Michael L. Carroll

Organic enrichment of sediments from salmon farming in Norway: environmental factors, management practices, and monitoring techniques

Abstract Environmental impacts of salmon cage aquaculture resulting from deposition of organic-rich particulate matter to the sea bottom have been thought to be a function of the local environmental conditions and management practices. However, testing of these suppositions have been limited by (1) widely varying monitoring methods employed, and (2) lack of data comparability resulting from the absence of standardized national monitoring schemes. In order to determine the sensitivity of different monitoring methods in detecting benthic environmental effects, a comparative analysis was undertaken of four methods commonly employed in Norway that vary in cost and expertise required: (1) visual diver surveys, (2) faunal analysis, (3) sediment chemistry, and (4) Sediment Profile Imagery (SPI). Results indicate that all methods agreed in the common “impact zone” under and immediately next to the cages. However, each of the methods differed in their sensitivity in detecting more subtle effects at greater distances from the cages. Data from 168 environmental survey samples located at various distances from working Norwegian salmon cage farms collected using similar methodology between 1996 and 1998 were analyzed to determine the relationship between environmental variables, management regimes, and levels of environmental impact. Total organic carbon (TOC) levels in sediments were significantly higher immediately adjacent to cages compared to reference sites, and approximately 32% of the samples under the cages showed significant degradation. At intermediate distances (50–100 m), influences from fish farming are not clearly detected by TOC analysis. Further, while neither depth nor current speed alone are good predictors for environmental management, the results suggest recovery of sites by periodic abandonment (or fallowing) is one of the best management tools for sustainable salmon farming in cold-water environments.

Towards a pan-Arctic inventory of the species diversity of the macro- and megabenthic fauna of the Arctic shelf seas

Although knowledge of Arctic seas has increased tremendously in the past decade, benthic diversity was investigated at regional scales only, and no attempt had been made to examine it across the entire Arctic. We present a first pan-Arctic account of the species diversity of the macro- and megabenthic fauna of the Arctic marginal shelf seas. It is based on an analysis of 25 published and unpublished species-level data sets, together encompassing 14 of the 19 marine Arctic shelf ecoregions and comprising a total of 2,636 species, including 847 Arthropoda, 668 Annelida, 392 Mollusca, 228 Echinodermata, and 501 species of other phyla. For the four major phyla, we also analyze the differences in faunal composition and diversity among the ecoregions. Furthermore, we compute gross estimates of the expected species numbers of these phyla on a regional scale. Extrapolated to the entire fauna and study area, we arrive at the conservative estimate that 3,900–4,700 macro- and megabenthic species can be expected to occur on the Arctic shelves. These numbers are smaller than analogous estimates for the Antarctic shelf but the difference is on the order of about two and thus less pronounced than previously assumed. On a global scale, the Arctic shelves are characterized by intermediate macro- and megabenthic species numbers. Our preliminary pan-Arctic inventory provides an urgently needed assessment of current diversity patterns that can be used by future investigations for evaluating the effects of climate change and anthropogenic activities in the Arctic.

Bivalves as indicators of environmental variation and potential anthropogenic impacts in the southern Barents Sea.

Identifying patterns and drivers of natural variability in populations is necessary to gauge potential effects of climatic change and the expected increases in commercial activities in the Arctic on communities and ecosystems. We analyzed growth rates and shell geochemistry of the circumpolar Greenland smooth cockle, Serripes groenlandicus, from the southern Barents Sea over almost 70 years between 1882 and 1968. The datasets were calibrated via annually-deposited growth lines, and growth, stable isotope (delta(18)O, delta(13)C), and trace elemental (Mg, Sr, Ba, Mn) patterns were linked to environmental variations on weekly to decadal scales. Standardized growth indices revealed an oscillatory growth pattern with a multi-year periodicity, which was inversely related to the North Atlantic Oscillation Index (NAO), and positively related to local river discharge. Up to 60% of the annual variability in Ba/Ca could be explained by variations in river discharge at the site closest to the rivers, but the relationship disappeared at a more distant location. Patterns of delta(18)O, delta(13)C, and Sr/Ca together provide evidence that bivalve growth ceases at elevated temperatures during the fall and recommences at the coldest temperatures in the early spring, with the implication that food, rather than temperature, is the primary driver of bivalve growth. The multi-proxy approach of combining the annually integrated information from the growth results and higher resolution geochemical results yielded a robust interpretation of biophysical coupling in the region over temporal and spatial scales. We thus demonstrate that sclerochronological proxies can be useful retrospective analytical tools for establishing a baseline of ecosystem variability in assessing potential combined impacts of climatic change and increasing commercial activities on Arctic communities.

Sympagic-pelagic-benthic coupling in Arctic and Atlantic waters around Svalbard revealed by stable isotopic and fatty acid tracers

Abstract Stable isotope and fatty acid trophic markers (FATMs) were used to assess carbon flow and trophic structures of sympagic, pelagic and benthic communities in high-Arctic Svalbard. Three regions were sampled: Northwest Svalbard – dominated by Atlantic water (AtW) and limited seasonal sea ice; Northern Svalbard – dominated by AtW and perennial sea ice; and Northeast Svalbard – dominated by Arctic water (ArW) and extensive seasonal sea ice. Three to four trophic levels (TL) were found in the three habitats, with a dominance of omnivores (TL = 2.4–2.7). Ice fauna relied on phytoplankton and ice algae, zooplankton primarily on phytoplankton, while benthos relied on ice algae/refractory material. Ice fauna (mean 39%; range 17–62%) and benthos (mean 25%; range 11–65%) had high proportions of diatom-FATMs, while zooplankton had equally high diatom- and Phaeocystis/dinoflagellate-FATMs (mean 11% and 15%, respectively). Calanus-FATMs were prominent in carnivorous ice fauna (up to 28%) and zooplankton (up to 38%), but also in benthic invertebrates (up to 41%). Ice fauna biomass was low. Biomass of zooplankton and benthic infauna were variable, but positively correlated to each other (r 2=0.89; p<0.01) and sedimentary pigment concentrations (r 2>0.40; p<0.05). The coinciding peak biomasses of zooplankton and benthos in Northeast Svalbard can be explained by allochthonous organic matter of ice algal origin and highly specialized Arctic zooplankton utilizing both ice algae and phytoplankton carbon sources.

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.

Barnacle population dynamics and recruitment regulation in southcentral Alaska

Abstract The role of recruitment in regulating population dynamics of three intertidal barnacle species was investigated by examining sources and scales of variation in recruitment and determining the nature of the relationship between recruitment density and resultant adult population size. The study was conducted in Kachemak Bay, Alaska (USA) from 1991 to 1993 to determine the extent to which recruitment influences population dynamics of species near their geographic limit. Year-to-year variation in recruitment was highly significant, with average maximum recruitment between 1991 and 1993 ranging from 0.85 to 8.71 cm−2. Recruitment densities on individual test surfaces ranged from 0–71 cm−2. Inter-site variation in recruitment was significant and the ranking of sites by recruitment density was consistent between years. Recruitment of Semibalanus cariosus (Pallas) in the low intertidal was 7–162 times greater than of S. balanoides (L.) and Balanus glandula Darwin in the upper intertidal. Predation significantly affected the survival of recruits during 1991, a year of comparatively low overall recruitment. Also, 1991 was a year during which there was a linear relationship between initial recruitment and subsequent adult density for all species. In 1992 and 1993, years when initial larval settlement of S. cariosus was much greater, recruits commonly exceeded adult saturation density in the lower intertidal, resulting in intense intra-specific competition for space and leading to decoupling of recruit and adult density. Despite high recruitment in 1992 and 1993, recruit survival to adulthood of all species was actually greatest in the low recruitment year (1991), suggesting that even comparatively low recruitment provides enough new individuals to maintain populations. Consequently, at sites near their geographic limit, recruitment is not the primary process limiting S. cariosus populations in the low intertidal, although its influence was evident for high intertidal S. balanoides and B. glandula populations.

Growth line deposition and variability in growth of two circumpolar bivalves (Serripes groenlandicus, and Clinocardium ciliatum)

Growth patterns of two common circumpolar bivalves, the Greenland cockle (Serripes groenlandicus), and the hairy cockle (Clinocardium ciliatum) have been used in previous studies to reconstruct environmental conditions in the arctic. To date, there has been no direct determination that growth lines in either species are deposited periodically, and there has been no examination of factors affecting growth. We placed calcein-marked individuals of both species on oceanographic moorings in two fjords (Rijpfjord and Kongsfjord) in the Svalbard archipelago for one and two (Kongsfjord only) years. Growth patterns were compared with concurrent in situ temperature and fluorescence data in order to assess environmental controls on growth. Dark growth lines are evident on the outer shell surface and internally in shell cross section in both S. groenlandicus and C. ciliatum, and both species deposited only one line per year, unequivocally confirming that internal lines are deposited annually. Growth line deposition in both species began in late summer to early fall, before the seasonal decline in temperature. There was no difference in growth of S. groenlandicus between the two fjords despite differences in water temperature (3°C), fluorescence (nearly threefold) and the onset and duration of the winter season. C. ciliatum, however, grew approximately 2.8 times faster in the warmer, more food-rich Kongsfjord than in Rijpfjord. Subannual lines were counted in two individuals of each species from each fjord, but deposition of these lines was not clearly related to number of growing days estimated by temperature and fluorescence.

Bivalve shell horizons in seafloor pockmarks of the last glacial‐interglacial transition: a thousand years of methane emissions in the Arctic Ocean

We studied discrete bivalve shell horizons in two gravity cores from seafloor pockmarks on the Vestnesa Ridge (∼1200 m water depth) and western Svalbard (79°00′ N, 06°55′ W) to provide insight into the temporal and spatial dynamics of seabed methane seeps. The shell beds, dominated by two genera of the family Vesicomyidae: Phreagena s.l. and Isorropodon sp., were 20–30 cm thick and centered at 250–400 cm deep in the cores. The carbon isotope composition of inorganic (δ13C from −13.02‰ to +2.36‰) and organic (δ13C from −29.28‰ to −21.33‰) shell material and a two-end member mixing model indicate that these taxa derived between 8% and 43% of their nutrition from chemosynthetic bacteria. In addition, negative δ13C values for planktonic foraminifera (−6.7‰ to −3.1‰), concretions identified as methane-derived authigenic carbonates, and pyrite-encrusted fossil worm tubes at the shell horizons indicate a sustained paleo-methane seep environment. Combining sedimentation rates with 14C ages for bivalve material from the shell horizons, we estimate the horizons persisted for about 1000 years between approximately 17,707 and 16,680 years B.P. (corrected). The seepage event over a 1000 year time interval was most likely associated with regional stress-related faulting and the subsequent release of overpressurized fluids.

Predator foraging behavior: effect of a novel prey species on prey selection by a marine intertidal gastropod

Abstract Diet breadth in predators has often been linked to maximization of energy intake in foraging models. The intertidal predatory gastropod Nucella (Thais) lamellosa (Gmelin) was presented with natural and novel prey species to examine the components of prey choice. In Washington (USA), Nucella consumes the high-quality barnacle Balanus glandula Darwin and low-quality Semibalanus cariosus (Pallas). In Alaska and British Columbia, the barnacle Semibalanus balanoides (L.) is also available as prey. S. balanoides was presented to Nucella from the San Juan Islands, Washington, in the laboratory to measure prey profitability and handling costs, and in field experiments to measure prey choice. The novel S. balanoides represents a high-quality prey, with profitability and handling costs equivalent to the highest-quality natural prey B. glandula . In the field, Nucella immediately added S. balanoides to its diet. This addition appears to be a result of active prey choice. This modification in foraging strategy is a function of the ability of Nucella to accurately assess changes to its food resource, and is consistent with the predictions of foraging models of predators which maximize energy intake.

The Application of Long-Lived Bivalve Sclerochronology in Environmental Baseline Monitoring

Assessments of the impact of construction, operation and removal of large infrastructures and other human activities on the marine environment are limited because they do not fully quantify the background baseline conditions and relevant scales of natural variability. Baselines as defined in Environmental Impact Assessments typically reflect the status of the environment and its variability drawn from published literature and augmented with some short term site specific characterization. Consequently, it can be difficult to determine whether a change in the environment subsequent to industrial activity is within or outside the range of natural background variability representative of an area over decades or centuries. An innovative approach that shows some promise in overcoming the limitations of traditional baseline monitoring methodology involves the analysis of shell material (sclerochronology) from molluscs living upon or within the seabed in potentially affected areas. Bivalves especially can be effective biomonitors of their environment over a wide range of spatial and temporal scales. A rapidly expanding body of research has established that numerous characteristics of the environment can be reflected in morphological and geochemical properties of the carbonate shell material in bivalve shells, as well as in functional responses such as growth rates. In addition, the annual banding pattern in shells can provide an absolute chronometer of environmental variability and/or industrial effects. Further, some species of very long-lived bivalves can be crossdated back in time, like trees, by comparing the annual banding patterns in their shells. It is therefore feasible to develop extended timeseries of certain marine environmental variables that can provide important insights into long temporal scales of baseline variability. We review recent innovative work on the shell structure, morphology and geochemistry of bivalves and conclude that they have substantial potential for use as monitors of environmental variability and the effects of pollutants and disturbance.