Lisa M. Clough

Hypoxia-induced metabolic and antioxidant enzymatic activities in the estuarine fish Leiostomus xanthurus

Abstract The Tar-Pamlico River basin in North Carolina is regularly the site of summertime fish kills. One possible cause of fish kills is hypoxia-induced metabolic stress. To examine hypoxia-induced stress at both the organismal and enzymatic levels, we exposed the common estuarine fish Leiostomus xanthurus Lacepede (spot) to various oxygen tensions (10% saturation, 0.8 mg/l; 25%, 2.0 mg/l; 50%, 4.0 mg/l; 100%, 8.0 mg/l). After 12 h of exposure, samples of gill, liver, and muscle tissue were extracted and subsequently analyzed for metabolic (citrate synthase [CS] and lactate dehydrogenase [LDH]) and antioxidant (catalase [CAT] and superoxide dismutase [SOD]) enzyme activity as well as protein content. There was a significant increase in lactate dehydrogenase activity, an indicator of anaerobic metabolism, in the 10% treatment in gill tissue, while there was no significant change in citrate synthase activity, an indicator of aerobic metabolism. Antioxidant enzymes were shown to operate independently of one another, with significant increases in superoxide dismutase activity in gill and muscle tissue under 10% saturation but no significant change in catalase activity across oxygen treatments. In several cases, we also noted that interindividual variation of enzyme activities within oxygen treatments was in excess of the variation in means between treatments. Hypoxia appears to trigger superoxide dismustase activity in spot, but each individuals response seems to be highly variable, perhaps due to prior exposure to hypoxia.

Infaunal density, biomass and bioturbation in the sediments of the Arctic Ocean

Abstract Little is known about the benthic communities of the Arctic Oceans slope and abyssal plains. Here we report on benthic data collected from box cores along a transect from Alaska to the Barents Abyssal Plain during the Arctic Ocean Section of 1994. We determined: (1) density and biomass of the polychaetes, foraminifera and total infauna; (2) concentrations of potential sources of food (pigment concentration and percent organic carbon) in the sediments; (3) surficial particle mixing depths and rates using downcore 210Pb profiles; and (4) surficial porewater irrigation using NaBr as an inert tracer. Metazoan density and biomass vary by almost three orders of magnitude from the shelf to the deep basins (e.g. 47 403 individuals m−2 on the Chukchi Shelf to 95 individuals m−2 in the Barents Abyssal Plain). Water depth is the primary determinant of infaunal density, explaining 39% of the total variability. Potential food concentration varies by almost two orders of magnitude during the late summer season (e.g. the phaeopigment concentration integrated to 10 cm varies from 36.16 mg m−2 on the Chukchi Shelf to 0.94 mg m−2 in the Siberia Abyssal Plain) but is not significantly correlated with density or biomass of the metazoa. Most stations show evidence of particle mixing, with mixing limited to ≤3 cm below the sediment-water interface, and enhanced pore water irrigation occurs at seven of the nine stations examined. Particle mixing depths may be related to metazoan biomass, while enhanced pore water irrigation (beyond what is expected from diffusion alone) appears to be related to total phaeopigment concentration. The data presented here indicate that Arctic benthic ecosystems are quite variable, but all stations sampled contained infauna and most stations had indications of active processing of the sediment by the associated infauna.

Meiobenthos of the central Arctic Ocean with special emphasis on the nematode community structure.

We investigated the abundance of the meiobenthos and the biomass and community structure of the nematodes in the central Arctic Ocean along two separate transects during 1991 and 1994. Meiobenthos abundances ranged from (100 to 600 individuals per 10 cm2, in the same order of magnitude as in other oligotrophic areas of the world’s deep ocean. Nematodes were the numerically dominant meiofaunal group at every station. Nematode biomass ranged from ( 1t o 48lg dry weight per 10 cm2. A combination of water depth and latitude explained 55% of the variability among stations in nematode biomass and 67% of the variability of total abundance, implying that both vertical and advective #uxes are important sources of food to the meiofaunal communities.The dominant nematode genus was Monhystera, a detrivorous/bacterivorous deposit feeder, suggesting that bacteria may play an important role in the food web of the meiobenthos in the Central Arctic. Multivariate analysis of genera abundances revealed di!erences among stations in the Eurasian and Amerasian Basins. During 1994, however, the deep stations in the Eurasian Basin were more similar to the other Amerasian stations, while the single deep station in the Makarov Basin was most similar to the other Eurasian Basin stations. The structure of meiofaunal communities in the central Arctic may provide insight into spatial variability in the Arctic Ocean. ( 2000 Elsevier Science Ltd. All rights reserved.

Rapid consumption of phytoplankton and ice algae by Arctic soft-sediment benthic communities: Evidence using natural and 13 C-labeled food materials

Reduction of sea ice in the Arctic may significantly alter the relative fluxes of phytoplankton and ice algae to the seafloor. To examine the response of Arctic benthic communities to changing food supplies, we incubated sediment cores collected from two sites (Smeerenburg Fjord, northwest Svalbard in May 2003 and Storfjord Trench, Barents Sea in May 2004) with controlled additions of natural phytoplankton and ice algal assemblages, and laboratory-cultured C-labeled ice algae (Nitzschia frigida, in 2004 only). We measured sediment respiration, pigments, lipid biomarkers, and compound-specific C signals over the course of incubations. Both communities responded rapidly to the addition of food materials: regardless of food type, concentrations of organic biomarkers (pigments and fatty acids) decreased to the levels of control cores within seven days. Although we found no evidence for selective ingestion of the different food types by macrofauna, fatty acids were differentially consumed. The enriched polyunsaturated fatty acids of the ice algae were preferentially utilized compared to saturated and monounsaturated fatty acids bound in ice algae. However, the saturated and monounsaturated fatty acids of phytoplankton (with depleted polyunsaturated fatty acids) are utilized more efficiently than those counterparts bound in ice algae. Bacterial activity was stimulated by food addition, indicated by the immediate increase of bacteria-specific fatty acids, but the direct assimilation of C-labeled carbon into bacterial biomass was limited. Our results imply that Arctic benthic communities can meet their energetic requirements by altering strategies to assimilate different components from variable food supplies.

Potential carbon sources for the head-down deposit-feeding polychaete Heteromastus filiformis

In this study we investigated potential carbon sources for the capitellid polychaete, Heteromastusfiliformis. It is a head-down deposit feeder ingesting sediment from at least 15 cm below the sediment-water interface. This orientation appears to minimize the worm’s ability to acquire food and oxygen and maximize its exposure to sulfide. The food sources we examined were metabolically active bacteria, benthic algae, detritus and chemoautotrophic bacteria. Carbon retention efficiencies from metabolically active bacteria, benthic algae and detritus by H. jilifomis were 26%, 8% and 4% respectively. These values are relatively low compared to other deposit feeding species suggesting that H. jiliformis does not possess unique digestive capabilities. Rubisco (Ribulose bisphosphate carboxylase) assays were negative, which indicates an absence of symbiotic chemoautotrophic bacteria in tissue or absorbed carbon. Average 6 13C were -12.83 for worms and -20.70 for 15 cm sediment, which indicates that external gardening of chemoautotrophs is not a major carbon source for H. filiformis. Nevertheless, several experiments showed that this capitellid worm had an unusually high gross heterotrophic COZ uptake. We suggest that H. jiliformis utilizes both dissolved and particulate carbon sources stored within anoxic and sulfidic sediments that are not utilized by other deposit feeding organisms.

Assessment of function in an oligohaline environment: Lessons learned by comparing created and natural habitats

Abstract Assessments of nursery area function were carried out over a 10-year period in a 3-ha oligohaline marsh and creek system (‘Project Area 2’) and four natural ‘control’ creeks (Drinkwater, Jacks, Jacobs, and Tooley) located in the Pamlico River estuary, North Carolina. Habitat function was assessed by comparing (1) growth and survival of fish; (2) long-term monitoring of water quality, sediment organic carbon, and the benthic infaunal community; and (3) measurement of benthic food availability. Growth (weight gain) and survival of the fish Leiostomus xanthurus held within enclosures were similar in both created and natural habitats. Species composition, total fauna density, and species richness of the infaunal community of the Project Area and the natural creeks were comparable within 3 years after construction of the Project Area. However, the sediments of the Project Area lacked the woody detrital cover, high peat content, and predominance of silt and clay characteristic of the natural creek sediments. There was no evidence of significant accretion of total organic carbon in the Project Area during the course of the study. This study has heuristically inspired four recommendations concerning assessment criteria of mitigation success. (1) Direct experimentation is needed to assess habitat function for motile species such as fish. (2) Studies of community structure need to be carried out long enough to permit testing of community stability, especially when working in areas exposed to stochastic abiotic and biotic stressors. (3) Measurements of nutritional content of the sediments should include estimates of overall organic quantity and nutritional quality. (4) Site design or restoration techniques should be included in the experimental design of each mitigation effort. Specifically, the lack of replication in these aspects of the mitigation process limits the inferential potential of the study, constrains the ability to make accurate predictions about the probability of success of future mitigation endeavors, and impedes our understanding of the critical mechanisms governing successful habitat creation, restoration, and enhancement.

Interpreting environmental change in coastal Alaska using traditional and scientific ecological knowledge

Humans who interact directly with local ecosystems possess traditional ecological knowledge that enables them to detect and predict ecosystem changes. Humans who use scientific ecological methods can use species such as mollusks that lay down annual growth rings to detect past environmental variation and use statistical models to make predictions about future change. We used traditional ecological knowledge shared by local Inupiaq, combined with growth histories of two species of mollusks, at different trophic levels, to study local change in the coastal ecosystems of Kotzebue, Alaska, an area in the Arctic without continuous scientific monitoring. For the mollusks, a combination of the Arctic Oscillation and total Arctic ice coverage, and summer air temperature and summer precipitation explained 79-80% of the interannual variability in growth of the suspension feeding Greenland cockle (Serripes groenlandicus) and the predatory whelk (Neptunea hero) respectively, indicating these mollusks seem to be impacted by local and regional environmental parameters, and should be good biomonitors for change in coastal Alaska. The change experts within the Kotzebue community were the elders and the fishers, and they observed changes in species abundance and behaviors, including benthic species, and infer that a fundamental change in the climate has taken place within the area. We conclude combining traditional and scientific ecological knowledge provides greater insight than either approach alone, and offers a powerful way to document change in an area that otherwise lacks widespread quantitative monitoring.

New U.S. icebreaker to advance Arctic Marine Science

The decades-long planning for a U.S. icebreaking vessel dedicated to Arctic marine science reached its goal with the entry into service of the UGCGC Healy, a polar research vessel operated by the U.S. Coast Guard for the U.S. science community. The ship is named for Captain Michael A. Healy, a legendary figure of Alaskan history who served as commanding officer of the U.S. Revenue Cutters Corwin (1884–1885) and Bear (1886–1895). Healy is 128 m long, 25 m wide, displaces 14,900 metric tons, and traverses up to 1.4 m ice at 1.65 m s−1, propelled by two 11.1-MW AC synchronous motors fed from DC diesel electric engines through cycloconverters. Thus, Healy is more powerful and somewhat larger than the German polar research vessel Polarstern or the Canadian icebreaker Louis S. St-Laurent. Healys power system responds quickly to the load changes common in icebreaking. The ship has a conventional icebreaker bow. The hull provides a sea-kindly ride and more stable work conditions in open water than do the U.S. Coast Guard Polar-class icebreakers. The ship is designed to work in any Arctic season.