Effects of Different Mixing Schedules on Phytoplankton, Zooplankton and Nutrients in Marine Microcosms

An experiment was carried out with different mixing schedules in marine microcosms. Continuous mixing resulted in higher chlorophyll concentrations, lower nutrient concentrations and lower zooplankton biomass than no mixing. No mixing caused water-column stratifications of chlorophyll and nutrients, as well as of organisms such as flagellates and rotifers adapted to low-mixing regimes. The most dramatic result was the low biomass of zooplankton in the continuously mixed microcosms and the high biomass of zooplankton in the unmixed microcosm

Seasonal patterns of sedimentary carbon and anaerobic respiration along a simulated eutrophication gradient

Concentrations of organic carbon and rates of dissimilative sulfate reduction in surface sediments of marine mesocosms were examined along an experimental eutrophication gradient. Phytoplankton biomass increased due to addition of inorganic nutrients (N. P, Si). This increase was especially pronounced during the winter spring diatom blooms, which increased in magnitude and duration along the nutrient gradient. Net system production in winter and spring resulted in carbon deposition and accumulation in surface sediments (maximum net accumulation 17 mol C m-2). Benthic remineralization of carbon exceeded depositional supply during summer and fall. Sediment carbon concentrations approached background levels in December and February, suggesting very little annual accumulation of sediment carbon Sediment oxygen consumption and sulfate reduction rates both increased as a result of carbon sedimentation. Sulfate reduction rates in organic enriched sediments were an order of magnitude higher than control and were correlated with temperature and carbon concentrations (r2 = 0.85). Anaerobic respiration rates in unenriched sediments were related only to seasonal patterns of temperature (r2 = 0.70). Anaerobic metabolism was the dominant metabolic pathway in control and treated sediments, with 50 to 70% of annual carbon remineralization due to sulfate reduction

Application of filtration rate models to field populations of bivalves: an assessment using experimental mesocosms

Gross sedimentation of 14C labelled carbon was 58% greater in mesocosms (13 m3) containing the bivalve Mercenaria mercenaria (16 in m-2) relative to controls without this filter feeder. This difference was attributed to the activities of M. mercenaria and presumably due to filtration of particles from the water column. Of this increase, 32% and 47% were attributable to assimilation into clam tissue and respiration by the benthic community respectively. Permanent biodeposition by the clams contributed the least (21%). The ability of 8 filtration rate models to predict the increase in gross sedimentation was examined. Those models (4) which were based on data for bivalves filtering natural suspensions of particulate matter gave estimates which agreed well with observed differences. Those models (4) which yielded poor predictions used dues or algal monocultures to generate data and overestimated gross sedimentation due to bivalves by up to an order of magnitude. Such overestimation may exaggerate the role of bivalves in enhancing sedimentation and controlling phytoplankton biomass in shallow waters

Are estuaries traps for anthropogenic nutrients? Evidence from estuarine mesocosms

A series of estuarine mesocosms is described, where nutrient budgets were used to determine rates of nitrogen and phosphorus trapping and export as a function of nutrient input level, season, and presence or absence of sediments. Regardless of treatment or season these experimental systems exported most of the N and P that they received. Control systems with sediments retained none of the inflowing N and P during summer, and 5 % of N and 25 % of P inputs during winter. Eutrophied systems with sediments initially retained 30 % of added N and P due to increases in water column and sediment nutrient standing stocks in response to daily inorganic nutrient additions; however, after 6 mo of daily nutrient loading, these treatments retained only 5 to 15 % of nutrients added. Results of this study suggest that well-mixed estuarine systems may export to offshore waters most of the nitrogen and phosphorus that they receive. For the small percentage of nutrients that were retained, there was more storage during winter than summer, more storage in treatments without sediments, and more retention of P than N. Nitrogen losses through sediment denitrification accounted for 10 to 20 % of the N input to controls, and less than 10% of the N input to eutrophied treatments. The addition of nutrients to the eutrophied treatments resulted in increases in the N and P content of surface sediments, and the rapid deposition of an N and P-rich detrital layer on the bottom of the treatments without sediments

Seasonal lags between organic carbon deposition and mineralization in marine sediments

The fate of phytoplankton detritus in the muddy sediments of shallow marine ecosystems was studied by labelling the water column of a 13 m3 microcosm with radiocarbon bicarbonate from January to July. By the end of the study, more than 9% of the original inorganic label was found as organic carbon in the top 10 cm of sediment. The accumulation of labelled organic carbon in the sediment totalled 14.5 gC/m2. We estimate that this amount represented 15% of daytime net primary production and roughly half of the labelled organic carbon that was deposited on the sediment. The finding of sedimentary carbon accumulation directly demonstrated that time lags on the order of months can exist between the deposition and mineralization of phytoplankton detritus in nature. Observed time lags may have occurred because heterotrophic activity was minimize by low winter and spring temperatures, pelagic and benthic grazing was minimal, and bioturbation rates were high. Mineralization of organic carbon may have been retarded by conditions in subsurface sediments. Detritus buried in the sediment during the winter and spring would have been available to the subsurface feeding benthos during the summer, when maximum metabolic demand occurs

Impacts of Climate Change on Narragansett Bay

The objective of this paper is to examine the impacts of global climate change on Rhode Island\u27s coastal ecosystems. Average annual air temperature in Rhode Island has increased by 1.7 °C since 1880, water temperatures of Narragansett Bay have increased by 1.2 °C since 1950, precipitation increased 27% between 1895 and 1999, and sea level rose 0.13 m between 1931 and 2007. We can already see the effects of these climatic changes on the Narragansett Bay ecosystem, including ecological changes in the Bay\u27s food web from phytoplankton and Zooplankton to fish, e.g., changes in phenology of seasonal phytoplankton blooms and dominant fish species (e.g., Pseudopleuronectes americanus [Winter Flounder]). These climatic changes have increased freshwater inputs and the concomitant pollutant loads into the Bay. Rising sea level has contributed to ongoing erosion of the coast and has put waterfront homes at increased risk. It is imperative to continue monitoring these effects

The effects of the filter-feeding clam Mercenaria mercenaria on carbon cycling in experimental marine mesocosms

The metabolism and the fate of 14C labelled carbon was examined in 4 outdoor mesocosm (13 m3) tanks containing both benthic and pelagic compartments. Mesocosms with (16/m2) and without the clam, Mercenaria mercenaria were compared. System production, net and gross sedimentation of particulate carbon and benthic remineralization of dissolved inorganic nitrogen were all greater in mesocosms with clams. A filtration rate model, dependent on clam size and temperature, explained between 74–114% of the increased gross sedimentation in clam tanks relative to controls.The higher production in the clam tanks was at least in part due to a greater flux of dissolved inorganic nitrogen from the benthos. Despite this greater production in the clam tanks, water column biomass remained similar to controls. Calculations based on the filtration rate model indicated that clams could have consumed between 30% and 46% of the excess biomass produced during the day. Loss of particles due to processes in the water column appeared to consume most of this excess biomass. Although clams enhanced production and sedimentation, they did not limit phytoplankton biomass in the water column through filtration

Decadal Patterns of Westerly Winds, Temperatures, Ocean Gyre Circulations and Fish Abundance: A Review

The purpose of this review is to describe the global scope of the multidecadal climate oscillations that go back at least, through several hundred years. Literature, historic data, satellite data and global circulation model output have been used to provide evidence for the zonal and meridional jet stream patterns. These patterns were predominantly zonal from the 1970s to 1990s and switched since the 1990s to a meridional wind phase, with weakening jet streams forming Rossby waves in the northern and southern hemispheres. A weakened northern jet stream has allowed northerly winds to flow down over the continents in the northern hemisphere during the winter period, causing some harsh winters and slowing anthropogenic climate warming regionally. Wind oscillations impact ocean gyre circulation affecting upwelling strength and pelagic fish abundance with synchronous behavior in sub Arctic gyres during phases of the oscillation and asynchronous behavior in subtropical gyres between the Atlantic and Pacific oceans

Climate Alters the Migration Phenology of Coastal Marine Species

Significant shifts in the phenology of life-cycle events have been observed in diverse taxa throughout the global oceans. While the migration phenology of marine fish and invertebrates is expected to be sensitive to climate change, the complex nature of these patterns has made measurement difficult and studies rare. With continuous weekly observations spanning 7 decades in Narragansett Bay, Rhode Island (USA), the University of Rhode Island Graduate School of Oceanography trawl survey provides an unprecedented opportunity to investigate the influence of climate on the migrations of marine species in the northwest Atlantic. Analyses of the survey observations of 12 species indicated that residence periods have changed by as much as 118 d, with shifts in the timing of both ingress to and egress from the coastal zone. The residence periods of warm-water species expanded while those of cold-water species contracted. Dirichlet regressions fit to the annual presence-absence patterns of each species identified interannual temperature variations, fluctuations in ocean circulation, and long-term warming all as having a significant effect on migration phenology. Additionally, temperature gradients within Narragansett Bay were shown by generalized additive models to cause detectable shifts in local spatial distributions during coastal residency. These novel findings mirror results found in the spatial domain and therefore suggest that the studied species are adapting their spatiotemporal distributions to track their thermal niche in a changing climate. If so, characterizing the spatial and temporal aspects of climate responses across species will be critical to understanding ongoing changes in marine ecosystems and successfully managing the fisheries they support

A comparison of system (O\u3csub\u3e2\u3c/sub\u3e and CO\u3csub\u3e2\u3c/sub\u3e) and C-14 measurements of metabolism in estuarine mesocosms

Metabolism in estuarine mesocosms was measured by total system oxygen and carbon dioxide and by C-14 bottle incubations to determine the effects of nutrient enrichment (6 levels) over a 9 mo period. These data provided an unprecedented opportunity for calculating metabolic ratios (photosynthetic quotient [P.Q.] and respiratory quotient [R.Q.]) based on the 3 measures of metabolism and determining the impact of other system processes. System metabolism ratios based on daily data varied from 0 to 5.0. System metabolism ratios of P.Q. and R Q. based on integrated data were highly correlated (r = 0.95 to 0.96) and similar to traditional ratios obtained in phytoplankton studies. A system photosynthetic quotient of 1.2 and a system respiratory quotient of 1.1 were calculated from the integrated data. These ratios were only slightly affected by carbon dioxide diffusion and 3 benthic processes: denitrification, sulfur metabolism and calcium carbonate dissolution. There was no trend for system metabolism ratios up the nutrient gradient. The C-14 estimations of productivity appeared nitrogen limited in the lower nutrient treatments and provided lower estimates than the 2 system measures of production