Posts Tagged 'Porifera'

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.

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

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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Climate change and sponges: an introduction

This chapter provides an introduction to our current understanding of the two most important features of climate change affecting marine sponges—ocean warming and ocean acidification. Of these two stressors, thermal stress associated with ocean warming is likely to have the greatest influence on the sponge assemblages through the induction of diseases and mortality by a decrease in the efficacy of defense mechanisms and development of pathogens. However, there is a considerable variability among species in their responses to increasing temperature, and some species have persisted during episodes of unusually high temperature. Conspicuous sublethal effects have also been described. Thermal stress can limit sponge reproductive capability and dispersal by causing the reabsorption of spermatic cysts and oocytes and by the disruption of the feedback mechanism that prevents the release of asexual propagules when ecological factors are unsuitable for propagule survival. Thermal stress also can affect sponge-feeding behavior by increasing or decreasing filtration rates and by decreasing choanocyte chamber density and size, causing shifts in the microbial communities of the host sponge, and can also increase the production of heat shock proteins, which leads to rapid upregulation of genes involved in cellular damage repair. The effects of ocean acidification on sponges are much less known, but recent studies have demonstrated the resistance of certain species to lowered pH conditions. It seems that this capacity to withstand OA lies in part in the ability of sponges to restructure their host-associated microbiomes mainly by acquiring new microbial components via horizontal transmission. The apparent resilience of some sponge species and the sensitivity of others highlight the need to understand the molecular basis of sponge responses to environmental stressors in order to determine if they will be able to adapt to rapidly changing ocean conditions. Future research focused on transcriptomic and metabolomic responses using genomic approaches will facilitate the assessment of molecular stress responses at different sponge life history stages.

Continue reading ‘Climate change and sponges: an introduction’

Combined effects of experimental acidification and eutrophication on reef sponge bioerosion rates

Health of tropical coral reefs depends largely on the balance between constructive (calcification and cementation) and destructive forces (mechanical-chemical degradation). Gradual increase in dissolved CO2 and the resulting decrease in carbonate ion concentration (“ocean acidification”) in ocean surface water may tip the balance toward net mass loss for many reefs. Enhanced nutrients and organic loading in surface waters (“eutrophication”), may increase the susceptibility of coral reef and near shore environments to ocean acidification. The impacts of these processes on coral calcification have been repeatedly reported, however the synergetic effects on bioerosion rates by sponges are poorly studied. Erosion by excavating sponges is achieved by a combination of chemical dissolution and mechanical chip removal. In this study, Cliona caribbaea, a photosymbiont-bearing excavating sponge widely distributed in Caribbean reef habitats, was exposed to a range of CO2 concentrations, as well as different eutrophication levels. Total bioerosion rates, estimated from changes in buoyant weights over 1 week, increased significantly with pCO2 but not with eutrophication. Observed chemical bioerosion rates were positively affected by both pCO2 and eutrophication but no interaction was revealed. Net photosynthetic activity was enhanced with rising pCO2 but not with increasing eutrophication levels. These results indicate that an increase in organic matter and nutrient renders sponge bioerosion less dependent on autotrophic products. At low and ambient pCO2, day-time chemical rates were ~50% higher than those observed at night-time. A switch was observed in bioerosion under higher pCO2 levels, with night-time chemical bioerosion rates becoming comparable or even higher than day-time rates. We suggest that the difference in rates between day and night at low and ambient pCO2 indicates that the benefit of acquired energy from photosynthetic activity surpasses the positive effect of increased pCO2 levels at night due to holobiont respiration. This implies that excavation must cost cellular energy, by processes, such as ATP usage for active Ca2+ and/or active proton pumping. Additionally, competition for dissolved inorganic carbon species may occur between bioerosion and photosynthetic activity by the symbionts. Either way, the observed changing role of symbionts in bioerosion can be attributed to enhanced photosynthetic activity at high pCO2 levels.

Continue reading ‘Combined effects of experimental acidification and eutrophication on reef sponge bioerosion rates’

Sponge bioerosion on changing reefs: ocean warming poses physiological constraints to the success of a photosymbiotic excavating sponge

Excavating sponges are prominent bioeroders on coral reefs that in comparison to other benthic organisms may suffer less or may even benefit from warmer, more acidic and more eutrophic waters. Here, the photosymbiotic excavating sponge Cliona orientalis from the Great Barrier Reef was subjected to a prolonged simulation of both global and local environmental change: future seawater temperature, partial pressure of carbon dioxide (as for 2100 summer conditions under “business-as-usual” emissions), and diet supplementation with particulate organics. The individual and combined effects of the three factors on the bioerosion rates, metabolic oxygen and carbon flux, biomass change and survival of the sponge were monitored over the height of summer. Diet supplementation accelerated bioerosion rates. Acidification alone did not have a strong effect on total bioerosion or survival rates, yet it co-occurred with reduced heterotrophy. Warming above 30 °C (+2.7 °C above the local maximum monthly mean) caused extensive bleaching, lower bioerosion, and prevailing mortality, overriding the other factors and suggesting a strong metabolic dependence of the sponge on its resident symbionts. The growth, bioerosion capacity and likelihood of survival of C. orientalis and similar photosymbiotic excavating sponges could be substantially reduced rather than increased on end-of-the-century reefs under “business-as-usual” emission profiles.

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Ocean acidification in the IPCC AR5 WG II

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