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

Abstract

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.

Three phyla—Two type specimens—One shell: History of a snail shell revealed by modern imaging technology

“…Recently, the effect of ocean acidification and its influence on bioerosion has been subject of several studies (Achlatis et al, ; Schonberg et al, ; Wisshak, Schönberg, Form, & Freiwald, ). Our study shows the usefulness of micro‐CT imaging as non‐destructive imaging techniques of internal bioeroders.…”

Paradise lost: End‐of‐century warming and acidification under business‐as‐usual emissions have severe consequences for symbiotic corals

“…Temperature and p CO 2 treatments were established using a computer‐controlled simulation system in which different levels of warming and acidification can be achieved (for a detailed description of the system, see Dove et al, as well as Achlatis et al, ; Supporting Information). Treatment conditions were created as offsets to a variable temperature and p CO 2 baseline, established by CSIRO and the NOAA Pacific Marine Environment Laboratory Ocean Program using two‐ or three‐hourly measurements over the previous summer at a reference location (Harry's Bommie) on Heron Island (Figures S1 and S2 in Supporting Information).…”

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

“…) and cannot survive ocean temperatures projected for 2100 (Achlatis et al. , Ramsby et al. ), therefore they will have a negligible impact on reef erosion or function.…”

“…A sponge-dominated reef is unlikely to be a long-term state since sponges are not producing calcium carbonate (with the exception of small amounts by calcareous sponges) to enable reef accretion. While there was some thought that bioeroding sponges could tolerate ocean warming (Fang et al 2014), recent work has shown that Cliona has not increased on inshore reefs over the past decade (Ramsby et al 2017) and cannot survive ocean temperatures projected for 2100 (Achlatis et al 2017, Ramsby et al 2018, therefore they will have a negligible impact on reef erosion or function. Importantly, since sponges require hard substrate for settlement and stability, they are not likely to persist if the primary reef structure has entirely broken down.…”