Physiological performance measures and tolerance limits of estuarine indicator species in South Florida

Current water management practices in South Florida have negatively impacted many species inhabiting Florida Bay. Variable and high salinity has been identified as a key stressor in these estuaries. The comprehensive Everglades Restoration Plan (CERP) includes water redistribution projects that will restore natural freshwater flows to northeastern Florida Bay. My studies focused on the following central theme and hypotheses: Biological performance measures (i.e., growth, reproduction, survival), behavior (i.e., habitat preference and locomotor behavior) and diversity of estuarine fish will be controlled by changes in salinity and water quality that will occur as a result of the restoration of freshwater flow to the bay. A series of acute and subchronic physiological toxicity studies were conducted to determine the effects of salinity changes on the life stages (embryo/larval, juvenile, adult) and fecundity of four native estuarine fish (Cyprinodon variegatus, Floridichthys carpio, Poecilia latipinna, and Gambusia holbrooki). Fishe were exposed to a range of salinity concentrations (freshwater to hypersaline) based on salinity profiles in the study areas. Growth (length, weight) and survival were measured. Salinity trials included both rapid and gradual change events. Results show negative effects of acute, abrupt salinity changes on fish survival, development and reproductive success as a result of salinity stress. Other studies targeted reproduction and critical embryo-larval/neonate development as key areas for detecting long-term population effects of salinity change in Florida Bay. Adults of C. variegatus and P. latipinna were also examined for behavioral responses to pulsed salinity changes. These responses include changes in swimming performance, locomotor behavior and zone preference. Finally, an ecological risk assessment was conducted for adverse salinity conditions in northeastern Florida Bay. Using the U.S. EPA's framework, the risk to estuarine fish species diversity was assessed against regional salinity profiles from a 17-year database. Based on the risk assessment, target salinity profiles for these areas are recommended for managers.

Productivity- and ocean circulation changes in the sub-Antarctic Atlantic during the last deglaciation and Marine Isotope Stage 3

Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean-atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air-sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and 14C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes.

Compilation of growth rate data for marine pelagic organisms

The metabolic rate of organisms may either be viewed as a basic property from which other vital rates and many ecological patterns emerge and that follows a universal allometric mass scaling law; or it may be considered a property of the organism that emerges as a result of the organism's adaptation to the environment, with consequently less universal mass scaling properties. Data on body mass, maximum ingestion and clearance rates, respiration rates and maximum growth rates of animals living in the ocean epipelagic were compiled from the literature, mainly from original papers but also from previous compilations by other authors. Data were read from tables or digitized from graphs. Only measurements made on individuals of know size, or groups of individuals of similar and known size were included. We show that clearance and respiration rates have life-form-dependent allometries that have similar scaling but different elevations, such that the mass-specific rates converge on a rather narrow size-independent range. In contrast, ingestion and growth rates follow a near-universal taxa-independent ~3/4 mass scaling power law. We argue that the declining mass-specific clearance rates with size within taxa is related to the inherent decrease in feeding efficiency of any particular feeding mode. The transitions between feeding mode and simultaneous transitions in clearance and respiration rates may then represent adaptations to the food environment and be the result of the optimization of tradeoffs that allow sufficient feeding and growth rates to balance mortality.

Geochemistry, chlorin concentrations and diatom abundance in sediments of lake Rotsee, Switzerland

The effects of eutrophication on short term changes in the microbial community were investigated using high resolution lipid biomarker and trace metal data for sediments from the eutrophic Lake Rotsee (Switzerland). The lake has been strongly influenced by sewage input since the 1850s and is an ideal site for studying an anthropogenically altered ecosystem. Historical remediation measures have had direct implications for productivity and microbial biota, leading to community composition changes and abundance shifts. The higher sewage and nutrient input resulted in a productivity increase, which led predominantly to a radiation in diatoms, primary producers and methanogens between about 1918 and 1921, but also affected all microorganism groups and macrophytes between about 1958 and 1972. Bacterial biomass increased in 1933, which may have been related to the construction of a mechanical sewage treatment plant. Biomarkers also allowed tracing of fossil organic matter/biodegraded oil contamination in the lake. Stephanodiscus parvus, Cyclotella radiosa and Asterionella formosa were the dominant sources of specific diatom biomarkers. Since the 1850s, the cell density of methanogenic Archaea (Methanosaeta spp.) ranged within ca. 0.5-1.8 x 10**9 cells/g dry sediment and the average lipid content of Rotsee Archaea was ca. 2.2 fg iGDGTs/cell. An altered BIT index (BITCH), indicating changes in terrestrial organic matter supply to the lake, is proposed.

Benthic foraminifera of the Red Sea

The distribution of living (Rose Bengal-stained), dead and fossil benthic foraminifera was investigated in six short cores (multicores, 30-32 cm total length) recovered from the central Red Sea. The ecological preferences as well as the relationship between the live and dead/fossil assemblages (preserved down-core) were examined. The sites, located along a W-E profile and between the depth of 366 and 1782 m, extend from the center of the oxygen minimum zone (OMZ, ~200-650 m), through its margin at ~600 m, and down to the well-aerated deep-water environment. Live (Rose-Bengal stained) and coexisting dead foraminifera were studied in the upper 5 cm of each of the sites, and the fossil record was studied down to ~32 cm. Q-mode Principal Component Analysis was used and four distinct foraminiferal fossil assemblages were determined. These assemblages follow different water mass properties. In the center of the OMZ, where the organic carbon content is highest and the oxygen concentration is lowest (<=0.5 ml O2/l), the Bolivina persiensis-Bulimina marginata-Discorbinella rhodiensis assemblage dominates. The slightly more aerated and lower organic-carbon-content seafloor, at the margin of the OMZ, is characterized by the Neouvigerina porrecta-Gyroidinoides cf. G. soldanii assemblage. The transitional environment, between 900-1200 m, with its well-aerated and oligotrophic seafloor, is dominated by the Neouvigerina ampullacea-Cibicides mabahethi assemblage. The deeper water (>1500 m), characterized by the most oxygenated and oligotrophic seafloor conditions, is associated with the Astrononion sp. A-Hanzawaia sp. A assemblage. Throughout the Red Sea extremely high values of temperature and salinity are constant below ~200 m depth, but the flux of organic matter to the sea floor varies considerably with bathymetry and appears to be the main controlling factor governing the distribution pattern of the benthic foraminifera. Comparison between live and the dead/fossil assemblages reveals a large difference between the two. Processes that may control this difference include species-specific high turnover rates, and preferential predation and loss of fragile taxa (either by chemical or microbial processes). Significant variations in the degree of loss of the organic-cemented agglutinants were observed down core. This group is preserved down to 5-10 cm at the shallow OMZ sites and down to greater depths at well-aerated and oligotrophic sites. The lower rate of disintegration of these forms, in the deeper locations of the Red Sea, may be related to low microbial activity. This results in the preservation of increasing numbers of organic-cemented shells down-core.

Standing stocks and carbon isotopes of live benthic foraminifera from the South Atlantic

Live (Rose Bengal stained) and dead benthic foraminifera of surface and subsurface sediments from 25 stations in the eastern South Atlantic Ocean and the Atlantic sector of the Southern Ocean were analyzed to decipher a potential influence of seasonally and spatially varying high primary productivity on the stable carbon isotopic composition of foraminiferal tests. Therefore, stations were chosen so that productivity strongly varied, whereas conservative water mass properties changed only little. To define the stable carbon isotopic composition of dissolved inorganic carbon (d13CDIC) in ambient water masses, we compiled new and previously published d13CDIC data in a section running from Antarctica through Agulhas, Cape and Angola Basins, via the Guinea Abyssal Plain to the Equator. We found that intraspecific d13C variability of all species at a single site is constantly low throughout their distribution within the sediments, i.e. species specific and site dependent mean values calculated from all subbottom depths on average only varied by +/-0.09 per mil. This is important because it makes the stable carbon isotopic signal of species independent of the particular microhabitat of each single specimen measured and thus more constant and reliable than has been previously assumed. So-called vital and/or microhabitat effects were further quantified: (1) d13C values of endobenthic Globobulimina affinis, Fursenkoina mexicana, and Bulimina mexicana consistently are by between -1.5 and -1.0 per mil VPDB more depleted than d13C values of preferentially epibenthic Fontbotia wuellerstorfi, Cibicidoides pachyderma, and Lobatula lobatula. (2) In contrast to the Antarctic Polar Front region, at all stations except one on the African continental slope Fontbotia wuellerstorfi records bottom water d13CDIC values without significant offset, whereas L. lobatula and C. pachyderma values deviate from bottom water values by about -0.4 per mil and -0.6 per mil, respectively. This adds to the growing amount of data on contrasting cibicid d13C values which on the one hand support the original 1:1-calibration of F. wuellerstorfi and bottom water d13CDIC, and on the other hand document severe depletions of taxonomically close relatives such as L. lobatula and C. pachyderma. At one station close to Bouvet Island at the western rim of Agulhas Basin, we interpret the offset of -1.5 per mil between bottom water d13CDIC and d13C values of infaunal living Bulimina aculeata in contrast to about -0.6 +/- 0.1 per mil measured at eight stations close-by, as a direct reflection of locally increased organic matter fluxes and sedimentation rates. Alternatively, we speculate that methane locally released from gas vents and related to hydrothermal venting at the mid-ocean ridge might have caused this strong depletion of 13C in the benthic foraminiferal carbon isotopic composition. Along the African continental margin, offsets between deep infaunal Globobulimina affinis and epibenthic Fontbotia wuellerstorfi as well as between shallow infaunal Uvigerina peregrina and F. wuellerstorfi, d13C values tend to increase with generally increasing organic matter decomposition rates. Although clearly more data are needed, these offsets between species might be used for quantification of biogeochemical paleogradients within the sediment and thus paleocarbon flux estimates. Furthermore, our data suggest that in high-productivity areas where sedimentary carbonate contents are lower than 15 weight %, epibenthic and endobenthic foraminiferal d13C values are strongly influenced by 13C enrichment probably due to carbonate-ion undersaturation, whereas above this sedimentary carbonate threshold endobenthic d13C values reflect depleted pore water d13CDIC values.