Posts Tagged 'adaptation'

Combined effects of ocean acidification with morphology, water flow, and algal acclimation on metabolic rates of tropical coralline algae

Coral reefs are currently facing multiple stressors that threaten their health and function, including ocean acidification (OA). OA has been shown to negatively affect many reef calcifiers, such as coralline algae that provide many critical contributions to reef systems. Past studies have focused on how OA independently influences coralline algae, but more research is necessary as it is expected that the effects of OA on coralline algae will vary depending on many other factors. To better understand how algal morphology, water flow, and algal acclimation interact with OA to affect coralline algae, three studies were conducted in Moorea, French Polynesia, from June 2015 to July 2016. In January 2016, I tested the hypothesis that algal individuals with higher morphological complexity would exhibit faster metabolic rates under ambient pCO2 conditions, but would also demonstrate higher sensitivity to OA conditions. For three species of crustose coralline algae, Lithophyllum kotschyanum, Neogoniolithon frutescens, and Hydrolithon reinboldii, algal individuals with more complex morphologies demonstrated faster rates of calcification, photosynthesis, and respiration in the ambient pCO2 treatment than individuals with simpler morphological forms. There also appeared to be a relationship between morphology and sensitivity to OA conditions, with calcification rates negatively correlated with higher morphological complexity. In the summers of 2015 and 2016, I conducted three experiments examining the effects of water flow and OA on different morphologies of coralline algae to test the hypotheses that increased flow would enhance metabolic rates and mitigate the effects of OA, and that algae with more complex morphologies would be more responsive to increased water flow and more sensitive to OA conditions. A field experiment investigating the effects of water flow on Amphiroa fragilissima, L. kotschyanum, N. frutescens, and H. reinboldii detected enhanced rates of calcification, photosynthesis, and respiration with increased flow, and this relationship appeared to be the strongest for the crustose algal species with the highest structural complexity. A flume manipulation examining the combined effects of water flow and OA on A. fragilissima, L. kotschyanum, N. frutescens, H. reinboldii, and Porolithon onkodes suggested that coralline algal species with high structural complexity were the most sensitive to OA conditions. Finally, A. fragilissima and L. kotschyanum were maintained in different pCO2 and water flow conditions in a long-term mesocosm experiment, which indicated that flow was unable to mitigate the effects of OA on coralline algae. In the summer of 2016, I investigated the acclimation potential of A. fragilissima and L. kotschyanum to OA, and predicted that the original treatment conditions would induce phenotypic modifications that would influence algal responses to the end treatment. There were negative effects of long-term exposure of coralline algae to elevated pCO2 conditions on calcification and photosynthesis, though partial acclimation in calcification to OA was observed. The instantaneous exposure of elevated pCO2 had negative impacts on algal calcification, but had a nominal effect on photosynthesis. No effects of long-term or instantaneous exposure to elevated pCO2 were observed for respiration. The results of these studies indicate that the coralline algal response to OA conditions will likely be complex and depend on numerous factors including water flow, morphology, and acclimation potential. Therefore, it is critical that future studies further investigate the effects of these factors; specifically examining the mechanisms that underlie these responses in order to better predict the future of coralline algae and thus coral reef ecosystems in a more acidic ocean.

Continue reading ‘Combined effects of ocean acidification with morphology, water flow, and algal acclimation on metabolic rates of tropical coralline algae’

Investigating the collective effect of two ocean acidification adaptation strategies on juvenile clams (Venerupis philippinarum)

Anthropogenic CO2 emissions have altered Earth’s climate system at an unprecedented rate, causing global climate change and ocean acidification. Surface ocean pH has increased by 26% since the industrial era and is predicted to increase another 100% by 2100. Additional stress from abrupt changes in carbonate chemistry in conjunction with other natural and anthropogenic impacts may push populations over critical thresholds. Bivalves are particularly vulnerable to the impacts of acidification during early life-history stages. Two substrate additives, shell hash and macrophytes, have been proposed as potential ocean acidification adaptation strategies for bivalves but there is limited research into their effectiveness. This study uses a split plot design to examine four different combinations of the two substratum treatments on juvenile Venerupis philippinarum settlement, survival, and growth and on local water chemistry at Fidalgo Bay and Skokomish Delta, Washington. Results show no macrophyte or shell hash treatment effect on V. philippinarum settlement or survival. A significant macrophyte treatment effect was detected on clam growth, with mean length higher when macrophytes were absent regardless of the presence or absence of shell hash. Additionally, the macrophyte treatment appeared to have an opposite effect on pH than was anticipated, where pH was higher outside of macrophyte beds than inside. Although these results do not support the use of either treatment as an ocean acidification adaptation strategy, the mixed results reported in the literature for both treatments highlight the nascent nature of this research. As atmospheric CO2 concentrations continue to increase, there is an exigent need for additional studies to determine the specific conditions under which these strategies might help produce conditions conducive to settlement, growth, and survival of bivalves and other calcifying organisms. Such research could help guide local adaptation actions, especially among resource-dependent communities that rely on sustainable fisheries for their health and well-being.

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Using fuzzy logic to determine the vulnerability of marine species to climate change

Marine species are being impacted by climate change and ocean acidification, although their level of vulnerability varies due to differences in species’ sensitivity, adaptive capacity and exposure to climate hazards. Due to limited data on the biological and ecological attributes of many marine species, as well as inherent uncertainties in the assessment process, climate change vulnerability assessments in the marine environment frequently focus on a limited number of taxa or geographic ranges. As climate change is already impacting marine biodiversity and fisheries, there is an urgent need to expand vulnerability assessment to cover a large number of species and areas. Here, we develop a modelling approach to synthesize data on species-specific estimates of exposure, and ecological and biological traits to undertake an assessment of vulnerability (sensitivity and adaptive capacity) and risk of impacts (combining exposure to hazards and vulnerability) of climate change (including ocean acidification) for global marine fishes and invertebrates. We use a fuzzy logic approach to accommodate the variability in data availability and uncertainties associated with inferring vulnerability levels from climate projections and species’ traits. Applying the approach to estimate the relative vulnerability and risk of impacts of climate change in 1074 exploited marine species globally, we estimated their index of vulnerability and risk of impacts to be on average 52 ± 19 SD and 66 ± 11 SD, scaling from 1 to 100, with 100 being the most vulnerable and highest risk, respectively, under the ‘business-as-usual’ greenhouse gas emission scenario (Representative Concentration Pathway 8.5). We identified 157 species to be highly vulnerable while 294 species are identified as being at high risk of impacts. Species that are most vulnerable tend to be large-bodied endemic species. This study suggests that the fuzzy logic framework can help estimate climate vulnerabilities and risks of exploited marine species using publicly and readily available information.

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Components of a flexible phenotype in two species of scleractinian coral under ocean acidification

A developmental reaction norm integrates three tightly linked factors of ontogeny, genotype, and environment to address the ability of an organism to deal with environmental change. This concept of organismic flexibility is termed plasticity, and is well characterized in coral reef systems. However, there has been little quantification of how phenotypic plasticity in scleractinian corals may modulate their response to ocean acidification. This thesis consists of two studies addressing the role of ontogeny, genotype, and environment as influences on phenotypic complexity in scleractinian corals that may affect their response to ocean acidification. In Chapter 2, to address ontogeny, I investigated the effects of elevated pCO2 on the movement and behavior of brooded Pocillopora damicornis larvae in Okinawa, Japan, in 2016. A change in behavior in this developmental stage may alter distribution and settlement patterns of adult colonies of P. damicornis. I found that brooded larvae freshly released from P. damicornis are able to regulate their vertical position in the seawater over at least 12 h, and that this response, likely driven by a combination of modified buoyancy and active swimming, is affected by high pCO2. A change in vertical position of larvae due to elevated pCO2 has the potential to mediate pelagic larval duration (PLD) by determining their exposure to differing horizontal strata of water, thereby mediating the extent of larval connectivity among populations. In Chapter 3, to address genotype and environment, I first observed the effect of genotype-specific variation within adult colonies of P. damicornis in their growth response to elevated pCO2 in Moorea, French Polynesia, in 2016. In this preliminary experiment, I found differences among genotypes in mean growth rate that varied among trials conducted in different months, likely due to the environmental history of the corals. To quantify plasticity in two different environments, I conducted an experiment in 2017 that investigated how a plastic response in a coral to an environment change might modulate success in a fitness trait under elevated pCO2. I quantified plasticity using a suite of morphological traits in Pocillopora verrucosa at two different depths, and measured growth of plastic genotypes in high pCO2. Results suggest that genotype-specific morphological plasticity does not influence success in growth in high pCO2. Overall, the goal of this thesis was to better understand the scope of a coral’s ability to deal with environmental heterogeneity (e.g. increasing ocean acidity) based on the formation and flexibility of its phenotype. Results indicate that under projected ocean acidification conditions, the formation of a coral’s phenotype (e.g. larval behavior) will be affected by high pCO2, but that a flexible phenotype in adult corals does not appear to modulate growth success in high pCO2.

Continue reading ‘Components of a flexible phenotype in two species of scleractinian coral under ocean acidification’

Plastic responses of bryozoans to ocean acidification

Phenotypic plasticity has the potential to allow organisms to respond rapidly to global environmental change, but the range and effectiveness of these responses are poorly understood across taxa and growth strategies. Colonial organisms might be particularly resilient to environmental stressors, as organizational modularity and successive asexual generations can allow for distinctively flexible responses in the aggregate form. We performed laboratory experiments to examine the effects of increasing dissolved carbon dioxide (i.e. ocean acidification) on the colonial bryozoan Celleporella cornuta sampled from two source populations within a coastal upwelling region of the northern California coast. Bryozoan colonies were remarkably plastic under these carbon dioxide (CO2) treatments. Colonies raised under high CO2 grew more quickly, investing less in reproduction and producing lighter skeletons when compared to genetically identical clones raised under current atmospheric values. Bryozoans held in high CO2 conditions also changed the Mg/Ca ratio of skeletal calcite and increased the expression of organic coverings in new growth, which may serve as protection against acidified water. We also observed strong differences between populations in reproductive investment and organic covering reaction norms, consistent with adaptive responses to persistent spatial variation in local oceanographic conditions. Our results demonstrate that phenotypic plasticity and energetic trade-offs can mediate biological responses to global environmental change, and highlight the broad range of strategies available to colonial organisms.

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Transgenerational exposure of North Atlantic bivalves to ocean acidification renders offspring more vulnerable to low pH and additional stressors

While early life-stage marine bivalves are vulnerable to ocean acidification, effects over successive generations are poorly characterized. The objective of this work was to assess the transgenerational effects of ocean acidification on two species of North Atlantic bivalve shellfish, Mercenaria mercenaria and Argopecten irradians. Adults of both species were subjected to high and low pCO2 conditions during gametogenesis. Resultant larvae were exposed to low and ambient pH conditions in addition to multiple, additional stressors including thermal stress, food-limitation, and exposure to a harmful alga. There were no indications of transgenerational acclimation to ocean acidification during experiments. Offspring of elevated pCO2-treatment adults were significantly more vulnerable to acidification as well as the additional stressors. Our results suggest that clams and scallops are unlikely to acclimate to ocean acidification over short time scales and that as coastal oceans continue to acidify, negative effects on these populations may become compounded and more severe.

Continue reading ‘Transgenerational exposure of North Atlantic bivalves to ocean acidification renders offspring more vulnerable to low pH and additional stressors’

Low recruitment due to altered settlement substrata as primary constraint for coral communities under ocean acidification

The future of coral reefs under increasing CO2 depends on their capacity to recover from disturbances. To predict the recovery potential of coral communities that are fully acclimatized to elevated CO2, we compared the relative success of coral recruitment and later life stages at two volcanic CO2 seeps and adjacent control sites in Papua New Guinea. Our field experiments showed that the effects of ocean acidification (OA) on coral recruitment rates were up to an order of magnitude greater than the effects on the survival and growth of established corals. Settlement rates, recruit and juvenile densities were best predicted by the presence of crustose coralline algae, as opposed to the direct effects of seawater CO2. Offspring from high CO2 acclimatized parents had similarly impaired settlement rates as offspring from control parents. For most coral taxa, field data showed no evidence of cumulative and compounding detrimental effects of high CO2 on successive life stages, and three taxa showed improved adult performance at high CO2 that compensated for their low recruitment rates. Our data suggest that severely declining capacity for reefs to recover, due to altered settlement substrata and reduced coral recruitment, is likely to become a dominant mechanism of how OA will alter coral reefs.

Continue reading ‘Low recruitment due to altered settlement substrata as primary constraint for coral communities under ocean acidification’

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Ocean acidification in the IPCC AR5 WG II

OUP book