Dye tracing of a subsurface chlorophyll maximum of a red-tide dinoflagellate to surface frontal regions

Rhodamine dye (3701) was injected into a 22-m subsurface chlorophyll maximum of the red-tide forming dinoflagellate Prorocentrum mariae-lebouriae var. minimum in the northern Chesapeake Bay (USA) and traced for a sixday period as it spread over a 600 km² area. The precise physical mechanisms, which resulted in the transfer of dye and organisms to the surface, are documented. The major component of the dye and organisms was transported from the central bay into major tributary estuaries via net nontidal flow of bottom waters and surfaced upstream in frontal regions. Once in surface waters, the dye and organisms flowed downriver toward the bay. Due to the three-layer flow of the rivers at this time, the dinoflagellate and the rhodamine re-entered the bay proper at middepth below the fresher Susquehanna plume, thus forming a near-surface chlorophyll maximum (4–6 m) flowing in an opposite direction to the deep subsurface chlorophyll maximum (18–26 m). Current meter arrays verified the opposite flows of these two lenses. The near-surface, southward-flowing lens was followed downstream to an area where the influence of the Susquehanna begins to subside as indicated by isopycnals inclined to the surface. Here the near-surface lens is mixed upward to the surface forming massive red tides (25 000 cells ml^–1) delineated by a frontal region. In addition to the predominant along channel flow, major cross stream Ekman transport and upwelling of dye and organisms was detected in response to wind forcing resulting in localized surface patch formation along the western shore shoaling regions of the bay proper. Thus, annual variations in the locations of surface red tides can be correlated to streamflow and windinduced variations in the locations of frontal regions.     

The delineation of two plankton communities from one sampling site (Fire Island Inlet,Long Island,N.Y.)

Zooplankton and phytoplankton communities were observed and recorded at Fire Island Inlet from 1971–1974. Species typical of a temperate, neritic environment were found. Sampling by net and bottle at several stations in the area revealed two populations, one representative of the bay water and the other representative of the ocean water. It was further found, by comparing frequency of occurrence relative abundance, rank order and indicator species, that these two populations could be monitored at one sampling station (Oak Beach) by sampling at the appropriate tidal intervals, i.e., midtide after slack current, on both the ebb and flow tides. Observations from one site of plankton communities representative of bay water and of ocean water, as they move into and out of the Inlet, could be of significance in monitoring the effects of proposed man-made changes in the environment. It is possible that other coastal areas could benefit by such a combined approach.Based on a thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, New York University, New York, N.Y.     

The distribution of intertidal phytopsammon in an Oregon estuary

The sediments of two tidal flats in Yaquina Bay, Oregon, USA, were studied to determine the distribution and abundance of the interstitial microalgal communities. The hydrography of the bay, as well as fluetuations in various physical and chemical parameters appear to regulate the biomass and the vertical and intertidal distribution of these organisms.     

Mitochondrial DNA Phylogeography and the Conservation of Endangered Lesser Antillean Icterus Orioles

Abstract: Recent natural and anthropogenic disturbances have endangered two of the three oriole species endemic to single islands in the Lesser Antilles. The ongoing eruption of the Soufriere Hills volcano may have doomed the Montserrat Oriole (   Icterus oberi ), whereas high levels of nest parasitism by a cowbird threaten the Martinique Oriole (   I. bonana ). These orioles and related Antillean and Central American forms have been considered part of the Icterus dominicensis superspecies complex, but the taxonomic status of the different Antillean island populations has been long debated. To investigate levels of evolutionary differentiation among threatened Lesser Antillean orioles, we analyzed 2507 nucleotides of protein-coding mitochondrial DNA (mtDNA) sequence from orioles on Martinique, Montserrat, St. Lucia (   I. laudabilis ), Puerto Rico (   I. dominicensis dominicensis ), Mexico (   I. d. prosthemelas ), and three Icterus outgroup species. Phylogenetic analyses of the mtDNA data supported the monophyly of Antillean members of the I. dominicensis complex and identified a star-like pattern of relationship among them. Mitochondrial distances between the Antillean populations were large (4.5–5.8% nucleotide divergence) and suggested that the Lesser Antillean orioles have been isolated evolutionarily from one another since the late Pliocene. The oriole taxa on Montserrat, Martinique, and St. Lucia meet species criteria under the phylogenetic species concept and represent evolutionarily significant units. The impending extinction of the phylogenetically unique Montserrat oriole highlights the vulnerability of island endemics to habitat degradation followed by rare and unpredictable natural catastrophes.     

Active swimming in meiobenthic copepods of seagrass beds: geographic comparisons of abundances and reproductive characteristics

The entry of meiobenthic copepods from sediments or seagrass blades into the water column and reproductive characteristics of actively migrating fauna were investigated from 1981–1986 in a temperate intertidal Zostera capricorni seagrass bed in Pautahanui Inlet, New Zealand and in a subtidal Thalassia testudinum bed in Tampa Bay, Florida, USA. Emergence of copepods in New Zealand varied over a tidalcycle, while in Florida a distinct diel periodicity was displayed. Selected copepod species in New Zealand had similar numbers emerging from sediments and/or blades over a 6 h period as the common copepods actively migrating from sediments in Florida. Daily abundances of emerging copepods (24 h) in Tampa Bay, Florida, were substantially greater than those in New Zealand, where migration is linked to tidal cover. In Z. capricorni meadows in New Zealand, sex ratios of copepods in sediments and on blades were dominated by females; males dominated water-column samples. In T. testudinum meadows in Tampa Bay, sex ratios of males to females, although of a lowermagnitude than in Z. capricorni beds, were higher in trap than in sediment samples. Differences in sex ratios, the availability in emergence traps of females of appropriate stage for mating, and observations on clasping in live samples from traps suggest that swimming behavior in copepods may be partly linked to prenuptial courtship. Meiobenthic copepods may use the water column as an important habitat for reproductive behavior.     

Long-term variation of organochlorine residues and assemblages of epibenthic organisms in a shallow North Florida (USA) estuary

A 4-year study (1972–1976) determined long-term trends of organochlorine residues (DDT, DDE, DDD, PCB's, mirex) and trawl-susceptible organisms in a shallow, river-dominated estuary in North Florida (Apalachicola Bay, USA). Moderate levels of such compounds were found in various species prior to the restricted use of DDT in 1972. A subsequent precipitous decline in organochlorine besidues was attributed to decreased upland usage, major flushing of the river basin in early 1973, and various factors associated with estuarine function. No mirex was found in sediments or aquatic organisms. Apparently, the half-life of organochlorines is relatively short in this bay system. Various statistical methods were used to test the relationships of different physico-chemical and biological parameters. During the 4-year study period, seasonal river flow fluctuations dominated water color, turbidity, salinity, nutrients (NO₃), chlorophyll a, and the temporal succession of fishes in the bay. Certain long-term trends of fish associations were noted; relative dominance of key fish species declined and stabilized while bay-wide species richness and diversity increased with time. Qualitative changes in species representation determined the long-term pattern of community variability. This was consonant with a distinctive fish fauna during the first year of sampling. The bay anchovy Anchoa mitchilli was dominant during 9 of the first 12 monts of the project; this influenced the time-related changes in community indices. Temporally clustered fish associations reflected the importance of river flow in the estuarine environment. Direct correlation of fish distribution with the rapid disappearance of organochlorine compounds was complicated by aperiodic natural phenomena such as storms and river fluctuations. Population and community trends appeared consistent with other studies showing similar patterns of dominance of stress-resistant fish populations and related changes in community parameters. In this case, the relatively predictable annual succession of fish associations allowed an appraisal of key forcing functions. Due to the high level of seasonal and annual biological variability in this estuary, there were some problems in the application of linear statistical models to the data base. Although the long-term trend of relative species representation is useful as an index of stress, new techniques are needed to analyze extensive field data so that functions such as trophic interactions are included in the estimation of causal relationships. There are indications that such effects could be related to the impact of organochlorine compounds on estuarine systems.     

Florida red bay (Persea borbonia) leaf extracts deter oviposition of a sympatric generalist herbivore, Papilio glaucus (Lepidoptera: Papilionidae)

Summary. The ability to perceive and respond to phytochemicals that reliably indicate poor suitability of a potential host plant confers a selective advantage to ovipositing female swallowtail butterflies. Papilio glaucus females are generalists that nonetheless do not oviposit on red bay (Persea borbonia: Lauraceae). Red bay is toxic to P. glaucus neonates but is commonly found in habitats alongside their principal host plant, Magnolia virginiana, in central Florida. The hypothesis that deterrent compounds present in the leaves of red bay mediate its rejection by P. glaucus was evaluated in our study. Florida populations of P. glaucus did not oviposit on host leaves sprayed with the methanol extract of red bay foliage, although they accepted solvent-treated and untreated tulip tree leaves in 3 choice bioassays. Additionally, tulip tree leaves sprayed with methanolic extracts of red bay also deterred oviposition by P. glaucus females from Ohio, Kentucky and Pennsylvania, although these populations do not naturally encounter red bay. Clearly, deterrent compounds found within this non-host are the basis of its rejection by populations of P. glaucus and such recognition is fundamental to the species, not just a reflection of local adaptations. Received 2 April 1999; accepted 11 June 1999.     

Etude du cycle annuel des Chaetognathes planctoniques de la rade de Villefranche par la méthode d'analyse des composantes principales

The study of the cycle of chaetognaths during 1967 was carried out using samples collected with a Juday-Bogorov net at 1 station in the entrance of the bay by vertical hauls (75 m-0 m). Among the 13 sorted categories of chaetognaths, the principal component analysis singles out 2 communities (made up from the abundant species) and 3 isolated species. The first 3 components carry 71.1% of the total variance. An attempt to identify components, using partial correlations, shows that the first component is a trophic relation, the second the vertical stability of the water, the third a factor of development of young stages. The correlation between the physical and biological factors and the components account for 45% of the total information.     

Impact of kraft pulp-mill effluents on estuarine and coastal fishes in Apalachee Bay,Florida, USA

A 2-year field study was carried out to determine the impact of kraft pulp-mill effluents on the fish fauna of a shallow-bay system in north Florida (Apalachee Bay, USA). Offshore areas that received kraft-mill effluents (KME) displayed significant increases in color and turbidity and reductions in (benthic) dissolved oxygen compared to a nearby control area. Estuarine and marsh fish assemblages in areas of acute impact were severely reduced in terms of numbers of individuals (N) and species (S). Offshore areas exposed to varying (chronic) levels of KME were characterized by complex interactions that included seasonal variations of impact. A broad offshore area showed reductions in numbers of individuals and species taken per month. However, the cumulative (annual) number of species taken was the same for polluted and unpolluted (control) areas due to a recruitment of relatively rare species in the areas of impact. Such polluted areas showed decreased dominance as well as qualitative differences in species composition compared to control areas. Inshore bay stations that were most severely affected by KME were dominated by the bay anchovy, Anchoa mitchilli. While species richness and species diversity were lower at the highly stressed stations, in other outlying areas of moderate impact (reduced N and S) there were no reductions of such parameters compared to control areas. Thus, species diversity was not an indicator of pollution per se, and was useful only when taken in conjunction with various other parameters. Transition areas (between polluted and unpolluted portions of the bay) showed substantial (although periodic) increases in N, S, and species diversity. Equitability indices were unchanged in polluted portions of the bay. In general, the effects of KME on offshore fish assemblages appeared to be due to a complex combination of habitat alteration, reduced benthic productivity, and individual behavioral reactions. The alterations of fish assemblages were compared to other studies in this area on benthic macrophytes and invertebrates in an effort to assess the usefulness of various indices in studies on the long-term effects of pollution on estuarine and coastal systems. It was found that kraft pulp-mill effluents had a pronounced effect on the benthic standing crop of plants and animals, but that intensive sampling over prolonged periods of time was necessary for an adequate assessment of the problem. Overall, there were some significant changes in the biota such as reduced dominance and productivity in polluted areas that were similar for the various types of organisms sampled.     

Spatial variation of growth and gonadal developments of Maurolicus muelleri in the Norwegian Sea and in a Norwegian fjord

The epibenthic megafauna of the high-Arctic Northeast Greenland shelf was investigated by means of seafloor photography and Agassiz trawl catches. At 54 stations in water depths between 40 and 770 m, sequences of color slides, each depicting about 1 m² of the seafloor, were obtained along photographic transects of about 100 to 600 m length. The photographs were quantitatively analyzed for abundance of epibenthic organisms identified by comparison with specimens collected from trawl catches. Megabenthic biomass was estimated by multiplying density values with averge body mass figures. For five dominant brittle star species, the population oxygen uptake and, thus, organic carbon mineralization potential were approximated by applying individual respiration rates of average-sized specimens to density figures. Multivariate analyses of the megabenthic species distribution revealed a distinct depth zonation. Shallow shelf banks (<150 m), characterized by coarse sediments, many stones and boulders as well as negative bottom water temperatures, housed a rich epifauna (30 to 340 ind m^–2, 1.8 to 10.5 g AFDW m^–2), strongly dominated (80 to 98% by numbers) by the brittle stars Ophiocten sericeum and Ophiura robusta. The oxygen uptake by brittle stars ranged from 0.4 to 95 mol O₂ m^–2 h^–1 (i.e., assuming a respiratory quotient of 0.8, an organic carbon mineralization of 0.1 to 21.9 mg C m^–2 d^–1). At the bank flanks sloping to the shelf troughs (100 to 580 m), finer sediments prevailed, stones were rare, and bottom water temperatures were positive due to the inflow of Atlantic water. Compared to bank sites, total epibenthic abundances as well as carbon mineralization by brittle stars were roughly ten times and total biomass about four times smaller. In deep shelf depressions as well as at the continental slope (200 to 770 m), stones were completely lacking, and sediments very fine. Epibenthic standing stock and carbon mineralization were one to two orders of magnitude lower than on the banks. The estimation of brittle star oxygen uptake indicates that a considerable portion of the organic carbon produced in the polynya and partitioned to the benthos may be remineralized by epibenthic bank assemblages.     

Animal-sediment relations and community analysis of a Florida estuary

Five species assemblages of the intertidal infauna of Old Tampa Bay, Florida, USA are identified. Two assemblages are judged to constitute distinct communities, while a third is shown to be an interdigitation of the two communities. Dominance by on species is the prevalent pattern within the assemblages. Numbers of deposit feeders are found to be inversely correlated to that of filter feeders, and both trophic types are found to be correlated to the sediment parameters of median grain size, sorting and skewness. Three transects with three stations each were established along the south side of Courtney Campbell Causeway in Tampa Bay, Florida. A faunal sample (0.4 m²), a sediment sample, and a water sample were taken at each station in September, December, and March of 1968/1969. Sediment samples were wet-seived. Animal samples were reduced to numbers of organisms and biomass per species. Trellis diagrams and correlation tests were generated. Support is shown for the trophic group-amensalims hypothesis, however, the silt-clay fraction is apparently of lesser importance to deposit feeders in Florida sediments than in Buzzards Bay sediments. An attempt is made to relate an analysis of the optimal grain size for filter feeders to the trophic group-amensalism hypothesis. A view of communities as abstractions from continua is more realistic than communities as discrete units.     

Population-related toxicity responses to two butyltin compounds by zoeae of the mud crab Rhithropanopeus harrisii

We exposed zoeae of the mud crab Rhithropanopeus harrisii to either bis(tri-n-butyltin) oxide (TBT) or di-n-butyltin dichloride (DBT). Experiments were repeated with zoeae from females collected from the Petaluma River, California in June–August 1983 and 1984 or from Sykes Creek, Florida (USA) in February 1985. Using probit analysis, we calculated LC₅₀ values for exposure lasting the duration of zoeal development. Tributyltin was 54 to 65 times more toxic than dibutyltin, the lower value characterizing the response of Florida zoeae. Increases in duration of zoeal development and reduction of dry weights of megalops, both sublethal responses, were dose-dependent for the two populations. However, zoeae from Florida consistently had shorter duration of zoeal development and higher megalopal weights at metamorphosis, indicating less sensitivity to an identical exposure to either organotin compound. The results of these experiments show that dibutyltin, a putative degradation product of tributyltin, is less toxic than the parent compound. In addition, early life-history stages of two populations may have significantly different responses to xenobiotic stress which, in the case of brachyuran larvae, is evident in a differential reduction of survival and growth and an increase in duration of zoeal development.     

Sclerochronological records of temperature and growth from shells of Mercenaria mercenaria from Narragansett Bay,Rhode Island

Annual internal growth increments in shells of hard clams (Mercenaria mercenaria) provide an accurate record of both growth history and some types of environmental change. These increments were used to determine age and growth rate of hard clams collected in 1984–1985 from ten sites in Narragansett Bay, Rhode Island, USA, and to assess geographic variation in growth within the bay. The regional comparisons were facilitated by modeling the clam growth using the von Bertalanffy equation and the parameter of Gallucci and Quinn. The optimum region for hard clam growth was near the head of the bay, with areas further north (Providence River) and south (lower bay) not as productive. The relationship between size and age was similar to that reported for hard clams from northern New Jersey. Using dendrochronological techniques, variations in growth were analyzed on a temporal (year-to-year) basis. The comparative longevity of the hard clams (individuals with 40 annual bands were encountered) demonstrated that sclerochronologies of several decades were possible. A 26 yr growth record based upon 100 individuals was established, covering the years 1959–1984. Significant temporal variations occurred in bivalve growth, and a broad trend of increasing growth indices over the last two decades of the record was noted. The yearly standardized growth index values were highly and positively correlated with mean annual water temperatures in Narragansett Bay for the same time interval. The incremental shell records of these bivalves provide a quantitative indication of marine climatic (temperature) variability and growth which can be used in hindcasting the effects of natural or anthropogenic environmental perturbations.     

Sponge-specific bacterial symbionts in the Caribbean sponge, Chondrilla nucula (Demospongiae, Chondrosida)

Marine sponges harbor dense and highly diverse bacterial communities, and some percentage of the microflora appears to be specialized for the sponge habitat. Bacterial diversity was examined in Chondrilla nucula Schmidt to test the hypothesis that some subset of sponge symbiont communities is highly similar regardless of the species of host or habitat requirements of the host. C. nucula was collected from a mangrove channel on Lower Matcumbe Key in the Florida Keys (25°53′N; 80°42′W) in August 1999. Domain-specific universal bacterial primers were used to amplify the 16S rDNA gene from genomic DNA that had been extracted from sponges and the surrounding water. An RFLP technique was used to assess diversity of sponge-associated and environmental bacterial communities. The clone library from C. nucula contained 21 operational taxonomic units (OTUs). None of the 53 OTUs from adjacent water samples were found in the C. nucula library indicating that a distinct community was present in the sponge. Sequence analysis indicated that C. nucula harbors a microbial community as diverse as the microbes from other sponges in different habitats around the world. Phylogenetic analysis placed several C. nucula clones in clades dominated by bacteria that appear to be sponge specialists (e.g., Acidobacteria, Bacteroidetes, and Cyanobacteria). Proportional representation of major bacterial taxonomic groups represented in symbiont communities was compared as a function of geographic location of sponge hosts. This study supports the hypothesis that sponges from different oceans existing in dissimilar habitats harbor closely related bacteria that are distinct from other bacterial lineages and appear specialized for residing within sponges.     

Distribution and structure of heterotrophic protist communities in the northeast equatorial Pacific Ocean

The distribution and structure of heterotrophic protist communities and size-fractionated chlorophyll a were studied during the Korea Deep Ocean Study 98 (KODOS 98) research expedition (July 1998) in the northeast equatorial Pacific Ocean (5–11°N). Areas of convergence and divergence formed at the boundaries of the South Equatorial Current (SEC), North Equatorial Current (NEC), and North Equatorial Counter Current (NECC) during the expedition. Water column physicochemical characteristics significantly influenced the size structure of heterotrophic protist communities. Intense vertical mixing and high nutrient and chlorophyll a concentrations characterized SEC and NECC areas, which were affected by converging and diverging water masses, respectively. Nanophytoplankton dominated in SEC and NECC areas; both areas also had relatively high heterotrophic protist biomasses (average 743 µg C m^–2). NEC areas were characterized by a stratified vertical structure, low nutrient and chlorophyll a concentrations, and picophytoplankton dominance. The heterotrophic protist biomass in NEC areas averaged 414 µg C m^–2; nanoprotists (<20 µm) dominated the community. The nanoprotist biomass comprised 49–54% of the total heterotrophic protist biomass in SEC/NECC areas and 67–72% in NEC areas. The biomass of heterotrophic protists was higher in SEC/NECC areas than in NEC areas, but the relative importance of nanoprotists was greater in NEC areas than in SEC/NECC areas. Heterotrophic dinoflagellates were dominant components of the <20 µm and >20 µm size classes in both water columns. The biomass of heterotrophic protists significantly correlated with the net-, nano-, and picophytoplankton biomass in SEC/NECC areas and with the nano- and picophytoplankton biomass in NEC areas. Heterotrophic protists and phytoplankton also showed strong positive correlation in the study area. The size structure of the phytoplankton biomass coincided with that of heterotrophic protists; the heterotrophic protist biomass positively correlated with the protists prey source. These relationships suggest that the community structure of heterotrophic protists and the microbial food web depended on size classes within the phytoplankton biomass. Microzooplankton grazing and phytoplankton growth rates were higher in SEC/NECC areas than in NEC areas. In contrast, the potential primary production grazed by microzooplankton was relatively high in NEC areas (127.3%) compared with SEC/NECC areas (94.6%). Our results indicate that the relative importance and size structure of heterotrophic protists might vary according to two distinct water column structures.Communicated by T. Ikeda, Hakodate     

Population structure of loggerhead turtle (Carettacaretta) nesting colonies in the Atlantic and Mediterranean as inferred from mitochondrial DNA control region sequences

Mitochondrial (mt) DNA control region sequences were analyzed for 249 Atlantic and Mediterranean loggerhead turtles (Carettacaretta Linnaeus, 1758) to elucidate nesting population structure and phylogeographic patterns. Ten haplotypes were resolved among individuals sampled between 1987 and 1993, from ten major loggerhead nesting areas in the region. Two distinct phylogenetic lineages were distinguished, separated by an average of 5.1% sequence divergence. Haplotype frequency comparisons between pairs of populations showed significant differentiation between most regional nesting aggregates and revealed six demographically independent groups, corresponding to nesting beaches from: (1) North Carolina, South Carolina, Georgia and northeast Florida, USA; (2) southern Florida, USA; (3) northwest Florida, USA; (4) Quintana Roo, Mexico; (5) Bahia, Brazil; and (6) Peloponnesus Island, Greece. The distribution of mtDNA haplotypes is consistent with a natal homing scenario, in which nesting colonies separated by a few hundred kilometers represent isolated reproductive aggregates. However, a strong exception to this pattern was observed in the first group defined by mtDNA data (North Carolina to northeast Florida), which included samples from four nesting locations spread across thousands of kilometers of coastline. These locations were characterized by a single haplotype in 104 out of 105 samples, providing inadequate resolution of population divisions. In view of the subdivisions observed elsewhere, we attribute the lack of differentiation between North Carolina and northeast Florida to recent colonization of these warm temperate coastlines (after the Wisconsin glaciation) not to ongoing gene flow among spatially distinct nesting locations. The relationships among observed haplotypes suggest a biogeographic scenario defined by climate, natal homing, and rare dispersal events. The redefined relationships among nesting aggregations in the western Atlantic region (southeastern USA and adjacent Mexico) prompt a reconsideration of management strategies for nesting populations and corresponding habitats in this region. Received: 28 October 1996 / Accepted: 24 October 1997     

Heavy metals contamination in mudflat and mangrove sediments (Mumbai,India)

The focus of this study, carried out on mudflat and mangrove sediments of Ulhas Estuary and Thane Creek in Mumbai, India, documents how sediment analysis in different ecosystems can help in understanding metal behaviour and pollution status of the region. Based on the the geoaccumulation index (I _geo ), the study shows that the estuarine and creek regions, being recipients of industrial and domestic wastes, display moderate pollution. Ulhas Estuary with higher clay and organic matter contents, exhibits higher amounts of metals than Thane Creek. Furthermore, using correlation and cluster analyses, the creek projects stable subenvironments with similar types of metal associations, with Fe and total organic carbon as the dominant metal carriers. By contrast, in the estuarine subenvironments, the metal associations do not reveal any distinct trend, which may be attributed to the disturbance caused by dredging activities routinely carried out in the region. Factor analysis carried out on I _geo data in both regions further helped in identifying polluted metal groups.     

Metabolism and model of an estuarine bay ecosystem affected by a coastal power plant

The effects of a coastal power plant on an outer estuarine bay ecosystem on the west coast of Florida were evaluated with measurements and an ecological model. Field measurements of community metabolism and biomass were taken from the thermally affected bay and from similar control bays. Model simulations were used to help understand these observations in terms of ecosystem structure and functioning.In the outer discharge bay the direct impact of the thermal plume was diluted and spread overlarge areas. The ecosystem developed structure and functions with lower biomass than in the control bays but with slightly faster rates of organic turnover. The productive turnover time of producer biomass during the summer was about 5 days in the discharge bay and about 6 days in the control bays. Power plant influence on total community metabolism was small with less than 10% difference in annual averages between the discharge and control bays (5.22 and 5.58 g O₂/m²/day). The selection for faster metabolic turnover rates in the discharge by was evidenced by a dominance of plankton metabolism over benthic metabolism. The annual average gross planktonic production was around 3 g O₂/m²/day in the discharge bay and around 2 g/m²/day in the control bays.In the model, temperature served as a stimulant to both productivity and respiration. When the isolated effects of increased temperature were simulated the model responded with lower producer biomass and faster rates of organic turnover, as was found in field measurements. These simulations also showed increased nutrient recycling and indicated patterns of temperature-induced migrations. Since power plant operation affected water exchange in the bays, several levels of total water exchange were simulated. These simulations indicated the importance of water exchange as a stabilizing factor, especially for sensitive compartments with rapid turnover rates (i.e. plankton and phosphorus stocks). Simulations of the effects of future power plant units on the bay ecosystem showed no large changes in total metabolism but indicated larger effects of plankton entrainment mortality and temperature-induced migrations of larger organisms.     

Spatial and temporal variability of phytoplankton biomass and taxonomic composition around Elephant Island,Antarctica, during the summers of 1990–1993

During the austral summers of 1990–1993, phytoplankton studies were conducted in the vicinity of Elephant Island, Antarctica, to investigate the spatial and temporal variability of phytoplankton biomass and taxonomic composition. There was much intraannual variability, with a trend for increasing biomass from January–February (Leg I) to February–March (Leg II), except in the 1993 studies. There was also a change in phytoplankton composition between the two legs. During 1990–1991 the increase was due mostly to diatoms, during 1992 mostly to an increase of flagellates; during 1993 there was a decrease in total biomass between the two legs, with diatoms decreasing, so that dinoflagellates, which increased slightly in numbers, dominated the biomass during the second leg. There was also much inter-annual variability, with the summers of 1990–1991 having greater biomass and higher proportions of microplanktonic diatoms than that of 1992–1993, which had a higher proportion of flagellates. Cluster analyses revealed the presence of four major phytoplankton assemblages, with varying geographical distributions. The northwestern portion of the grid (Drake Passage waters), was characterized by nanoplanktonic diatoms during 1990–1991 and 1993, but by nanoplanktonic flagellates during 1992. The central area (Drake-Bransfield confluence) was characterized by microplanktonic diatoms in 1990–1991, but by cryptophytes or flagellates in 1992–1993. The south and southeastern portion of the area (Bransfield Strait waters) was characterized mainly by either cryptophytes or other flagellates during all 4 yr. The spatial and temporal variability of phytoplankton could not be ascribed specifically to the geographical extent of the different water masses found in the study area, but appears to be due to changing growth conditions in the upper water column as influenced by physical mixing and meteorological conditions, as well as to effects of differential grazing.     

Nitrogen supply,tissue composition and frond growth rates for Macrocystis pyrifera off the coast of southern California

Seasonal changes in ambient NO ₃ ^– and NH ₄ ⁺ , tissue composition (N, C, and C/N ratio), and frond growth rates for Macrocystis pyrifera (L.) Agardh were examined. Ambient NO ₃ ^– showed distinct seasonal variations. Frond growth rates were variable, but showed no clear correlation to ambient NO ₃ ^– . The average N content of plant tissue did, however, show the same seasonal variations as ambient NO ₃ ^– . The longitudinal distribution of total tissue N and various components of tissue N along fronds were also analyzed. Several distinct patterns were found: high levels of protein N at growing tips and elevated levels of soluble N in lower parts of the frond. Free amino acids accounted for a major portion of the soluble N, but neither NO ₃ ^– nor NH ₄ ⁺ accumulated in the plant tissue. The longitudinal distribution of N along the fronds is compared to reported variations in C metabolism, and it is concluded that C and N sourcesink relations do not always coincide and bidirectional translocation may occur.