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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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2014 July

Contents

Some Gulf Shrimp May be Shrimpier after Exposure to Deepwater Horizon Oil
Small Boats can Carry Invaders North to Alaska
Low Oxygen, Low Productivity: Hypoxia Related to Decreased Macrobenthic Production in Chesapeake Bay
A Better Way to See Seagrass?


Some Gulf Shrimp May be Shrimpier after Exposure to Deepwater Horizon Oil

The images of oil gushing out of a damaged Deepwater Horizon wellhead on the floor of the Gulf of Mexico in the spring of 2010 raised alarm about potential consequent effects on the marine ecosystem. It will likely be years, if not decades, before the full implications of the spill are understood. Early work suggests a range of impacts of the oil on Gulf organisms and habitats, including inshore wetlands, where oil was carried by winds and currents. One recent study examined the effect of lingering oil residues in coastal marshes on the growth of juvenile brown shrimp and white shrimp, two commercially and ecologically critical species.

One year after the spill, investigators placed shrimp into mesocosms at Barataria Bay sites that had received varying degrees of oiling according to NOAA surveys; some mesocosms were supplied with supplemental food and some were not. In addition to shrimp growth, sediment contamination and biomass of benthic infauna (potential food items for the shrimp) were also measured. Brown shrimp grew more slowly at sites that were heavily oiled than at sites that had very light or no oiling, exhibiting a reduction in daily biomass production of about 60%. Brown shrimp growth rates also declined with increasing concentrations of sediment PAHs measured during the time frame of the study (a year after the spill). No relationship between oiling levels or sediment PAH levels and white shrimp growth was detected. Both species grew more rapidly in mesocosms where food had been added, indicating the sites are food-limited.

The authors explain that the white shrimp may have been exposed to lower levels of contaminants than the brown shrimp, both because they don’t burrow into the sediments as much as the brown shrimp and because overall oil levels were higher in the mesocosms in May (when the brown shrimp experiments were conducted) than in August (when the white shrimp were tested). Nevertheless, the authors contend that field experiments such as these are critical for determining real-world responses of ecosystems to large pollution events.

Source: Rozas, L. P., T. J. Minello, and M. S. Miles. 2014. Effect of Deepwater Horizon oil on growth rates of juvenile Penaeid shrimp. Estuaries and Coasts 37 (January 2014). DOI: 10.1007/s12237-013-9766-1.


Small Boats can Carry Invaders North to Alaska

Invasions by non-native species have occurred in marine ecosystems world-wide, often when biofouling organisms hitch a ride from their native waters on the hull of a boat. On the West Coast of North America, marine invasions appear to follow a latitudinal gradient, with high rates of invasion in Southern California (more than 250 invasions) tapering to very low levels of invasion in Alaska, where only ten invasives are currently known. However, studies of recorded invasions have suggested a general trend of northward spread of nonindigenous species. In addition, predicted ocean warming and increased boat traffic may mean that Alaska will not remain uninvaded for long.

A recent study examined the potential for small recreational and fishing vessels to serve as vectors for introducing nonindigenous species to Alaskan waters. Investigators characterized small vessel traffic patterns for the port of Ketchikan, a southern gateway to Alaskan waters, and examined the submerged portions of small transient vessels entering the port using SCUBA and underwater photography to characterize their biofouling communities. They documented a striking seasonality and directionality of vessel traffic: most vessels arrive in Ketchikan between April and September (peak spawning season for many invasives), and 95% of them arrive from the south. While most of the vessels sampled harbored few hitchhikers, some carried large numbers of fouling organisms (one third of the vessels sampled carried more than 100 organisms). Several living, nonindigenous invasive species were recorded, including two that are not known to be established in Alaskan waters.

The authors suggest that invasions could occur in Alaska in a hub-and-spoke pattern, with Ketchikan serving as the hub. Because invasion rates are still fairly low in Alaska, the good news is that the port could serve as an ideal site for educating boat owners about nonindigenous invasive species, and an important site for monitoring and management.

Source: Ashton, G., I. Davidson, and G. Ruiz. 2014. Transient small boats as long-distance coastal vector for dispersal of biofouling organisms. Estuaries and Coasts 37 (March 2014). DOI: 10.1007/s12237-014-9782-9


Low Oxygen, Low Productivity: Hypoxia Related to Decreased Macrobenthic Production in Chesapeake Bay

Seasonal hypoxia in the Chesapeake Bay system has grown in magnitude and extent over the decades it has been studied, with serious consequences at all trophic levels. Many benthic organisms can’t outrun hypoxic waters, so they may be particularly sensitive to low-oxygen conditions. Because macrobenthos (macroscopic bottom-dwellers) are a critical link in the food web, their susceptibility to hypoxia could lead to significant ecosystem-wide effects. How does low DO affect macrobenthic productivity? A recent study attempted to answer this question using benthic and environmental samples collected in 1996-2004 in the mainstem Chesapeake and its major tributaries (the York, Potomac, and Rappahannock Rivers). The investigators used production theory and a previously-developed empirical model to quantify macrobenthic production, and they related that production to DO levels.

Fluctuations in macrobenthic production were significantly correlated with dissolved oxygen: production was 90% lower overall under hypoxic conditions compared to normoxic conditions. For some taxa, production losses of 95% or greater occurred. Based on the area of mild to severe hypoxia recorded at the times of sampling, the authors estimate that the Bay experienced an average biomass loss of about 7,320-13,200 metric tons of C, which represents an annual loss of 20% to 35% of the Bay’s summer macrobenthic production. This massive loss of macrobenthic production is detrimental to the overall health of the Bay, coming at a time of year when predators have high energy demands. This loss of productivity could translate into economic losses if upper trophic levels – ones that humans harvest for their own consumption – are affected.

Source: Sturdivant, S. K., R. J. Diaz, R. LlansĪŒ, and D. M. Dauer. 2014. Relationship between hypoxia and macrobenthic production in Chesapeake Bay. Estuaries and Coasts 37 (January 2014). DOI: 10.1007/s12237-013-9763-4


A Better Way to See Seagrass?

Accurate, fine-scale, quantitative measurements of seagrass beds are critical for good management of these important habitats. A number of methods have been used to track seagrass bed densities and areas at the landscape scale, including aerial photography and satellite-based remote sensing. Each of these methods comes with challenges and limitations, from resolution to cost. Researchers working in St. Joseph’s Bay, FL, demonstrated the ability of a high-resolution airborne hyperspectral sensor to produce estimates of abundance of both submerged and floating seagrass beds in an optically challenging environment, confirming the applicability of this tool to mapping seagrasses.

The research team used an airborne hyperspectral sensor, the Spectroscopic Aerial Mapping System with On-board Navigation, with a 1 m resolution to conduct seagrass surveys in the bay. Optical complexities at the site include turbid water and the presence of both macroalgae and seagrass. Processed images were compared to in situ measurements of seagrass abundance.

The sensor was able to provide highly accurate estimates of abundance of submerged and floating seagrasses, red algae, bare sand habitats, and optically deep water. This information enabled precise calculations of landscape-scale statistics including seagrass and algal density, biomass, and primary production. A comparison to previous estimates indicated that no dramatic change in vegetative cover has occurred during the past 30 years. The authors suggest that this method will be valuable to managers who want to detect change and evaluate ecosystem health.

Source: Hill, V. J., R. C. Zimmerman, W. P. Bissett, H. Dierssen, and D. D. R. Kohler. 2014. Evaluating light availability, seagrass biomass, and productivity using hyperspectral airborne remote sensing in Saint Joseph’s Bay, Florida. Estuaries and Coasts 37 (January 2014). DOI: 10.1007/s12237-013-9764-3