Interactive effects of temperature and pCO₂ on sponges: from the cradle to the grave

Abstract

As atmospheric CO concentrations rise, associated ocean warming (OW) and ocean acidification (OA) are predicted to cause declines in reef-building corals globally, shifting reefs from coral-dominated systems to those dominated by less sensitive species. Sponges are important structural and functional components of coral reef ecosystems, but despite increasing field-based evidence that sponges may be 'winners' in response to environmental degradation, our understanding of how they respond to the combined effects of OW and OA is limited. To determine the tolerance of adult sponges to climate change, four abundant Great Barrier Reef species were experimentally exposed to OW and OA levels predicted for 2100, under two CO Representative Concentration Pathways (RCPs). The impact of OW and OA on early life-history stages was also assessed for one of these species to provide a more holistic view of species impacts. All species were generally unaffected by conditions predicted under RCP6.0, although environmental conditions projected under RCP8.5 caused significant adverse effects: with elevated temperature decreasing the survival of all species, increasing levels of tissue necrosis and bleaching, elevating respiration rates and decreasing photosynthetic rates. OA alone had little adverse effect, even under RCP8.5 concentrations. Importantly, the interactive effect of OW and OA varied between species with different nutritional modes, with elevated pCO exacerbating temperature stress in heterotrophic species but mitigating temperature stress in phototrophic species. This antagonistic interaction was reflected by reduced mortality, necrosis and bleaching of phototrophic species in the highest OW/OA treatment. Survival and settlement success of Carteriospongia foliascens larvae were unaffected by experimental treatments, and juvenile sponges exhibited greater tolerance to OW than their adult counterparts. With elevated pCO providing phototrophic species with protection from elevated temperature, across different life stages, climate change may ultimately drive a shift in the composition of sponge assemblages towards a dominance of phototrophic species.

Using a thermistor flowmeter with attached video camera for monitoring sponge excurrent speed and oscular behaviour

“…Given potential decreases in carbonate accretion by corals (Hoegh-Guldberg et al, 2007), C. orientalis abundance may increase in the future. Furthermore, sponges in general (Bell et al, 2013) and photosynthetic sponges in particular (Bennett et al, 2016) will likely increase in abundance under projected climate change scenarios. This increase would be concurrent with an increased effect of sponge pumping on ecosystem processes (e.g., element cycling), and could even lead to a positive feedback loop that enhances sponge and algal growth while decreasing coral recovery potential (Pawlik, Burkepile & Thurber, 2016).…”

Climate change alterations to ecosystem dominance: how might sponge‐dominated reefs function?

“…, Bennett et al. ). Further declines in coral abundance or direct increases in sponge abundance as a result of increased productivity (Bennett et al.…”

“…, Bennett et al. , ). While transitions to algal‐dominated reefs have been well described (Roff and Mumby ), few studies have assessed how these new states may function (but see Graham et al.…”

Elucidating the sponge stress response; lipids and fatty acids can facilitate survival under future climate scenarios

“…Climate change conditions projected for 2,100 combined with ongoing degradation from local stressors, are expected to cause significant declines in coral cover and create space for other more tolerant organisms (Bell, Davy, Jones, Taylor, & Webster, ; Kroeker, Micheli, & Gambi, ; Norström, Nyström, Lokrantz, & Folke, ). Some coral reef sponges are able to tolerate elevated temperature and oceanic p CO 2 , suggesting a capacity to proliferate on coral reefs as space is made available by declines in more sensitive reef species (Bell et al., ; Bennett et al., ; Duckworth & Peterson, ; Duckworth, West, Vansach, Stubler, & Hardt, ; Fang et al., ; Lesser, Fiore, Slattery, & Zaneveld, ; Stubler, Furman, & Peterson, ; Vicente, Silbiger, Beckley, Raczkowski, & Hill, ; Wisshak, Schönberg, Form, & Freiwald, ). To date, climate change research on marine sponges has focused primarily on the physiological response of these sessile organisms to predicted OW and OA.…”