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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 November

Contents

Keeping the Pressure on in Chesapeake Bay
Red Drum and Spotted Seatrout (Come and) Go with the Flow
The Future Is Now in New England
Deep Trouble for Pools?

Keeping the Pressure on in Chesapeake Bay

If Bay restoration goals are to be met in the age of climate change, more non-point source nutrient reductions will be needed

Much of our current understanding of nutrient cycling and eutrophication in estuaries was learned in the living laboratory of the Chesapeake Bay, the “poster child” for anthropogenic nutrient overenrichment in coastal systems. Management measures in the Bay have been in place since the 1980s to reach nutrient reduction goals and restore the health and function of the system. Despite decades of management and research, all is not yet well in the Chesapeake. While nutrient loadings have been reduced, reduction goals have not all been met, and significant eutrophic conditions still occur. A recent long-term modeling study of the Bay revealed that climatic conditions, reflected in the model as freshwater discharge from the Susquehanna River, have significant effects on nutrient loadings and phytoplankton concentrations.

The model used long-term data collected by the Chesapeake Bay Program adjusted for climate effects on hydrology. With the inclusion of the hydrologic data, the model replicated known historical patterns of nutrient loading and eutrophication: the period of 1945-1980 was characterized by high nutrient loading and eutrophication, followed by a period of modest N reductions (1981-2012), with weaker-than-expected reduction of eutrophication. The model also revealed that much of the Bay is producing more chlorophyll a per unit of total N than in previous years. This means that more aggressive action will be needed to counter anthropogenic eutrophication and to meet nutrient reduction goals. Non-point nutrient reduction is going to be even more critical given predictions of climate change-driven rainfall increases and incidence of tropical cyclones in the Bay area from 2030 to the end of the century.

Source: Harding Jr., L.W., C. L. Gallegos, E. S. Perry, W. D. Miller, J. E. Adolf, M. E. Mallonee, and H. W. Paerl. 2015. Long-term trends of nutrients and phytoplankton in Chesapeake Bay. Estuaries and Coasts (August 2015). DOI:  10.1007/s12237-015-0023-7.

Red Drum and Spotted Seatrout (Come and) Go with the Flow

Distribution, abundance, and resilience of two key species in Tampa Bay related to freshwater inflow

Fluctuations in freshwater inputs to estuaries can be important drivers of many aspects of their ecological function, from habitat quality to food availability. In Tampa Bay and the rivers that feed it, recent research revealed that for two economically and culturally important fish species, spotted seatrout and red drum, population abundance, distribution, and resilience to disturbance are significantly related to freshwater inputs. Given that freshwater inputs are projected to be heavily influenced by climate change (and in fact already have been), this finding could have important implications for dynamics of these two species, and for managing their populations.

In this study the investigators collected data on distribution and abundance of juveniles of both fish species over 13 years in the shallow waters of Tampa Bay, and examined the relationship between these data and freshwater inputs over the same time span. Responses differed by species and size class. For seatrout, freshwater inflow was positively correlated with both distribution and abundance of smaller juveniles (15-50 mm standard length (SL)), but it was unrelated to either parameter for larger (51-100 mm SL) juveniles. For red drum, freshwater inflow was positively correlated with both distribution and abundance of the larger juveniles. Inflow was related to abundance but not distribution of the smaller juveniles, suggesting that inflow may increase habitat quality but perhaps not quantity for this earlier life stage. In a companion study, the authors also examined the resilience (measured in recovery of distribution and abundance) of both species to major perturbations that occurred during the study period, including an acid spill in one of the rivers, drought, and a red tide event. The species recovered more quickly from the acid spill, which occurred during a high flow period when the fish were more abundant and more widely distributed, than from the red tide, which was followed by a substantial drought that limited abundance and distribution.

The authors conclude that it is useful to compare abundance and distribution relationships of multiple fish species in order to identify more vulnerable species – red drum, in this case – whose distributions are more limited during some environmental conditions; this information could be useful in identifying priority nursery habitat conservation targets and regulating freshwater flow. In addition, managers might consider limiting human disturbances such as shoreline modification or dredging to certain flow conditions.

Sources: Whaley, S. D., M. C. Christman, and J. J. Burd, Jr. 2015. Spatial distribution-abundance relationships in juvenile (age-0) red drum (Sciaenops ocellatus) and spotted seatrout (Cynoscion nebulosus). I: Influence of freshwater inflow. Estuaries and Coasts (August 2015). DOI:  http://dx.doi.org/10.1007/s12237-015-0027-3.

Whaley, S. D., M. C. Christman, and J. J. Burd, Jr. 2015. Spatial distribution-abundance relationships in juvenile (age-0) red drum (Sciaenops ocellatus) and spotted seatrout (Cynoscion nebulosus). II: Influence of major disturbances. Estuaries and Coasts (October 2015). DOI: 10.1007/s12237-015-0035-3.

The Future Is Now in New England

Marshes gaining Spartina alterniflora at the expense of S. patens

Global climate change is a present day reality, not simply a concern to address in the future. One place where the current effects of climate change can be readily seen is in coastal New England, where sea level has been rising over the past 80 years, with rates accelerating in the past one to two decades. Sea level rise (SLR) is a particularly significant stressor for coastal marshes, which can drown unless sufficient sediment supply allows accretion or the marshes can migrate landward. Through the 1980s and 90s, vertical accretion allowed New England marshes to remain above water, but recent acceleration in rates of SLR and reduced sediment supplies seem to be leading to loss of marsh area throughout the region. A recent study of the vegetation communities of marshes in several Rhode Island salt marshes over time determined that high marsh habitat dominated by salt marsh hay (Spartina patens) is declining in response to sea level rise and flooding events.

The authors documented changes over time in a pair of intensively-studied marshes in Narragansett Bay, RI and assessed current conditions in 38 marsh units that span coastal areas in Rhode Island and Massachusetts. Intensive long-term monitoring documented a decline in S. patens in both marshes, a loss that accelerated during periods of extreme high water levels such as those observed in 2009-2010. S. patens is frequently replaced by encroaching S. alterniflora via two mechanisms: S. alterniflora invades S. patens habitats as sea level rises, and vegetative dieback areas caused by extreme flooding are re-colonized more quickly by S. alterniflora than S. patens. The condition assessments documented lower S. patens cover in low elevation marshes that are more susceptible to SLR. The authors suggest possible management measures to combat the loss of S. patens marshes, including enhancing drainage of waterlogged areas, adding sediment to marsh surfaces, and, interestingly, rethinking Phragmites control since that invasive plant does tend to enhance marsh accretion rates.

Source: Raposa, K. B., R. L. J. Weber, M. C. Ekberg, and W. Ferguson. 2015. Vegetation dynamics in Rhode Island salt marshes during a period of accelerating sea level rise and extreme sea level events. Estuaries and Coasts (August 2015). DOI:  10.1007/s12237-015-0018-4.

Deep Trouble for Pools?

Sea level rise could change distribution of Hawaiian anchialine pools and help spread invasive species

An increasing body of research has examined how coastal marshes will fare with sea level rise (including Raposa et al., above), given the potential for high water to waterlog and flood these critical habitats. But how will other coastal habitats fare as the sea rises? One unique habitat type that could be affected is anchialine pools, small land-locked water bodies with subterranean connections to the ocean like those found on the porous lava substrate of Hawaii. These pools are fed by groundwater as well as seawater, resulting in a brackish environment, and are often home to endemic species such as shrimp. In Hawaii, introduced fish species are also found in some pools, notably poeciliid fish and tilapia species.

A recent survey on the island of Hawaii in six sets of anchialine pools recorded patterns of endemic shrimp and fish distribution. In addition, sea level rise projections were combined with current pool locations and other information to determine potential effects of sea level rise on the distribution and formation of pool habitats. In the existing pools, endemic shrimp species were significantly less likely to be observed when invasive fish species were present. Based on sea level rise projections and coastal topography, many existing pools are likely to be inundated with seawater, and new pools will emerge in low-lying, undeveloped areas. While the shrimp will likely populate new pools via subterranean connections in the coastal aquifer, the invasive fish will spread to new pools via surface water connections provided by rising sea levels (they may need as little as 3 mm water depth to move from one pool to the next, according to previous research). The author urges managers to use this type of analysis to determine where new pools are likely to form, and then to protect those areas from development. Removal of invasive fish species will also help minimize their spread to newly-formed pools

Source: Marrack, L. 2015. Modeling potential shifts in Hawaiian anchialine pool habitat and introduced fish distribution due to sea level rise. Estuaries and Coasts (August 2015). DOI: 10.1007/s12237-015-0025-5.