CESN Main Page

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.

February 2011


Even Small Oil Spills Can Have Lingering Effects on Biota, Study Says
Searching for Patterns in Estuarine Recovery: Restoration Can Take Decades
Trouble in Paradise: Tracking Pollutant Sources in Hanalei Bay, Hawaii
Red Tide Pummels Tampa Bay Nekton Community, But Only Temporarily

Even Small Oil Spills Can Have Lingering Effects on Biota, Study Says

An oil spill in the ocean doesn’t have to be the size of the Exxon Valdez or the Deepwater Horizon to have serious consequences for marine life. A study of the aftermath of a relatively small spill (270 tons) of heavy fuel oil off of an exposed sandy coastline in eastern Australia demonstrated that ecological recovery of sandy beaches can take time, even if the cleanup of surface oil is rapid.

The team compared benthic assemblages at several oiled beach sites and control sites one week and three months after the spill and its associated cleanup. They found that benthic invertebrate assemblages in the lower shore had significantly fewer individuals of fewer species one week after the spill, and these differences persisted for three months post-spill. There was no detectable biological change in the assemblages in the mid- and upper shore zones. The authors suggest that the greatest impact was observed in the lower shore because the oil observed in the upper shore zones, deposited by large waves and tides at the time of the incident, was dried and tar-like in appearance, and likely weathered and therefore less toxic. By contrast, on the lower shore the lower molecular-weight (and thus more toxic) components of the spill were suspended in the water column and then reworked into the sediment in and near the swash zone.

A common approach to managing coastal spills is to purposely direct the oil to sandy areas and away from vegetated habitats, as beaches are considered more resilient to the effects of spills and it seems easier to clean oil off beaches than off plants. However, the Australian team shows that oil can have a continuing detrimental effect on benthic communities in these sandy environments. Because the worst component of the spill is invisible to the eye, is worked into the sediments, and persists long after cleanup efforts are complete, alternate approaches may need to be considered. At the very least, the authors argue, longer-term monitoring of oiled sites is needed to determine the true effects of an oil spill.

Source: Schlacher, T. A., A. Holzheimer, T. Stevens, and D. Rissik. 2010. Impacts of the ‘Pacific Adventurer’ oil spill on the macrobenthos of subtropical sandy beaches. Estuaries and Coasts 33(December 2010). DOI: 10.1007/212237-010-9354-6.

Searching for Patterns in Estuarine Recovery: Restoration Can Take Decades

Long attention spans are often needed to see estuarine restoration projects through to ecological recovery, but the precise horizon for complete restoration depends on a number of factors. Those were some of the conclusions reached at a special session at the 2009 American Society of Limnology and Oceanography meeting, which explored medium and long-term recovery of marine and estuarine systems. A recent paper uses some of the session’s findings in a meta-analysis of restoration studies.

The authors reviewed 51 studies in which restoration or management projects were undertaken to address anthropogenic changes and medium to long term monitoring took place. They found that the time to recovery after removal of anthropogenic stressor depended on the type and duration of disturbance. Generally, severe and persistent impacts required 10-25 years for complete recovery, whereas restoration after shorter-term physical disturbances that did not leave any “legacy” stressors, such as sediment contamination, occurred over 1.5 to 10 years. Recovery time also varied depending on which parameters were evaluated in the affected system. For example, meiofauna took less time to recover than fish assemblages with variable recruitment, which often took 2-10 years to recover. The authors explored one case study in detail, the Nervión River Estuary in northern Spain, a system where industrial and urban effluents caused severe degradation. Sewage treatment and other management initiatives were put in place in the late 1980s and the system was monitored. The authors provide a timeline for this estuary’s recovery, which was nearly complete 10 years after management steps were completed.

The authors suggest that ecosystem restoration goals and criteria for defining recovery need to be agreed upon at the outset of any restoration project or program. Even then, the authors found examples of systems that have never been restored to their historic state, so managers need to be prepared for their system of interest to arrive at a new equilibrium.

Source: Borja, Á., D. M. Dauer, M. Elliott and C. A. Simenstad. 2010. Medium- and long-term recovery of estuarine and coastal ecosystems: patterns, rates and restoration effectiveness. Estuaries and Coasts 33(December 2010). DOI: 10.1007/s12237-010-9347-5.

Trouble in Paradise: Tracking Pollutant Sources in Hanalei Bay, Hawaii

Even in the clear turquoise waters of Hawaii, coastal water quality is a serious issue. Residents and tourists alike are concerned about water quality in Hanalei Bay, Kauai. The beaches there are located adjacent to the Hanalei River, which has some of the worst water quality in the state: water samples taken there regularly exceed bacterial water quality criteria and nutrient pollution is also a concern. The first step in addressing these problems is tracking down the pollutants’ sources in order to prioritize remediation activities.

Researchers recently examined nutrient and fecal indicator bacteria concentrations in four major watersheds draining into the bay during two dry-weather sampling periods in order to determine the sources of these pollutants to Hanalei Bay. Two microbial source tracking tools were also used: host-specific Bacteroidales and human enterovirus. Nutrient and fecal indicator bacteria loadings were highest from the watersheds with the largest urban and cultivated land cover. The largest tributary, the Hanalei River, represented 50% of the bacterial load and the other three streams combined represented the other 50%. The microbial source tracking results indicate that pigs, ruminants, and humans are all sources of bacteria to the bay.

This study provides important evidence that human development can affect pollutant loadings to tropical coastal waters, a relationship already well-established in temperate systems. While further work needs to be done in this system, particularly examining loadings during wet weather, these preliminary findings suggest that remediation and management activities might focus first on the Hanalei River. The state is currently working on a TMDL for the river.

Source: Boehm, A. B., K. M. Yamahara, S. P. Walters, B. A. Layton, D. P. Keymer, R. S. Thompson, K. L. Knee, and M. Rosener. 2010. Dissolved inorganic nitrogen, soluble reactive phosphorous, and microbial pollutant loading from tropical rural watersheds in Hawai’i to the coastal ocean during non-storm conditions. Estuaries and Coasts 33(December 2010). DOI: 10.1007/212237-010-9352-8.

Red Tide Pummels Tampa Bay Nekton Community, But Only Temporarily

The eastern Gulf of Mexico experiences regular red tide blooms of the dinoflagellate Karenia brevis, which routinely cause extensive fish kills and occasional low-oxygen events along Florida’s southwestern shore. While the accumulation of dead fish along the beaches near Tampa Bay is an obvious indication that these blooms can inflict ecological damages as they are occurring, do they have long-term impacts on ecosystem structure and function?

An unusual bloom of K. brevis in 2005, in which a high abundance of the dinoflagellate persisted in the Tampa Bay area for a year, gave researchers an opportunity to examine long-term effects of blooms on the nekton community. Using data collected by a pre-existing fishery-independent survey, the investigators analyzed Tampa Bay nekton community structure during and after the 2005 bloom, and compared these results to historical data (1996 – 2006). Their analyses included a particular focus on five recreationally important sport fish species: spotted sea trout, sand sea trout, red drum, sheepshead, and snook. The consistent seasonal pattern exhibited by the nekton community prior to 2005 was disrupted in 2005 and early 2006. The diversity of small-bodied nekton was also depressed during this time period. However, by the fall of 2006, the nekton community had returned to normal, suggesting that these communities are resilient to red tide events. Declines in recruitment of the two sea trout species and red drum were observed during 2005 and 2006, but sub-adult and adult stages exhibited no significant changes in abundance during or after the bloom.

Because these results revealed that response to the bloom was species- and life stage-specific, they could have important sport fish management implications. The authors acknowledge that it is difficult to draw strong conclusions from their study because of the coarse spatial and temporal scales of sampling, and also because concentration of actual toxin in the water was not measured. It would be useful if future monitoring addressed some of these issues.

Source: Flaherty, K. E. and J. H. Landsberg. 2010. Effects of a persistent red tide (Karenia brevis) bloom on community structure and species-specific relative abundance of nekton in a Gulf of Mexico estuary. Estuaries and Coasts 33(December 2010). DOI: 10.1007/s12237-010-9350-x.