Jeffrey B. Frithsen

NUTRIENTS AND THE PRODUCTIVITY OF ESTUARINE AND COASTAL MARINE ECOSYSTEMS

SUMMARY Recent research on estuarine and coastal marine systems has revealed two particularly interesting things about nutrients and productivity. First is the observation that these areas are among the most intensively fertilized environments on earth. Second is the common finding that much of the characteristically high primary productivity of these shallow waters is supported by nutrients released or recycled by pelagic and benthic microheterotrophs. Since nutrient inputs to coastal areas have probably been increasing and are likely to continue to do so, it is particularly important to understand the relationship between nutrient loading and nutrient cycling and the extent to which their interactions may set the levels of primary and secondary production in coastal systems. That some direct relationship exists between the input of nutrients and the productivity of higher trophic levels has been a principle of marine ecology since the turn of the century. It is surprisingly difficult, however, to find q...

Meiofaunal prominence and benthic seasonality in a coastal marine ecosystem

SummaryThe muds of a shallow (7 m) site in Narragansett Bay, Rhode Island contained higher abundances of meiofauna (averaging 17×106 individuals per m2 and ash free dry weight of 2.9 g/m2 during a 3 year period) than have been found in any other sediment. The majority of sublittoral muds, worldwide, have been reported to contain about 106 individuals per m2. This difference is attributed primarily to differences in sampling techniques and laboratory processing.Extremely high meiofaunal abundances may have also occurred because Narragansett Bay sediments were a foodrich environment. While the quantity of organic deposition in the bay is not unusually high for coastal waters, this input, primarily composed of diatom detritus, may contain an unusually high proportion of labile organics. Furthermore, meiofauna could have thrived because of spatial segregation of meiofauna and macrofauna. While meiofauna were concentrated at the sediment-water interface, most macrofauna were subsurface deposit feeders. Macrofaunal competition with, and ingestion of meiofauna may thus have been minimized.The seasonal cycles of meiofauna and macrofauna were similar. Highest abundances and biomass were observed in May and June and lowest values in the late summer and fall. Springtime increases of meiofaunal abundance were observed in all depth horizons, to 10 cm. We hypothesize that phytoplankton detritus accumulated in the sediment during the winter and early spring, and that the benthos responded to this store of food when temperatures rose rapidly in the late spring. By late summer, the stored detritus was exhausted and the benthos declined.

Eutrophication of a Coastal Marine Ecosystem — An Experimental Study Using the Merl Microcosms

The potential importance of nutrients, especially nitrogen, phosphorus, and silica, in influencing the productivity of the sea has been recognized for over 80 years (Brandt, 1899), though this long awareness has not necessarily produced a thorough understanding. Analytical techniques capable of resolving the concentrations of nutrients usually found in marine waters did not become available until the 1920s and 1930s (for example, Deniges, 1921; Harvey, 1928; Atkins, 1932). Ammonia, the most active form of nitrogen, was not commonly measured until after the publication of Solorzano’s direct colormetric technique in 1969. An early enthusiasm for describing, and in some cases quantifying the often dramatic reciprocal seasonal cycles in the concentrations of nutrients and the standing crop of phytoplankton waned as the patterns became better known (for example, Atkins, 1930; Cooper, 1933). It was also perceived early on that rapid nutrient cycles and transformations were probably taking place at rates which could not then be measured. As a result, there was little real advance in the study of nutrients in marine systems for some 25–30 years following the pioneering descriptive work of the 1930s.

The Use of Experimental Ecosystems for Evaluating the Environmental Impact of Pollutants: A Comparison of an Oil Spill in the Baltic Sea and Two Long-Term, Low-Level Oil Addition Experiments in Mesocosms

Scientific work with large experimental marine mesocosms has thus far received funding largely on the grounds that such research will help us to better evaluate the threat that various pollutants pose to the marine environment. Yet an authority in the field recently concluded that “large experimental ecosystems have probably taught us more about the general ecological interactions in such systems than about subtle long-term effects of pollutants” (Steele 1979). Does this mean that mesocosm research will not produce the kind of information needed by environmental protection agencies? One way to try to answer this question is to compare the effect of pollutants in experimental ecosystems with their effects in real ecosystems after intentional or accidental release. We present here such a comparison of two long-term, low-level oil-addition experiments in the mesocosms of the Marine Ecosystems Research Laboratory (MERL), University of Rhode Island, with the Tsesis oil spill study in the Baltic, and discuss how well the effects of an actual spill (Tsesis) could have been predicted on the basis of mesocosm experiments (MERL).

Structuring factors in a marine soft bottom community during eutrophication: an experiment with radio-labelled phytodetritus

The quantitative development and uptake of radio-labelled phytodetritus in benthic macro- and meiofauna was studied in a 5-month experiment in two mesocosms, one of which received a single large nutrient (N and P) addition, while the other served as control. In reponse to the 12-fold increase in phytoplankton biomass noted after 2 weeks and the resulting enhanced accumulation of fresh phytodetritus, the abundance and biomass of the polychaetes Mediomastus ambiseta and Polydora ligni and the mud anemone Cerianthiopsis americanus increased significantly in the enriched tank. The abundances of P. ligni and M. ambiseta increased 37-fold and 12-fold, respectively, within the first two months of the experiment. No other macrofaunal or meiofaunal taxa showed any consistent positive quantitative response to the increased input of phytodetritus. In the control tank no considerable change in the benthic community structure was noted. The measurements of radio-label uptake within the benthic fauna showed that the quantitatively most successful species utilized fresh phytodetritus highly. However, a high degree of utilization of fresh detritus was also shown by taxa that did not respond quantitatively within the 5 month of the experiment, and almost all taxa showed a preference for fresh detritus over older organic material. Within the benthic meiofauna, kinorhynchs and especially foraminiferans showed a remarkably low preference for fresh detritus. A budget calculation comparing the total amounts of labelled organic carbon bound in animal tissue and in the sediment indicated that at any time at least 75% of this carbon was available for assimilation by deposit feeders. These results suggest that factors other than the availability of food, such as competition for space by a few opportunistic macrofauna species, limited the response of other species within this benthic community to the increased input of phytodetritus.

Active enhancement of particle removal from the water column by Tentaculate Benthic Polychaetes

Abstract Two independent experiments were conducted to measure the effects of benthic community structure on the removal rate of 16 µm diameter, radiolabeled particles introduced into unstratified, experimental ecosystems. Particle-removal rates increased in the presence of large numbers of the benthic spionid polychaetes Streblospio benedicti Webster and Polydora ligni Webster. This enhanced particle removal was due to the activities of the worms and not merely to the presence of tube structures projecting above the sea-bed and into the benthic boundary layer.

A new, flow-through corer for the quantitative sampling of surface sediments

A new, flow-through benthic corer is described and compared to other commonly used coring methods. The new corer compares favorably with diver coring and is superior to coring with a ball-type, check valve corer, based on recovery of meiofauna, macrofauna, and particle bound hydrocarbons. Check valve corers yielded the most variable results. The new corer may be used to efficiently obtain samples of surface sediments from shallow (<6 m) water, where a reasonably stable working platform is available.

Metal incorporation by benthic fauna: Relationships to sediment inventory

A radionuclide addition experiment was conducted in a large-scale experimental mesocosm to study the behaviour and fate of trace metals in a coastal marine environment. Twelve radionuclides (7Be, 109Cd, 134Cs, 58Co, 60Co, 51Cr, 59Fe, 54Mn, 203Hg, 233Pa, 113Sn, and 65Zn) were added and their concentrations in benthic organisms and sediments were measured during the following nine months. The ability of benthic organisms to concentrate radionuclides was related to the vertical distribution and feeding behaviour of the organisms. Surface living fauna incorporated more radionuclides than deeper fauna. Calculations of total annual radionuclide incorporation by benthic fauna indicated that meiofauna incorporated a similar amount of the labelled metals as the macrofauna, even though the latter have a larger standing stock biomass. These calculations suggest that benthic metazoan fauna can annually cycle from 1% (Sn) to nearly 50% (Cd) of the amount of added radionuclides measured in sediments.

Using Single-Species and Whole Ecosystem Tests to Characterize the Toxicity of a Sewage Treatment Plant Effluent

A four-month experiment was conducted to evaluate the toxicity of a sewage effluent using both single-species and whole ecosystem tests. Fresh effluent from the East Greenwich, Rhode Island, sewage treatment plant was added daily to six experimental ecosystems (mesocosms). Sewage effluent additions were made at 0.1, 1.0, and 10% of the daily seawater input (960 L/day) from Narragansett Bay. Reagent grade, inorganic nutrients were added to the control, 0.1% and 1.0% effluent treatments to normalize nutrient loadings in all treatments. The Arbacia punctulata sea urchin sperm cell test was conducted on effluent and mesocosm samples. In the mesocosms, measurements of responses at the population, community, and ecosystem levels of biological organization were made. The single-species toxicity test indicated the mean EC 5 0 of the sewage effluent was 1.1%. Toxicity decayed rapidly over time, and was unrelated to carbon, nutrient, residual chlorine, or metal concentrations. Toxicity in the mesocosms was variable due to short-term (4 to 5 h), incomplete mixing of the effluent. There was no evidence for a buildup of toxicity in the mesocosms. Mesocosm effluent additions decreased phytoplankton standing stock and produced an imbalance between total system production and respiration leading to hypoxia. At the 10% effluent loading, net system production was negative. Results indicated both single-species and mesocosm approaches were useful to assess toxicity. The single-species test was best utilized to characterize the magnitude and persistence of toxicity, and the mesocosm experiments were best employed to identify sensitive communities and processes.