Bivalve Laternula Elliptica Research Articles

Metabolic demand, oxygen supply, and critical temperatures in the Antarctic bivalve Laternula elliptica.

Oxygen consumption (Mo(2)), heartbeat rate and form, and circulating hemolymph oxygen content were measured in relation to temperature in the large Antarctic infaunal bivalve Laternula elliptica. After elevations in temperature from 0 degrees to 3 degrees, 6 degrees, and then 9 degrees C, Mo(2) and heartbeat rate rose to new levels, whereas maximum circulating hemolymph oxygen content fell. At 0 degrees C, Mo(2) was 19.6 micromol O(2) h(-1) for a standard animal of 2-g tissue ash-free dry mass, which equates to a 8.95-g tissue dry-mass or 58.4-g tissue wet-mass animal. Elevation of metabolism following temperature change had acute Q(10) values between 4.1 and 5, whereas acclimated figures declined from 3.4 (between 0 degrees and 3 degrees C) to 2.2 (3 degrees -6 degrees C) and 1.9 (6 degrees -9 degrees C). Heartbeat rate showed no acclimation following temperature elevations, with Q(10) values of 3.9, 3.2, and 4.3, respectively. Circulating hemolymph oxygen content declined from 0 degrees to 3 degrees and 6 degrees C but stayed at a constant Po(2) (73-78 mmHg) and constant proportion ( approximately 50%) of the oxygen content of the ambient water. At 9 degrees C, Mo(2) and heartbeat rate both peaked at values 3.3 times those measured at 0 degrees C, which may indicate aerobic scope in this species. After these peaks, both measures declined rapidly over the ensuing 5 d to the lowest measured in the study, and the bivalves began to die. Hemolymph oxygen content fell dramatically at 9 degrees C to values between 2% and 12% of ambient water O(2) content and had a maximum Po(2) of around 20 mmHg. These data indicate an experimental upper lethal temperature of 9 degrees C and a critical temperature, where a long-term switch to anaerobic metabolism probably occurs, of around 6 degrees C for L. elliptica. Concurrent measures of mitochondrial function in the same species had indicated strong thermal sensitivity in proton leakage costs, and our data support the hypothesis that as temperature rises, mitochondrial maintenance costs rapidly outstrip oxygen supply mechanisms in cold stenothermal marine species.

The seasonal energetics of the Antarctic bivalve Laternula elliptica (King and Broderip) at Rothera Point, Adelaide Island

Seasonal changes in feeding activity, metabolic rate and major tissue energy concentrations of the infaunal bivalve Laternula elliptica were monitored over a 12°month period in relation to phytoplankton standing stock. Chlorophyll a concentration displayed the prolonged winter minima and intense annual summer peak characteristic of polar environments. Divers made regular observations on the feeding activity of L. elliptica throughout the year, and siphons were completely withdrawn below the sediment surface at the start of the study in early September 1998. Siphons reappeared as chlorophyll concentrations rose at the end of September and these concentrations continued until late May 1999 when siphons were again withdrawn. There were, therefore, around 4 months in the austral winter when L. elliptica did not feed. Oxygen consumption rates were highly seasonal, varying from 4.3 µmol h–1 late in the winter (August 1999) to 12.9 µmol h–1 in summer (March 1999) for a 50°mm shell height individual, indicating a summer increase in oxygen consumption over winter levels of H×3.0. Nitrogen was excreted as 90% ammonium and 10% urea, and excretion rates were also highly seasonal. The O:N ratio did not vary significantly with size in winter (September, August), but declined with shell length in summer (November, January and March), indicating that larger bivalves used a higher proportion of protein to fuel metabolism than younger animals when feeding in summer. O:N ratios in August 1999 ranged from 3 to 16, indicating a predominantly protein-based metabolism. ANCOVA showed that regressions of dry tissue masses of major non-reproductive body components (musculature, ctenidia and digestive tissue) against shell height did not change between late winter and late summer. ANCOVA also showed that the regression slope for gonad mass against shell height was greater in late summer than late winter (slope F=7.37, P=0.009), and gonad mass was greater in all animals by late summer. Although tissue masses remained constant, energy content of non-reproductive tissues (especially musculature) declined from summer to winter. Muscle tissue also showed the greatest reduction in protein content, which was consistent with O:N estimates of primarily protein-based metabolism, especially in winter. Reduction in whole body energy content (5.84 kJ) agreed closely with total power utilisation during winter estimated from oxygen consumption (5.78 kJ). The data also showed that in contrast to temperate bivalve species, L. elliptica survives the prolonged polar winter with little reduction in body mass.

Mitochondrial function and critical temperature in the Antarctic bivalve, Laternula elliptica

Thermal sensitivities of maximum respiration and proton leakage were compared in gill mitochondria of the Antarctic bivalve Laternula elliptica for an assessment of the contribution of mitochondrial mechanisms to limiting temperature tolerance. Proton leakage was measured as the oxygen consumption rate during blockage of oxidative phosphorylation (state IV respiration+oligomycin). The maximum capacity of NADP dependent mitochondrial isocitrate dehydrogenase (IDH) was investigated as part of a proposed mitochondrial substrate cycle provoking proton leakage by the action of transhydrogenase. State III and IV+respiration rose exponentially with temperature. Thermal sensitivities of proton leakage and IDH were unusually high, in accordance with the hypothesis that H + leakage is an enzyme catalysed process with IDH being involved. In contrast to proton leakage, state III respiration exhibited an Arrhenius break temperature at 9°C, visible as a drop in thermal sensitivity close to, but still above the critical temperature of the species (3–6°C). Progressive uncoupling of mitochondria led to a drop in RCR values and P/O ratios at high temperature. The same discontinuity as for state III respiration was found for the activity of mitochondrial IDH suggesting that this enzyme may influence the thermal control of mitochondrial respiration. In general, the high thermal sensitivity of proton leakage may cause an excessive rise in mitochondrial oxygen demand and a decreased efficiency of oxidative phosphorylation. This may exceed the whole animal capacity of oxygen uptake and distribution by ventilation and circulation and set a thermal limit, characterized by the transition to anaerobic metabolism.

Benthic faunal associations on soft substrates at Potter Cove, King George Island, Antarctica

Associations of benthic invertebrates from Potter Cove (Antarctica) were defined from photo-transects. Density, percentage cover, species richness S′, diversity index H′, evenness index J′ and mean-size estimations were studied in relation to water depth down to 30 m. A clear bathymetric pattern was evident, with two different communities at 15 and 30 m, and a transition area between 20 and 25 m. At 15 m we observed a small number of taxa (nine in total), a high percentage of bare substratum (95%), and the dominant species were pennatulids and the bivalve Laternula elliptica. From 20 to 30 m the dominant species was the ascidian Molgula pedunculata and there was a slight increase in S′, H′ and J′, as well as in the mean size of individuals, especially in M. pedunculata, while the proportion of bare substratum showed a constant decrease with depth. Using multivariate analyses, three faunal assemblages related to depth were defined and a strong association of some species, mainly predators and opportunistic necrophages, with M. pedunculata was revealed. Ice impact (icebergs and anchor ice) seems to be the major regulating factor of benthic assemblages in shallow waters.

Stable isotopes prove shell growth bands in the Antarctic bivalve Laternula elliptica to be formed annually

Growth marks in calcareous shells or skeleton parts of benthic invertebrates are often assumed to be formed annually and hence are used for ageing purposes. For some Antarctic species this assumption has been validated by tagging experiments or direct monitoring of growth throughout the year. Here we use the record of stable isotope ratios (δ18O and δ13C) deposited in shell carbonate of Laternula elliptica from King George Island to demonstrate that shell growth bands are formed annually in this species.

Oxygen and Carbon Isotopic Composition and Shell Microstructure of the Bivalve Laternula elliptica from Antarctica

Oxygen and carbon isotopic measurements were obtained from microsamples of an adult Laternula elliptica, an infaunal, aragonitic, Antarctic bivalve. The δ 18 O values of samples from the exterior surface are, on average (∼ 4.5‰), similar to calculated values inferred to represent precipitation in equilibrium with ambient environmental conditions. This indicates that bulk samples as well as many microsamples from the exterior surface would provide reliable isotopic estimates of paleotemperatures and paleosalinities. Nevertheless, both oxygen and carbon isotopic values from discrete shell areas may be influenced by vital effects

Enhanced particle flux through the biodeposition by the Antarctic suspension-feeding bivalve Laternula elliptica in Marian Cove, King George Island

The infaunal lamellibranch Laternula elliptica (Laternulidae), one of the most common Antarctic bivalves, is widely distributed in shallow waters around the Antarctic Continent. In order to evaluate the contribution of this species to organic carbon flux in an Antarctic coastal ecosystem, biodeposition rates by L. elliptica were measured and compared with sedimentation without this bivalve species in laboratory experiments during one austral summer. The amount of deposited material increased in the presence of L. elliptica. Weight-specific biodeposition rates varied from 0.26 to 2.17 mg dry wt·g wet wt −1 · d −1 and the rate decreased with increase in body weight. Due to massive inflows of terrigenous sediment through coastal meltwater stream into the coastal water, fecal and pseudofecal material contained a considerable amount of mineral particles and only a small percentage of organic carbon (1.6–5.2%). Estimated particulate organic carbon flux through the biodeposition of L. elliptica is ≈95 mg C·m −2·d −1, an amount comparable to that of a typical suspension-feeding bivalve, Mytilus edulis. L. elliptica is apparently an important agent for sedimentation of both lithogenic particles and organic particles. Thus, this study suggests that L. elliptica play an important role in enhancing particle flux from water column to sea bed through biodeposition and possibly nourishing other benthic fauna, particularly in phytoplankton-impoverished nearshore waters.