Posts Tagged 'community composition'

Changes in fish communities due to benthic habitat shifts under ocean acidification conditions

Highlights

• Ocean acidification-mediated habitat shifts and decreased complexity affect associated fish communities.

• Altered fish traits and reduced diversity occurred under near-future ocean acidification levels.

• Ocean acidification may oppose the poleward-shift of tropical fish species under warming.

Abstract

Ocean acidification will likely change the structure and function of coastal marine ecosystems over coming decades. Volcanic carbon dioxide seeps generate dissolved CO2 and pH gradients that provide realistic insights into the direction and magnitude of these changes. Here, we used fish and benthic community surveys to assess the spatio-temporal dynamics of fish community properties off CO2 seeps in Japan. Adding to previous evidence from ocean acidification ecosystem studies conducted elsewhere, our findings documented shifts from calcified to non-calcified habitats with reduced benthic complexity. In addition, we found that such habitat transition led to decreased diversity of associated fish and to selection of those fish species better adapted to simplified ecosystems dominated by algae. Our data suggest that near-future projected ocean acidification levels will oppose the ongoing range expansion of coral reef-associated fish due to global warming.

Continue reading ‘Changes in fish communities due to benthic habitat shifts under ocean acidification conditions’

Responses of intertidal bacterial biofilm communities to increasing pCO2

The effects of ocean acidification on ecosystems remain poorly understood, because it is difficult to simulate the effects of elevated CO2 on entire marine communities. Natural systems enriched in CO2 are being used to help understand the long-term effects of ocean acidification in situ. Here, we compared biofilm bacterial communities on intertidal cobbles/boulders and bedrock along a seawater CO2 gradient off Japan. Samples sequenced for 16S rRNA showed differences in bacterial communities with different pCO2 and between habitat types. In both habitats, bacterial diversity increased in the acidified conditions. Differences in pCO2 were associated with differences in the relative abundance of the dominant phyla. However, despite the differences in community composition, there was no indication that these changes would be significant for nutrient cycling and ecosystem function. As well as direct effects of seawater chemistry on the biofilm, increased microalgal growth and decreased grazing may contribute to the shift in bacterial composition at high CO2, as documented by other studies. Thus, the effects of changes in bacterial community composition due to globally increasing pCO2 levels require further investigation to assess the implications for marine ecosystem function. However, the apparent lack of functional shifts in biofilms along the pCO2 gradient is a reassuring indicator of stability of their ecosystem functions in shallow ocean margins.

Continue reading ‘Responses of intertidal bacterial biofilm communities to increasing pCO2’

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’

Ocean acidification affects microbial community and invertebrate settlement on biofilms

Increased atmospheric CO2 is driving ocean acidification (OA), and potential changes in marine ecosystems. Research shows that both planktonic and benthic communities are affected, but how these changes are linked remains unresolved. Here we show experimentally that decreasing seawater pH (from pH 8.1 to 7.8 and 7.4) leads to reduced biofilm formation and lower primary producer biomass within biofilms. These changes occurred concurrently with a re-arrangement of the biofilm microbial communities. Changes suggest a potential shift from autotrophic to heterotrophic dominated biofilms in response to reduced pH. In a complimentary experiment, biofilms reared under reduced pH resulted in altered larval settlement for a model species (Galeolaria hystrix). These findings show that there is a potential cascade of impacts arising from OA effects on biofilms that may drive important community shifts through altered settlement patterns of benthic species.

Continue reading ‘Ocean acidification affects microbial community and invertebrate settlement on biofilms’

A high biodiversity mitigates the impact of ocean acidification on hard-bottom ecosystems

Biodiversity loss and climate change simultaneously threaten marine ecosystems, yet their interactions remain largely unknown. Ocean acidification severely affects a wide variety of marine organisms and recent studies have predicted major impacts at the pH conditions expected for 2100. However, despite the renowned interdependence between biodiversity and ecosystem functioning, the hypothesis that the species’ response to ocean acidification could differ based on the biodiversity of the natural multispecies assemblages in which they live remains untested. Here, using experimentally controlled conditions, we investigated the impact of acidification on key habitat-forming organisms (including corals, sponges and macroalgae) and associated microbes in hard-bottom assemblages characterised by different biodiversity levels. Our results indicate that, at higher biodiversity, the impact of acidification on otherwise highly vulnerable key organisms can be reduced by 50 to >90%, depending on the species. Here we show that such a positive effect of a higher biodiversity can be associated with higher availability of food resources and healthy microbe-host associations, overall increasing host resistance to acidification, while contrasting harmful outbreaks of opportunistic microbes. Given the climate change scenarios predicted for the future, we conclude that biodiversity conservation of hard-bottom ecosystems is fundamental also for mitigating the impacts of ocean acidification.

Continue reading ‘A high biodiversity mitigates the impact of ocean acidification on hard-bottom ecosystems’

Symbiont community diversity is more variable in corals that respond poorly to stress

Coral reefs are declining globally as climate change and local water quality press environmental conditions beyond the physiological tolerances of holobionts—the collective of the host and its microbial symbionts. To assess the relationship between symbiont composition and holobiont stress tolerance, community diversity metrics were quantified for dinoflagellate endosymbionts (Family: Symbiodiniaceae) from eight Acropora millepora genets that thrived under or responded poorly to various stressors. These eight selected genets represent the upper and lower tails of the response distribution of 40 coral genets that were exposed to four stress treatments (and control conditions) in a 10‐day experiment. Specifically, four ‘best performer’ coral genets were analyzed at the end of the experiment because they survived high temperature, high pCO2, bacterial exposure, or combined stressors, whereas four ‘worst performer’ genets were characterized because they experienced substantial mortality under these stressors. At the end of the experiment, seven of eight coral genets mainly hosted Cladocopium symbionts, whereas the eighth genet was dominated by both Cladocopium and Durusdinium symbionts. Symbiodiniaceae alpha and beta diversity were higher in worst performing genets than in best performing genets. Symbiont communities in worst performers also differed more after stress exposure relative to their controls (based on normalized proportional differences in beta diversity), than did best performers. A generalized joint attribute model estimated the influence of host genet and treatment on Symbiodiniaceae community composition and identified strong associations among particular symbionts and host genet performance, as well as weaker associations with treatment. Although dominant symbiont physiology and function contribute to host performance, these findings emphasize the importance of symbiont community diversity and stochasticity as components of host performance. Our findings also suggest that symbiont community diversity metrics may function as indicators of resilience and have potential applications in diverse disciplines from climate change adaptation to agriculture and medicine.

Continue reading ‘Symbiont community diversity is more variable in corals that respond poorly to stress’

A unique temperate rocky coastal hydrothermal vent system (Whakaari–White Island, Bay of Plenty, New Zealand): constraints for ocean acidification studies

In situ effects of ocean acidification are increasingly studied at submarine CO2 vents. Here we present a preliminary investigation into the water chemistry and biology of cool temperate CO2 vents near Whakaari–White Island, New Zealand. Water samples were collected inside three vent shafts, within vents at a distance of 2 m from the shaft and at control sites. Vent samples contained both seawater pH on the total scale (pHT) and carbonate saturation states that were severely reduced, creating conditions as predicted for beyond the year 2100. Vent samples showed lower salinities, higher temperatures and greater nutrient concentrations. Sulfide levels were elevated and mercury levels were at concentrations considered toxic at all vent and control sites, but stable organic and inorganic ligands were present, as deduced from Cu speciation data, potentially mediating harmful effects on local organisms. The biological investigations focused on phytoplankton, zooplankton and macroalgae. Interestingly, we found lower abundances but higher diversity of phytoplankton and zooplankton at sites in the direct vicinity of Whakaari. Follow-up studies will need a combination of methods and approaches to attribute observations to specific drivers. The Whakaari vents represent a unique ecosystem with considerable biogeochemical complexity, which, like many other vent systems globally, require care in their use as a model of ‘future oceans’.

Continue reading ‘A unique temperate rocky coastal hydrothermal vent system (Whakaari–White Island, Bay of Plenty, New Zealand): constraints for ocean acidification studies’


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Ocean acidification in the IPCC AR5 WG II

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