[Show abstract][Hide abstract] ABSTRACT: Assessments of benthic coastal seawater carbonate chemistry in Antarctica are sparse. The studies that have been performed have generally been short in duration, during the austral spring/summer, under sea ice, or offshore in ice-free water. Herein we present multi-frequency measurements for seawater collected from the shallow coastal benthos on a weekly schedule over one-year (May 2012 – May 2013), daily schedule over three months (March – May 2013), and semidiurnal schedule over five weeks (March – April 2013). A notable pH increase (max pH = 8.62) occurred in the late austral spring/summer (November - December 2012), coinciding with sea ice break out and subsequent increase in primary productivity. We detected semidiurnal variation in seawater pH with a maximum variation of 0.13 pH units during the day and 0.11 pH units during the night. Daily variation in pH is likely related to biological activity, consistent with previous research. We calculated the variation in dissolved inorganic carbon (DIC) over each seawater measurement frequency, focusing on the primary DIC drivers in the Palmer Station region. From this, we estimated net biological activity and found it accounts for the greatest variations in DIC. Our seasonal data suggest that this coastal region tends to act as a carbon dioxide (CO2) source during austral winter months and as a strong sink during the summer. These data characterize present-day seawater carbonate chemistry and the extent to which these measures vary over multiple time scales. This information will inform future experiments designed to evaluate the vulnerability of coastal benthic Antarctic marine organisms to ocean acidification.
Polar Research 07/2015; 34(25582). DOI:10.3402/polar.v34.25582 · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Anthropogenic climate change is causing a global increase in sea-surface temperatures with some of the largest increases expected in the subtropical regions of the Northern Hemisphere. Populations of the sea urchin Lytechinus variegatus in the Gulf of Mexico are especially vulnerable as they are already living near the upper limit of their thermal tolerance and cannot migrate further north to escape rising seawater temperatures. In regular echinoids, neuromuscular-mediated behaviors including the covering and righting responses, and the Aristotle's lantern reflex can be employed as organismal level “indicators” of well-being under these near-future conditions. Individuals of the regular sea urchin L. variegatus were collected in Eagle Harbor, FL and held in the laboratory under a 12L:12D light cycle at both 28 °C (current summer seawater temperature) and 32 °C (predicted near-future summer seawater temperature) for acute (one day) and chronic (ten day) exposures. Covering and righting responses and Aristotle's lantern reflexes were measured. Individuals chronically exposed to 32 °C covered themselves with less material than did individuals acutely exposed to either 28 °C or 32 °C. They also righted less frequently and had lantern reflexes less often than individuals in the other acute or chronic temperature treatments. Moreover, although individuals acutely exposed to 28 °C and 32 °C covered their tests more during daylight periods, individuals chronically exposed to these temperatures did not, indicating that these individuals had an impaired ability to cover in response to increased light levels. Our results suggest that near-future elevated seawater temperatures may impair important neuromuscular-mediated behaviors that could negatively impact population and community dynamics.
Journal of Experimental Marine Biology and Ecology 06/2015; 467. DOI:10.1016/j.jembe.2015.02.019 · 2.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gastropod assemblages associated with eight common macroalgae from the hard-bottom subtidal communities near Palmer Station, western Antarctic Peninsula, were investigated in order to establish a species inventory and determine abundance, distribution, and diversity. Four different sites within the area were sampled. Using SCUBA, selected algae were gently removed from the substrate and enclosed in a fine mesh bag. Shortly thereafter, all epibionts were removed and preserved. Twenty-one different gastropod taxa were identified, two of which not to species level. A total of 3486 individuals were quantified with Skenella umbilicata the numerically dominant, followed by Laevilacunaria antarctica and Eatoniella calignosa. Most individuals (86 %) were
[Show abstract][Hide abstract] ABSTRACT: As mean global temperatures continue to rise, regional seawater temperature measurements have revealed that some geographic areas are warming faster than others. One region that is experiencing particularly rapid warming is the western Antarctic Peninsula. Previous studies investigating direct effects of warming on Antarctic marine invertebrates have established that small increases in temperature can have significant impacts on aspects of behavior, physiology, and growth rates in these largely stenothermal organisms. To investigate how warming may impact feeding preferences of an ecologically important mesograzer on macroalgae of the Antarctic Peninsula, we examined the impacts of exposure to acute elevated temperature on the ecologically important omnivorous amphipod Gondogeneiea antarctica (Chevreux) at Palmer Station, Antarctica (64°46′S, 64°03′W) in April–May 2011. Amphipods were exposed to 1.5 °C (mean monthly upper summer temperature) or 3.5 °C (representative of current transient summer temperature peaks and projected mean for 2100) for a 24 h period. These amphipods were then used in choice-feeding assays with artificial food containing chemical extracts from six species of sympatric macroalgae known to produce feeding deterrents. We found that during acute exposure to elevated temperature (+2.0 °C), amphipods lost their feeding preferences in assays with artificial foods containing lipophilic (one macroalga), hydrophilic (three macroalgae), or combined lipophilic/hydrophilic (one macroalga) extracts. Our findings suggest that increased frequency in transient peaks and longer-term upward trends in ambient summer seawater temperature have the potential to alter feeding preferences in a common mesograzer that could influence macroalgal communities that dominate benthic communities along the western Antarctic Peninsula.
[Show abstract][Hide abstract] ABSTRACT: This study examines climate change impacts (increased temperature and pCO2) on canopy-forming Desmarestia anceps and D. menziesii from the western Antarctic Peninsula during the austral summer–winter of 2013. These are ecologically important species that play a role functionally equivalent to kelp forests in this region. Two-way factorial microcosm experiments with treatments reflecting near-future ocean conditions were run with these species and include increased temperature alone (3.5 °C × pH 8.0), reduced pH alone (1.5 °C × pH 7.6), and both factors combined (3.5 °C × pH 7.6). Phlorotannin concentration, chlorophyll a concentration, growth, and photosynthetic parameters (slope to saturation of photo centers (α), saturating irradiance (E
k), maximum electron transport rate (ETRmax), and maximum quantum yield of photosystem II (F
m)) were used to assess the physiological responses of the individuals to the different climate change treatments. Few significant impacts were observed: In D. menziesii,
k at the midpoint (after 39 days) was significantly higher in the 3.5 °C × pH 7.6 treatment and phlorotannin concentration was significantly higher in the 1.5 °C × pH 7.6 treatment than others at the end point of the experiment (79 days). All individuals in the experiment grew quickly through the midpoint, but growth declined thereafter. The photosynthetic apparatus of these species acclimated to microcosm conditions, and photo-physiological parameters changed between initial, midpoint, and end point measurements. Results indicate that D. menziesii is the more sensitive of the two species and that climate change factors can have a synergistic effect on this species. However, neither species responds negatively to climate change factors at the level of change used in this study, though the observed shifts in phlorotannin concentration and photosynthetic characteristics may have an unforeseen impact on the community dynamics in this geographic area.
[Show abstract][Hide abstract] ABSTRACT: Endophytic organisms are known to have varied effects on their host organism in terrestrial and marine environments. In previous studies on marine algae, these symbioses range from innocuous to path-ogenic depending on the host and endophyte species. The present study further assessed a pathogenic relationship between filamentous algal endophytes and a red algal host from the western Antarctic Peninsula. We analyzed endophyte presence (appearance of fila-mentous thalli) in the three life history stages of Iri-daea cordata and potential impacts on fertility in the fertilized female gametophytes (carposporophytes) and tetrasporophytes. We found that endophytes proliferate throughout significantly more thallus area in tet-rasporophyte and unfertilized gametophyte hosts than in carposporophyte hosts, but there was no correlation between endophyte cover and fertility in these individuals. This study also provides a demographic analysis of I. cordata populations surrounding Palmer Station, Antarctica, showing that these populations are hap-loid dominated (∼78% of individuals). The differential presence of filamentous algal endophytes indicates that endophyte pathogenicity indirectly has greater effect on tetrasporophytes and unfertilized gametophytes than on the carposporophytes, which house the products of sexual recombination.
[Show abstract][Hide abstract] ABSTRACT: Land-based aquaculture facilities experience occasional hypercapnic conditions due to the accumulation of the metabolic waste product carbon dioxide. Pre-gonadal Lytechinus variegatus (horizontal diameter = 20 mm) were exposed to control (608 μatm pCO2, pH 8.1) or hypercapnic conditions (1738 μatm pCO2, pH 7.7) in synthetic seawater for 14 weeks. Sea urchins exposed to hypercapnic conditions exhibited significantly slower growth (reduced dry matter production), primarily due to reduced test production. Higher fecal production rates and lower ash absorption efficiency (%) in individuals exposed to hypercapnic conditions suggest the ability to process or retain dietary carbonates may have been affected. Significant increases in neutral lipid storage in the gut and increased soluble protein storage in the gonads of individuals exposed to hypercapnic conditions suggest alterations in nutrient metabolism and storage. Furthermore, organic production and energy allocation increased in the lantern of those individuals exposed to hypercapnic conditions. These results suggest chronic exposure to hypercapnic conditions alters nutrient allocation to organ systems and functions, leading to changes in somatic and reproductive production.
Marine behaviour and physiology 11/2014; 47(1). DOI:10.1080/10236244.2013.875273
[Show abstract][Hide abstract] ABSTRACT: The threat that ocean acidification (OA) poses to marine ecosystems is now recognized and U.S. funding agencies have designated specific funding for the study of OA. We present a research framework for studying OA that describes it as a biogeochemical event that impacts individual species and ecosystems in potentially unexpected ways. We draw upon specific lessons learned about ecosystem responses from research on acid rain, carbon dioxide enrichment in terrestrial plant communities, and nitrogen deposition. We further characterize the links between carbon chemistry changes and effects on individuals and ecosystems, and enumerate key hypotheses for testing. Finally, we quantify how U.S. research funding has been distributed among these linkages, concluding that there is an urgent need for research programs designed to anticipate how the effects of OA will reverberate throughout assemblages of species. ■ INTRODUCTION Rising atmospheric CO 2 is linked to global warming and changes to terrestrial ecosystems. 1 In the oceans, increasing CO 2 alters surface seawater chemistry by decreasing ocean pH and calcium carbonate saturation state. 2,3 Collateral changes in biological systems are already apparent 4 and further alterations are expected. While there is no clear boundary between the role of CO 2 in Earth's climate and its role in seawater chemistry, the term ocean acidification (OA) is used to refer to the subset of changes in ocean chemistry that propagate from the addition of anthropogenic CO 2 to seawater. On time scales shorter than centuries, the primary concern with OA is a potential reconfiguration of marine ecosystems. 5
[Show abstract][Hide abstract] ABSTRACT: Marine macroalgae can release reactive oxygen species (ROS) upon wounding and grazing. Here we address the potential role of ROS in herbivore defense. We performed feeding assays in the presence of varying concentrations of hydrogen peroxide (H2O2), a common type of ROS. H2O2 inhibited feeding by a marine amphipod grazer, Gondogeneia antarctica, over broad levels of concentration, and its potency was strongly dependent on its rate of decay in natural seawater. Because it is possible that the inhibitory levels of H2O2 are encountered in the vicinity of a sympatric macroalgal wound, we suggest that H2O2 has the potential to act as a direct anti-grazing defense in marine ecosystems. Since some sympatric macroalgae release a burst of non-H2O2 ROS, we also performed experiments to evaluate the role of these naturally-produced ROS on sympatric grazers. The presence of wounded Ascoseira mirabilis (which releases a burst of non-H2O2 ROS after wounding) during a feeding assay inhibited feeding of G. antarctica compared to the presence of intact A. mirabilis. These data are consistent with a role for ROS as a direct anti-herbivore defense in nature. However, the data are also consistent with hypotheses that involve other putative activated anti-grazing defenses.
Journal of Experimental Marine Biology and Ecology 09/2014; 458:34–38. DOI:10.1016/j.jembe.2014.04.012 · 2.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Whale falls provide a substantial, nutrient-rich resource for species in areas of the ocean that may otherwise be largely devoid of food. We report the discovery of a natural whale fall at 1430 m depth in the cold waters of the continental slope off the western Antarctic Peninsula. This is the highest latitude whale fall reported to date. The section of the carcass we observed—the tail fluke—was more complete than any previously reported natural whale fall from the deep sea and in the early stages of decomposition. We estimate the entire cetacean to measure 5 to 8 m in length. The flesh remained almost intact on the carcass but the skin was missing from the entire section except for the end of the fluke, clearly exposing blubber and soft tissue. The absence of skin indicates rapid and homogenous loss. The dominant macrofauna present were crustaceans, including most prominently the lithodid crab Paralomis birsteini, and zoarcid fish typical of the ‘mobile-scavenger' successional stage. The density of mobile macrofauna was greatest on the carcass and declined to background levels within 100 m, indicating that they were attracted to the whale fall. This whale fall offers an important opportunity to examine the decomposition of a carcass under deep-sea conditions at polar latitudes.
Deep Sea Research Part A Oceanographic Research Papers 08/2014; 90. DOI:10.1016/j.dsr.2014.04.013
[Show abstract][Hide abstract] ABSTRACT: Warming seawater temperatures and ocean acidification on the coastal western Antarctic Peninsula pose unique challenges to stenothermal marine invertebrates. The present study examines prospective sub-lethal effects of elevated temperature, pCO2, and resultant decrease in seawater pH, on righting behavior and maximal escape speeds for two common gastropods, the limpet Nacella concinna (Strebel) and mesogastropod snail Margarella antarctica (Lamy). Replicate individuals held in individual containers were exposed to four combinations of seawater temperature (1.5 °C — current average, 3.5 °C — projected average by 2100) and pH (pH 8.0 — current average, pH 7.8 — projected average by 2100 as a result of elevated pCO2 levels) for a period of 6 weeks. Following this chronic exposure, righting behavior, determined for the limpets as proportion to right over 24 h and for snails as time to right, as well as maximum escape speed following contact with a sea star predator were measured. We found no significant differences in proportions of limpets displaying the capacity to right among the four temperature–pH treatments. However, there was a significant temperature–pH interaction effect for mean righting times in snails, indicating that the effect of pH on the time to right is dependent on temperature. We found no significant effects of temperature or pH on mean maximal escape speed in limpets. Additionally, we observed a significant temperature–pH interaction effect for mean maximal escape speed in snails. These interactive effects make it difficult to make clear predictions about how these environmental factors may impact behavioral responses.
Journal of Experimental Marine Biology and Ecology 08/2014; 457:90–96. DOI:10.1016/j.jembe.2014.04.005 · 2.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: There is concern that the use of natural volcanic CO2 vents as analogs for studies of the impacts of ocean acidification on marine organisms are biased due to physiochemical influences other than seawater pH alone. One issue that has been raised is whether potentially harmful trace elements in sediments that are rendered more soluble and labile in low pH environments are made more bioavailable, and sequestered in the local flora and fauna at harmful levels. In order to evaluate this hypothesis, we analyzed the concentrations of trace elements in shells (an established proxy for tissues) of four species of gastropods (two limpets, a topshell and a whelk) collected from three sites in Levante Bay, Vulcano Island. Each sampling site increased in distance from the primary CO2 vent and thus represented low, moderate, and ambient seawater pH conditions. Concentrations of As, Cd, Co, Cr, Hg, Mo, Ni, Pb, and V measured in shells using ICP-OES were below detection thresholds for all four gastropod species at all three sites. However, there were measurable concentrations of Sr, Mn, and U in the shells of the limpets Patella caerulea, P. rustica, and the snail Osilinus turbinatus, and similarly, Sr, Mn, U, and also Zn in the shells of the whelk Hexaplex trunculus. Levels of these elements were within the ranges measured in gastropod shells in non-polluted environments, and with the exception of U in the shells of P. caerulea, where the concentration was significantly lower at the collecting site closest to the vent (low pH site), there were no site-specific spatial differences in concentrations for any of the trace elements in shells. Thus trace element enhancement in sediments in low-pH environments was not reflected in greater bioaccumulations of potentially harmful elements in the shells of common gastropods.
[Show abstract][Hide abstract] ABSTRACT: Hard bottom communities along the western Antarctic Peninsula region are dominated by thick macroalgal forests, which support high densities of mesograzers, particularly amphipods, and also numerous gastropods. The macroalgae are chemically defended from consumption by the mesograzers and other herbivores and they provide the mesograzers a chemically defended refuge from predation by omnivorous fish. The macroalgae benefit in return because the mesograzers remove epiphytic algae from them. Since these two assemblages are major components of the community, this can be viewed as a community-wide mutualism. Most subcomponents of these interactions have also been documented in lower latitude communities and the similarities and differences between the communities in Antarctica and in other regions are discussed.
Journal of Phycology 12/2013; 50(1). DOI:10.1111/jpy.12137 · 2.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Filamentous algal endophytes are common in many species of macroalgae along the Antarctic Peninsula, but their influence on host physiology is unknown. However, worldwide endophyte–macroalgae symbioses are known to be detrimental to vital functions of a host. The growth and survival of four Antarctic rhodophyte species were examined in situ under varying loads of endophyte infection. Growth was measured through relative growth rate and surface-area-corrected growth rate, and survivorship of individuals was documented throughout the experiment. The relationship between hosts and their endophytes was best described as innocuous in Myriogramme manginii, mildly pathogenic in Gymnogongrus turquetii and Trematocarpus antarcticus, and pathogenic in Iridaea cordata. Deterioration of thalli and decreased growth rates may be natural in the late austral summer when this experiment took place; however, the effects of increased infection probably expedited deterioration of the host. Endophytes in this study were pigmented green and brown filamentous algae, most of which are never seen as free-living thalli, and some of which may be obligate endophytes.
[Show abstract][Hide abstract] ABSTRACT: Shallow-water communities along the western Antarctic Peninsula support forests of large, mostly chemically defended macroalgae and dense assemblages of macroalgal-associated amphipods, which are thought to exist together in a community-wide mutualism. The amphipods benefit the chemically defended macrophytes by consuming epiphytic algae and in turn benefit from an associational refuge from fish predation. In the present study, we document an exception to this pattern. The amphipod Paradexamine fissicauda is able to consume Plocamium cartilagineum and Picconiella plumosa, 2 species of sympatric, chemically defended red macroalgae. In previous studies, Plocamium cartilagineum was one of the most strongly deterrent algae in the community to multiple consumers, and was found here to be unpalatable to 5 other amphipod species which utilize it as a host in nature. Paradexamine fissicauda maintained on a diet of Plocamium cartilagineum for 2 mo were much less likely to be eaten by fish than Paradexamine fissicauda maintained on a red alga which does not elaborate chemical defenses, or than a different but morphologically similar sympatric amphipod species. Halogenated secondary metabolites produced by Plocamium cartilagineum were identified from tissues of the Paradexamine fissicauda that had eaten it but not those which had eaten the undefended red alga. This indicates that P. fissicauda is sequestering the potent chemical defenses of Plocamium cartilagineum for its own use.