Posts Tagged 'South Pacific'

Effects of ocean acidification on the larval settlement and metamorphosis of marine invertebrates

Future Ocean acidification (OA) has the potential to negatively affect marine ecosystems and the organisms they support, with the early life-history stages particularly sensitive to reduced seawater pH and carbonate saturation states. Most marine organisms reproduce through an indirect lifecycle, which includes a free-swimming larval stage. In benthic or sessile taxa, the lifecycle is marked by the larval settlement and metamorphosis processes. Here, at the end of the free-living (generally planktonic) stage, larvae selectively search for a preferred settlement substrate for attachment, with metamorphosis occurring before or after it. Larval settlement and metamorphosis are arguably the most important processes in the life cycle of marine invertebrates, since they determine and optimize the final location of the organisms. Altered larval settlement rates will therefore influence the ecology, abundances and distributions of future coastal communities.

The aim of this thesis was to investigate whether OA could affect the larval settlement success of marine invertebrates, and whether these impacts would be mediated through direct, indirect or carry-over mechanisms. Three key New Zealand coastal marine invertebrates were used as model organisms: the sea urchin Evechinus chloroticus, the black-footed abalone (Haliotis iris) or pāua and the serpulid polychaete Galeolaria hystrix.

Continue reading ‘Effects of ocean acidification on the larval settlement and metamorphosis of marine invertebrates’

Near-future ocean warming and acidification alter foraging behaviour, locomotion, and metabolic rate in a keystone marine mollusc

Environmentally-induced changes in fitness are mediated by direct effects on physiology and behaviour, which are tightly linked. We investigated how predicted ocean warming (OW) and acidification (OA) affect key ecological behaviours (locomotion speed and foraging success) and metabolic rate of a keystone marine mollusc, the sea hare Stylocheilus striatus, a specialist grazer of the toxic cyanobacterium Lyngbya majuscula. We acclimated sea hares to OW and/or OA across three developmental stages (metamorphic, juvenile, and adult) or as adults only, and compare these to sea hares maintained under current-day conditions. Generally, locomotion speed and time to locate food were reduced ~1.5- to 2-fold when the stressors (OW or OA) were experienced in isolation, but reduced ~3-fold when combined. Decision-making was also severely altered, with correct foraging choice nearly 40% lower under combined stressors. Metabolic rate appeared to acclimate to the stressors in isolation, but was significantly elevated under combined stressors. Overall, sea hares that developed under OW and/or OA exhibited a less severe impact, indicating beneficial phenotypic plasticity. Reduced foraging success coupled with increased metabolic demands may impact fitness in this species and highlight potentially large ecological consequences under unabated OW and OA, namely in regulating toxic cyanobacteria blooms on coral reefs.

Continue reading ‘Near-future ocean warming and acidification alter foraging behaviour, locomotion, and metabolic rate in a keystone marine mollusc’

State and trends of Australia’s oceans: ocean acidification

The pH and aragonite saturation state of surface seawaters around Australia
are influenced by the large-scale circulation, and superimposed on this are the
effects of seasonal changes due largely to biological activity and temperature
change. Maximum values of aragonite saturation state tend to develop over
summer-early autumn, while pH values are typically greatest in winter.
Biological production contributes to increases of both pH and aragonite
saturation state in the spring-summer, while warming acts to increase the
saturation state and decrease pH. Seasonal ranges of both variables are
already estimated to be outside the ranges that many of Australia’s marine
ecosystems are likely to have experienced in the late 1800s.

Continue reading ‘State and trends of Australia’s oceans: ocean acidification’

State and trends of Australia’s ocean report: ocean acidification and calcifying zooplankton

There is no evidence of a decline in calcifying zooplankton at the IMOS National
Reference Stations over the past 10 years, suggesting ocean acidification
over this time span is unlikely to be having a substantial impact on calcifying
zooplankton. However, there is some evidence that calcifying zooplankton
might at Maria Island and Yongala be sensitive to the aragonite saturation state
at the range of values currently observed.

Continue reading ‘State and trends of Australia’s ocean report: ocean acidification and calcifying zooplankton’

Corals exhibit distinct patterns of microbial reorganisation to thrive in an extreme inshore environment

Climate change threatens the survival of scleractinian coral from exposure to concurrent ocean warming, acidification and deoxygenation; how corals can potentially adapt to this trio of stressors is currently unknown. This study investigates three coral species (Acropora muricata, Acropora pulchra and Porites lutea) dominant in an extreme mangrove lagoon (Bouraké, New Caledonia) where abiotic conditions exceed those predicted for many reef sites over the next 100 years under climate change and compared them to conspecifics from an environmentally more benign reef habitat. We studied holobiont physiology as well as plasticity in coral-associated microorganisms (Symbiodiniaceae and bacteria) through ITS2 and 16S rRNA sequencing, respectively. We hypothesised that differences in coral-associated microorganisms (Symbiodiniaceae and bacteria) between the lagoonal and adjacent reef habitats may support coral host productivity and ultimately the ability of corals to live in extreme environments. In the lagoon, all coral species exhibited a metabolic adjustment of reduced photosynthesis-to-respiration ratios (P/R), but this was accompanied by highly divergent coral host-specific microbial associations. This was substantiated by the absence of shared ITS2-type profiles (proxies for Symbiodiniaceae genotypes). We observed that ITS2 profiles originating from Durusdinium taxa made up < 3% and a novel Symbiodinium ITS2 profile A1-A1v associated with A. pulchra. Bacterial community profiles were also highly divergent in corals from the lagoonal environment, whereas corals from the reef site were consistently dominated by Hahellaceae, Endozoicomonas. As such, differences in host–microorganism associations aligned with different physiologies and habitats. Our results argue that a multitude of host–microorganism associations are required to fulfill the changing nutritional demands of corals persisting into environments that parallel climate change scenarios.

Continue reading ‘Corals exhibit distinct patterns of microbial reorganisation to thrive in an extreme inshore environment’

Key biological responses over two generations of the sea urchin Echinometra sp. A under future ocean conditions

Few studies have investigated the effects of ocean warming and acidification on marine benthic organisms over ecologically relevant time scales. We used an environmentally controlled coral reef mesocosm system to assess growth and physiological responses of the sea urchin species Echinometra sp. A over 2 generations. Each mesocosm was controlled for temperature and pCO2 over 29 mo under 3 climate change scenarios (present day and predicted states in 2050 and 2100 under RCP 8.5). The system maintained treatment conditions including annual temperature cycles and a daily variation in pCO2. Over 20 mo, adult Echinometra exhibited no significant difference in size and weight among the treatments. Growth rates and respiration rates did not differ significantly among treatments. Urchins from the 2100 treatment had elevated ammonium excretion rates and reduced O2:N ratios, suggesting a change in catabolism. We detected no difference in spawning index scores or oocyte size after 20 mo in the treatments, suggesting that gonad development was not impaired by variations in pCO2 and temperature reflecting anticipated climate change scenarios. Larvae produced from experimentally exposed adults were successfully settled from all treatments and raised for 5 mo inside the mesocosm. The final size of these juveniles exhibited no significant difference among treatments. Overall, we demonstrated that the mesocosm system provided a near natural environment for this urchin species. Climate change and ocean acidification did not affect the benthic life stages investigated here. Importantly, in previous short-term (weeks to months) experiments, this species exhibited reductions in growth and gonad development, highlighting the potential for short-term experiments with non-acclimated animals to yield contrasting, possibly erroneous results.

Continue reading ‘Key biological responses over two generations of the sea urchin Echinometra sp. A under future ocean conditions’

Year-long effects of high pCO2 on the community structure of a tropical fore reef assembled in outdoor flumes

In this study, fore reef coral communities were exposed to high pCO2 for a year to explore the relationship between net accretion (Gnet) and community structure (planar area growth). Coral reef communities simulating the fore reef at 17-m depth on Mo’orea, French Polynesia, were assembled in three outdoor flumes (each 500 l) that were maintained at ambient (396 µatm), 782 µatm, and 1434 µatm pCO2, supplied with seawater at 300 l h−1, and exposed to light simulating 17-m depth. The communities were constructed using corals from the fore reef, and the responses of massive Porites spp., Acropora spp., and Pocillopora verrucosa were assessed through monthly measurements of Gnet and planar area. High pCO2 depressed Gnet but did not affect colony area by taxon, although the areas of Acropora spp. and P. verrucosa summed to cause multivariate community structure to differ among treatments. These results suggest that skeletal plasticity modulates the effects of reduced Gnet at high pCO2 on planar growth, at least over a year. The low sensitivity of the planar growth of fore reef corals to the effects of ocean acidification (OA) on net calcification supports the counterintuitive conclusion that coral community structure may not be strongly affected by OA.

Continue reading ‘Year-long effects of high pCO2 on the community structure of a tropical fore reef assembled in outdoor flumes’

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Ocean acidification in the IPCC AR5 WG II

OUP book