Posts Tagged 'porifera'

Biodiversity of coral reef cryptobiota shuffles but does not decline under the combined stressors of ocean warming and acidification

Significance

Although climate change is expected to decimate coral reefs, the combined impacts of ocean-warming and acidification on coral reef biodiversity remains largely unmeasured. Here, we present a two-year mesocosm experiment to simulate future ocean acidification and ocean-warming to quantify the impacts on species richness, community composition, and community structure. We find that species richness is equivalent between the dual-stressor and present-day treatments but that the community shuffles, undoubtedly altering ecosystem function. However, our ability to predict the outcomes of such community shuffling remains limited due to the critical knowledge gap regarding ecological functions, life histories, and distributions for most members of the cryptobenthic community that account for the majority of the biodiversity within these iconic ecosystems.

Abstract

Ocean-warming and acidification are predicted to reduce coral reef biodiversity, but the combined effects of these stressors on overall biodiversity are largely unmeasured. Here, we examined the individual and combined effects of elevated temperature (+2 °C) and reduced pH (−0.2 units) on the biodiversity of coral reef communities that developed on standardized sampling units over a 2-y mesocosm experiment. Biodiversity and species composition were measured using amplicon sequencing libraries targeting the cytochrome oxidase I (COI) barcoding gene. Ocean-warming significantly increased species richness relative to present-day control conditions, whereas acidification significantly reduced richness. Contrary to expectations, species richness in the combined future ocean treatment with both warming and acidification was not significantly different from the present-day control treatment. Rather than the predicted collapse of biodiversity under the dual stressors, we find significant changes in the relative abundance but not in the occurrence of species, resulting in a shuffling of coral reef community structure among the highly species-rich cryptobenthic community. The ultimate outcome of altered community structure for coral reef ecosystems will depend on species-specific ecological functions and community interactions. Given that most species on coral reefs are members of the understudied cryptobenthos, holistic research on reef communities is needed to accurately predict diversity–function relationships and ecosystem responses to future climate conditions.

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DNA metabarcoding to examine the biodiversity of coral reef cryptobiota

Coral reefs are among the most biologically diverse, complex, and productive of ecosystems. The vast majority of coral reef biodiversity is made up of the small and cryptic organisms living unseen by most within the reef matrix. This hidden community, the cryptobiota, are a critical component of coral reef trophic dynamics and play an essential role in nutrient recycling that enable reefs to thrive in oligotrophic environments. Despite their ecological importance, the cryptobiota are often ignored because they live deep within the reef matrix and require significant taxonomic expertise and time to collect and identify. As a result, our perceptions of coral reef biodiversity across marine gradients and how it will respond to climatic change is based on observable surface-dwelling taxa, such as corals and fish. Using DNA metabarcoding technology, this research fills an extensive knowledge gap about the diversity and distribution of the important and understudied coral reef cryptobiota community. The objectives of this dissertation were to (i) evaluate metabarcoding performance on marine sponges, a prominent and ecologically vital member of the cryptobenthos that is one of the most difficult metazoans to identify to species using both taxonomic and molecular methods; (ii) investigate the individual and combined effects of ocean warming and acidification on cryptobiota biodiversity; and (iii) examine cryptobiota diversity along the most striking macrospatial diversity gradient in the marine tropics. Contrary to expectations, this research (i) demonstrated that the metabarcoding approach performs much better than expected in capturing sponge richness; (ii) discovered that diversity shuffles but does not decline under the combined stressors of ocean warming and acidification; and (iii) cryptobiotic diversity undermines the tropical Pacific longitudinal diversity gradient defined by corals and fish. These results contribute towards reshaping the way we consider coral reef biodiversity under different oceanographic, geographic and climatic regimes.

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The effect of global warming and ocean acidification on Halichondira panicea bacteria

Marine sponges are becoming an increasing source of novel biomedical and antibacterial compounds. Many of these compounds are synthesized as secondary metabolites from symbiotic bacteria and have immense potential in the pharmaceutical industry. However, climate change may pose a threat to the viability of marine sponges and result in the loss of future medical discoveries. Therefore, this paper looks at the effect climate change may have on marine sponges by subjecting fragments of the marine sponge, Halichondria panicea, into aquaria representing different climate change scenarios to study the effect that global warming and ocean acidification may have on its symbiotic bacteria. To model climate change towards the end of the 21st century, conditions from the IPCC’s 2014 climate change report were simulated to determine specific growth conditions. The fragments were placed in the different RCP growth conditions for two weeks, then dissociated, filtered, and the extracts incubated on Hektoen enteric agar for 48 hours. The results showed that climate change has adverse effects on the marine sponge, Halichondria panicea, by decreasing their symbiotic bacterial population by around 18 %

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Microbiome diversity and host immune functions influence survivorship of sponge holobionts under future ocean conditions

The sponge-associated microbial community contributes to the overall health and adaptive capacity of the sponge holobiont. This community is regulated by the environment and the immune system of the host. However, little is known about the effect of environmental stress on the regulation of host immune functions and how this may, in turn, affect sponge–microbe interactions. In this study, we compared the bacterial diversity and immune repertoire of the demosponge, Neopetrosia compacta, and the calcareous sponge, Leucetta chagosensis, under varying levels of acidification and warming stress based on climate scenarios predicted for 2100. Neopetrosia compacta harbors a diverse microbial community and possesses a rich repertoire of scavenger receptors while L. chagosensis has a less diverse microbiome and an expanded range of pattern recognition receptors and immune response-related genes. Upon exposure to RCP 8.5 conditions, the microbiome composition and host transcriptome of N. compacta remained stable, which correlated with high survival (75%). In contrast, tissue necrosis and low survival (25%) of L. chagosensis was accompanied by microbial community shifts and downregulation of host immune-related pathways. Meta-analysis of microbiome diversity and immunological repertoire across poriferan classes further highlights the importance of host–microbe interactions in predicting the fate of sponges under future ocean conditions.

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Ocean acidification and direct interactions affect coral, macroalga, and sponge growth in the Florida Keys

Coral reef community composition, function, and resilience have been altered by natural and anthropogenic stressors. Future anthropogenic ocean and coastal acidification (together termed “acidification”) may exacerbate this reef degradation. Accurately predicting reef resilience requires an understanding of not only direct impacts of acidification on marine organisms but also indirect effects on species interactions that influence community composition and reef ecosystem functions. In this 28-day experiment, we assessed the effect of acidification on coral–algal, coral–sponge, and algal–sponge interactions. We quantified growth of corals (Siderastrea radians), fleshy macroalgae (Dictyota spp.), and sponges (Pione lampa) that were exposed to local summer ambient (603 μatm) or elevated (1105 μatm) pCO2 seawater. These species are common to hard-bottom communities, including shallow reefs, in the Florida Keys. Each individual was maintained in isolation or paired with another organism. Coral growth (net calcification) was similar across seawater pCO2 and interaction treatments. Fleshy macroalgae had increased biomass when paired with a sponge but lost biomass when growing in isolation or paired with coral. Sponges grew more volumetrically in the elevated seawater pCO2 treatment (i.e., under acidification conditions). Although these results are limited in temporal and spatial scales due to the experimental design, they do lend support to the hypothesis that acidification may facilitate a shift towards increased sponge and macroalgae abundance by directly benefiting sponge growth which in turn may provide more dissolved inorganic nitrogen to macroalgae in the Florida Keys.

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Microbiome diversity and host immune functions may define the fate of sponge holobionts under future ocean conditions

The sponge-associated microbial community contributes to the overall health and adaptive capacity of the sponge holobiont. This community is regulated by the environment, as well as the immune system of the host. However, little is known about the effect of environmental stress on the regulation of host immune functions and how this may, in turn, affect sponge-microbe interactions. In this study, we compared the microbiomes and immune repertoire of two sponge species, the demosponge, Neopetrosia compacta and the calcareous sponge, Leucetta chagosensis, under varying levels of acidification and warming stress. Neopetrosia compacta harbors a diverse bacterial assemblage and possesses a rich repertoire of scavenger receptors while L. chagosensis has a less diverse microbiome and an expanded range of pattern recognition receptors and proteins with immunological domains. Upon exposure to warming and acidification, the microbiome and host transcriptome of N. compacta remained stable, which correlated with high survival. In contrast, the bacterial community of L. chagosensis exhibited drastic restructuring and widespread downregulation of host immune-related pathways, which accompanied tissue necrosis and mortality. Differences in microbiome diversity and immunological repertoire of diverse sponge groups highlight the central role of host-microbe interactions in predicting the fate of sponges under future ocean conditions.

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Potential local adaptation of corals at acidified and warmed Nikko Bay, Palau

Ocean warming and acidification caused by the increase of atmospheric carbon dioxide are now thought to be major threats to coral reefs on a global scale. Here we evaluated the environmental conditions and benthic community structures in semi-closed Nikko Bay at the inner reef area in Palau, which has high p CO 2 and seawater temperature conditions with high zooxanthellate coral coverage. This bay is a highly sheltered system with organisms showing low connectivity with surrounding environments, making this bay a unique site for evaluating adaptation and acclimatization responses of organisms to warmed and acidified environments. Seawater p CO 2 /Ω arag showed strong graduation ranging from 380 to 982 µatm (Ω arag : 1.79-3.66) and benthic coverage, including soft corals and turf algae, changed along with Ω arag while hard coral coverage did not. In contrast to previous studies, net calcification was maintained in Nikko Bay even under very low mean Ω arag (2.44). Reciprocal transplantation of the dominant coral Porites cylindrica showed that the calcification rate of corals from Nikko Bay did not change when transplanted to a reference site, while calcification of reference site corals decreased when transplanted to Nikko Bay. Corals transplanted out of their origin sites also showed the highest interactive respiration (R) and lower photosynthesis (P) to respiration (P:R). The results of this study give important insights about the potential local acclimatization and adaptation capacity of corals to different environmental conditions including p CO 2 and temperature.

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Cross‐generational effects of climate change on the microbiome of a photosynthetic sponge

Coral reefs are facing increasing pressure from rising seawater temperatures and ocean acidification. Sponges have been proposed as possible winners in the face of climate change; however, little is known about the mechanisms underpinning their predicted tolerance. Here we assessed whether microbiome‐mediated cross‐generational acclimatization could enable the photosynthetic sponge Carteriospongia foliascens to survive under future climate scenarios. To achieve this, we first established the potential for vertical (cross‐generational) transmission of symbionts. Sixty‐four amplicon sequence variants accounting for >90% of the total C. foliascens microbial community were present across adult, larval and juvenile life stages, showing that a large proportion of the microbiome is vertically acquired and maintained. When C. foliascens were exposed to climate scenarios projected for 2050 and 2100, the host remained visibly unaffected (i.e. no necrosis/bleaching) and the overall microbiome was not significantly different amongst treatments in adult tissue, the respective larvae or recruits transplanted amongst climate treatments. However, indicator species analysis revealed that parental exposure to future climate scenarios altered the presence and abundance of a small suite of microbial taxa in the recruits, thereby revealing the potential for microbiome‐mediated cross‐generational acclimatization through both symbiont shuffling and symbiont switching within a vertically acquired microbiome.

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Warming and acidification threaten glass sponge Aphrocallistes vastus pumping and reef formation

The glass sponge Aphrocallistes vastus contributes to the formation of large reefs unique to the Northeast Pacific Ocean. These habitats have tremendous filtration capacity that facilitates flow of carbon between trophic levels. Their sensitivity and resilience to climate change, and thus persistence in the Anthropocene, is unknown. Here we show that ocean acidification and warming, alone and in combination have significant adverse effects on pumping capacity, contribute to irreversible tissue withdrawal, and weaken skeletal strength and stiffness of A. vastus. Within one month sponges exposed to warming (including combined treatment) ceased pumping (50–60%) and exhibited tissue withdrawal (10–25%). Thermal and acidification stress significantly reduced skeletal stiffness, and warming weakened it, potentially curtailing reef formation. Environmental data suggests conditions causing irreversible damage are possible in the field at +0.5 °C above current conditions, indicating that ongoing climate change is a serious and immediate threat to A. vastus, reef dependent communities, and potentially other glass sponges.

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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.

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Changes in the metabolic potential of the sponge microbiome under ocean acidification

Anthropogenic CO2 emissions are causing ocean acidification, which can affect the physiology of marine organisms. Here we assess the possible effects of ocean acidification on the metabolic potential of sponge symbionts, inferred by metagenomic analyses of the microbiomes of two sponge species sampled at a shallow volcanic CO2 seep and a nearby control reef. When comparing microbial functions between the seep and control sites, the microbiome of the sponge Stylissa flabelliformis (which is more abundant at the control site) exhibits at the seep reduced potential for uptake of exogenous carbohydrates and amino acids, and for degradation of host-derived creatine, creatinine and taurine. The microbiome of Coelocarteria singaporensis (which is more abundant at the seep) exhibits reduced potential for carbohydrate import at the seep, but greater capacity for archaeal carbon fixation via the 3-hydroxypropionate/4-hydroxybutyrate pathway, as well as archaeal and bacterial urea production and ammonia assimilation from arginine and creatine catabolism. Together these metabolic features might contribute to enhanced tolerance of the sponge symbionts, and possibly their host, to ocean acidification.

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So long and thanks for all the sponge: cryptic intertidal communities, consequences of ocean acidification, and new directions for science education

Ocean acidification (OA), defined as the reduction in the pH of global oceans, is predicted to have negative impacts on marine invertebrates. Within the past two decades there have been hundreds of studies on the effects of OA on the fitness, survival, and growth of many marine organisms, and yet there are several large gaps in our understanding. Many OA studies focus on one population (e.g. only sample from one site/location) of a widespread species and then make generalizations about that species as a whole. This is problematic for species that are spread between habitats with different levels of acidification. My work in Chapters 3 and 4 addresses the response of multiple populations of an important intertidal invertebrate to ocean acidification conditions on the Oregon coast; I describe the impacts of OA on the early life history (Chapter 3) and adult physiology (Chapter 4) of the common breadcrumb sponge Halichondria panicea. To investigate if H. panicea are adapted to local conditions, I utilized the persistent pattern of acidification that exists on the cape scale along the Oregon coast. I compared the responses of sponge populations that persist in areas of high, intermediate, and low acidification. I used both field and laboratory experiments to investigate the potential for local adaptation or acclimatization to OA conditions in H. panicea. In Chapter 3 I found that sponge larvae from areas that experience persistently high levels of ocean acidification may be less resilient to future levels of OA vs. larvae from other less acidified regions. Negative carryover effects for early exposure during brooding may result in increased larval mortality and faster rates of settlement; there were no effects of treatment on post-settlement processes for either population. Chapter 3 highlights a novel response of sponges to OA and reveals a potential population bottleneck during the critical larval stage for pre-exposed sponges under future OA conditions. Chapter 4 builds on the work of Chapter 3 by examining the response of adult sponges from high, middle, and low areas of OA along the Oregon coast. I used a common garden approach to untangle the effects of environmental acclimation and adaptation in a reciprocal transplant and mesocosm experiment. I observed changes in survival, mass, and Chlorophyll a (Chl- a) concentration. Consistent with Chapter 3, I found that prior exposure to OA resulted in increased mortality during the transplant and mesocosm experiment, although we found no evidence of treatment- or population-dependent effects on mass and chlorophyll a concentration in H. panicea populations. Combined, results of Chapters 3 and 4 suggests that sponges from highly acidified regions may be living near a threshold, past which the fitness of both larvae and adults would be compromised, with implications for the population as a whole.

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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.

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Modelling the environmental niche space and distributions of cold-water corals and sponges in the Canadian northeast Pacific Ocean

Highlights

• We present the first comparison of realized niche space among six major, habitat-forming cold-water coral and sponge (CWCS) groups (sponge classes: Hexactinellida, Demospongiae; coral orders: Alcyonacea, Scleractinia, Antipatharia, Pennatulacea) occurring in the Northeast Pacific region of Canada (NEPC).
• The environmental gradients influencing CWCS niche space and breadth is driven by dissolved inorganic carbon, total alkalinity, and dissolved oxygen.
• Significant niche separation occurs among CWCS groups; high tolerance and marginality generally identify CWCS as specialists occurring in uncommon habitat conditions within the NEPC.
• Species distribution models developed for each CWCS group all share severely low dissolved oxygen ([O2] < 0.5 ml L−1) as a major predictor of habitat.
• Areas that are predicted to be suitable habitat for multiple CWCW groups primarily occurs primarily within 500–1400 m bottom depths on the continental slope and at offshore seamounts that have summits that reach into this depth range.

Abstract

Cold water coral and sponge communities (CWCS) are important indicators of vulnerable marine ecosystems (VMEs) and are used to delineate areas for marine conservation and fisheries management. Although the Northeast Pacific region of Canada (NEPC) is notable for having unique CWCS assemblages and is the location of >80% of Canadian seamounts, the extent of potential CWCS-defined VMEs in this region is unknown. Here, we used a diverse set of environmental data layers (n=30) representing a range of bathymetric derivatives, physicochemical variables, and water column properties to assess the primary factors influencing the niche separation and potential distributions of six habitat-forming groups of CWCS in the NEPC (sponge classes: Hexactinellida, Demospongiae; coral orders: Alcyonacea, Scleractinia, Antipatharia, Pennatulacea). The primary environmental gradients that influence niche separation among CWCS are driven by total alkalinity, dissolved inorganic carbon, and dissolved oxygen. Significant niche separation among groups indicates CWCS to be primarily specialists occurring in rare habitat conditions in the NEPC. Species distribution models (SDMs) developed for each CWCS group shared severely low dissolved oxygen levels ([O2] < 0.5 ml L−1) as a top predictor for habitat suitability in the NEPC. Niche separation is further emphasized by differences in the model-predicted areas of suitable habitat among CWCS groups. Although niches varied among taxa, the general areas of high habitat suitability for multiple CWCS groups in the NEPC occurred within the 500–1400 m bottom depth range which is strongly associated with the extensive oxygen minimum zone (OMZ) characterizing this region. As a result, the largest continuous area of potential CWCS habitat occurred along the continental slope with smaller, isolated patches also occurring at several offshore seamounts that have summits that extend into OMZ depths. Our results provide insight into the factors that influence the distributions of some of the most important habitat-forming taxa in the deep ocean and create an empirical foundation for supporting cold-water coral and sponge conservation in the NEPC.

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Sponge bioerosion versus aqueous pCO2: morphometric assessment of chips and etching fissures

Bioeroding sponges are important macroborers that chemically cut out substrate particles (chips) and mechanically remove them, thereby contributing to reef-associated sediment. These chemical and mechanical proportions vary with elevated levels of partial pressure of carbon dioxide (pCO2). To assess related impacts, the morphometric parameters “chip diameter” and “etching fissure width” were analyzed for Cliona orientalis Thiele, 1900, hypothesizing that their dimensions would differ with different pCO2 exposures (72 h at ca. 400, 750 and 1700 μatm). Under ambient conditions, we obtained a mean chip diameter of 21.6 ± 0.7 μm and a mean fissure width of 0.29 ± 0.01 μm. Chips were evenly distributed across the medium and coarse silt fractions regardless of treatment. We could not find a reliable pCO2 treatment effect for chip diameter and fissure width, but we observed strong data variability not related to our key questions. A hierarchical data design further reduced the test power. Fissure width was the more sensitive, but also more variable parameter. Sample size analyses nevertheless indicated that we had processed enough data. Thus, we reject our scenario of an increase in fissure width and consequent reduction in chip size to explain why chemical sponge bioerosion increases more strongly than the mechanical counterpart. Instead, we propose that a lowered ambient pH may favor respiratory acid build-up in the sponge tissue, possibly leading to a less localized bioerosion, causing bias towards more chemical bioerosion. Overall, this does not seem to affect the morphometry of sponge chips and the quality of sponge-generated sediment.

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pH regulation and tissue coordination pathways promote calcium carbonate bioerosion by excavating sponges

Coral reefs are threatened by a multitude of environmental and biotic influences. Among these, excavating sponges raise particular concern since they bore into coral skeleton forming extensive cavities which lead to weakening and loss of reef structures. Sponge bioerosion is achieved by a combination of chemical dissolution and mechanical chip removal and ocean acidification has been shown to accelerate bioerosion rates. However, despite the ecological relevance of sponge bioerosion, the exact chemical conditions in which dissolution takes place and how chips are removed remain elusive. Using fluorescence microscopy, we show that intracellular pH is lower at etching sites compared to ambient seawater and the sponge’s tissue. This is realised through the extension of filopodia filled with low intracellular pH vesicles suggesting that protons are actively transported into this microenvironment to promote CaCO3 dissolution. Furthermore, fusiform myocyte-like cells forming reticulated pathways were localised at the interface between calcite and sponge. Such cells may be used by sponges to contract a conductive pathway to remove chips possibly instigated by excess Ca2+ at the boring site. The mechanism underlying CaCO3 dissolution by sponges provides new insight into how environmental conditions can enhance dissolution and improves predictions of future rates of coral dissolution due to sponge activity.

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Sponges to be winners under near-future climate scenarios

Sponges are functionally important components of global benthic environments and have been proposed as potential winners under future climate scenarios. We review the evidence to support this hypothesis by examining the individual and combined effects of ocean warming (OW) and ocean acidification (OA) on sponges and comparing sponge responses with tolerance thresholds for other benthic organisms. Although sponges are generally tolerant of OA and may even benefit from elevated partial pressure of carbon dioxide, they are often sensitive to seawater temperatures only a few degrees higher than their normal range. Sponge responses to the combined effects of OA and OW are generally more positive than their response to OW alone. We found that sponges are generally less affected by OW or OA than are a number of currently dominant benthic organisms, such as corals. Therefore, sponges are expected to benefit under near-future climate scenarios, although species-specific differences in tolerance will likely shift the sponge assemblage composition toward more resilient species.

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In situ responses of the sponge microbiome to ocean acidification

Climate change is causing rapid changes in reef structure, biodiversity, and function, though most sponges are predicted to tolerate conditions projected for 2100. Sponges maintain intimate relationships with microbial symbionts, with previous studies suggesting that microbial flexibility may be pivotal to success under ocean acidification. We performed a reciprocal transplantation of the coral reef sponges Coelocarteria singaporensis and Stylissa cf. flabelliformis between a control reef site and an adjacent CO2 vent site in Papua New Guinea to explore how the sponge microbiome responds to ocean acidification. Microbial communities of C. singaporensis, which differed initially between sites, did not shift towards characteristic control or vent microbiomes, even though relative abundances of Chloroflexi and Cyanobacteria increased and that of Thaumarchaeota decreased seven months after transplantation to the control site. Microbial communities of S. cf. flabelliformis, which were initially stable between sites, did not respond specifically to transplantation but collectively exhibited a significant change over time, with a relative increase in Thaumarchaeota and decrease in Proteobacteria in all treatment groups. The lack of a community shift upon transplantation to the vent site suggests that microbial flexibility, at least in the adult life-history stage, does not necessarily underpin host survival under ocean acidification.

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Eating in an acidifying ocean: a quantitative review of elevated CO2 effects on the feeding rates of calcifying marine invertebrates

Feeding is fundamental for all heterotrophic organisms, providing the means to acquire energy for basic life processes. Recent studies have suggested that experimental ocean acidification (OA) can alter the feeding performance of marine calcifying invertebrates, but results have been inconsistent. While several reviews pertaining to the biological effects of OA exist, none provide a synthesis of OA effects on feeding performance. Here, we provide a quantitative analysis of published experiments testing for effects of elevated CO2 on feeding rates of marine calcifying invertebrates. Results revealed that suspension-feeding molluscs and predatory and grazing echinoderms experienced depressed feeding rates under elevated CO2, while arthropods appeared unaffected; larval and juvenile animals were more susceptible to CO2 effects than adults. Feeding strategy did not appear to influence the overall taxonomic trend, nor did habitat, although exposure time did have an effect. AIC model selection revealed that Phylum best predicted effect size; life stage and exposure time were also included in candidate models. Based on these results, we synthesize potential physiological attributes of different taxa that may drive OA sensitivities in feeding rates, which could potentially result in community-level impacts. We also discuss CO2 effects on calcifier feeding in the context of elevated temperature and other global marine change stressors, and highlight other areas for future research.

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Responses of two temperate sponge species to ocean acidification

There are still major gaps in our understanding of the impact of ocean acidification (OA) on some groups of organisms within different geographic regions. We investigated the effect of OA on two common and ecologically important temperate sponge species in New Zealand (Tethya bergquistae and Crella incrustans). Sponges were kept at pH 8 (control) and 7.6 for 4 weeks. Responses of the two species varied, with T. bergquistae kept at pH 7.6 showing some mortality in response to reduced pH and evidence of tissues necrosis. In contrast, only one C. incrustans died in the pH 7.6 treatment and showed little evidence of any tissue degradation. Only T. bergquistae showed evidence for physiological effects of reduced pH as respiration rates were generally higher in the pH 7.6 treatment. Our results provide preliminary evidence to support a general tolerance of temperate sponges to reduced pH, but that some species-specific responses may exist.

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