Wells Beach Station, ME, United States
Wells Beach Station, ME, United States

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Bullard S.G.,University of Hartford | Carman M.R.,Woods Hole Oceanographic Institution | Rocha R.M.,Federal University of Paraná | Dijkstra J.A.,Wells National Estuarine Research Reserve | Goodin A.M.,Massachusetts College of Liberal Arts
Aquatic Invasions | Year: 2011

Little is known about the ascidian fauna of Pacific Panama. Ascidian surveys were conducted in the southern Gulf of Chiriquí on the Pacific coast of Panama in January 2008 and 2009. Surveys along linear transects at 2-3 m depth (snorkel, 2008) and 5 and 12 m depth (SCUBA, 2009) were conducted at multiple sites within a chain of islands extending out from the mainland. Twelve different ascidian taxa were observed with mean densities of up to ~17 ascidians m -2. The most abundant species was Rhopalaea birkelandi. Two of the most abundant taxa (Ascidia sp., Pyura sp.) appear to represent previously undescribed species. Several species of didemnids were also abundant. Ascidians were most abundant near the coast of the mainland and were less abundant near the islands farthest offshore. These data on Panamanian ascidian communities provide a baseline of local biodiversity against which it will be possible to determine whether the communities change over time, if additional species become introduced to the region, or if native Panamanian species become invasive in other parts of the world. © 2011 The Author(s).


Vincent R.E.,National Oceanic and Atmospheric Administration | Vincent R.E.,University of New Hampshire | Burdick D.M.,University of New Hampshire | Dionne M.,Wells National Estuarine Research Reserve
Estuaries and Coasts | Year: 2013

Anthropogenic activities in New England salt marshes have altered hydrologic flows in various ways, but unintended consequences from some types of habitat modifications have received little attention. Specifically, ditches have existed on salt marshes for decades, but the effects of these hydrologic alterations are only poorly understood. Ditch-plugging is a more recent methodology used for salt marsh habitat enhancement and mosquito control, but the long-term effects from this management practice are also unclear. The interactions involving marsh surface elevation, soil characteristics, and hydrologic regimes result in feedbacks that regulate the salt marsh self-maintenance process, and these interactions vary with hydrologic modification. Using natural tidal creeks and pools as controls, we examined the effects of ditching and plugging, respectively, on hydrology, surface elevations, and soils. Results showed the most apparent effects of altered hydrology from ditching are prolonged pore-water retention in the rooting zone and significantly lower soil bulk density and mineral content when compared with natural creek habitat. From a management perspective, the important question is whether the combined alterations to physical and biological processes will hinder the marsh's ability to keep pace with increasing rates of sea level rise, especially in more heavily ditched marshes. In contrast, ditch-plugging results in the decoupling of feedback processes that promote salt marsh self-maintenance and in doing so, threatens marsh stability and resilience to climate change. High surface water levels, permanently saturated soils, marsh subsidence, and significantly lower bulk density, carbon storage, soil strength, and redox levels associated with hydrologic alterations from ditch-plugging all support this conclusion. © 2013 Coastal and Estuarine Research Federation.


Dijkstra J.A.,University of New Hampshire | Dijkstra J.A.,Wells National Estuarine Research Reserve | Westerman E.L.,Yale University | Harris L.G.,University of New Hampshire
Global Change Biology | Year: 2011

Climate change and its role in altering biological interactions and the likelihood of invasion by introduced species in marine systems have received increased attention in recent years. It is difficult to forecast how climate change will influence community function or the probability of invasion as it alters multiple marine environmental parameters including rising water temperature, lower salinity and pH. In the present study, we correlate changes in environmental parameters to shifts in species composition in a subtidal community in Newcastle, NH through comparison of two, 3-year periods separated by 23 years (1979-1981 and 2003-2005). We observed concurrent shifts in climate related factors and in groups of organisms that dominate the marine community when comparing 1979-1981 to 2003-2005. The 1979-1981 community was dominated by perennial species (mussels and barnacles). In contrast, the 2003-2005 community was dominated by annual native and invasive tunicates (sea-squirts). We also observed a shift in the environmental factors that characterized both communities. Dissolved inorganic nitrogen and phosphate characterized the 1979-1981 community while sea surface temperature, pH, and chlorophyll a characterized the 2003-2005 community. Elongated warmer water temperatures, through the fall and early winter months of the 2000s, extended the growing season of native organisms and facilitated local dominance of invasive species. Additionally, beta-diversity was greater between 2003-2005 than 1979-1981 and driven by larger numbers of annual species whose life-history characteristics (e.g., timing and magnitude of recruitment, growth and mortality) are driven by environmental parameters, particularly temperature. © 2010 Blackwell Publishing Ltd.


Vincent R.E.,National Oceanic and Atmospheric Administration | Vincent R.E.,University of New Hampshire | Burdick D.M.,University of New Hampshire | Dionne M.,Wells National Estuarine Research Reserve
Estuaries and Coasts | Year: 2014

Salt marsh plant communities are regulated by feedback processes involving hydrologic regimes, disturbance, and marsh physical characteristics, and as expected differ among habitat types. Using three barrier beach salt marshes along the Gulf of Maine, we examined the effects of ditching and ditch-plugging on plant characteristics by means of comparisons to natural creek and pool habitats. Results indicated that ditch and creek habitats were similar in terms of species richness and diversity of emergent vascular plants, but cover and biomass were significantly higher in habitat adjacent to creeks. Plant composition in ditch habitat was distinguished by the higher percentage of forb species (associated with poor drainage), while the proportion of tall-form Spartina alterniflora was much higher in creek habitat (associated with sloping banks of creeks). These results are indicative of differences in hydrologic and disturbance regimes that can influence competitive and facilitative interactions, habitat structure, and heterogeneity. Results for pool comparisons indicated that plant characteristics were significantly different between ditch-plug and natural pools. Species richness, diversity, and biomass were significantly lower in ditch-plug habitat compared with all other habitats, and plant cover averaged only 30 % in habitat adjacent to ditch-plugs, which was significantly lower than all other habitats. These differences have ecological implications in terms of habitat structure and function of ditch-plug habitat. In addition, increased stress leading to plant dieback due to ditch-plugging has resulted in subsidence that can decrease the stability of ditch-plug habitat and expedite the loss of salt marsh habitat, especially with rising sea levels. © 2013 Coastal and Estuarine Research Federation.


Eberhardt A.L.,University of New Hampshire | Burdick D.M.,University of New Hampshire | Dionne M.,Wells National Estuarine Research Reserve
Restoration Ecology | Year: 2011

In recent years, salt marsh restoration projects have focused upon restoring hydrology through culvert enlargement to return functional values lost due to reduced tidal flow. To evaluate culvert effects on upstream nekton assemblages, fyke nets were set upstream of tidally restricted creeks, creeks recently restored with larger culverts, and paired reference creeks in New Hampshire and Maine, U.S.A. Subtidal habitats created or enlarged by scour were found immediately upstream of undersized culverts. All marshes supported similar assemblages and densities of fish, suggesting that marshes upstream of moderately restrictive culverts provide suitable habitat to support fish communities. However, densities of Crangon septemspinosa (sand shrimp) were significantly reduced upstream of culverts. A mark-recapture study was conducted in tidally restricted, restored, and reference marsh creeks to evaluate culvert effects on the movement of Fundulus heteroclitus (mummichog), the numerically dominant fish species in New England salt marshes. Recapture data indicated that small culvert size and consequently increased water velocity significantly decreased fish passage rates. We infer that upstream subtidal habitats and greater water velocities due to undersized culverts decreased nekton movements between upstream and downstream areas, resulting in segregated nekton populations. Restoration of salt marsh hydrology by the installation of adequately sized culverts will support increased fish access to marsh habitats and nekton-mediated export of marsh-derived production to coastal waters. © 2010 Society for Ecological Restoration International.


Dijkstra J.A.,Wells National Estuarine Research Reserve | Buckman K.L.,Dartmouth College | Ward D.,Humboldt State University | Evans D.W.,National Oceanic and Atmospheric Administration | And 2 more authors.
PLoS ONE | Year: 2013

Marine food webs are the most important link between the global contaminant, methylmercury (MeHg), and human exposure through consumption of seafood. Warming temperatures may increase human exposure to MeHg, a potent neurotoxin, by increasing MeHg production as well as bioaccumulation and trophic transfer through marine food webs. Studies of the effects of temperature on MeHg bioaccumulation are rare and no study has specifically related temperature to MeHg fate by linking laboratory experiments with natural field manipulations in coastal ecosystems. We performed laboratory and field experiments on MeHg accumulation under varying temperature regimes using the killifish, Fundulus heteroclitus. Temperature treatments were established in salt pools on a coastal salt marsh using a natural temperature gradient where killifish fed on natural food sources. Temperatures were manipulated across a wider range in laboratory experiments with killifish exposed to MeHg enriched food. In both laboratory microcosms and field mesocosms, MeHg concentrations in killifish significantly increased at elevated temperatures. Moreover, in field experiments, other ancillary variables (salinity, MeHg in sediment, etc.) did not relate to MeHg bioaccumulation. Modeling of laboratory experimental results suggested increases in metabolic rate as a driving factor. The elevated temperatures we tested are consistent with predicted trends in climate warming, and indicate that in the absence of confounding factors, warmer sea surface temperatures could result in greater in bioaccumulation of MeHg in fish, and consequently, increased human exposure.


Dijkstra J.A.,Wells National Estuarine Research Reserve | Nolan R.,University of New Hampshire
Aquatic Invasions | Year: 2011

Didemnum vexillum is a globally invasive species and a major pest to the aquaculture industry. Like other colonial ascidians, D. vexillum can readily overgrow aquaculture nets and cultured species. Recently, the species has been found in great abundance on seafloor habitats, where it is often associated with commercially important shellfish species such as sea scallops, Placopecten magellanicus. Despite the increasing abundance of D. vexillum in areas that are regularly fished for sea scallops, little work has been conducted on the ascidians impact on scallop behavior. This study examined the effect of overgrowth of the sea scallop by D. vexillum using four measures: time to initial exhaustion, swimming speed, horizontal and vertical displacement. Scallops covered by D. vexillum became exhausted more quickly, and were not able to swim as far in either the horizontal or vertical direction as the control sea scallops without D. vexillum encrustation. The expansion of D. vexillum into sea scallop habitat may increase the vulnerability of sea scallops to predation and limit their ability to access food rich habitats. © 2011 The Author(s).


Tyrrell M.C.,Wells National Estuarine Research Reserve | Tyrrell M.C.,Wellfleet | Dionne M.,Wells National Estuarine Research Reserve | Eberhardt S.A.,University of Hawaii at Manoa
Estuaries and Coasts | Year: 2012

Salt marsh fucoid algae are a conspicuous component of north temperate marshes, yet comparatively little research has been conducted to examine their ecological effects. We examined the influence of salt marsh fucoids on physical conditions and the biotic community in a manipulative experiment conducted in a southern Maine back-barrier salt marsh. The biomass of salt marsh fucoids was higher than that of aboveground Spartina alterniflora in the zone where we conducted the experiment. Average daytime temperatures at the sediment surface were significantly reduced by the presence of salt marsh fucoids. Density and biomass of standing-dead S. alterniflora was significantly higher when salt marsh fucoids were removed. In contrast, the abundance of various species of epifauna and infauna were significantly enhanced by the presence of salt marsh fucoids. A regional survey indicated that results from the study site may be conservative because the biomass of salt marsh fucoids was lowest among other back-barrier marshes. Salt marsh fucoids are little studied ecosystem engineers whose presence affects the microclimate and biotic community, especially the animals that constitute the basal components of the salt marsh trophic relay. © 2011 Coastal and Estuarine Research Federation (outside the USA).


Griffin P.J.,University of Southern Maine | Theodose T.,University of Southern Maine | Dionne M.,Wells National Estuarine Research Reserve
Wetlands | Year: 2011

Most salt marshes are dominated by graminoids, but patches dominated by a diverse assemblage of perennial forbs, known as forb pannes, occur on marshes in north temperate areas. These pannes and their associated species diversity appear to be highly responsive to anthropogenic change, including climate warming. We mapped all of the forb pannes on a salt marsh in Wells, Maine in order to 1) determine if geospatial features were related to panne location and species composition, and 2) record a baseline to compare with future responses to anthropogenic change. Forb pannes occupied approximately 5% of the high marsh surface, with sizes ranging from 7 m 2 to 5000 m 2. Pannes themselves were clustered at river/creek edges and near pools. Within pannes, species diversity was highest away from pools and the river mouth, and relative abundance of Plantago maritima was related to spatial variables. These results suggest that forb panne distribution and community structure are influenced by spatial variables and reinforce the notion that forb pannes may be used to track salt marsh responses to global change. © 2011 Society of Wetland Scientists.


Dijkstra J.A.,Wells National Estuarine Research Reserve | Boudreau J.,Wells National Estuarine Research Reserve | Dionne M.,Wells National Estuarine Research Reserve
Oikos | Year: 2012

Foundation species can provide habitat that modify abiotic and biotic processes that contribute to ecosystem function. While many studies have focused on the processes and consequences of a focal foundation species, understanding the ecological equivalence of co-occurring foundation species is important to identify key species responsible for ecosystem function. Here, we investigated the relative contributions of co-occurring foundation species on abiotic (temperature) and biotic responses of invertebrate species (recruitment, persistence, growth and survival). In a series of experimental field studies, we manipulated foundation species to measure invertebrate recruitment, persistence, and predation. A laboratory experiment measured foundation species effects on herbivore growth. Results demonstrated that macroalgal (Fucus vesiculosus ecad and Ascophyllum nodosum ecad scorpioides) intermediate foundation species provide habitat, food, and alleviate abiotic stress for dominant littorinid herbivores that surpass that provided by the primary species (Spartina alterniflora). These foundation effects were species-specific with F. vesiculosus ecad important for early life-history stages (enhanced recruitment and early growth of littorinid snails) and A. nodosum ecad important later on as a refuge from predators (Carcinus meanas) and stressful temperature. Understanding of the different effects of co-occurring foundation species on population and community processes is necessary for predicting community response to natural disturbance, species invasion, and ecosystem-based management actions. © 2011 The Authors. Oikos © 2011 Nordic Society Oikos.

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