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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 February

Contents

More People, More Nutrients, More Microbes? Microbial Response to Nutrient Loading in Runoff and Groundwater
Human Development near Mangroves can Affect Habitat for Fish and Crustaceans
Don’t Underestimate Ecological Contributions of Non-reef Oysters in Tampa Bay
The Buzz about Mangrove Pollination: In Australian Temperate Regions, Exotic Honeybees Do Almost all of the Work

More People, More Nutrients, More Microbes? Microbial Response to Nutrient Loading in Runoff and Groundwater

Nutrient loading impacts entire estuarine food webs, starting with the smallest strands: microbes are one of the first responders when nutrients enter an estuary. However, direct responses of these organisms to estuarine nutrient inputs are rarely assessed. One recent study tackled this topic, using a bioassay approach to determine the response of microbial (and phytoplankton) productivity to surface and groundwater additions from developed and pristine areas.

The investigators collected surface runoff and groundwater samples from developed and forested areas in coastal South Carolina. They measured dissolved organic carbon (DOC) and other nutrients in the samples, added them to water taken from a third, undeveloped site, and measured microbial and primary productivity after incubation. Nutrient concentrations and DOC in the samples were higher in surface runoff than in groundwater, with a larger difference in the developed than the forested areas. Both phytoplankton and microbial production were most strongly stimulated by surface runoff from the developed sites (which had the highest nutrient concentrations out of all of the samples) and least by groundwater from the forested sites (which had the lowest). Overall, runoff inputs appeared to stimulate bacterial production more than phytoplankton communities, which could translate into reduced dissolved oxygen in the field.

The authors point out that the extensive paved surfaces of urban landscapes prevent rainwater from percolating into the ground, where it can be filtered naturally and undergo microbial processing. Instead, rainwater accumulates contaminants as it travels over the surface of urbanized areas, and is discharged unfiltered into coastal waters, with significant implications for microbial and phytoplankton production as well as water quality. This phenomenon will likely continue to affect water quality in coastal areas in the southeastern U.S., as development is expected to continue.

Source: Hutchins, P. R., E. M. Smith, E. T. Koepfler, R. F. Viso, and R. N. Peterson. 2014. Metabolic responses of estuarine microbial communities to discharge of surface runoff and groundwater from contrasting landscapes. Estuaries and Coasts 37 (January 2014). DOI: 10.1007/s12237-013-9719-8.

Human Development near Mangroves can Affect Habitat for Fish and Crustaceans

The Tampa Bay watershed is typical of many urbanized coastal areas. Human development has increased impervious surface and brought with it many of the other common effects of urbanization. Tidal creeks in this southeastern, mangrove-dominated estuary have been hit especially hard because of their location immediately downstream of urbanizing areas. More than two-thirds of Tampa Bay’s small tidal tributary watersheds have experienced moderate to heavy development.

What impact does this ecosystem alteration have on the animals that live there? A team of Florida investigators set out to shed some light on this question with an extensive study of urbanization and nekton (i.e., fish and crustaceans) in the tidal creeks of Tampa Bay. They began by documenting land use for 55 of Tampa Bay’s tidal creeks and several man-made mosquito ditches, and then chose 11 for further study in four land-use categories: man-made mosquito ditches (2), undeveloped (3), industrial (3), and urban (3). The researchers collected water-quality data and metrics describing the creeks’ nekton communities, including community and physiological parameters, in each creek.

Although nekton density was independent of land use, urban creeks generally supported a less diverse nekton community with lower densities of economically important species than non-urban creeks. Five of the nine most common taxa found throughout the study area were rarely collected in urban creeks; grass shrimp, for example, were nearly absent in urban creeks and the few individuals found in these systems were in poor physiological condition.

The results of the physiological parameters were mixed. For six of the nine taxa studied, there was no difference in body condition in animals sampled from the undeveloped, industrial, and man-made tributaries. Several nekton taxa were in better condition in the urban creeks: Sailfin mollies, an ecologically important and numerically dominant species, had higher energy reserves in urban as compared to non-urban creeks. However, reproductive output was reduced for mollies and grass shrimp in urban tributaries.

Statistical analysis revealed differences between urban and non-urban tributaries that explained 36% of the variation in nekton quality among tributaries. Specifically, urban tributaries had greater impervious surface, less natural mangrove shoreline, higher frequency of hypoxia, and lower, more variable salinities.

This study provides support for the idea that urban development along small, tidal tributaries can alter the available habitat and result in differences in nekton communities in urban tributaries. Based on the results, the authors state that efforts to improve habitat quality in the Tampa Bay watershed should focus on reducing impervious surfaces. In addition, the success of restoration and conservation projects should be evaluated based on metrics other than simple nekton densities.

Sources: Krebs, J. M., C. C. McIvor, and S. S. Bell. 2013. Nekton community structure varies in response to coastal urbanization near mangrove tidal tributaries. Estuaries and Coasts 37 (January 2014). DOI: 10.1007/s12237-013-9726-9.

Krebs, J. M., S. S. Bell, and C. C. McIvor. 2013. Assessing the link between coastal urbanization and the quality of nekton habitat in mangrove tidal tributaries. Estuaries and Coasts 37 (January 2014). DOI: 10.1007/s12237-013-9724-y.

 Don’t Underestimate Ecological Contributions of Non-reef Oysters in Tampa Bay

Oysters piled high in dense clusters provide critical habitat and help improve water quality in estuaries as they filter-feed. If these reefs are oyster “cities,” what about the oysters that live in the “suburbs,” on mangrove roots and man-made structures such as seawalls? Few studies have examined the oysters in these “alternative” habitats. Do these oysters provide similar ecosystem services? How do they compare in terms of health, reproductive potential, and abundance?

A Tampa Bay study examined whether oysters colonizing non-reef substrates differ from reef-dwellers by comparing several metrics of oyster health and biology among oysters found in natural reefs, mangrove prop roots, seawalls, and restoration substrates. For many of the parameters measured, no significant differences among habitat types were found, including reproductive and recruitment-related parameters. However, oyster density and biomass were found to be highest on seawalls and lowest on natural reefs, whereas reefs and restoration substrates had the largest mean shell heights. In addition, infection rate and intensity by the disease organism P. marinus (dermo) was significantly higher for oysters on natural reefs. The authors speculate that this may be because reef-associated oysters were likely older (based on mean shell sizes) than those in the other habitats, and therefore have been exposed to the disease longer.

The authors conclude that oysters on these non-reef substrates contribute significantly to overall oyster populations, as their reproduction and recruitment are the same as reef oysters, and should not be overlooked in surveys and assessments. Because many of the ecosystem services oyster provide (water filtration, for example) are density- and size-dependent, and these parameters differed among habitats, it is important to evaluate non-reef oysters separately when ecosystem-wide assessments are conducted.

Source: Drexler, M., M. L. Parker, S. P. Geiger, W. S. Arnold, and P. Hallock. 2013. Biological assessment of Eastern oysters (Crassostrea virginica) inhabiting reef, mangrove, seawall, and restoration substrates. Estuaries and Coasts 37 (January 2014). DOI: 10.1007/s12237-013-9727-8.

 The Buzz about Mangrove Pollination: In Australian Temperate Regions, Exotic Honeybees Do Almost all of the Work

Despite the importance of mangrove habitats in temperate Australian estuaries, very little is known about mangrove pollination. It has been generally assumed that mangroves support a wide range of pollinators; however, while previous reports in the literature provide lists of “visitors” to the mangroves, none have taken the step of determining how many of these species actually act as pollinators. Australian researchers recently undertook a project to document the pollinators of the temperate mangrove Avicennia marina at sites on the Georges and Minnamurra Rivers in New South Wales, and found, surprisingly, that the European honeybee is the only major pollinator of this species in the estuaries studied.

Although the authors documented visits by 38 species to mangrove trees at their temperate Australian study sites, including ants, beetles, moths, and honeybees, only three species, an ant, a beetle, and the European honeybee, carried mangrove pollen on their bodies. Honeybees carried pollen on all of their body parts, notably the parts that contact the mangrove flower anthers and stigmas, resulting in pollination. The bees were found to be relatively faithful to their target plants and were found to be very effective at both removing and depositing pollen.

The investigators concluded that the honeybees have displaced an unknown set of native pollinators, and this shift may have altered the pattern of pollen dispersal for this mangrove species. Impacts on fitness are unknown, and would be difficult to detect. However, the authors state, “Our study … [suggests] that A. mellifera [the honeybee] is not having a major detrimental impact on A. marina, at least in terms of fruit production because viable propagules are abundant.”

Source: Hermansen, T. D., D. R. Britton, D. J. Ayre, and T. E. Minchinton. 2013. Identifying the real pollinators? Exotic honeybees are the dominant flower visitors and only effective pollinators of Avicennia marina in Australian temperate mangroves. Estuaries and Coasts 37 (January 2014). DOI: 10.1007/s12237-013-9711-3.