Posts Tagged 'South Pacific'

Sponge bioerosion on changing reefs: ocean warming poses physiological constraints to the success of a photosymbiotic excavating sponge

Excavating sponges are prominent bioeroders on coral reefs that in comparison to other benthic organisms may suffer less or may even benefit from warmer, more acidic and more eutrophic waters. Here, the photosymbiotic excavating sponge Cliona orientalis from the Great Barrier Reef was subjected to a prolonged simulation of both global and local environmental change: future seawater temperature, partial pressure of carbon dioxide (as for 2100 summer conditions under “business-as-usual” emissions), and diet supplementation with particulate organics. The individual and combined effects of the three factors on the bioerosion rates, metabolic oxygen and carbon flux, biomass change and survival of the sponge were monitored over the height of summer. Diet supplementation accelerated bioerosion rates. Acidification alone did not have a strong effect on total bioerosion or survival rates, yet it co-occurred with reduced heterotrophy. Warming above 30 °C (+2.7 °C above the local maximum monthly mean) caused extensive bleaching, lower bioerosion, and prevailing mortality, overriding the other factors and suggesting a strong metabolic dependence of the sponge on its resident symbionts. The growth, bioerosion capacity and likelihood of survival of C. orientalis and similar photosymbiotic excavating sponges could be substantially reduced rather than increased on end-of-the-century reefs under “business-as-usual” emission profiles.

Continue reading ‘Sponge bioerosion on changing reefs: ocean warming poses physiological constraints to the success of a photosymbiotic excavating sponge’

Future marine ecosystem drivers, biodiversity, and fisheries maximum catch potential in Pacific Island countries and territories under climate change

Highlights

  • Under the RCP 8.5 scenario, tropical Pacific temperature will rise by ≥ 3 °C by 2100.
  • This is accompanied by declines in dissolved oxygen, pH, and net primary production.
  • This will lead to local extinctions of up to 80% of marine species in some regions.
  • 9 of 17 Pacific Island entities experience ≥ 50% declines in maximum catch potential.
  • Impacts can be greatly reduced by mitigation measures under the RCP 2.6 scenario.


Abstract

The increase in anthropogenic CO2 emissions over the last century has modified oceanic conditions, affecting marine ecosystems and the goods and services that they provide to society. Pacific Island countries and territories are highly vulnerable to these changes because of their strong dependence on ocean resources, high level of exposure to climate effects, and low adaptive capacity. Projections of mid-to-late 21st century changes in sea surface temperature (SST), dissolved oxygen, pH, and net primary productivity (NPP) were synthesized across the tropical Western Pacific under strong climate mitigation and business-as-usual scenarios. These projections were used to model impacts on marine biodiversity and potential fisheries catches. Results were consistent across three climate models, indicating that SST will rise by ≥ 3 °C, surface dissolved oxygen will decline by ≥ 0.01 ml L−1, pH will drop by ≥ 0.3, and NPP will decrease by 0.5 g m−2 d−1 across much of the region by 2100 under the business-as-usual scenario. These changes were associated with rates of local species extinction of > 50% in many regions as fishes and invertebrates decreased in abundance or migrated to regions with conditions more suitable to their bio-climate envelope. Maximum potential catch (MCP) was projected to decrease by > 50% across many areas, with the largest impacts in the western Pacific warm pool. Climate change scenarios that included strong mitigation resulted in substantial reductions of MCP losses, with the area where MCP losses exceeded 50% reduced from 74.4% of the region under business-as-usual to 36.0% of the region under the strong mitigation scenario.

Continue reading ‘Future marine ecosystem drivers, biodiversity, and fisheries maximum catch potential in Pacific Island countries and territories under climate change’

Low recruitment due to altered settlement substrata as primary constraint for coral communities under ocean acidification

The future of coral reefs under increasing CO2 depends on their capacity to recover from disturbances. To predict the recovery potential of coral communities that are fully acclimatized to elevated CO2, we compared the relative success of coral recruitment and later life stages at two volcanic CO2 seeps and adjacent control sites in Papua New Guinea. Our field experiments showed that the effects of ocean acidification (OA) on coral recruitment rates were up to an order of magnitude greater than the effects on the survival and growth of established corals. Settlement rates, recruit and juvenile densities were best predicted by the presence of crustose coralline algae, as opposed to the direct effects of seawater CO2. Offspring from high CO2 acclimatized parents had similarly impaired settlement rates as offspring from control parents. For most coral taxa, field data showed no evidence of cumulative and compounding detrimental effects of high CO2 on successive life stages, and three taxa showed improved adult performance at high CO2 that compensated for their low recruitment rates. Our data suggest that severely declining capacity for reefs to recover, due to altered settlement substrata and reduced coral recruitment, is likely to become a dominant mechanism of how OA will alter coral reefs.

Continue reading ‘Low recruitment due to altered settlement substrata as primary constraint for coral communities under ocean acidification’

Overcalcified forms of the coccolithophore Emiliania huxleyi in high CO2 waters are not pre-adapted to ocean acidification

Marine multicellular organisms inhabiting waters with natural high fluctuations in pH appear more tolerant to acidification than conspecifics occurring in nearby stable waters, suggesting that environments of fluctuating pH hold genetic reservoirs for adaptation of key groups to ocean acidification (OA). The abundant and cosmopolitan calcifying phytoplankton Emiliania huxleyi exhibits a range of morphotypes with varying degrees of coccolith mineralization. We show that E. huxleyi populations in the naturally acidified upwelling waters of the Eastern South Pacific, where pH drops below 7.8 as is predicted for the global surface ocean by the year 2100, are dominated by exceptionally overcalcified morphotypes whose distal coccolith shield can be almost solid calcite. Shifts in morphotype composition of E. huxleyi populations correlate with changes in carbonate system parameters. We tested if these correlations indicate that the hypercalcified morphotype is adapted to OA. In experimental exposures to present-day vs. future pCO2 (400 µatm vs. 1200 µatm), the overcalcified morphotypes showed the same growth inhibition (−29.1 ± 6.3 %) as moderately calcified morphotypes isolated from non-acidified water (−30.7 ± 8.8 %). Under OA conditions, production rates of particulate organic carbon (POC) increased, while production rates of particulate inorganic carbon (PIC) were maintained or decreased slightly (but not significantly), leading to lowered PIC/POC ratios in all strains. There were no consistent correlations of response intensity with strain origin. OA affected coccolith morphology equally or more strongly in overcalcified strains compared to moderately calcified strains. OA conditions appear not to directly select for exceptionally overcalcified morphotypes over other morphotypes directly, but perhaps indirectly by ecologically correlated factors. More generally, these results suggest that oceanic planktonic microorganisms, despite their rapid turn-over and large population sizes, do not necessarily exhibit adaptations to naturally high CO2 upwellings, and this ubiquitous coccolithophore may be near a limit of its capacity to adapt to ongoing ocean acidification.
Continue reading ‘Overcalcified forms of the coccolithophore Emiliania huxleyi in high CO2 waters are not pre-adapted to ocean acidification’

Ocean acidification and pathogen exposure modulate the immune response of the edible mussel Mytilus chilensis

Highlights

  • Exposure to futuristic concentration of pCO2 modulates innate immune response.
  • After OA-stress, gene expression is partially counteracted after pathogen challenge.
  • pCO2 might trigger specific immune-related genes at early stages of infection.
  • Combination of OA and bacterial infection seems to have partial antagonistic effects.


Abstract

Ocean acidification (OA) is one of the main consequences of increasing atmospheric carbon dioxide (CO2), impacting key biological processes of marine organisms such as development, growth and immune response. However, there are scarce studies on the influence of OA on marine invertebrates’ ability to cope with pathogens. This study evaluated the single and combined effects of OA and bacterial infection on the transcription expression of genes related to antioxidant system, antimicrobial peptides and pattern recognition receptors in the edible mussel Mytilus chilensis. Individuals of M. chilensis were exposed during 60 days at two concentrations of pCO2 (550 and 1200 μatm) representing respectively current and future scenario of OA and were then injected with the pathogenic bacterium Vibrio anguillarum. Results evidenced an immunomodulation following the OA exposure with an up-regulation of C-type Lectin and Mytilin B and a down-regulation of Myticin A and PGRP. This immunomodulation pattern is partially counteracted after challenge with V. anguillarum with a down-regulation of the C-type lectin and Mytilin B and the up-regulation of Myticin A. In turn, these results evidence that pCO2-driven OA scenarios might triggers specific immune-related genes at early stages of infection, promoting the transcription of antimicrobial peptides and patterns recognition receptors. This study provides new evidence of how the immune response of bivalves is modulated by higher CO2 conditions in the ocean, as well one factor for the resilience of marine population upon global change scenarios.

Continue reading ‘Ocean acidification and pathogen exposure modulate the immune response of the edible mussel Mytilus chilensis’

Diel CO2 cycles reduce severity of behavioural abnormalities in coral reef fish under ocean acidification

Elevated CO2 levels associated with ocean acidification (OA) have been shown to alter behavioural responses in coral reef fishes. However, all studies to date have used stable pCO2 treatments, not considering the substantial diel pCO2 variation that occurs in shallow reef habitats. Here, we reared juvenile damselfish, Acanthochromis polyacanthus, and clownfish, Amphiprion percula, at stable and diel cycling pCO2 treatments in two experiments. As expected, absolute lateralization of A. polyacanthus and response to predator cue of Am. percula were negatively affected in fish reared at stable, elevated pCO2 in both experiments. However, diel pCO2 fluctuations reduced the negative effects of OA on behaviour. Importantly, in experiment two, behavioural abnormalities that were present in fish reared at stable 750 µatm CO2 were largely absent in fish reared at 750 ± 300 µatm CO2. Overall, we show that diel pCO2 cycles can substantially reduce the severity of behavioural abnormalities caused by elevated CO2. Thus, past studies may have over-estimated the impacts of OA on the behavioural performance of coral reef fishes. Furthermore, our results suggest that diel pCO2 cycles will delay the onset of behavioural abnormalities in natural populations.

Continue reading ‘Diel CO2 cycles reduce severity of behavioural abnormalities in coral reef fish under ocean acidification’

Biochemical composition of turbinid snails and its sensitivity to ocean climate change

Information on the biochemical composition of under-utilised species, such as turban snails, is required to establish their nutritional quality, and improve consumer acceptance as a novel food source. Turbo militaris, Lunella undulata and L. torquata are large common gastropod species with overlapping distributions in eastern Australia. The edible foot tissue from these three species was analysed for comparison of their proximate composition, fatty acids and mineral elements. All species were found to have a high protein content and low lipid levels that are rich in polyunsaturated fatty acids (PUFAs), with a favourable ratio of omega–3/omega–6 PUFAs for human consumption. Turban snails also provide a good source of essential elements. To quantify the temporal changes in nutritional properties, L. undulata was collected monthly from the same site, Evans head, NSW from December 2013 to January 2015. Sex, shell sizes and gonadosomatic index (GSI) were recorded in order to investigate if these parameters influence the condition index (CI), meat yield (MY), proximate composition and trace elements of the edible foot tissue. The flesh of L. undulata can be considered nutritious and generally safe for human consumption all year round, but for the purpose of sustainable harvest, the peak spawning should be avoided to allow for successful reproduction. A manipulative experiment to investigate the effects of 38-day exposure to near-future ocean warming and acidification revealed that temperature alone affects the percentages of PUFAs in the foot tissue. Nevertheless, the main nutritional properties of high protein and low lipids dominated by PUFAs were consistently found in the Turbinidae. Toxic heavy metal elements remained well below the maximum allowed under Australia and New Zealand Food Standards. Based on their upper thermal limit, turban snails may be resilient to near-future ocean-warming, but they prefer lower temperatures, which could result in a southward retraction of the distribution of these species in NSW, Australia. Overall, this study shows that turban snails can provide a fisheries resource of similar quality to abalone, but ocean warming may influence the range of the target populations and the quality of lipids, but the product would be otherwise little-affected.

Continue reading ‘Biochemical composition of turbinid snails and its sensitivity to ocean climate change’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

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