Posts Tagged 'Porifera'

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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Bleaching and mortality of a photosymbiotic bioeroding sponge under future carbon dioxide emission scenarios

The bioeroding sponge Cliona orientalis is photosymbiotic with dinoflagellates of the genus Symbiodinium and is pervasive on the Great Barrier Reef. We investigated how C. orientalis responded to past and future ocean conditions in a simulated community setting. The experiment lasted over an Austral summer under four carbon dioxide emission scenarios: a pre-industrial scenario (PI), a present-day scenario (PD; control), and two future scenarios of combined ocean acidification and ocean warming, i.e., B1 (intermediate) and A1FI (extreme). The four scenarios also simulated natural variability of carbon dioxide partial pressure and temperature in seawater. Responses of C. orientalis generally remained similar between the PI and PD treatments. C. orientalis under B1 displayed a dramatic increase in lateral tissue extension, but bleached and displayed reduced rates of respiration and photosynthesis. Some B1 sponge replicates died by the end of the experiment. Under A1FI, strong bleaching and subsequent mortality of all C. orientalis replicates occurred at an early stage of the experiment. Mortality arrested bioerosion by C. orientalis under B1 and A1FI. Overall, the absolute amount of calcium carbonate eroded by C. orientalis under B1 or A1FI was similar to that under PI or PD at the end of the experiment. Although bioerosion rates were raised by short-term experimental acidification in previous studies, our findings from the photosymbiotic C. orientalis imply that the effects of bioerosion on reef carbonate budgets may only be temporary if the bioeroders cannot survive long-term in the future oceans.

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The sponge holobiont in a changing ocean: from microbes to ecosystems

The recognition that all macroorganisms live in symbiotic association with microbial communities has opened up a new field in biology. Animals, plants, and algae are now considered holobionts, complex ecosystems consisting of the host, the microbiota, and the interactions among them. Accordingly, ecological concepts can be applied to understand the host-derived and microbial processes that govern the dynamics of the interactive networks within the holobiont. In marine systems, holobionts are further integrated into larger and more complex communities and ecosystems, a concept referred to as “nested ecosystems.” In this review, we discuss the concept of holobionts as dynamic ecosystems that interact at multiple scales and respond to environmental change. We focus on the symbiosis of sponges with their microbial communities—a symbiosis that has resulted in one of the most diverse and complex holobionts in the marine environment. In recent years, the field of sponge microbiology has remarkably advanced in terms of curated databases, standardized protocols, and information on the functions of the microbiota. Like a Russian doll, these microbial processes are translated into sponge holobiont functions that impact the surrounding ecosystem. For example, the sponge-associated microbial metabolisms, fueled by the high filtering capacity of the sponge host, substantially affect the biogeochemical cycling of key nutrients like carbon, nitrogen, and phosphorous. Since sponge holobionts are increasingly threatened by anthropogenic stressors that jeopardize the stability of the holobiont ecosystem, we discuss the link between environmental perturbations, dysbiosis, and sponge diseases. Experimental studies suggest that the microbial community composition is tightly linked to holobiont health, but whether dysbiosis is a cause or a consequence of holobiont collapse remains unresolved. Moreover, the potential role of the microbiome in mediating the capacity for holobionts to acclimate and adapt to environmental change is unknown. Future studies should aim to identify the mechanisms underlying holobiont dynamics at multiple scales, from the microbiome to the ecosystem, and develop management strategies to preserve the key functions provided by the sponge holobiont in our present and future oceans.

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Future research directions and gaps in our knowledge

In this final chapter, we explore the current gaps in our understanding of ocean acidification and increased sea surface temperature on sponges and highlight some future research directions to address these gaps. We particularly focus on the geographic spread of the currently available studies, the mechanisms of acclimation and the potential for long-term adaptation. We also highlight the need for more multiple stressor impact studies and a better understanding of the ecosystem consequences of changing sponge abundance. With this information, we will be able to better predict future impacts of environmental change on sponges.

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Bioeroding sponges and the future of coral reefs

Bioeroding sponges play a central role in carbonate cycling on corals reefs. They may respond differently to habitat deterioration than many other benthic invertebrates, because at some locations, their abundances increased after disturbance. We reviewed literature on these sponges in context of environmental change and provide meta-analyses at global level. A difficult taxonomy and scarce scientific expertise leave them inadequately studied, even though they are the best-known internal bioeroders. They are sheltered within the substrate they erode, appear to be comparatively resilient against environmental change and can have heat-resistant photosymbionts and ‘weedy’ traits, including multiple pathways to reproduce or disperse and fast growth and healing abilities. Especially temperature stress appears to disable calcifiers stronger than bioeroding sponges. Moreover, increases in bioeroding sponge abundances have been related to eutrophication and disturbances that led to coral mortality. Chemical sponge bioerosion is forecast to double with doubled partial pressure of carbon dioxide, but reduced substrate density may counteract this effect, as dominant sponges erode more in denser substrates. Case examples portray shifting impacts of bioeroding sponges with environmental change, with some reefs already being erosional. Most available data and the largest known species record are from the Caribbean. Data from the Coral Triangle and India are largely restricted to faunistic records. Red Sea, Japanese and cold-water reef bioeroding sponges are the least studied. We need more quality research on functions and interaction effects, about which we are still insufficiently informed. With many calcifiers increasingly failing and bioeroding sponges still doing well, at least at intermediate levels of local and global change, these sponges may continue to significantly affect coral reef carbonate budgets. This may transform them from valuable and necessary recyclers of calcium carbonate to problem organisms.

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Sponge reefs of the British Columbia, Canada Coast: impacts of climate change and ocean acidification

Sponge reefs living in deeper shelf waters on the western margin of North America are somewhat insulated from surface water effects of localized ocean warming but are susceptible to increasing hypoxia associated with ocean stratification and increasing upwelling. The largest reef complexes are projected to experience increasing upwelling and low-oxygen events in the future as part of the observed and projected changes in ocean ventilation accompanying increased atmospheric carbon dioxide concentrations. Inshore and shallow reefs are subjected to surface water warming in fiords. Surface water productivity is anticipated to change slightly likely having limited negative impact on the sponge reefs which are adapted to relatively low-nutrient situations. It is unknown the extent to which glass sponges might be resilient to lower oxygen conditions. While filtration is an energetically costly method of feeding, glass sponges appear to be adapted to reduce their energetic needs by using ambient flow to assist filtration. Populations that experience extreme hypoxia in some fiords may be extirpated by extreme anoxic events. Ocean acidification will not have as large an effect on the siliceous skeleton sponges as it will on corals and other carbonate-dependent organisms though it is possible changing pH will affect tissue functioning and homeostasis by compromising membrane pumps. Hexactinellid sponges and sponge reefs have been resilient to changing climate and ocean environments in the geologic past.

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Molecular responses of sponges to climate change

We live in a time of concern regarding predicted environmental damage due to climate change, i.e. sea temperature increase and a reduction in ocean pH. Such changes will have severe consequences for at least some marine organisms. Developments in molecular and genomic techniques allow for genome-wide comparisons of genes and proteins that may be impacted by such changes with knock-on consequences for cell and organism function. Understanding of impacts at the molecular level is important to understand how organisms will respond to changes and to develop conservation strategies accordingly. Despite sponges having a very simple body plan, they possess gene diversity and genome complexity that mirrors other metazoa. The cellular stress response and adaptation of sponges to increased temperature and low pH are varied and diverse with many genes implicated and their expression patterns complex. Survival thresholds differ between species in their tolerance to temperature increase and lowering of ocean pH. The expression patterns of a variety of genes have been investigated particularly with regard to change in temperature but in few sponge species. Likewise genome and transcriptome data exists for few species, and even fewer studies focus on applying these approaches to stress response. Despite the requirement for more studies in this area, existing data suggests that some sponge species will be severely impacted if climate change predictions hold, while other species will adapt and thrive.

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Ocean acidification in the IPCC AR5 WG II

OUP book