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.
April 2006
Contents
More Fresh Water Brings Long-term Change to New Zealand Estuary
Wild Celery Beds Extend Nursery Habitat for Fishery Species
Where in the World (Or at Least in the Estuary) is Centropomus undecimalis?
Viruses Tested as Alternative Sewage Indicator
More Fresh Water Brings Long-term Change to New Zealand Estuary
What constitutes a long-term data record in your coastal system? Twenty years? One hundred years? How about 900 years? In one New Zealand system, sediment cores have been used to document changes in estuarine communities from the late Holocene through the modern era, a long-term record that dates back to before human colonization of the area. The cores, taken from two sites near Auckland, reveal precipitous declines and disappearances of mollusks and ostracods and significant changes in diatom communities. Clues to the causes of these changes were contained in the same cores: using the composition of foraminiferal assemblages in the cores as a proxy for salinity, it was clear that salinity at both sites has declined over time, likely because of increasing freshwater runoff to the estuary. While each site experienced a period of particularly rapid change, the timing of these changes differed. In the larger catchment, the greatest change in salinity coincided with early European clearance of the forest (1840-1870), while in the smaller basin the greatest changes occurred with the urbanization of the 1960s-70s. Sediment grain size, nutrients, and heavy metal loadings did not seem to be associated with the community shifts.
The changes in the cores parallel those that occur along salinity gradients in modern estuaries, supporting the study’s conclusion that the observed community changes are due to changes in freshwater inflow. One lesson that can be taken from this study is that freshwater flow alone can affect estuarine communities, independently of nutrients, contaminants, or suspended sediments.
Source: Hayward, B. W., H. R. Grenfell, A. T. Sabaa, M. S. Morley, and M. Horrocks. 2006. Effect and timing of increased freshwater runoff into sheltered harbor environments around Auckland City, New Zealand. Estuaries and Coasts 29(2): 165-182. (View Abstract)
Wild Celery Beds Extend Nursery Habitat for Fishery Species
River diversions planned to combat coastal land loss on the Gulf Coast may freshen coastal waters significantly, thereby increasing the area of wild celery (Vallisneria americana) beds, a common low-salinity submerged plant. What impact on estuarine habitat will this change have? According to one study comparing use of Vallisneria beds to marsh and unvegetated bottom habitats by fishery species in Barataria Bay, LA, more Vallisneria might benefit some key species. Blue crabs were found to be 8-10 times more abundant in Vallisneria beds than in non-vegetated habitat (depending on the season), and white shrimp were 30 times more abundant in Vallisneria in the fall. The few brown shrimp and spotted sea trout captured in the study were found exclusively in Vallisneria beds. The abundance and species richness of other organisms were greater in Vallisneria than at unvegetated sites, and similar to measurements observed in marsh sites, which are well-known to provide nursery habitat to many of these species. Location and spatial extent of the SAV beds proved important, as beds nearer to marsh sites harbored more species in greater abundance than beds further from marshes. Because Vallisneria grows subtidally and does not die back in winter, it may extend the spatial and temporal availability of structured habitats such as marshes. This alternative structural habitat may be especially important during times of low water for blue crab and white shrimp, as other data collected as part of this study suggest that these species use Vallisneria beds as nursery habitat.
Source: Rozas, L. P., and T. J. Minello. 2006. Nekton use of Vallisneria americana Michx. (wild celery) beds and adjacent habitats in coastal Louisiana. Estuaries and Coasts 29(2): 297-310. (View Abstract)
Where in the World (Or at Least in the Estuary) is Centropomus undecimalis?
PIT Tags Can Help
An estuary can be a big place when you’re trying to find a small fish. Many fishery scientists and managers would love to be able to track the whereabouts of individual fish of their study species, particularly when they are trying to determine use of specific habitats. Passive Integrated Transponder (PIT) tags have long been used in freshwater environments to track movements of fish, but these studies have usually required fish to be physically recaptured and scanned for tag presence. As a recent study in Charlotte Harbor, FL, shows, PIT tags can not only be used successfully with juvenile fish in estuarine systems, but tagged fish can be detected by an autonomous antenna system without having to physically recapture them. Lab experiments showed that 100% of common snook larger than 120 mm retained PIT tags and none died as a result of tagging. In the field the antenna detection field covered 48% of the creek water column and field experiments determined that 67% of tagged fish were detected. The overall “recapture” rate using the antenna array of greater than 40% was higher than is typical for traditional mark-recapture studies. The successful testing of this technology is good news for those interested in studying estuarine habitat use in fishes or comparing quality of various habitats. PIT tags can easily be applied in these systems.
Source: Adams, A. J., R. K. Wolfe, W. E. Pine III, and B. L. Thornton. 2006. Efficacy of PIT tags and an autonomous antenna system to study the juvenile life stage of an estuarine-dependent fish. Estuaries and Coasts 29(2): 311-317. (View Abstract)
Viruses Tested as Alternative Sewage Indicator
Used as a proxy for fecal or sewage contamination, fecal coliform bacteria have been an indicator of choice for monitoring the health of waterways and beaches for decades.
Despite their ubiquitous use, coliform bacteria are actually far from ideal indicators, especially in tropical waters where they may replicate, giving an inflated picture of levels of contamination, or die off more rapidly than other pathogens such as viruses and protozoa. The search for a better indicator of sewage contamination has led European researchers to test phages (viruses) specific to the host bacterium Bacteroides fragilis, a common human fecal bacterium. Advantages of phages as indicators are that they do not replicate in the environment and their environmental decay rate is similar to that of human enteroviruses so their abundance can be more easily associated with a particular level of contamination. A recent study set out to evaluate whether these phages would be useful in tropical regions of the U.S. Investigators measured the abundance of two Bacteroides phages, each specific to a different host bacterial strain (denoted as HSP and RYC), at 22 stations in Tampa Bay, and compared their abundance with commonly used fecal pollution indicators. Both phages were found in low numbers in the bay, likely because the sites were not receiving direct discharge of untreated sewage. The abundance of one of the two phages, the one infecting the RYC host strain, was well correlated with that of two other indicators, coliphages and enterococci, but no other correlations were observed (the HSP strain phage was not correlated with any other indicators measured). While all sewage influent samples taken contained both types of phages, three of the seven chlorinated effluent samples tested positive for the RYC strain but the HSP strain was not detected. The authors of the study note that Bacteroides phages might only be applicable in limited situations, such as when untreated sewage inputs are suspected, where there is a need to strengthen evidence of human fecal inputs, and in tropical environments where traditional indicators may either regrow or die off too quickly to be useful.
Source: McLaughlin, M. R., and J. B. Rose. 2006. Application of Bacteroides fragilis phage as an alternative indicator of sewage pollution in Tampa Bay, Florida. Estuaries and Coasts 29(2): 246-256. (View Abstract)
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