elevation relative to sea level by accumulating aboveground biomass, promoting sediment deposition at the marsh’s surface, and building belowground biomass. But studies have shown that northern marshes tend to accumulate more belowground biomass than southern ones, which may be help them to avoid freezing during colder winters and generate new growth in the spring. So how will northern marsh plants respond to the warmer temperatures expected with climate change, and what does that mean for their ability to keep up with sea level?

One recent study examined these latitudinal differences in Spartina growth at eight marshes from Massachusetts to South Carolina. In their home marshes, northern plants produced more belowground biomass than southern plants, and southern plants grew more aboveground biomass. Reciprocal transplant studies revealed that northern plants decreased allocation to belowground biomass when moved south, whereas southern plants displayed an increase in belowground biomass when moved north. Mortality of northern transplants was also higher than that of southern transplants. These results suggest that northern plants may have difficulty tolerating warmer temperatures, and may begin to exhibit more southern traits as temperatures warm. This shift could occur via either phenotypic plasticity or by the replacement of northern plants by southern-adapted genotypes. This could result in less belowground biomass accumulation, which would impair their ability to keep up with sea level rise.

Source: Crosby, S. C., A. Angermeyer, J. M. Adler, M. D. Bertness, L. A. Deegan, N. Sibinga, and H. M. Leslie. 2016. Spartina alterniflora biomass allocation and temperature: implications for salt marsh persistence with sea-level rise. Estuaries and Coasts (August 2016). DOI: 10.1007/s12237-016-0142-9.

Better than Ever

Invertebrate communities in restored Delmarva eelgrass beds exhibit higher diversity than nearby natural beds ten years after restoration

While it is relatively straightforward to determine whether restoration projects have successfully reestablished habitat structure – are there more plants? A greater area of oyster beds? More reef structure? – it is more difficult to determine whether ecosystem function has returned to a restoration site. What better place to explore trajectories of functional recovery than at the largest eelgrass restoration site in the nation? An 1800 ha seagrass restoration effort was undertaken in the 1990s in the bays of the Delmarva Peninsula on the eastern U.S. coast. A team of researchers examined the epifaunal invertebrate community in restored eelgrass beds in South Bay and a reference site in Chincoteague Bay 100 km away, where seagrass meadows weathered the pandemic decline of the 1930s without anthropogenic restoration. The researchers looked at the two sites during an early restoration period (2001-2003) and a later period (2010-2013).

Although the investigators expected that the invertebrate community at the restoration site would gradually grow to resemble that of the control site, they found that no differences in most community metrics after only one year. Furthermore, functional diversity was actually higher in the restored meadow than the control meadow. Ten years later, most community metrics and measures of functional diversity were significantly higher in the restored meadow. Statistical analyses suggested that this result is attributable to the larger area and density of eelgrass at the restored site.

The immense success of this restoration project appears to be attributable to good water quality and the rapid life histories of many of the colonizing invertebrates. Given that the extent of natural meadows in the region have tended to decline over time, the continuation of restoration efforts will be important.

Source: Lefcheck, J. S., S. R. Marion, and R. J. Orth. 2016. Restored eelgrass (Zostera marina L.) as a refuge for epifaunal biodiversity in mid-western Atlantic coastal bays. Estuaries and Coasts (August 2016). DOI:10.1007/s12237-016-0141-x.

Learning While Doing

Advances in coastal adaptive management and adaptive restoration are explored in the annual H.T. Odum Synthesis Essay

In some ways, adaptive management is nothing new: for generations, indigenous peoples have used information accumulated via experience to adjust their practices in the face of ecological uncertainty. Only relatively recently has this approach taken hold in mainstream ecological management. The 2016 H. T. Odum Synthesis Essay in Estuaries and Coasts, written by Dr. Joy Zedler, recently-retired Professor of Botany and Aldo Leopold Chair in Restoration Ecology at the University of Wisconsin, discusses recent advances in adaptive management and a related approach, adaptive restoration.

Adaptive management uses rigorously-collected scientific evidence to examine outcomes of management action and adjust management approaches accordingly. This approach is especially valuable for managing estuaries and coasts, which face “uncertainties on two fronts,” the land and the water. Zedler provides global examples of adaptive management projects that have incorporated the necessary approaches of engaging stakeholders, addressing uncertainty, improving governance, emphasizing science, and prioritizing actions. Adaptive management projects highlighted as exemplary case studies include those implemented in Tasmania’s Derwent Estuary and the Black Sea’s Danube Delta and river basin, and current challenges in the Sacramento-San Joaquin Delta.

Adaptive restoration uses adaptive management approaches in restoration projects; the ideal adaptive restoration projects test alternative approaches, comparing multiple actions in phased tests, with the goal of improving restoration. Case studies highlighted include restorations in salt marshes in the Netherlands and southern California, ponds in Spain’s Guadalquivir Estuary, and a coastal prairie in Oregon. Zedler concludes by advocating for the establishment of a National Restoration Act to fund adaptive restoration in the U.S.

Source: Zedler, J. 2017. What’s new in adaptive management and restoration of coasts and estuaries? Estuaries and Coasts (January 2017). DOI: 10.1007/s12237-016-0162-5.