Shell Growth Rate Research Articles

Microencapsulated diets using thraustochytrids and macroalgae side streams for nursery rearing of Mytilus galloprovincialis spat

AbstractGlobal expansion of bivalve aquaculture can drive sustainable protein production. Inland culture of mussel spat can play an important role in supporting extensive mussel farming. Nursery culture of bivalves is, however, dependent on nutritious, cost‐efficient, and more reliable diets for spat. The aim of this study was to assess the impact of dietary alternatives to commercial algal feeds (Shellfish Diet 1800) on the survival and growth of Mytilus galloprovincialis spat, widely farmed in Europe. Spat (6.8 ± 1.1 mm) were supplied with different diets for 6 weeks: commercial microalgal diet (A), microencapsulated feeds containing a 1:1 blend of the macroalga Undaria pinnatifida and the microalga Schizochytrium (BioBullets; BB), or commercial microalgae and BioBullets combined (ABB). Unsupplemented spat showed no growth and little change in body condition (CI). Spat fed microcapsules grew at comparable rates, and body condition rose at higher levels (shell growth rates: 8.5 ± 3.7 μm day−1; ΔCI: 6.1 ± 1.1%) relative to those fed commercial microalgae (8.5 ± 5.7 μm day−1; ΔCI: 3.3 ± 0.8%). Supplementing microencapsulated feeds with the commercial microalgal diet did not significantly improve growth performances (9.3 ± 2.3 μm day−1; ΔCI: 4.7 ± 1.4%) relative to mussels fed microcapsules alone. Microencapsulated feeds for M. galloprovincialis spat production can significantly reduce nursery costs compared with commercial feeds or cultured microalgae. By sourcing encapsulated algae from aquaculture side streams, microencapsulated feeds can further promote circular economies.

Effect of fresh and spray-dried microalgal diets on the growth, digestive enzymatic activity, and gut microbiota of juvenile winged pearl oyster Pteria penguin

The effects of fresh and spray-dried microalgal diets on the growth, digestive enzymatic activity, and gut microbial community were investigated in juveniles of the winged pearl oyster Pteria penguin. A total of 240 pearl oysters were fed either live or spray-dried unialgal diets of the species Isochrysis zhanjiangensis and Platymonas subcordiformis at a final concentration of 150,000 cells/mL. The experiment was performed over 28 days in triplicate feeding trials under laboratory conditions. At the end of the feeding trials, the hepatopancreas and gut tissue were dissected to quantify the digestive enzymatic activity and analyze the gut bacterial community. The survival rate of the oyster juveniles in all trials was > 90 %. Moreover, the animals fed a spray-dried P. subcordiformis diet exhibited slightly higher shell growth rates. However, the mean shell height and the total wet weight were not significantly different among all experimental groups (P > 0.05). The digestive enzymes amylase, pepsin, and lipase exhibited significantly higher activity levels in oysters fed spray-dried diets than in those provided live microalgae. The different diets also provoked changes in the gut microbiota of the pearl oysters. A total of 27 phyla and 482 genera were detected within all groups examined; the Proteobacteria, Cyanobacteria, Bacteroidetes, and Spirochaetes were the dominant phyla. In general, spray-dried diets exhibited a higher number of operational taxonomic units (OTUs), Chao1, and Simpson and Shannon indices, implying the ability of these diets to promote high microbial biodiversity. Thus, these diets benefitted the maintenance of the intestinal micro-ecological balance and health. The study findings will help optimize intermediate culture technology and management of P. penguin juveniles.

Parental exposure of Eastern oysters (Crassostrea virginica) to elevated pCO2 mitigates its negative effects on early larval shell growth and morphology

AbstractLarvae of marine calcifying organisms are particularly vulnerable to the adverse effects of elevated pCO2 on shell formation because of their rapid calcification rates, reduced capacity to isolate calcifying fluid from seawater, and use of more soluble polymorphs of calcium carbonate. However, parental exposure to elevated pCO2 could benefit larval shell formation through transgenerational plastic responses. We examined the capacity of intergenerational exposure to mitigate the adverse effects of elevated pCO2 on Eastern oyster (Crassostrea virginica) early larval shell growth, shell morphology, and survival. Adult oysters were exposed to control (572 ppm pCO2) or elevated pCO2 (2827 ppm pCO2) conditions for 30 d during reproductive conditioning. Offspring from each parental treatment were produced using a partial North Carolina II cross design and grown under control and elevated pCO2 conditions for 3 d. We found evidence of transgenerational plasticity in early larval shell growth and morphology, but not in survival, in response to the parental pCO2 exposure. Larvae from parents exposed to elevated pCO2 exhibited faster shell growth rates than larvae from control parents, with this effect being significantly larger when larvae were grown under elevated pCO2 compared to control conditions. Parental exposure to elevated pCO2, however, was insufficient to completely counteract the adverse effects of the prescribed elevated pCO2 on early larval shell formation and survival. Nevertheless, these results suggest that oysters have some capacity to acclimate intergenerationally to ocean acidification.

Importance of Weighting High-Resolution Proxy Data From Bivalve Shells to Avoid Bias Caused by Sample Spot Geometry and Variability in Seasonal Growth Rate

Shells of bivalve mollusks serve as archives for past climates and ecosystems, and human-environmental interactions as well as life history traits and physiology of the animals. Amongst other proxies, data can be recorded in the shells in the form of element chemical properties. As demonstrated here with measured chemical data (10 elements) from 12 Arctica islandica specimens complemented by numerical simulations, mistakes during sclerochronological data processing can introduce significant bias, adding a further source of error to paleoenvironmental or biological reconstructions. Specifically, signal extraction from noisy LA-ICP-MS (Laser Ablation—Inductively Coupled Plasma—Mass Spectrometry) data generated in line scan mode with circular LA spots requires a weighted rather than an arithmetic moving average. Otherwise, results can be in error by more than 41%. Furthermore, if variations of seasonal shell growth rate remain unconsidered, arithmetic annual averages of intra-annual data will be biased toward the fast-growing season of the year. Actual chemical data differed by between 3.7 and 33.7% from weighted averages. Numerical simulations not only corroborated these findings, but indicated that arithmetic annual means can overestimate or underestimate the actual environmental variable by nearly 40% relative to its seasonal range. The magnitude and direction of the error depends on the timing and rate of both seasonal shell growth and environmental change. With appropriate spatial sampling resolution, weighting can reduce this bias to almost zero. On average, the error reduction attains 80% at a sample depth of 10, 92% when 20 samples were analyzed and nearly 100% when 100 samples were taken from an annual increment. Under some exceptional, though unrealistic circumstances, arithmetic means can be superior to weighted means. To identify the presence of such cases, a numerical simulation is advised based on the shape, amplitude and phase relationships of both curves, i.e., seasonal shell growth and the environmental quantity. To assess the error of the offset induced by arithmetic averaging, Monte Carlo simulations should be employed and seasonal shell growth curves randomly generated based on observed variations.

The effect of environmental factors on shell growth and repair in Buccinum undatum

The processes and factors which affect shell growth and repair in molluscs are poorly understood. In this study, the capabilities of shell growth and repair in the marine gastropod Buccinum undatum were investigated experimentally by implementing laboratory-controlled mechanical damage to the shell margin/lip. Three key factors, life stage (juvenile or adult), seawater temperature (5–15 °C) and food availability (unfed, weekly, or daily feeding), were investigated in a series of controlled laboratory experiments to establish their roles in the processes of shell growth and repair. Significant differences in rates of shell growth and repair between food and temperature regimes were observed, with the greatest difference occurring with different life stages. Rates of shell growth in non-damaged whelks were slightly faster but not significantly different from damaged individuals in any of the experiments. Tank-reared juveniles maintained in the highest seawater temperature regime (15 °C) displayed significantly faster rates of shell repair (F = 6.47, p < 0.05) than conspecifics held at lower seawater temperatures. Through characterising both biological and environmental factors affecting shell growth and repair, it is demonstrated that there are multiple aspects influencing shell growth and shell repair. It is important to be able to understand and establish differences in rates of growth to better manage this commercial species.

Nitrogen Isotope Sclerochronology—Insights Into Coastal Environmental Conditions and Pinna nobilis Ecology

Pinna nobilis is a large bivalve endemic to the Mediterranean Sea that lives in shallow coastal areas. Due to its size and relatively fast shell growth rates, it is an interesting taxon for high-resolution study of nitrogen isotopes of carbonate bound organic matter (δ15NCBOM). In this study we tested if P. nobilis shells can be used as an indicator of the nitrogen isotope baseline of the system, if it can provide high-resolution data on environmental δ15N variability, and if the chemical properties of the shell and biomineralization process change in response to mass mortality events spreading in the Mediterranean. Shells were opportunistically collected during 2019 and 2020 by skin diving, as a part of a project on mortality monitoring, from four shallow coastal localities in the eastern Adriatic. Shell powder for δ15NCBOM analysis was collected by milling sample swaths from the internal (low-resolution) and external (high resolution) shell surface. Significant differences in δ15NCBOM, obtained from the internal shell surface, were observed between sampling localities with different anthropogenic influences, with lowest values (∼3–4‰) recorded for shells obtained from Pag Bay, and highest (∼6–8‰) for shells sampled in Lim and Kaštela Bays. High-resolution samples from the external shell surface of Pinna nobilis showed spatial and temporal variations in δ15NCBOM values, with temporal resolution of 1–3 weeks. High-resolution δ15NCBOM data obtained from the shell Kas1 corresponded to a time interval from spring 2018 to summer 2019 and had a pronounced increase of δ15NCBOM values closest to the shell margin coupled with a decrease in δ13Cshell values, indicating that this animal was experiencing stressful conditions several months prior to its death. According to our findings, δ15NCBOM values from P. nobilis shells can serve as an indicator of the isotopic baseline of the ecosystem potentially as a powerful tool to study bivalve physiology.

Microstructural Mapping of Arctica islandica Shells Reveals Environmental and Physiological Controls on Biomineral Size

The shells of long-lived bivalves record environmental variability in their geochemical signatures and are thus used extensively in marine high-resolution paleoclimate studies. To possibly overcome the limitations of the commonly employed temperature proxy, the δ18Oshell value, which requires knowledge of the seawater δ18O signature and is prone to diagenetic overprint, the shell microstructures and the morphological properties of individual biomineral units (BMUs) recently attracted research interest as an alternative paleoclimate proxy. In shells of A. islandica, one of the most extensively used and best studied sclerochronological archives, the size of the BMUs increases in warmer temperatures under laboratory circumstances. This study assesses whether this relationship persists under natural growth conditions or whether additional environmental and physiological factors control the BMU size and bias temperature reconstructions. For this purpose, shells from the surface waters of NE Iceland and the Baltic Sea, as well as from deeper waters of the North Sea (100 and 243 m) were analyzed by means of SEM. The BMU sizes were measured by means of image processing software. Results demonstrate a strong effect of temperature on the BMU size at NE Iceland and in the North Sea at 100 m depth. At 243 m depth, however, temperature variability was likely too low (1.2°C) to evoke a microstructural change. At the Baltic Sea, the BMUs remained small, possibly due to physiological stress induced by low salinity and/or hypoxia. Thus, the size of BMUs of A. islandica shells only serves as a relative temperature indicator in fully marine habitats, as long as seasonal temperature amplitudes exceed ca. 1°C. Furthermore, BMU size varied through lifetime with the largest units occurring during age seven to nine. This pattern is possibly linked to the shell growth rate or to the amount of metabolic energy invested in shell growth.

Effects of the toxic dinoflagellate Karenia brevis on the development of the marine gastropod Crepidula fornicata

With harmful algal blooms increasing in frequency and range, it is important to study how exposure to harmful algae may affect the development of marine organisms. Our studies examined the susceptibility of the early life stages of the Atlantic slipper limpet Crepidula fornicata to the toxic red tide dinoflagellate Karenia brevis (strain FWC1010), testing the effects of exposure to 3 algal bloom concentrations (100, 1000, or 5000 cells ml-1), representing medium to high bloom conditions in nature, on survival, growth, clearance rates, metamorphosis, and post-metamorphic survival and growth. Larvae were given either a mixed diet of K. brevis together with the non-toxic phytoplankton Tisochrysis lutea (clone TISO), a unialgal diet of K. brevis, or a control diet of unialgal TISO. In some experiments, larvae were raised to metamorphosis on the different diets and were then observed as juveniles in a non-toxic environment to see if there were any latent effects of larval exposure to K. brevis on subsequent juvenile survival or growth (in terms of both shell length and percent inorganic weight). There were no significant effects of larval exposure to K. brevis on larval or juvenile survival. However, we observed several notable sub-lethal effects of larval exposure to high K. brevis concentrations (1000 and 5000 cells ml-1), including slower larval shell growth rates, delayed competence for metamorphosis, lower responses to natural metamorphic cues, and reduced rates of post-metamorphic growth (in terms of both shell length per day and percent inorganic weight) when juveniles were reared under control conditions.

Emission characteristics of GaInN/GaN multiple quantum shell nanowire-based LEDs with different p-GaN growth conditions

Abstract Improving current injection into r- and m-planes of nanowires (NWs) is essential to realizing efficient GaInN/GaN multiple quantum shell (MQS) NW-based light-emitting diodes (LEDs). Here, we present the effects of different p-GaN shell growth conditions on the emission characteristics of MQS NW-LEDs. Firstly, a comparison between cathodoluminescence (CL) and electroluminescence (EL) spectra indicates that the emission in NW-LEDs originates from the top region of the NWs. By growing thick p-GaN shells, the variable emission peak at around 600 nm and degradation of the light output of the NW-LEDs are elaborated, which is attributable to the localization of current in the c-plane region with various In-rich clusters and deep-level defects. Utilizing a high growth rate of p-GaN shell, an increased r-plane and a reduced c-plane region promote the deposition of indium tin oxide layer over the entire NW. Therefore, the current is effectively injected into both the r- and m-planes of the NW structures. Consequently, the light output and EL peak intensity of the NW-LEDs are enhanced by factors of 4.3 and 13.8, respectively, under an injection current of 100 mA. Furthermore, scanning transmission electron microscope images demonstrate the suppression of dislocations, triangular defects, and stacking faults at the apex of the p-GaN shell with a high growth rate. Therefore, localization of current injection in nonradiative recombination centers near the c-plane was also inhibited. Our results emphasize the possibility of realizing high efficacy in NW-LEDs via optimal p-GaN shell growth conditions, which is quite promising for application in the long-wavelength region.

Meta-analysis of growth and mortality rates of net cultured sea scallops across the Northwest Atlantic

Scallops are one of the most heavily traded and widely consumed seafood in the world and the vast majority of production comes from aquaculture. In 2018, the global value of scallop aquaculture was over $5.8 billion USD with farms producing nearly three times the biomass as the entirety of the wild harvest. North American (specifically U.S. and Canadian) scallop aquaculture lags far behind the rest of the world. The U.S. is home to a valuable Atlantic sea scallop (Placopecten magellanicus) fishery. Yet demand for scallops far outstrips supply and the U.S. imports an almost equal amount, by value, of farmed scallop products. To capitalize on this trade imbalance, U.S. and Canadian aquaculturists have been developing a farmed sea scallop (hereafter scallop) industry, employing the Japanese practices of suspended net culture and the sale of whole and “roe-on” products. We examined the combined effects of culture method and environment on scallop shell growth and mortality. We compiled all published net cultured scallop shell growth and mortality rates recorded in the last 45 years in the Northwest Atlantic. Using generalized additive models (GAMs), we identified significant nonlinear interactions between growth, mortality, environmental conditions, and culture methods applicable from Maine, USA to Newfoundland, Canada. Optimum shell growth occurs within a temperature window of 10–15 °C. Growth is higher in pearl nets than in lantern nets, and is also highly sensitive to stocking density, which has large implications for farm sizes and thinning practices. Maximum mortality occurs at the highest temperatures in our dataset (~17 °C), while stocking density is only a significant predictor of product loss at high densities. Scallops are also more susceptible to mortality at shell heights under 25 mm. Both mortality rates and shell height growth rates were lower in the late spring and early summer after accounting for temperature effects. Careful temperature based site selection and proactive low density stocking can mitigate the effects of intraspecific competition and reduce handling related mortality. Identifying lease sites that provide both optimal environmental conditions and adequate space for low density net culture will be an important step in expanding scallop aquaculture in the Northwest Atlantic.

Effects of flood-associated stressors on growth and survival of early life stage oysters (Crassostrea virginica)

Oyster reefs provide essential ecosystem services but are severely degraded worldwide. Extreme flooding events, which can be intensified by water management decisions, reduce water quality in estuaries and further threaten oyster populations. Restoration and conservation of oysters is dependent on the success of early oyster life stages. This study examined the effect of water quality stressors associated with flooding events on the growth and survival of larval and juvenile oysters (Crassostrea virginica). In 96-h assays, we exposed D-stage larvae to a range of dissolved oxygen, microcystin-LR, pH, and salinity concentrations. These conditions were selected based on water quality data from the Mississippi Sound during a 2019 freshwater flooding event caused by the Bonnet Carré Spillway opening. There was no negative effect of microcystin-LR or pH on early veligers at the concentrations tested, but low salinity significantly reduced shell growth, and hypoxia (< 2 mg L−1 O2) decreased both larval growth and survival. Post-metamorphosis juvenile oysters were exposed to the same water quality stressors for 24 days in the lab. Low DO, pH, and salinity treatments reduced juvenile change in wet weight and shell growth rates, but had no effects on survival. These laboratory-exposed juveniles were subsequently deployed into the field to assess the ability of juveniles to recover from short-term exposure to simulated flooding-associated stressors. After deployment to natural conditions in the Mississippi Sound, juvenile oysters were able to compensate for reduced growth during the lab exposure, even though survival was reduced for juveniles previously exposed to low pH during the first two weeks in the field. In general, early oyster life stages were relatively tolerant of the duration and stressor concentrations tested, but negative sublethal impacts of flood-associated stressors must be considered in the face of increasing frequency and duration of flooding events due to climate change.

Optimal sediment grain size and sorting for survival and growth of juvenile Manila clams, Venerupis philippinarum

The characteristics of the sedimentary environment are considered significant for increasing the aquaculture production of Manila clams, Venerupis philippinarum. Among these, the grain size and sorting of the sediment, which determine the amount of pore-water-dissolved oxygen and organic matter content, can affect the growth and survival of clams. To determine the optimal grain size and sediment sorting in relation to the conditions of Manila clams (e.g., survival, growth, burrowing behavior, and condition index), we conducted three experiments. First, juvenile clams were incubated in four different grain sizes (coarse sand, 0.335–710 mm; medium sand, 0.180–0.335 mm; fine sand, 0.090–0.180 mm; and very fine sediment, < 0.09 mm). Survival was significantly higher in medium sand than in very fine sediment. The condition index of the Manila clams was higher in the medium sand than in the coarse and very fine sediments. However, the sediment grain size did not influence the shell growth or clam emergence behavior. Second, juvenile clams were incubated in three different treatments of sediment sorting (well-sorted sediment: 0.58 mm; moderately-sorted sediment: 0.46 mm; and poorly-sorted sediment: 0.37 mm). The shell growth rate was significantly higher in the poorly-sorted sediment than in any other treatment, while sediment sorting did not influence the survivorship, condition index, or emergence behavior. Third, juvenile Manila clams were incubated for 30 days in the sediment taken from two locations on the clam culturing mudflat, where a structure was installed to facilitate the settling of clam larvae (which was more poorly-sorted) or without a structure (the control). Although the survival and emergence behavior were not significantly different between the two treatments, the shell growth rate in the sediment under the structure was higher than that in the sediment with no structure. Moreover, the condition index of the Manila clams in the sediment under the structure was significantly higher than that under no structure. The results suggest that poorly-sorted sediment with an average grain size of medium sand is optimal for the survival and growth of Manila clams.

Oyster biomineralization under ocean acidification: From genes to shell.

Biomineralization is one of the key processes that is notably affected in marine calcifiers such as oysters under ocean acidification (OA). Understanding molecular changes in the biomineralization process under OA and its heritability, therefore, is key to developing conservation strategies for protecting ecologically and economically important oyster species. To do this, in this study, we have explicitly chosen the tissue involved in biomineralization (mantle) of an estuarine commercial oyster species, Crassostrea hongkongensis. The primary aim of this study is to understand the influence of DNA methylation over gene expression of mantle tissue under decreased ~pH 7.4, a proxy of OA, and to extrapolate if these molecular changes can be observed in the product of biomineralization-the shell. We grew early juvenile C. hongkongensis, under decreased ~pH 7.4 and control ~pH 8.0 over 4.5months and studied OA-induced DNA methylation and gene expression patterns along with shell properties such as microstructure, crystal orientation and hardness. The population of oysters used in this study was found to be moderately resilient to OA at the end of the experiment. The expression of key biomineralization-related genes such as carbonic anhydrase and alkaline phosphatase remained unaffected; thus, the mechanical properties of the shell (shell growth rate, hardness and crystal orientation) were also maintained without any significant difference between control and OA conditions with signs of severe dissolution. In addition, this study makes three major conclusions: (1) higher expression of Ca2+ binding/signalling-related genes in the mantle plays a key role in maintaining biomineralization under OA; (2) DNA methylation changes occur in response to OA; however, these methylation changes do not directly control gene expression; and (3) OA would be more of a 'dissolution problem' rather than a 'biomineralization problem' for resilient species that maintain calcification rate with normal shell growth and mechanical properties.

Seagrass-driven changes in carbonate chemistry enhance oyster shell growth.

Quantifying the strength of non-trophic interactions exerted by foundation species is critical to understanding how natural communities respond to environmental stress. In the case of ocean acidification (OA), submerged marine macrophytes, such as seagrasses, may create local areas of elevated pH due to their capacity to sequester dissolved inorganic carbon through photosynthesis. However, although seagrasses may increase seawater pH during the day, they can also decrease pH at night due to respiration. Therefore, it remains unclear how consequences of such diel fluctuations may unfold for organisms vulnerable to OA. We established mesocosms containing different levels of seagrass biomass (Zostera marina) to create a gradient of carbonate chemistry conditions and explored consequences for growth of juvenile and adult oysters (Crassostrea gigas), a non-native species widely used in aquaculture that can co-occur, and is often grown, in proximity to seagrass beds. In particular, we investigated whether increased diel fluctuations in pH due to seagrass metabolism affected oyster growth. Seagrasses increased daytime pH up to 0.4 units but had little effect on nighttime pH (reductions less than 0.02 units). Thus, both the average pH and the amplitude of diel pH fluctuations increased with greater seagrass biomass. The highest seagrass biomass increased oyster shell growth rate (mmday-1) up to 40%. Oyster somatic tissue weight and oyster condition index exhibited a different pattern, peaking at intermediate levels of seagrass biomass. This work demonstrates the ability of seagrasses to facilitate oyster calcification and illustrates how non-trophic metabolic interactions can modulate effects of environmental change.

Ecophenotypic plasticity in shell growth direction of asari clamRuditapes philippinarum

AbstractAsari clam (or Manila clam)Ruditapes philippinarumis an important bivalve for local fisheries. This species exhibits a large variation in shell morphology, and the shell roundness tends to be greater in more unsuitable habitats. To test whether the increments in shell size parameters (length, height and width) were affected solely by environmental conditions or by internal factors such as initial shell shapes or growth rate, a field caging experiment was conducted at two different sites of unsuitable and suitable habitats in Matsukawaura Lagoon, Japan, where shell shapes of wild clams were significantly different between the habitats. In the experiment, clams were released from the two sites to the same site or to the other site and were re-collected after 3, 6 and 12 months of caging. Caged clams originating from unsuitable habitats and released to suitable habitats showed a reduction in shell height relative to shell length, while clams from suitable habitats introduced to unsuitable habitats showed marked increases in both shell height and width. Generalized linear mixed models suggested that the increase in shell height was affected largely by the release habitat (environment) whereas the increase in shell width was affected largely by the individual growth rate. These results suggest that marginal growths in shell height and width respond differently to external and internal factors of clams, resulting in plasticity in their shell shapes according to the environments to which they are translocated.

Investigation on hydrate growth at the oil–water interface: In the presence of asphaltene

Natural gas hydrates can readily form in deep-water oil production processes and pose a great threat to the oil industry. Moreover, the coexistence of hydrate and asphaltene can result in more severe challenges to subsea flow assurance. In order to study the effects of asphaltene on hydrate growth at the oil–water interface, a series of micro-experiments were conducted in a self-made reactor, where hydrates nucleated and grew on the surface of a water droplet immersed in asphaltene-containing oil. Based on the micro-observations, the shape and growth rate of the hydrate shell formed at the oil–water interface were mainly investigated and the effects of asphaltene on hydrate growth were analyzed. According to the experimental results, the shape of the water droplet and the interfacial area changed significantly after the formation of the hydrate shell when the asphaltene concentration was higher than a certain value. A mechanism related to the reduction of the interfacial tension caused by the absorption of asphaltenes on the interface was proposed for illustration. Moreover, the growth rate of the hydrate shell decreased significantly with the increasing asphaltene concentration under experimental conditions. The conclusions of this paper could provide preliminary insight how asphaltene affect hydrate growth at the oil–water interface.

Mn/Ca in shells of Arctica islandica (Baltic Sea) – A potential proxy for ocean hypoxia?

Oxygen depletion threatens an increasing number of shallow water environments, specifically habitats below the seasonal halocline in coastal settings of the Baltic Sea. To understand the natural variations of dissolved oxygen levels on seasonal and inter-annual time-scales prior to the instrumental era, high-resolution archives are urgently required. The present study evaluates the potential use of Mn/Ca values in shells of the bivalve, Arctica islandica to infer concentrations of past dissolved oxygen concentrations. This study is based on laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) data of six contemporaneous specimens and demonstrates that background variations of shell Mn/Ca are inversely linked to dissolved oxygen concentrations in the water column (r = −0.68; R2 = 0.46, p < 0.0001), which in turn are coupled to the amount of dissolved Mn. The regular seasonal changes were superimposed by sharp Mn/Ca peaks, most likely resulting from the ingestion of a large amount of Mn-rich organic particles. The availability of such particles can increase due to the resuspension of food particles by strong bottom currents or alternatively, result from increased particle flux from surface waters after major river discharges and subsequent phytoplankton blooms. Besides sharp Mn/Ca peaks, often accompanied by sharp Ba/Ca peaks and increased shell growth rate. In addition, after exceptional major barotropic inflows from the North Sea, the biogeochemical steady-state conditions remained disturbed for up to ca. two years, because the redox-sensitive elements were removed from the water column by oxygenated waters, and it took time for them to build up again in the water column. Therefore, subsequent to such Major Baltic Inflows (MBIs), dissolved Mn levels and shell Mn/Ca values were strongly reduced despite summertime low-oxygen conditions. As demonstrated here, Mn/Ca data of A. islandica shells can potentially serve as a proxy for dissolved oxygen levels in the water column. To further develop this proxy, a set of additional environmental and physiological proxies such as shell Ba/Ca values and growth rate should be critically assessed and used in combination with shell Mn/Ca.

A Review and Meta-Analysis of Potential Impacts of Ocean Acidification on Marine Calcifiers From the Southern Ocean

Understanding the vulnerability of marine calcifiers to ocean acidification is a critical issue, especially in the Southern Ocean (SO), which is likely to be the one of the first, and most severely affected regions. Since the industrial revolution, ~30% of anthropogenic CO2 has been absorbed by the global oceans. Average surface seawater pH levels have already decreased by 0.1 and are projected to decline by ~0.3 by the year 2100. This process, known as ocean acidification (OA), is shallowing the saturation horizon, which is the depth below which calcium carbonate (CaCO3) dissolves, likely increasing the vulnerability of many resident marine calcifiers to dissolution. The negative impact of OA may be seen first in species depositing more soluble CaCO3 mineral phases such as aragonite and high-Mg calcite (HMC). Ocean warming could further exacerbate the effects of OA in these particular species. Here we combine a review and a quantitative meta-analysis to provide an overview of the current state of knowledge about skeletal mineralogy of major taxonomic groups of SO marine calcifiers and to make projections about how OA might affect a broad range of SO taxa. We consider a species' geographic range, skeletal mineralogy, biological traits, and potential strategies to overcome OA. The meta-analysis of studies investigating the effects of the OA on a range of biological responses such as shell state, development and growth rate illustrates that the response variation is largely dependent on mineralogical composition. Species-specific responses due to mineralogical composition indicate that taxa with calcitic, aragonitic, and HMC skeletons, could be at greater risk to expected future carbonate chemistry alterations, and low-Mg calcite (LMC) species could be mostly resilient to these changes. Environmental and biological control on the calcification process and/or Mg content in calcite, biological traits, and physiological processes are also expected to influence species-specific responses.

Effects of elevated temperature and pCO2 on the respiration, biomineralization and photophysiology of the giant clam Tridacna maxima.

Many reef organisms, such as the giant clams, are confronted with global change effects. Abnormally high seawater temperatures can lead to mass bleaching events and subsequent mortality, while ocean acidification may impact biomineralization processes. Despite its strong ecological and socio-economic importance, its responses to these threats still need to be explored. We investigated physiological responses of 4-year-old Tridacna maxima to realistic levels of temperature (+1.5°C) and partial pressure of carbon dioxide (pCO2) (+800 μatm of CO2) predicted for 2100 in French Polynesian lagoons during the warmer season. During a 65-day crossed-factorial experiment, individuals were exposed to two temperatures (29.2°C, 30.7°C) and two pCO2 (430 μatm, 1212 μatm) conditions. The impact of each environmental parameter and their potential synergetic effect were evaluated based on respiration, biomineralization and photophysiology. Kinetics of thermal and/or acidification stress were evaluated by performing measurements at different times of exposure (29, 41, 53, 65days). At 30.7°C, the holobiont O2 production, symbiont photosynthetic yield and density were negatively impacted. High pCO2 had a significant negative effect on shell growth rate, symbiont photosynthetic yield and density. No significant differences of the shell microstructure were observed between control and experimental conditions in the first 29days; however, modifications (i.e. less-cohesive lamellae) appeared from 41days in all temperature and pCO2 conditions. No significant synergetic effect was found. Present thermal conditions (29.2°C) appeared to be sufficiently stressful to induce a host acclimatization response. All these observations indicate that temperature and pCO2 are both forcing variables affecting T. maxima's physiology and jeopardize its survival under environmental conditions predicted for the end of this century.

Factors limiting oyster growth in Willapa Bay (Washington, USA) evaluated with in situ feeding experiments

Natural and anthropogenic environmental changes in estuaries affect the growth and health of organisms living there, often along spatiotemporal gradients. Throughout the world's estuaries, aquaculture and wild oyster populations support food and cultural systems, so quantifying factors affecting growth may inspire interventions to prevent future losses of oyster productivity. In Willapa Bay (Washington, USA), an estuary that produces 10–20% of US oysters, oysters are primarily harvested for market from the lower estuary, putatively due to food limitation up-estuary. We present studies in which in situ experimental systems were designed to manipulate food availability in the upper, and in one case contrasting to the lower, estuary. Contrary to expectations, food addition did not improve survival, shell growth rate or tissue mass of post-metamorphosis juvenile Pacific oysters, Crassostrea gigas. Instead, the experiment did not recapitulate the impaired growth up-estuary that typifies on-bottom oyster outplants, and irrespective of food addition, growth rates in the upper estuary were equivalent to rapid summer growth (>10 mm month−1) in other regions of the bay. Multiple lines of evidence suggest that elevating oysters above the substrate in the experimental systems removed food limitation caused by reduced clearance rates, thus allowing oysters to grow rapidly, even when other environmental conditions such as carbonate chemistry were poor. This observation is consistent with experience of shellfish growers and a valuable observation for managers of wild and aquaculture shellfish in estuaries.