Posts Tagged 'abundance'

Effects of in situ CO2 enrichment on epibiont settlement on artificial substrata within a Posidonia oceanica meadow

Highlights

  • Ocean acidification (OA) may cause community shifts by effecting early life stages.
  • pH was lowered in situ and maintained as an offset within a FOCE setup.
  • Settlement/colonization of molluscs and peracarid crustaceans were robust to OA.
  • Crustose coralline algae and calcifying polychaetes were vulnerable at early life.

Abstract

Alterations to colonization or early post-settlement stages may cause the reorganization of communities under future ocean acidification conditions. Yet, this hypothesis has been little tested by in situ pH manipulation. A Free Ocean Carbon Dioxide Enrichment (FOCE) system was used to lower pH by a ~ 0.3 unit offset within a partially enclosed portion (1.7 m3) of a Posidonia oceanica seagrass meadow (11 m depth) between 21 June and 3 November 2014. Epibiont colonization and early post settlement stages were assessed within the FOCE setup, as part of the larger community-level study, to better understand the outcome for a multispecies assemblage and the ecological processes that result in reported community shifts under altered carbonate chemistry. Two types of artificial collectors (tiles and scourers) were placed within three treatments: a pH-manipulated enclosure, an un-manipulated control enclosure, and an open plot in the ambient meadow. Tiles and scourers were collected after one to four months. Additionally, to see whether the outcome differed for communities in a later successional stage, previously settled scourer-collectors were also placed in the same three treatments. Enclosures acted to reduce settlement and migrant colonization. Scourers deployed for one to four months within the open-plot contained a community assemblage that could be distinguished from the assemblages within the enclosures. However, a comparison of enclosure assemblages on tiles showed evidence of a pH effect. There was lowered coverage of crustose coralline algae and fewer calcareous tube-forming polychaetes (Spirorbis sp. and Spirobranchus sp.) on tiles placed in the pH-manipulated enclosure compared to the un-manipulated enclosure. For assemblages in scourer collectors, shared and common taxa, in all treatments, were invertebrate polychaetes Psamathe fusca, Sphaerosyllis sp., Chrysopetalum sp., arthropods Harpacticoida, and Amphipoda, and the juvenile bivalve Lyonsia sp. Similar organism composition and abundance, as well as taxonomic richness and evenness, were found in scourers from both enclosures. Pre-settled scourers contained greater numbers of individuals and more calcified members, but the assemblage, as well as the growth rate of a juvenile bivalve Lyonsia sp., appeared unaffected by a two-month exposure to lowered pH and calcium carbonate saturation state. Results from this case study support the hypothesis that early stages of specific calcifiers (crustose coralline algae and calcareous tube-forming polychaetes) are sensitive to near future ocean acidification conditions yet suggest that negative effects on sessile micro-invertebrate assemblages will be minimal.

Continue reading ‘Effects of in situ CO2 enrichment on epibiont settlement on artificial substrata within a Posidonia oceanica meadow’

Climate change effects on photosynthetic symbionts in the sea anemone Anthopleura xanthogrammica

The giant green sea anemone (Anthopleura xanthogrammica) inhabits the rocky intertidal zone in California and Oregon. Two photosynthetic algal symbionts, zooxanthellae and zoochlorellae, make these anemones important primary producers in the intertidal zone. This study investigated the effects of changes in temperature and pH on anemones and their symbionts over a natural environmental gradient along the coast of California and Oregon. Zoochlorellae responded negatively to warmer temperatures and positively to more acidic conditions, while zooxanthellae responded positively to warmer temperatures and lower pH. Temperature and pH did not significantly affect chlorophyll a concentrations or anemone protein biomass. Depending on the magnitude of future changes in ocean temperatures and acidity, changes in the ranges of the two types of symbionts and increased densities of sea anemones in the rocky intertidal could be expected to occur.

Continue reading ‘Climate change effects on photosynthetic symbionts in the sea anemone Anthopleura xanthogrammica’

Ecological performance of construction materials subject to ocean climate change

Artificial structures will be increasingly utilized to protect coastal infrastructure from sea-level rise and storms associated with climate change. Although it is well documented that the materials comprising artificial structures influence the composition of organisms that use them as habitat, little is known about how these materials may chemically react with changing seawater conditions, and what effects this will have on associated biota. We investigated the effects of ocean warming, acidification, and type of coastal infrastructure material on algal turfs. Seawater acidification resulted in greater covers of turf, though this effect was counteracted by elevated temperatures. Concrete supported a greater cover of turf than granite or high-density polyethylene (HDPE) under all temperature and pH treatments, with the greatest covers occurring under simulated ocean acidification. Furthermore, photosynthetic efficiency under acidification was greater on concrete substratum compared to all other materials and treatment combinations. These results demonstrate the capacity to maximise ecological benefits whilst still meeting local management objectives when engineering coastal defense structures by selecting materials that are appropriate in an ocean change context. Therefore, mitigation efforts to offset impacts from sea-level rise and storms can also be engineered to alter, or even reduce, the effects of climatic change on biological assemblages.

Continue reading ‘Ecological performance of construction materials subject to ocean climate change’

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’

The combined effects of ocean warming and acidification on shallow-water meiofaunal assemblages

Highlights

  • Higher seawater temperature did not effect meiofaunal abundance.
  • Lower seawater pH did reduce meiofaunal abundance and species richness.
  • Nematode assemblages showed increased dominance under a future OW/OA scenario.


Abstract

Climate change due to increased anthropogenic CO2 in the atmosphere is causing an increase in seawater temperatures referred to as ocean warming and a decrease in seawater pH, referred to as ocean acidification. The meiofauna play an important role in the ecology of marine ecosystems and the functions they provide. Using microcosms, meiofaunal assemblages were exposed to two temperatures (15 and 19 °C) and two pHs (pCO2 of 400 and 1000 ppm), both individually and in combination, for a period of 90 days. The hypothesis that increased temperature will increase meiofaunal abundance was not supported. The hypothesis that a reduced pH will reduce meiofaunal abundance and species richness was supported. The combination of future conditions of temperature and pH (19 °C and pCO2 of 1000 ppm) did not affect overall abundance but the structure of the nematode assemblage changed becoming dominated by a few opportunistic species.

Continue reading ‘The combined effects of ocean warming and acidification on shallow-water meiofaunal assemblages’

The sibling polychaetes Platynereis dumerilii and Platynereis massiliensis in the Mediterranean Sea: are phylogeographic patterns related to exposure to ocean acidification?

High pCO2 environments, such as volcanic carbon dioxide (CO2) vents, which mimic predicted near-future scenarios of ocean acidification (OA), offer an opportunity to examine effects of low pH conditions on marine biodiversity and adaptation/acclimatization of marine organisms to such conditions. Based on previous field studies in these systems, it is predicted that the stress owing to increasing CO2 concentrations favours the colonization by invertebrate species with a brooding habit. The goal of this study was to investigate the relative occurrence of the two sibling species Platynereis dumerilii (Audouin & Milne-Edwards, 1834) (free spawner) and Platynereis massiliensis (Moquin-Tandon, 1869) (egg brooder) in two shallow CO2 vents off Ischia and Vulcano islands (Italy, Tyrrhenian Sea), and in various areas with ambient pH conditions, where they represent one of the dominant genera. Phylogeographic analyses were integrated with reproductive biology and life-history observations on some selected populations thriving in the vent areas. This approach revealed the presence of four distinct Platynereis clades. Whereas two clades primarily inhabit CO2 vents and are presumably all brooders, the other two clades dominate the non-acidified sites and appear to be epitokous free spawners. We postulate that one of the brooding, vent-inhabiting clades represents P. massiliensis and one of the free spawning, non-vent-inhabiting clades represents P. dumerilii, although confirmation of the species status with sequence data from the respective-type localities would be desirable.

Continue reading ‘The sibling polychaetes Platynereis dumerilii and Platynereis massiliensis in the Mediterranean Sea: are phylogeographic patterns related to exposure to ocean acidification?’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book