Effects of predators and food resources on the macrobenthos of salt marsh creeks

We tested whether predation, disturbance and food resources controlled the density and taxonomic composition of benthic macrofauna in salt marsh tidal creeks by manipulating predator and food abundance. Cages that excluded fish, crabs, and shrimp were placed in two urea fertilized and two control creeks at Great Sippewissett Marsh, MA, in late May 1979 and were sampled over a 15-week period.Densities of macrofauna peaked in early summer, then decreased markedly in natural sediments and inside partial cages that provided access to predator/disturbers. Inside predator exclusion cages, macrofaunal densities increased and remained high throughout the experiment. Comparisons of densities in natural and caged sediments indicated that predation and/or disturbance by fish, crabs, and shrimp depleted populations of Paranais litoralis, Streblospio benedicti, Hydrobia sp., Nematostella vectensis, and Capitella spp. during summer. In late summer few individuals remained in the natural community and no species was common. Bulk sediment properties were not significantly changed by cages.The urea fertilizer treatment increased chlorophyll a concentration and percent nitrogen and carbon in sediments. Despite improved food value of fertilized sediments to deposit feeders, no increases in density or biomass of macrofauna were detected in fertilized creeks relative to controls. This indicates that food does not limit macrofaunal abundance in this habitat, even in the absence of predator/disturbers. Fertilization did prompt changes in the species composition of the macrofauna indicative of a stressed community. The oligochaete P. litoralis was the numerical dominant in fertilized creeks, which averaged fewer species per sample than control creeks. A polychaete, S. benedicti, predominated in control creeks

Effects of watershed land use on nitrogen concentrations and δ15 Nitrogen in groundwater

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 77 (2006): 199-215, doi:10.1007/s10533-005-1036-2.Eutrophication is a major agent of change affecting freshwater, estuarine, and marine systems. It is largely driven by transportation of nitrogen from natural and anthropogenic sources. Research is needed to quantify this nitrogen delivery and to link the delivery to specific land-derived sources. In this study we measured nitrogen concentrations and δ15N values in seepage water entering three freshwater ponds and six estuaries on Cape Cod, Massachusetts and assessed how they varied with different types of land use. Nitrate concentrations and δ15N values in groundwater reflected land use in developed and pristine watersheds. In particular, watersheds with larger populations delivered larger nitrate loads with higher δ15N values to receiving waters. The enriched δ15N values confirmed nitrogen loading model results identifying wastewater contributions from septic tanks as the major N source. Furthermore, it was apparent that N coastal sources had a relatively larger impact on the N loads and isotopic signatures than did inland N sources further upstream in the watersheds. This finding suggests that management priorities could focus on coastal sources as a first course of action. This would require management constraints on a much smaller population.This work was supported by funds from the Woods Hole Oceanographic Institution Sea Grant Program, from the Cooperative Institute for Coastal and Estuarine Environmental Technology, from Massachusetts Department of Environmental Protection to Applied Science Associates, Narragansett, RI, as well as from Palmer/McLeod and NOAA National Estuarine Research Reserve Fellowships to Kevin Kroeger. This work is the result of research sponsored by NOAA National Sea Grant College Program Office, Department of Commerce, under Grant No. NA86RG0075, Woods Hole Oceanographic Institution Sea Grant Project No. R/M-40

Microbial community composition in sediments resists perturbation by nutrient enrichment

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in The ISME Journal 5 (2011): 1540–1548, doi:10.1038/ismej.2011.22.Functional redundancy in bacterial communities is expected to allow microbial assemblages to survive perturbation by allowing continuity in function despite compositional changes in communities. Recent evidence suggests, however, that microbial communities change both composition and function as a result of disturbance. We present evidence for a third response: resistance. We examined microbial community response to perturbation caused by nutrient enrichment in salt marsh sediments using deep pyrosequencing of 16S rRNA and functional gene microarrays targeting the nirS gene. Composition of the microbial community, as demonstrated by both genes, was unaffected by significant variations in external nutrient supply, despite demonstrable and diverse nutrient–induced changes in many aspects of marsh ecology. The lack of response to external forcing demonstrates a remarkable uncoupling between microbial composition and ecosystem-level biogeochemical processes and suggests that sediment microbial communities are able to resist some forms of perturbation.Funding for this research came from NSF(DEB-0717155 to JEH, DBI-0400819 to JLB). Support for the sequencing facility came from NIH and NSF (NIH/NIEHS-P50-ES012742-01 and NSF/OCE 0430724-J Stegeman PI to HGM and MLS, and WM Keck Foundation to MLS). Salary support provided from Princeton University Council on Science and Technology to JLB. Support for development of the functional gene microarray provided by NSF/OCE99-081482 to BBW. The Plum Island fertilization experiment was funded by NSF (DEB 0213767 and DEB 0816963)

Mangroves enhance the biomass of coral reef fish communities in the Caribbean

Mangrove forests are one of the world's most threatened tropical ecosystems with global loss exceeding 35% (ref. 1). Juvenile coral reef fish often inhabit mangroves, but the importance of these nurseries to reef fish population dynamics has not been quantified. Indeed, mangroves might be expected to have negligible influence on reef fish communities: juvenile fish can inhabit alternative habitats and fish populations may be regulated by other limiting factors such as larval supply or fishing. Here we show that mangroves are unexpectedly important, serving as an intermediate nursery habitat that may increase the survivorship of young fish. Mangroves in the Caribbean strongly influence the community structure of fish on neighbouring coral reefs. In addition, the biomass of several commercially important species is more than doubled when adult habitat is connected to mangroves. The largest herbivorous fish in the Atlantic, Scarus guacamaia, has a functional dependency on mangroves and has suffered local extinction after mangrove removal. Current rates of mangrove deforestation are likely to have severe deleterious consequences for the ecosystem function, fisheries productivity and resilience of reefs. Conservation efforts should protect connected corridors of mangroves, seagrass beds and coral reefs

Ecological Effects of Major Storms on Coastal Watersheds and Coastal Waters: Hurricane Bob on Cape Cod

Hurricane Bob, a category 3 storm, made landfall on Cape Cod in August 1991, and its effects on watersheds and adjoining estuaries were detected in the ongoing studies being caried out as part of the Waquoit Bay Land Margin Ecosystems Research project. On land, Bob had only minor overall effects on forests; localized wind bursts did snap and break trees in small and widely scattered forest parcels. Wind stripped up to half the leaves of deciduous trees and many herbaceous plants on the watershed, and most remaining leaves were damaged by salt, so that by the end of Aug, Cape Cod forests were defoliated. Damaged growing tips of exposed trees were evident for several growing seasons. The salt exposure was followed by a burst of growth and bloom in some plants during Sep-Oct. Forest invertebrates were disturbed by the storm. Nests of hornets and wasps, for example, were apparently destroyed and the survivors became a serious pest problem: hospital records show a ten-fold increase in cases of wasp stings just after Bob. Populations of these insects did not return to earlier abundance for several years. Birds and mammals did not appear to have suffered much damage. Leaching of salt to soils released previously-adsorbed soil ammonium. Such loss of critical nitrogen may be in part responsible for the characteristically dwarfed near-shore coastal forests, as well as adds nitrogen to groundwater that in turn transports the nitrogen to receiving waters. On the Bay, Bob thoroughly mixed the water column, but the stratification was restored within 1-2 days after passage of the storm. Short recovery times might be characteristic of shallow bays with short (2-3 d) water residence times. Bob opened a new inlet to Waquoit Bay, which remains open. The new inlet exerts only minor effects on circulation within the Bay, but did create localized damage to dune and eelgrass habitats near the new inlet. The mixing of the water column released major amounts of nutrients that were held within the macroalgal canopy and upper sediments, into the upper layers, and prompted a short-lived (2-3 d) phytoplankton bloom. Biomass of unattached macroalgae was not affected by Bob. Respiration and nitrogen content of the dominant macroalgal species were elevated after passage of the storm, but returned to normal rates after several days. Nearly all above-sediment eelgrass biomass was removed, but returned to previous biomass during the next growing season. There was no visible damage to fringing salt marsh habitats. Damage to aquatic animals appears to have been minimal. A small decrease in water temperature and increased respiration by macroalgae led to decreased total net ecosystem production and increased net ecosystem respiration, but the decreases disappeared after 2 d. The effects of Hurricane Bob seemed more intense and protracted on land than on aquatic ecosystems. Recovery from the various disturbances took hours to days in the aquatic system, but months to decades in terrestrial components. Rigid, larger organisms attached or rooted to substrates seem most subject to storm-related disturbances

Macrophyte abundance in Waquoit Bay : effects of land-derived nitrogen loads on seasonal and multi-year biomass patterns

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Estuaries and Coasts 31 (2008): 532-541, doi:10.1007/s12237-008-9039-6.Anthropogenic inputs of nutrients to coastal waters have rapidly restructured coastal ecosystems. To examine the response of macrophyte communities to land-derived nitrogen loading, we measured macrophyte biomass monthly for six years in three estuaries subject to different nitrogen loads owing to different land uses on the watersheds. The set of estuaries sampled had nitrogen loads over the broad range of 12 to 601 kg N ha-1 y-1. Macrophyte biomass increased as nitrogen loads increased, but the response of individual taxa varied. Specifically, biomass of Cladophora vagabunda and Gracilaria tikvahiae increased significantly as nitrogen loads increased. The biomass of other macroalgal taxa tended to decrease with increasing load, and the relative proportion of these taxa to total macrophyte biomass also decreased. The seagrass, Zostera marina, disappeared from the higher loaded estuaries, but remained abundant in the estuary with the lowest load. Seasonal changes in macroalgal standing stock were also affected by nitrogen load, with larger fluctuations in biomass across the year and higher minimum biomass of macroalgae in the higher loaded estuaries. There were no significant changes in macrophyte biomass over the six years of this study, but there was a slight trend of increasing macroalgal biomass in the latter years. Macroalgal biomass was not related to irradiance or temperature, but Z. marina biomass was highest during the summer months when light and temperatures peak. Irradiance might, however, be a secondary limiting factor controlling macroalgal biomass in the higher loaded estuaries by restricting the depth of the macroalgal canopy. The relationship between the bloom-forming macroalgal species, C. vagabunda and G. tikvahiae, and nitrogen loads suggested a strong connection between development on watersheds and macroalgal blooms and loss of seagrasses. The influence of watershed land uses largely overwhelmed seasonal and inter-annual differences in standing stock of macrophytes in these temperate estuaries.This research was supported by the National Oceanic and Atmospheric Administration (NOAA), Cooperative Institute for Coastal and Estuarine Environmental Technologies (CICEET-UNH#99-304, NOAA NA87OR512), NOAA National Estuarine Research Reserve Graduate Research Fellowship NERRS GRF, #NA77OR0228), and an Environmental Protection Agency (EPA) STAR Fellowship for Graduate Environmental Study (U-915335-01-0) awarded to J. Hauxwell. S. Fox was supported by a NOAA NERRS GRF (#NA03NOS4200132) and an EPA STAR Graduate Research Fellowship. We also thank the Quebec-Labrador Foundation Atlantic Center for the Environment's Sounds Conservancy Program and the Boston University Ablon/Bay Committee for their awarding research funds

Effects of external nutrient sources and extreme weather events on the nutrient budget of a Southern European coastal lagoon

The seasonal and annual nitrogen (N), phosphorus (P), and carbon (C) budgets of the mesotidal Ria Formosa lagoon, southern Portugal, were estimated to reveal the main inputs and outputs, the seasonal patterns, and how they may influence the ecological functioning of the system. The effects of extreme weather events such as long-lasting strong winds causing upwelling and strong rainfall were assessed. External nutrient inputs were quantified; ocean exchange was assessed in 24-h sampling campaigns, and final calculations were made using a hydrodynamic model of the lagoon. Rain and stream inputs were the main freshwater sources to the lagoon. However, wastewater treatment plant and groundwater discharges dominated nutrient input, together accounting for 98, 96, and 88 % of total C, N, and P input, respectively. Organic matter and nutrients were continuously exported to the ocean. This pattern was reversed following extreme events, such as strong winds in early summer that caused upwelling and after a period of heavy rainfall in late autumn. A principal component analysis (PCA) revealed that ammonium and organic N and C exchange were positively associated with temperature as opposed to pH and nitrate. These variables reflected mostly the benthic lagoon metabolism, whereas particulate P exchange was correlated to Chl a, indicating that this was more related to phytoplankton dynamics. The increase of stochastic events, as expected in climate change scenarios, may have strong effects on the ecological functioning of coastal lagoons, altering the C and nutrient budgets.Portuguese Science and Technology Foundation (FCT) [POCI/MAR/58427/2004, PPCDT/MAR/58427/2004]; Portuguese Science and Technology Foundation (FCT

Organism-sediment interactions govern post-hypoxia recovery of ecosystem functioning

Hypoxia represents one of the major causes of biodiversity and ecosystem functioning loss for coastal waters. Since eutrophication-induced hypoxic events are becoming increasingly frequent and intense, understanding the response of ecosystems to hypoxia is of primary importance to understand and predict the stability of ecosystem functioning. Such ecological stability may greatly depend on the recovery patterns of communities and the return time of the system properties associated to these patterns. Here, we have examined how the reassembly of a benthic community contributed to the recovery of ecosystem functioning following experimentally-induced hypoxia in a tidal flat. We demonstrate that organism-sediment interactions that depend on organism size and relate to mobility traits and sediment reworking capacities are generally more important than recovering species richness to set the return time of the measured sediment processes and properties. Specifically, increasing macrofauna bioturbation potential during community reassembly significantly contributed to the recovery of sediment processes and properties such as denitrification, bedload sediment transport, primary production and deep pore water ammonium concentration. Such bioturbation potential was due to the replacement of the small-sized organisms that recolonised at early stages by large-sized bioturbating organisms, which had a disproportionately stronger influence on sediment. This study suggests that the complete recovery of organism-sediment interactions is a necessary condition for ecosystem functioning recovery, and that such process requires long periods after disturbance due to the slow growth of juveniles into adult stages involved in these interactions. Consequently, repeated episodes of disturbance at intervals smaller than the time needed for the system to fully recover organism-sediment interactions may greatly impair the resilience of ecosystem functioning.