Posts Tagged 'South Pacific'

The Great Barrier Reef: vulnerabilities and solutions in the face of ocean acidification

As living carbonate-based structures, coral reefs are highly vulnerable to ocean acidification. The Great Barrier Reef (GBR) is the largest continuous coral reef system in the world. Its economic, social, and icon assets are valued at AU$56 billion (Deloitte Access Economics, 2017), owing to its vast biodiversity and services related to commercial and recreational fisheries, shoreline protection, and reef-related tourism and recreation. Ocean acidification poses a significant risk to these ecological and socioeconomic services, threatening not only the structural foundation of the GBR but the livelihoods of reef-dependent sectors of society. To assess the vulnerabilities of the GBR to ocean acidification, we review the characteristics of the GBR and the current valuation and factors affecting potential losses across three major areas of socioeconomic concern: fisheries, shoreline protection, and reef-related tourism and recreation. We then discuss potential solutions, both conventional and unconventional, for mitigating ocean acidification impacts on the GBR and propose a suite of actions that would help assess and increase the region’s preparedness for the effects of ocean acidification.

Continue reading ‘The Great Barrier Reef: vulnerabilities and solutions in the face of ocean acidification’

Future ocean climate homogenizes communities across habitats through diversity loss and rise of generalist species

Predictions of the effects of global change on ecological communities are largely based on single habitats. Yet in nature, habitats are interconnected through the exchange of energy and organisms, and the responses of local communities may not extend to emerging community networks (i.e. metacommunities). Using large mesocosms and meiofauna communities as a model system, we investigated the interactive effects of ocean warming and acidification on the structure of marine metacommunities from three shallow‐water habitats: sandy soft‐bottoms, marine vegetation and rocky reef substrates. Primary producers and detritus – key food sources for meiofauna – increased in biomass under the combined effect of temperature and acidification. The enhanced bottom‐up forcing boosted nematode densities but impoverished the functional and trophic diversity of nematode metacommunities. The combined climate stressors further homogenized meiofauna communities across habitats. Under present‐day conditions metacommunities were structured by habitat type, but under future conditions they showed an unstructured random pattern with fast‐growing generalist species dominating the communities of all habitats. Homogenization was likely driven by local species extinctions, reducing interspecific competition that otherwise could have prevented single species from dominating multiple niches. Our findings reveal that climate change may simplify metacommunity structure and prompt biodiversity loss, which may affect the biological organization and resilience of marine communities.

Continue reading ‘Future ocean climate homogenizes communities across habitats through diversity loss and rise of generalist species’

A future 1.2 °C increase in ocean temperature alters the quality of mangrove habitats for marine plants and animals

• Mangrove habitats are more resilient to climate change than other habitats.

• Climate change might have positive effects on mangrove-root species communities.

• Using mesocosms we show that an increase of 1.2 °C leads to community homogenisation.

• Warming also led to diversity loss and flattening of mangrove root epibiont communities.

• Juvenile fish altered their use of mangrove habitats under warming and acidification.

Global climate stressors, like ocean warming and acidification, contribute to the erosion of structural complexity in marine foundation habitats by promoting the growth of low-relief turf, increasing grazing pressure on structurally complex marine vegetation, and by directly affecting the growth and survival of foundation species. Because mangrove roots are woody and their epibionts are used to ever-changing conditions in highly variable environments, mangrove habitats may be more resilient to global change stressors than other marine foundation species. Using a large-scale mesocosm experiment, we examined how ocean warming and acidification, under a reduced carbon emission scenario, affect the composition and structural complexity of mangrove epibiont communities and the use of mangrove habitat by juvenile fishes. We demonstrate that even a modest increase in seawater temperature of 1.2 °C leads to the homogenisation and flattening of mangrove root epibiont communities. Warming led to a 24% increase in the overall cover of algal epibionts on roots but the diversity of the epibiont species decreased by 33%. Epibiont structural complexity decreased owing to the shorter stature of weedy algal turfs which prospered under elevated temperature. Juvenile fishes showed alterations in mangrove habitat use with ocean warming and acidification, but these were independent of changes to the root epibiont community. We reveal that the quality of apparently resilient mangrove habitats and their perceived value as habitat for associated fauna are still vulnerable under a globally reduced carbon emission scenario.

Continue reading ‘A future 1.2 °C increase in ocean temperature alters the quality of mangrove habitats for marine plants and animals’

Changes in coral reef community structure in response to year-long incubations under contrasting pCO2 regimes

Coral reefs are threatened by ocean acidification (OA), which depresses net calcification of corals, calcified algae, and coral reef communities. These effects have been quantified for many organisms, but most experiments last weeks-to-months, and do not test for effects on community structure. Here, the effects of OA on back reef communities from Mo’orea, French Polynesia (17.492 S, 149.826 W), were tested from 12 November 2015 to 16 November 2016 in outdoor flumes maintained at mean pCO2 levels of 364 µatm, 564 µatm, 761 µatm, and 1067 µatm. The communities consisted of four corals and two calcified algae, with change in mass (Gnet, a combination of gross accretion and dissolution) and percent cover recorded monthly. For massive Porites and Montipora spp., Gnet differed among treatments, and at 1067 µatm (relative to ambient) was reduced and still positive; for Porolithon onkodes, all of which died, Gnet was negative at high pCO2, revealing dissolution (sample sizes were too small for analysis of Gnet for other taxa). Growth rates (% cover month−1) were unaffected by pCO2 for Montipora spp., P. rus, Pocillopora verrucosa, and Lithophyllum kotschyanum, but were depressed for massive Porites at 564 µatm. Multivariate community structure changed among seasons, and the variation under all elevated pCO2 treatments differed from that recorded at 364 µatm, and was greatest under 564 µatm and 761 µatm pCO2. Temporal variation in multivariate community structure could not be attributed solely to the effects of OA on the chemical and physical properties of seawater. Together, these results suggest that coral reef community structure may be more resilient to OA than suggested by the negative effects of high pCO2 on Gnet of their component organisms.

Continue reading ‘Changes in coral reef community structure in response to year-long incubations under contrasting pCO2 regimes’

Long-term acclimation to near-future ocean acidification has negligible effects on energetic attributes in a juvenile coral reef fish

Increased levels of dissolved carbon dioxide (CO2) drive ocean acidification and have been predicted to increase the energy use of marine fishes via physiological and behavioural mechanisms. This notion is based on a theoretical framework suggesting that detrimental effects on energy use are caused by plasma acid–base disruption in response to hypercapnic acidosis, potentially in combination with a malfunction of the gamma aminobutyric acid type A (GABAA) receptors in the brain. However, the existing empirical evidence testing these effects primarily stems from studies that exposed fish to elevated CO2 for a few days and measured a small number of traits. We investigated a range of energetic traits in juvenile spiny chromis damselfish (Acanthochromis polyacanthus) over 3 months of acclimation to projected end-of-century CO2 levels (~ 1000 µatm). Somatic growth and otolith size and shape were unaffected by the CO2 treatment across 3 months of development in comparison with control fish (~ 420 µatm). Swimming activity during behavioural assays was initially higher in the elevated CO2 group, but this effect dissipated within ~ 25 min following handling. The transient higher activity of fish under elevated CO2 was not associated with a detectable difference in the rate of oxygen uptake nor was it mediated by GABAA neurotransmitter interference because treatment with a GABAA antagonist (gabazine) did not abolish the CO2 treatment effect. These findings contrast with several short-term studies by suggesting that end-of-century levels of CO2 may have negligible direct effects on the energetics of at least some species of fish.

Continue reading ‘Long-term acclimation to near-future ocean acidification has negligible effects on energetic attributes in a juvenile coral reef fish’

Wasting away in the intertidal: the fate of chiton valves in an acidifying ocean

Chitons are locally common in New Zealand, and several studies have suggested that their valves are resistant to dissolution, so it seems contradictory that they are under-represented in the sediment and fossil records of New Zealand. Indeed, special resistance to dissolution seems counterintuitive since the valves are primarily made of aragonite. Here we examine the resistance of chiton skeletal material to dissolution in order to expand our understanding of how taphonomic forces affect chitons and to provide insight into the preservation potential of chiton valves. Live individuals of eight species of chitons were collected from Otago Peninsula, South Island, New Zealand. The valves were subjected to one of two pH treatments: ambient pH of 8.10 and reduced pH of 7.70. Notoplax violacea, Sypharochiton pelliserpentis, and S. sinclairi were the most resistant to dissolution while Acanthochitona zelandica, Chiton glaucus, Onithochiton neglectus, and Ischnochiton maorianus were more vulnerable to dissolution. Leptochiton inquinatus lost the most mass in both treatments, but did not show a significant difference between them. SEM images of the dorsal and ventral surfaces on each valve revealed low-pH damage to crystal structures in the articulamentum, while the tegmentum showed no significant damage. Chiton skeletal material in general does not appear to resist dissolution any better than other examined mollusks, but the resistant tegmentum confers considerable resilience to lowered pH. Chiton valves can last up to an estimated 45 years before becoming unrecognizable, which is much shorter than the normal temperate shallow-water exposure time of hundreds to thousands of years.

Continue reading ‘Wasting away in the intertidal: the fate of chiton valves in an acidifying ocean’

Effects of coralline algal diffusion boundary layers on growth of newly settled sea urchins: implications for ocean acidification conditions

Macroalgae are able to modify their local environment via biological processes, thereby creating a diffusive boundary layer (DBL) where the chemical and physical environment differs from the overlying bulk seawater. In slow flow environments, the DBL has the potential to modulate effects of reduced seawater pH associated with ocean acidification (OA). OA poses a major threat to marine ecosystems and particularly to calcifying organisms. While implications for macroalgae and corals in the DBL have been studied, the effects on invertebrates settling and inhabiting the DBL are not well understood. This study examines
the oxygen and pH conditions within coralline algal DBLs that change as a result of irradiance, flow and bulk seawater pH, in order to understand the effects of these variable conditions on growth of juvenile sea urchins in the DBL. Oxygen concentrations, used as a proxy for pH based on previous research, were measured above crustose coralline algal surfaces to determine DBL thickness and pH levels within the DBL. Newly settled juvenile sea urchins Pseudechinus huttoni were subsequently grown in these conditions for up to 11 days. Morphological measurements (test diameter and spine length) and scanning electron microscopy were used to examine growth and calcification of sea urchins.

Seawater pH levels above CCA varied as a result of irradiance, flow and bulk seawater pH. In static flow, CCA increased pH at its surface up to approximately 0.8 units above the overlying bulk seawater in the light, but only decreased pH up to nearly 0.09 units below bulk seawater in the dark. DBLs were thickest at zero or slow flow (1 cm s-1 ) in the light. pH levels in the DBL varied from approximately pHT 7.4 to 8.6, but there was no strong effect of these varying pH levels within the DBL on post-settlement growth of P. huttoni juveniles. Life in
the diffusion boundary has allowed juveniles to adapt to grow and calcify in naturally fluctuating pH environments. This finding supports observations seen in other juvenile sea urchins, and is significant because it indicates that the early post-settlement stage may not be as sensitive to OA as the larval stage, where negative effects have been previously documented. Life in thick diffusion boundary layers above CCA in slow-flow fjord environments may have increased tolerance of juvenile P. huttoni to reduced bulk seawater pH, thereby conferring greater resilience to future ocean acidification conditions.

Continue reading ‘Effects of coralline algal diffusion boundary layers on growth of newly settled sea urchins: implications for ocean acidification conditions’

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Ocean acidification in the IPCC AR5 WG II

OUP book