Springer Science and Business Media LLC

Fluctuations in abundance of dominant species can cause competitive release of resources with consequences on community structure and functioning. In the present study, changes in the intertidal macroinfauna community of an exposed sandy beach were evaluated during two contrasting periods characterized by low and high densities of the yellow clam Amarilladesma mactroides. The increase in clam abundance and biomass was associated with a significant decrease in abundance of the rest of the community. In particular, a decline was observed for the pea crab Austinixa patagoniensis, a commensal species that lives in the burrows of the shrimp Sergio mirim. Our study demonstrates that fluctuations in clam abundance lead to long-term changes in community structure, suggesting the presence of competitive interactions. The environmental stability over the two periods strengthens the hypothesis that the competition between species is crucial for shaping the ecological community. Stable isotope analysis allows discarding trophic competition as mechanism of exclusion. Image maps reveal complementary distribution of species, showing the relevance of the spatial competition, which is mediated by changes in abundance of a third species. Indeed, high densities of A. mactroides reduce the available area for the establishment of the S. mirim burrows, limiting the foraging behavior of its commensal, the pea crab. Such an interaction drives density-dependent exclusion of the pea crab from the intertidal zone following the establishment of the yellow clam population. This study illustrates that spatial competition triggered by the increase of a bed-forming species can have community-wide consequences in exposed sandy beaches.

Mortality, litter fall, and patterns of stem growth were examined in Rhizophora- and Ceriops-dominated forests located upstream and downstream in four tidally dominated creeks within a beach reef embayment on the northern Great Barrier Reef coast. Although patterns of stem densities, basal area, and diameter-at-breast height (DBH) between upstream–downstream sites and creeks were inconsistent, aboveground biomass, wood production, litter fall, and aboveground net primary productivity (ANPP) were greater in the Rhizophora-dominated forests. Incremental growth of stems (SI, cm year−1) was slow compared to other mangroves, declining among species as follows: Rhizophora stylosa (mean = 0.080) > Bruguiera exaristata (0.066) = Xylocarpus australasicus (0.064) = Ceriops australis (0.056); SI was greater upstream than downstream, possibly due to nutrient inputs from upland sugarcane cultivation. The DBH of dead trees were less than the DBH of live trees, suggesting natural mortality, which was greatest for X. australasicus (annual rate = 3.27%), followed by B. exaristata (0.84%), C. australis (0.48%), and R. stylosa (0.33%). Rates of litter fall were seasonal and equivalent to those measured in other mangroves, but rates of ANPP were, on average, low in most plots. Salinity was likely the main factor limiting growth as correlations of salinity with tree growth and production were negative. Nutrients may have also played a key regulatory role, with positive correlations between mangrove production and N and P content of soils and leaves and the comparatively low nutrient content of these sandy soils. The low ratio of wood to litter production suggests that these forests are in a mature stage of development.

The article Effects of Local Shoreline and Subestuary Watershed Condition on Waterbird Community Integrity: Influences of Geospatial Scale and Season in the Chesapeake Bay, written by Diann J. Prosser, Jessica L. Nagel, Shay Howlin, Paul R. Marbán, Daniel D. Day, and R. Michael Erwin.

The article Growth and Movements of Mummichogs (Fundulus heteroclitus) Along Armored and Vegetated Estuarine Shorelines, written by Kevin P. Crum, Richard G. Balouskus, and Timothy E. Targett, was originally published electronically on the publisher’s internet portal (currently SpringerLink).

Young-of-the-year (YOY) bluefish, Pomatomus saltatrix, reside in some contaminated estuaries of the mid-Atlantic bight during their early life history, and as a result of this exposure, they may bioaccumulate high levels of contaminants, including polychlorinated biphenyls (PCBs), pesticides, and methyl mercury. Young-of-the-year bluefish from the Tuckerton, NJ, area of Great Bay (TK) were fed daily in a laboratory with common prey fish, menhaden, and mummichog from two sites: TK (reference) or Hackensack River (HR) (contaminated). Bluefish fed HR prey and the HR prey themselves had significantly elevated concentrations of PCBs, pesticides, and total mercury compared to TK counterparts. The bluefish fed contaminated prey for 4 months displayed significantly reduced feeding, spontaneous activity, and growth compared to the bluefish fed TK prey. Alterations of bluefish behavior and growth from exposure to contaminants may have detrimental effects on migration, overwinter survival, and recruitment success.

Long-term monitoring of eelgrass (Zostera marina L.) beds in the central subtidal portion of the Great Bay Estuary showed declines at both transplanted sites and reference beds. Eelgrass beds transplanted as mitigation for habitat loss from port development reached comparable functions (e.g., primary production, canopy structure) to natural reference sites by the late 1990s, within 6 years of transplanting. Data from 2001 to the present show significant declines in eelgrass parameters (biomass, shoot density, canopy height, leaf area) at all sites, suggesting that these declines are the result of an estuary-wide factor.

Gut content analyses and fatty acid profiles were used to identity food consumption and assimilation in a dominant grazing snail (Turbo smaragdus) in rocky shore and estuarine habitats, at Waiwera Estuary, northern New Zealand. Gut contents of freshly collected individuals indicated that snails utilize a wide range of food sources within their habitats, including microalgae and foliose-corticated macrophytes (rocky intertidal), and mangrove tissue and filamentous algae (mangrove stand). Laboratory feeding experiments revealed thatT. smaragdus prefers microalgae and possibly filamentous epiphytes, regardless of snail size or habitat of origination. The fatty acid profiles of snails fed different diets (brown algae [Hormosira banksii], diatoms, mangrove pneumatophores, and filamentous green algae [Chaetomorpha sp.]) confirmed the assimilation of the given foods, except for the mangrove treatment, which resulted in a low, long chain, fatty acid (LCFA) signature. Incongruities between the gut content analyses (high number of mangrove particles) and fatty acid profiles (low LCFA signature) of field and laboratory snails exposed to a mangrove diet suggest that snails target microalgal and filamentous epiphyte food sources on the pneumatophores and inadvertently ingest mangrove particles. Snails within all food treatments, except diatoms, had a relatively strong bacterial signature (18∶1n–7, Σ15+Σ17). Bacteria may have readily accumulated in the experimental tanks and been selected by snails as an alternative food source. In the field, snails and other grazers may ingest detritus and biofilms to access dense populations of bacteria. This research highlights the need for a comprehensive and multianalytical approach to elucidate the role of grazers in algal-plant dominated ecosystems.

Small-scale fisheries, which are often distributed over large spatial scales and occur in rural settings, tend to lack financial resources and capacity to conduct research on local issues. One approach to overcome this challenge is to use relatively inexpensive environmental monitoring methods with stakeholder engaged science and participatory modeling. Here, we present a case study focused on water pollution impacts and tidal circulation in a mid-coast Maine (USA) estuary to develop a simulation model and a partnership approach that can support soft-shell clamming communities to effectively address water quality, namely bacteriological closures of mudflats. We deployed multiple low-cost drifter buckets, Lagrangian flotation devices that measured surface current speeds and provided validation data for a hydrodynamic model based on finite volume community ocean model (FVCOM). The drifter buckets resolved the influence of wind, tidal currents, and bathymetry on surface water circulation patterns between the main channel and adjacent mudflats, highlighting the impact of cross-estuary winds during slack tides on potential bacterial transport. We calculated residence time using the validated FVCOM model: in the prohibited area (~ 2.5 days), and the conditional area (~ 0.5 days). This information has already influenced local management decisions and helped shape new conservation projects. In addition to contributing new understanding about tidal patterns in this coastal region, our novel methodology of combining field techniques, FVCOM modeling, and stakeholder engagement helps show how engaged research approaches can improve regulatory outcomes for small-scale fisheries while also protecting public health.

Predation within the marine environment has been well-studied and shown to be of major importance in shaping patterns of biodiversity. Typically larger predators, such as fishes, are examined because of the ease of manipulation and strong detectable results, whereas effects of smaller micro-predators are much more difficult to evaluate. Here, we examined the distribution and prey consumption of the polyclad flatworm, Euplana gracilis, in the Chesapeake Bay. Euplana gracilis is a common, micro-predator, but no data exist on its ecological function. Flatworms were found to actively prey upon a single species, the tube-building amphipod Apocorophium lacustre, in lab trials when tested against several other commonly encountered species. To examine natural population densities of flatworms, large-scale field sampling was conducted via benthic grabs and E. gracilis abundances were found to be significantly correlated with A. lacustre particularly in areas close to the shoreline. Some predator-prey interactions were examined including timed observations of consumption, predator size, and tube protection. Flatworm body size was found to correlate strongly with the number of prey consumed over time. Tubes constructed by amphipods were examined as a means of refuge when in the presence of E. gracilis, but provided very little protection as flatworms could easily penetrate tubes in search of prey. Our results are the first to show predation of an estuarine/marine polyclad flatworm on amphipods as well as provide some insight into the dynamics of this previously unknown predator-prey relationship.