Barbara K. Sullivan

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...

Timing and size of blooms of the ctenophore Mnemiopsis leidyi in relation to temperature in Narragansett Bay, RI

The ctenophore Mnemiopsis leidyi is at the northern extreme of its geographic range in Narragansett Bay, an estuary on the northeast coast of the United States. Blooms have typically been observed in late summer and fall according to records from 1950 to 1979. We document an expansion of the seasonal range of this important planktonic predator to include springtime blooms during the 1980s and 1990s. This shift to an earlier seasonal maximum is associated with increasing water temperature in Narragansett Bay. Temperatures in spring have risen, on average, 2 °C from 1950 to 1999 with warm years being associated with the positive phase of the North Atlantic Oscillation. During 1999, M. leidyi appeared earlier in spring and was more abundant than during any previous year for which records are available. Changes in the seasonal pattern and abundance of this predator are likely to have important effects on planktonic ecosystem dynamics of Narragansett Bay. These include reduction of zooplankton abundance in spring followed by increases in size and frequency of summer phytoplankton blooms. Earlier blooms of M. leidyi may also reduce survival of eggs and larvae of fish because, as in 1999, they coincide with the period of peak spawning.

The use of life-tables for evaluating the chronic toxicity of pollutants toMysidopsis bahia

This study examines the application of population statistics to laboratory-derived toxicological data for the purpose of developing a predictive model that assesses the population consequences of pollutant and environmentally-induced stress. Life tables are used to calculate age-specific survivorship, fecundity, intrinsic rate of population increase (r), and reproductive value (Va), for populations of Mysidopsis bahia chronically exposed, in separate tests, to mercury and nickel. The population statistics, r, and Va, and pollutant dose are defined quantitatively, and the critical value (r = 0) for the intrinsic rate of population increase is compared with traditional toxicological measures of acute and chronic toxicity.

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.

Voracious planktonic hydroids: unexpected predatory impact on a coastal marine ecosystem

Abstract-Hydroids are typically attached, benthic cnidarians that feed on a variety of small prey. During sampling on Georges Bank in spring 1994, we found huge numbers of hydroids suspended in the plankton. They fed on young stages of copepods that are an important prey for fish, as well as on young fish themselves. Two independent methods were used to estimate feeding rates of the hydroids; both indicate that the hydroids are capable of consuming from 50% to over 100% of the daily production of young copepods. These results suggest that hydroids can have a profound effect on the population dynamics of zooplankton and young fish on Georges Bank. Copyright 0 1996 Elsevier Science Ltd INTRODUCTION The life history of marine hydrozoans (Phylum Cnidaria) is typically an alternation between a sessile hydroid phase and a motile medusa. The hydroids form colonies attached to seaweed, rocks or other organisms, and their feeding polyps (hydranths) prey on small organisms, eggs and detrital matter. The medusae are usually released to feed and disperse in the plankton (Hyman, 1940). We report observations from Georges Bank on the occurrence of suspended colony fragments of the hydroid

Ammonia toxicity to larval copepods in eutrophic marine ecosystems a comparison of results from bioassays and enclosed experimental ecosystems

In an experiment designed to simulate eutrophication of a shallow coastal ecosystem, nutrients were added to experimental ecosystems (MERL mesocosms) in six different treatment levels. We observed large reductions in the numbers of normally dominant copepods of the species Acartia tonsa and A. hudsonica associated with high concentrations of unionized ammonia (NH 3 ) in the two most nutrient enriched treatments. Comparison of 48 h LC 50 values of 10–15 μM·l −1 NH 3 obtained from laboratory bioassays with concentrations of NH 3 associated with increased mortality in the MERL tanks indicated that bioassay data correctly predicted trends of high and low mortality as well as fluctuations in the numbers of copepods in MERL tanks. Actual mortality rates of the mesocosm copepods was sometimes higher than predicted, however.

Biodegradable Blends of Cellulose Acetate and Starch: Production and Properties

Abstract Blends of cellulose acetate (2.5 degree of substitution) and starch were melt processed and evaluated for mechanical properties, biodegradability during composting, and marine and soil toxicity. Formulations containing, on a weight basis, 57% cellulose acetate (CA), 25% corn starch (St) and 19% propylene glycol (PG) had mechanical properties similar to polystyrene. Increasing plasticizer or starch content lowered tensile strength. Simulated municipal composting of cellulose acetate alone showed losses of 2−3 and 90% dry weight after 30 and 90 days, respectively. CA/St/PG blends in both soil burial and composting experiments indicate that propylene glycol and starch are degraded first. Extended incubations are required to detect losses from cellulose acetate. Marine toxicity tests using polychaete worms and mussels showed no toxicity of cellulose acetate or starch. High doses had an adverse effect due to oxygen depletion in the marine water due to rapid biodegradation of the polymers. Preliminary ...

Distribution, abundance and benthic-pelagic coupling of suspended hydroids on Georges Bank

Abstract Clytia spp. hydroids (Phylum Cnidaria), typically attached to a substrate during their asexual, polyp stage, have been found in significant numbers within the mesozooplankton on Georges Bank, North Atlantic Ocean. We examined unpublished historical records of the 1939–1941 cruises of the R/V Atlantis and obtained samples at four-study sites on Georges Bank in June/July 1995 in an attempt to (1) quantify the planktonic and benthic distributions of hydroids on Georges Bank, and (2) determine the coupling between benthic and pelagic habitats of this population. We found that planktonic hydroids have a patchy distribution, varying both spatially and temporally (most abundant in summer months, absent in winter). In 1939–1941 the planktonic hydroids were most broadly distributed following a spring (1940) with strong wind events; hydroids were absent from all samples in 1941. In 1995 we found the highest abundance of planktonic Clytia spp. hydroids (6213.5±1343.6 hydranths m−3) in the central crest of the bank, “downstream” in the Georges Bank circulation pattern from sites along the northeast peak of the Bank where large populations of benthic Clytia spp. hydroids were found (up to 6465 hydranths m−2). Our plankton sampling did not show significant numbers of hydroids in the water column at the Northeast peak sites, indicating that large numbers of planktonic hydroids are not being introduced into the Banks circulation patterns from off-Bank sites to the northeast (e.g. Scotian shelf). The source population for planktonic hydroids found in the central region of the Bank is most likely the benthic habitats on the northeast peak of the Bank. We hypothesize, and our limited data suggest, that hydroids are detached from the benthos by storm action or other disturbance, advected clockwise with the mean residual circulation, and concentrated and retained in the central, low-advective region of the Bank.

Effects of biodegradable plastic components on metabolism of an estuarine benthos

We examined the metabolic response of an estuarine benthic community to additions of three materials being considered for use in manufacture of biodegradable substitutes for plastics. Diver-collected cores containing benthos were dosed with 59 g/m2 of three test materials, cornstarch, a bacterial polyester (PHBV), and ethylene vinyl alcohol (EVOH), or left undisturbed as controls. Fluxes of dissolved nutrients (ammonia, nitrate + nitrite, phosphate, silica) and dissolved inorganic carbon (DIC) were similar in control cores and cores dosed with EVOH during a 1-month test period at 20°C. Fluxes in cores dosed with starch and PHBV differed significantly from controls but not from each other. After 2 weeks of incubation, production of DIC was higher in cores containing starch and PHBV, while efflux of ammonia, nitrate, and nitrite was reduced. After 4 weeks of incubation, production of DIC was similar among all treatments and controls, while efflux of ammonia was high in the starch- and PHBV-containing cores compared to controls and cores with EVOH. Fluxes of silica and phosphate were similar in all cores during the experiment. These results indicate that both starch and PHBV are carbon-rich substrates readily metabolized by the benthic community but that their presence significantly alters normal nutrient exchange patterns. This response is expected because of the high carbon-to-nitrogen ratio of starch and PHBV and indicates that impacts of these two materials would be similar. However, the high biological oxygen demand of such materials and resulting disturbance of normal nutrient regeneration patterns of the benthos (delayed ammonia efflux and potential stimulation of denitrification) must be considered in developing strategies for their disposal.