Posts Tagged 'community composition'

Epibenthic community variation along an acidified tropical estuarine system

The benthic communities associated with hard substrata in tropical estuaries (rocky surfaces and mangrove roots) are underexplored compared to sediment-associated communities. Being unaffected by within-sediment chemistry, rocky surface communities are exposed to water-column chemistry. Natural and anthropogenic acidic inflows into estuaries are common, yet understanding of how low pH estuarine water impacts communities is limited. This study investigated variation in a rocky substratum benthic community along a steep pH and carbonate saturation gradient in a tropical estuary. Samples (n=72) samples were collected from four stations in the Brunei estuarine system, South East Asia (pH 5.78 – 8.1, salinity 0.1 – 29.5 psu). Species richness, diversity and abundance were greatest at the seaward end of the estuary (where pH and salinity were high), reduced in the middle estuary, and relatively high again in the upper estuary. A total of 34 species were recorded, with station abundances varying between 95 and 336 individuals/100 cm2. At a coarse taxonomic level (class/order), multivariate analyses revealed three distinct communities, a tanaid–polychaete dominated community, a mussel–dipteran community, and a mussel–amphipod–dipteran community. The observed shift from amphipod-dominance to polychaete-dominance along a decreasing pH gradient is consistent with the community changes seen in open ocean systems influenced by elevated pCO2. This study is the first description of community structure variation for hard-substratum invertebrates in an old-world tropical estuary. It shows that acidified estuaries offer insights into community-level responses to marine acidification in general.

Continue reading ‘Epibenthic community variation along an acidified tropical estuarine system’

Ocean acidification and warming effects on the physiology, skeletal properties, and microbiome of the purple-hinge rock scallop


• Is the physiology of Crassadoma gigantea affected by warming and acidification?

• Warming and acidification reduced shell strength & increased total lipid content.

• Exposed scallops reorganized fatty acids to sustain metabolic functions.

• Treatments lead to differences in microbiome community composition.

• This was the first multi-stressor experiment on Crassadoma gigantea.

• This was the first multi-stressors experiment to define a core microbiome in a bivalve.


Ocean acidification and increased ocean temperature from elevated atmospheric carbon dioxide can significantly influence the physiology, growth and survival of marine organisms. Despite increasing research efforts, there are still many gaps in our knowledge of how these stressors interact to affect economically and ecologically important species. This project is the first to explore the physiological effects of high pCO2 and temperature on the acclimation potential of the purple-hinge rock scallop (Crassadoma gigantea), a widely distributed marine bivalve, important reef builder, and potential aquaculture product. Scallops were exposed to two pCO2 (365 and 1050 μatm) and temperature (14 and 21.5 °C) conditions in a two-factor experimental design. Simultaneous exposure to high temperature and high pCO2 reduced shell strength, decreased outer shell density and increased total lipid content. Despite identical diets, scallops exposed to high pCO2 had higher content of saturated fatty acids, and lower content of polyunsaturated fatty acids suggesting reorganization of fatty acid chains to sustain basic metabolic functions under high pCO2. Metagenomic sequencing of prokaryotes in scallop tissue revealed treatment differences in community composition between treatments and in the presence of genes associated with microbial cell regulation, signaling, and pigmentation. Results from this research highlight the complexity of physiological responses for calcifying species under global change related stress and provide the first insights for understanding the response of a bivalve’s microbiome under multiple stressors.

Continue reading ‘Ocean acidification and warming effects on the physiology, skeletal properties, and microbiome of the purple-hinge rock scallop’

Life in the freezer : the role of dimethylsulfoniopropionate (DMSP) in the physiological and biochemical adaptations of Antarctic microalgae

Marine microalgae are the fuel of the Antarctic ecosystem and changes in primary production can impact the entire food web, as well as the nutritional value at the base of the food web which is dependant not only on biomass but also the macromolecular content of the individual species. Primary production by Antarctic microalgae is also of key importance in the biogeochemical cycling of carbon and sulfur. Antarctica has a unique and dynamic environment where microalgae are evolutionarily adapted to live in freezing temperatures under extreme and oscillating environmental gradients exposing them to solar, osmotic, oxidative and nutrient stress. This thesis investigated the physiological and biochemical adaptations of Antarctic microalgae, focusing on the role dimethylsulfoniopropionate (DMSP) plays in surviving in the harsh Antarctic environment. This thesis provides new knowledge into who are the DMSP producers in Antarctica, the spatial dynamics and role of DMSP in natural Antarctic microbial communities. In a screening study, 16 species of Antarctic microalgae were characterised by their growth rates, physiological health, carbon content, DMSP production and DMSP lyase activity. We found that DMSP production and rates of lyase activity were species-specific, varying within taxa, and that diatom species can produce significant levels of DMSP, in the same magnitude as known DMSP producing haptophytes, 𝘗𝘩𝘢𝘦𝘰𝘤𝘺𝘴𝘵𝘪𝘴 𝘴𝘱𝘱.. In a descriptive study, we take a geographical look at the DMSP content and lyase activity, macromolecular profiles and productivity of three different Antarctic microalgal communities from three unique Antarctic environments; the open ocean to the sea ice and a hypersaline lake. We reveal that species diversity is reduced with more challenging environmental conditions and the species with the greatest phenotypic plasticity dominate in harsher settings. This thesis found that macromolecular content of microalgae changes based on environment, whereby sea-ice microalgae were higher in caloric value due to heavy investment in lipids compared to pelagic species. Using manipulative laboratory studies, we delivered new insight into the response of DMSP to environmental stress and future climate change scenarios as well as macromolecular responses at the species and community levels. Exposure to hypersaline conditions did not induce increased DMSP production, potentially due to the salinity shift being too rapid. In addition, there was no significant change in DMSP or macromolecular concentrations in response to ocean acidification at the species level, however there was a difference at the community level due to a shift in community composition.

Continue reading ‘Life in the freezer : the role of dimethylsulfoniopropionate (DMSP) in the physiological and biochemical adaptations of Antarctic microalgae’

Marine microbial community dynamics and responses to ocean acidification

Marine microbes, including both eukaryotes and prokaryotes, are the basal components of marine food webs and play a fundamental role in global biogeochemical cycling. Marine phytoplankton are responsible for approximately 50% of Earth’s primary production, while heterotrophic bacteria and archaea modulate carbon and nutrient cycling in the marine environment. The structure and function of marine microbial communities are closely coupled. Consequently, understanding the factors which govern the distribution of marine microbes through space and time has key implications for food webs and biogeochemical cycling. The development of high-throughput sequencing technologies has revolutionised marine microbial ecology by facilitating the profiling of microbial communities in high taxonomic resolution. In this thesis high-throughput sequencing of the 16S and 18S rRNA genes was used to achieve two major aims. The first aim was to investigate the ecological processes which underpin microbial community assembly in the marine environment. The second aim was to investigate the responses of marine microbial communities to near- future ocean acidification.

Two studies were performed towards the first aim of this thesis. In the first study, the microbial biogeography of the South Pacific Gyre was characterised across three depths at 22 stations along a 2,000 km longitudinal transect of the region. Microbial community composition was homogenous across horizontal spatial scales in the surface waters of the South Pacific Gyre, but varied significantly between surface waters and the deep chlorophyll maximum. A null model approach was used to unveil the ecological processes driving microbial community assembly in the region. Microbial communities in the surface waters were assembled primarily through the deterministic process of homogeneous selection, indicating that selection pressures were sufficient to overwhelm the influence of dispersal effects and ecological drift across vast horizontal spatial distances in the region. Dispersal limitation was comparatively more influential in the assembly of microbial communities between the surface waters and the deep chlorophyll maximum, indicating that stochastic processes play a significant role in microbial community assembly between these contiguous water masses.

In the second study, the bacterioplankton and protist biogeography of the Southland Front system was characterised in surface waters at 24 stations spanning four water masses. Both bacterioplankton and protist communities displayed significant structuring according to water mass, although this effect was most pronounced in bacterioplankton communities. A null model approach revealed that bacterioplankton communities were primarily assembled through homogeneous selection, while protist communities were primarily assembled through dispersal limitation and ecological drift across the Southland Front system. These findings highlight that distinct ecological processes can underpin the assembly of co- occurring bacterioplankton and protist communities, and that hydrographic features such as oceanic fronts play an important role in structuring both bacterioplankton and protist communities.

Two studies were conducted towards the second aim of this thesis. In the first study, the effect of ocean acidification and warming on bacterioplankton communities was investigated at the fringe and ultra-oligotrophic centre of the South Pacific Gyre using trace-metal clean deckboard incubation experiments. Bacterioplankton community composition and function were resistant to ocean acidification alone, and combined with warming, at the fringe of the South Pacific Gyre. Subtle but significant responses of bacterioplankton community composition to ocean acidification were observed at the ultra- oligotrophic centre of the South Pacific Gyre. These results suggest that bacterioplankton community responses to ocean acidification may be modulated by nutrient regimes. Nonetheless, the findings of this study did not diverge substantially from the narrative that bacterioplankton communities are resistant to near-future acidification.

In the second study, the effect of ocean acidification on both prokaryotic and eukaryotic biofilm communities was investigated at the Shikine-Jima CO2 seep system in Japan. The composition of both prokaryotic and eukaryotic communities was profoundly affected by ocean acidification through early successional stages, though these responses were not associated with shifts in community diversity or evenness. Notably, the relative abundance of the nuisance algae Prymnesium sp. and Biddulphia biddulphiana were enhanced under high CO2 conditions. These findings suggest that benthic biofilm communities may be vulnerable to near-future ocean acidification, and that changes in biofilm community composition may contribute to the reorganisation of coastal ecosystem observed at CO2 seeps globally.

In its entirety, this thesis significantly contributes to our understanding of the spatial dynamics of marine microbial communities by revealing the highly deterministic nature of bacterioplankton community assembly in the coastal waters and central gyre of the South Pacific Ocean. Furthermore, the findings of this thesis highlight the dominance of stochastic processes in structuring marine protist communities across short spatial scales, which may contribute to challenges in correlating abiotic environmental variables with marine protist community composition through space. The resistance of bacterioplankton communities to ocean acidification at the fringe of the South Pacific Gyre, and subtle responses to ocean acidification at the ultra-oligotrophic centre of the South Pacific Gyre broadly support the notion that bacterioplankton communities are resilient to near-future ocean acidification. In contrast, the composition of both prokaryotic and eukaryotic biofilm communities was profoundly affected by ocean acidification, leading to the proliferation of harmful algae with potentially severe consequences for coastal marine environments.

Continue reading ‘Marine microbial community dynamics and responses to ocean acidification’

Abiotic drivers of interannual phytoplankton variability and a 1999–2000 regime shift in the North Sea examined by multivariate statistics

The Dutch coastal zone is a region of the North Sea with a marked interannual and long‐term abiotic and phytoplankton variability. To investigate the relationship between abiotic variability and phytoplankton composition, two routine water monitoring data sets (1991–2005) were examined. Multivariate statistics revealed two significant partitions in the data. The first consisted of interannual abiotic fluctuations that were correlated to Rhine discharge that affected the abundance of summer and autumn diatom species. The second partition was caused by a shift in the abiotic data from 1998 to 1999 that was followed by a shift in phytoplankton composition from 1999 to 2000. Important factors in the abiotic shift were decreases in suspended matter (SPM) and phosphate (DIP) concentrations, as well as in pH. The decrease in SPM was caused by a reduction in wind speed. The increase in water column daily irradiance from the decrease in SPM led to increases in the abundance of winter–spring species, notably the prymnesiophyte Phaeocystis globosa. Because wind speed is related to the North Atlantic Oscillation (NAO) index it was possible to correlate NAO index and P. globosa abundance. Only five abiotic variables representing interannual and long‐term variability, including Rhine discharge and NAO index, were needed to model the observed partitions in phytoplankton composition. It was concluded that interannual variability in the coastal phytoplankton composition was related to year‐to‐year changes in river discharge while the long‐term shift was caused by an alternating large‐scale meteorological phenomenon.

Continue reading ‘Abiotic drivers of interannual phytoplankton variability and a 1999–2000 regime shift in the North Sea examined by multivariate statistics’

Mangrove lagoons of the Great Barrier Reef support coral populations persisting under extreme environmental conditions

Global degradation of coral reefs has increased the urgency of identifying stress-tolerant coral populations, to enhance understanding of the biology driving stress tolerance, as well as identifying stocks of stress-hardened populations to aid reef rehabilitation. Surprisingly, scientists are continually discovering that naturally extreme environments house established coral populations adapted to grow within extreme abiotic conditions comparable to seawater conditions predicted over the coming century. Such environments include inshore mangrove lagoons that carry previously unrecognised ecosystem service value for corals, spanning from refuge to stress preconditioning. However, the existence of such hot-spots of resilience on the Great Barrier Reef (GBR) remains entirely unknown. Here we describe, for the first time, 2 extreme GBR mangrove lagoons (Woody Isles and Howick Island), exposing taxonomically diverse coral communities (34 species, 7 growth morphologies) to regular extreme low pH (<7.6), low oxygen (7°C) conditions. Coral cover was typically low (0.5 m diameter), with net photosynthesis and calcification rates of 2 dominant coral species (Acropora millepora, Porites lutea) reduced (20-30%), and respiration enhanced (11-35%), in the mangrove lagoon relative to adjacent reefs. Further analysis revealed that physiological plasticity (photosynthetic ‘strategy’) and flexibility of Symbiodiniaceae taxa associations appear crucial in supporting coral capacity to thrive from reef to lagoon. Prevalence of corals within these extreme conditions on the GBR (and elsewhere) increasingly challenge our understanding of coral resilience to stressors, and highlight the need to study unfavourable coral environments to better resolve mechanisms of stress tolerance.

Continue reading ‘Mangrove lagoons of the Great Barrier Reef support coral populations persisting under extreme environmental conditions’

CO2 effects on diatoms: a synthesis of more than a decade of ocean acidification experiments with natural communities (update)

Diatoms account for up to 50 % of marine primary production and are considered to be key players in the biological carbon pump. Ocean acidification (OA) is expected to affect diatoms primarily by changing the availability of CO2 as a substrate for photosynthesis or through altered ecological interactions within the marine food web. Yet, there is little consensus how entire diatom communities will respond to increasing CO2. To address this question, we synthesized the literature from over a decade of OA-experiments with natural diatom communities to uncover the following: (1) if and how bulk diatom communities respond to elevated CO2 with respect to abundance or biomass and (2) if shifts within the diatom communities could be expected and how they are expressed with respect to taxonomic affiliation and size structure. We found that bulk diatom communities responded to high CO2 in ∼60 % of the experiments and in this case more often positively (56 %) than negatively (32 %) (12 % did not report the direction of change). Shifts among different diatom species were observed in 65 % of the experiments. Our synthesis supports the hypothesis that high CO2 particularly favours larger species as 12 out of 13 experiments which investigated cell size found a shift towards larger species. Unravelling winners and losers with respect to taxonomic affiliation was difficult due to a limited database. The OA-induced changes in diatom competitiveness and assemblage structure may alter key ecosystem services due to the pivotal role diatoms play in trophic transfer and biogeochemical cycles.

Continue reading ‘CO2 effects on diatoms: a synthesis of more than a decade of ocean acidification experiments with natural communities (update)’

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Ocean acidification in the IPCC AR5 WG II

OUP book