Posts Tagged 'community composition'

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’

Effect of pH on the bacterial community present in larvae and spat of Crassostrea gigas

Changes in marine environments, including pH changes, have been correlated to alterations in the physiology and disease susceptibility of cultured organisms at the early stages of development. In this study, high-throughput sequencing of the V3-V4 region of the 16S rRNA gene was performed to evaluate the bacterial
biodiversity of Crassostrea gigas pediveliger larvae and spat under acidic stress compared to that of larvae at normal pH value. The evaluation was performed in an experimental system with continuous water flow and pH
manipulation by CO2 bubbling to simulate acidification (pH 7.38 ± 0.039), using the current ocean pH conditions (pH 8.116 ± 0.023) as a reference. The results indicated that the bacterial communities associated with both pediveliger larvae and spat were modified in response to acidic conditions. The families Rhodobacteraceae and Campylobacteraceae were the most affected by the change in pH, with increases in Vibrionaceae in pediveliger larvae and Planctomycetaceae and Phyllobacteriaceae in spat detected. The results of this study demonstrate that the bacterial communities associated with C. gigas pediveliger larvae and spat are responsive to changes in ocean acidification

Continue reading ‘Effect of pH on the bacterial community present in larvae and spat of Crassostrea gigas’

Paleobiological traits that determined Scleractinian coral survival and proliferation during the late Paleocene and early Eocene hyperthermals

Coral reefs are particularly sensitive to environmental disturbances, such as rapid shifts in temperature or carbonate saturation. Work on modern reefs has suggested that some corals will fare better than others in times of stress and that their life history traits might correlate with species survival. These same traits can be applied to fossil taxa to assess whether life history traits correspond with coral survival through past intervals of stress similar to future climate predictions. This study aims to identify whether ecological selection (based on physiology, behavior, habitat, etc.) plays a role in the long‐term survival of corals during the late Paleocene and early Eocene. The late Paleocene‐early Eocene interval is associated with multiple hyperthermal events that correspond to rises in atmospheric pCO2 and sea surface temperature, ocean acidification, and increases in weathering and turbidity. Coral reefs are rare during the late Paleocene and early Eocene, but despite the lack of reef habitat, corals do not experience an extinction at the generic level and there is little extinction at the species level. In fact, generic and species richness increases throughout the late Paleocene and early Eocene. We show that corals with certain traits (coloniality, carnivorous, or suspension feeding diet, hermaphroditic brooding reproduction, living in clastic settings) are more likely to survive climate change in the early Eocene. These findings have important implications for modern coral ecology and allow us to make more nuanced predictions about which taxa will have higher extinction risk in present‐day climate change.

Continue reading ‘Paleobiological traits that determined Scleractinian coral survival and proliferation during the late Paleocene and early Eocene hyperthermals’

Kelp beds and their local effects on seawater chemistry, productivity, and microbial communities

Kelp forests are known as key habitats for species diversity and macroalgal productivity; however, we know little about how these biogenic habitats interact with seawater chemistry and phototroph productivity in the water column. We examined kelp forest functions at three locales along the Olympic Peninsula of Washington state by quantifying carbonate chemistry, nutrient concentrations, phytoplankton productivity, and seawater microbial communities inside and outside of kelp beds dominated by the canopy kelp species Nereocystis luetkeana and Macrocystis pyrifera. Kelp beds locally increased the pH, oxygen, and aragonite saturation state of the seawater, but lowered seawater inorganic carbon content and total alkalinity. While kelp beds depleted nitrate and phosphorus concentrations, ammonium and DOC concentrations were enhanced. Kelp beds also decreased chlorophyll concentrations and carbon fixed by phytoplankton, although kelp carbon fixation more than compensated for any difference in phytoplankton production. Kelp beds also entrained distinct microbial communities, with higher taxonomic and phylogenetic diversity compared to seawater outside of the kelp bed. Kelp forests thus had significant effects on seawater chemistry, productivity and the microbial assemblages in their proximity. Thereby, the diversity of pathways for carbon and nitrogen cycling was also enhanced. Overall, these observations suggest that the contribution of kelp forests to nearshore carbon and nitrogen cycling is greater than previously documented.

Continue reading ‘Kelp beds and their local effects on seawater chemistry, productivity, and microbial communities’

Nutrient enrichment promotes eutrophication in the form of macroalgal blooms causing cascading effects in two anthropogenically disturbed coastal ecosystems

Humans are impacting almost every major ecological process that structures communities and ecosystems. Examples of how human activity can directly control key processes in ecosystems include destruction of habitat changing trophic structure, nutrient pollution altering competitive outcomes, overharvesting of consumers reducing top down control, and now climate change impacting virtually every global biogeochemical cycle. These human impacts may have an independent effect on the ecosystem, but they also have the potential to cause cascading effects and promote subsequent stressors. Also, these impacts are not limited to a particular system or geographic location making research on their overall effects vital for management practices. For example, tropical reefs have been transitioning from coral to mixed communities dominated by macroalgae, motivating research on how macroalgae respond to anthropogenic stressors and interact with each other during these stressful events. Further, while eutrophication of coastal estuaries due to increased anthropogenic supplies of nutrients has been of critical global concern for decades, the potential for eutrophication to drive new stressors is a growing concern. To address these knowledge gaps, I investigated how human stressors impact two different and major coastal ecosystems known to be vulnerable to anthropogenic disturbances.

In chapter 1, I demonstrate that anthropogenic stressors in the form of increased nutrients in the water and sediments have strong impacts on interspecific interactions of coral reef macroalgae. Abiotic stressors such as nutrients have been linked to phase-shifts from coral to algal domination on tropical reefs. However, few studies have considered how these stressors impact changes in the biotic and abiotic constituents of dominant species of calcifying macroalgae, and how this may be mediated by species-species interactions. I conducted 4 mesocosm experiments to examine whether different nutrient sources (water column vs. terrestrial sediment) as well as species interactions (alone vs. mixed species) affected total mass (biomass + calcium carbonate (CaCO3)) of two common calcifying macroalgae (Padina boryana and Galaxaura fasciculata). P. boryana gained total mass with increased water column nutrients but declined with increased nutrients supplied by the sediment. Conversely, G. fasciculata gained total mass with increased nutrients in the sediment but declined with increased water column nutrients. In both interactions, the “winner” (i.e., G. fasciculata in the sediment experiment) also had a greater % of thallus mass comprised of CaCO3, potentially due to the subsequent decomposition of the “loser” as this result was not found in the alone treatments. These findings ultimately suggest that nutrient stressors can cause cascading effects, such as promoting calcification and biomass growth or loss in these macroalgal communities, and the potential for domination or decline is based on the nutrient source and community composition.

In chapter 2, I demonstrate that decomposition of macroalgal blooms cause a sequence of biogeochemical processes that can drive acidification in shallow coastal estuaries, and that these processes are mediated by a dynamic microbial community. Eutrophication and ocean acidification are both widely acknowledged as major human-induced stressors in marine environments. While the link between eutrophication and acidification has been established for phytoplankton, it is unclear whether eutrophication in the form of macroalgal blooms can cause cascading effects like acidification in shallow eutrophic estuaries. I conducted seasonal field surveys and assessed microbial communities and functional genes to evaluate changes in biotic and abiotic characteristics between seasons that may be associated with acidification in Upper Newport Bay, CA, USA. Acidification, measured as a drop in pH of 0.7, occurred in summer at the site with the most macroalgal cover. Microbial community composition and functional gene expression provide evidence that decomposition processes contributed to acidification, and also suggest that other biogeochemical processes like nitrification and degradation of polyphosphate also contributed to acidification. To my knowledge, my findings represent the first field evidence that eutrophication of shallow coastal estuaries dominated by green macroalgal blooms can cascade to acidification.

In chapter 3, I demonstrate that macroalgal blooms in shallow estuaries are strong drivers of key microbially-mediated biogeochemical processes that can cause cascading effects, such as acidification and nutrient fluxing, regardless of simulated tidal flushing. Estuaries are productive and diverse ecosystems and are vulnerable to eutrophication from increased anthropogenic nutrients. While it is known that enhanced tidal flushing can reduce adverse effects of anthropogenic disturbances in larger, deeper estuarine ecosystems, this is unexplored for eutrophication in shallow coastal estuaries where macroalgae usually dominate. I simulated eutrophication as a macroalgal bloom in a mesocosm experiment, varied tidal flushing (flushed daily vs unflushed), and assessed the effects on water column and sediment biogeochemical processes and the sediment microbial community. While flushing did not ameliorate the negative effects of the macroalgal bloom, it caused transient differences in the rate of change in biogeochemical processes and promoted increased fluxes of nutrients from the sediment. In the beginning, the macroalgal bloom induced basification and increased total alkalinity, but during decomposition, acidification and the accumulation of nutrients in the sediment and water column occurred. The findings from this chapter ultimately suggest that macroalgal blooms have the potential to be the cause of, yet may also offer a partial solution to, global ecological changes to biogeochemical processes.

Overall, my results indicate that anthropogenic disturbances, particularly in the form of increased nutrients, can cause cascading effects like macroalgal blooms that in turn cause acidification, basification, increased interspecific interactions, nutrient depletion, and nutrient fluxing in multiple ecosystems. These data advance our current understanding of the ecological consequences of eutrophication in the form of macroalgal blooms in different ecosystems. It also provides mechanistic links to microbial communities and biogeochemical processes not previously identified for shallow coastal estuaries. As human population and subsequent nutrient pollution increases in watersheds globally, ecological phenomenon such as eutrophication will only be intensified, and macroalgal communities will continue to dominate. Consequently, this dominance, especially during decomposition as shown here, can drive a multitude of subsequent stressors that can impact the entire ecosystem.

Continue reading ‘Nutrient enrichment promotes eutrophication in the form of macroalgal blooms causing cascading effects in two anthropogenically disturbed coastal ecosystems’

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

Diatoms account for 40 % 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: 1) if and how bulk diatom communities respond to elevated CO2; 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 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 favors larger species as 12 out of 13 experiments which investigated cell size found a shift towards larger species. Unraveling winners and losers with respect to taxonomic affiliation was difficult due to a limited database, but there is evidence that the genus Pseudo-nitzschia could be among the losers. We conclude that OA-induced changes in diatom competitiveness and assemblage structure must be classified as a “risk for 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’

In situ response of Antarctic under-ice primary producers to experimentally altered pH

Elevated atmospheric CO2 concentrations are contributing to ocean acidification (reduced seawater pH and carbonate concentrations), with potentially major ramifications for marine ecosystems and their functioning. Using a novel in situ experiment we examined impacts of reduced seawater pH on Antarctic sea ice-associated microalgal communities, key primary producers and contributors to food webs. pH levels projected for the following decades-to-end of century (7.86, 7.75, 7.61), and ambient levels (7.99), were maintained for 15 d in under-ice incubation chambers. Light, temperature and dissolved oxygen within the chambers were logged to track diurnal variation, with pH, O2, salinity and nutrients assessed daily. Uptake of CO2 occurred in all treatments, with pH levels significantly elevated in the two extreme treatments. At the lowest pH, despite the utilisation of CO2 by the productive microalgae, pH did not return to ambient levels and carbonate saturation states remained low; a potential concern for organisms utilising this under-ice habitat. However, microalgal community biomass and composition were not significantly affected and only modest productivity increases were noted, suggesting subtle or slightly positive effects on under-ice algae. This in situ information enables assessment of the influence of future ocean acidification on under-ice community characteristics in a key coastal Antarctic habitat.

Continue reading ‘In situ response of Antarctic under-ice primary producers to experimentally altered pH’


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Ocean acidification in the IPCC AR5 WG II

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