Effects of suspended sediments on the sponge holobiont with implications for dredging management

Abstract

Dredging can cause high suspended sediment concentrations (SSC) in the water column, posing a hazard to filter feeding organisms like sponges as sediment may clog their aquiferous systems and reduce feeding. In order to provide pressure−response values for sponges to SSC and tease apart the cause:effect pathways of dredging pressures, five heterotrophic and phototrophic species were experimentally exposed to a range of dredging-relevant SSC of up to 100 mg L−1, with light compensation across treatments to ensure that SSC was the primary physical parameter. This study shows that some sponge species exposed to high SSC (≥23 mg L−1) for extended periods (28 d) have lower survival, increased necrosis and depletion of energy reserves. In contrast, SSC of ≤10 mg L−1 caused few, if any, negative effects and is thus suggested as a prudent sub-lethal threshold for sponges. Microbial communities did not change significantly among SSC treatments, although a nutritional shift from mixotrophy towards increased phototrophy was detected for some sponge species exposed to high SSC. Importantly however, it is expected that the combined effect of SSC with low light availability and sediment smothering as occurs during dredging operations will increase the negative effects on sponges.

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

“…, Pineda et al. , b), there is still a major knowledge gap about how sponge‐associated macrofauna respond to these environmental pressures and how this impacts host health and fitness.…”

The effects of seasonal anoxia on the microbial community structure in demosponges in a marine lake (Lough Hyne, Ireland)

“…Sponge holobionts play a key role in marine ecosystems, contributing to reef formation, benthic-pelagic nutrient coupling, and biogeochemical cycling (30)(31)(32). Some of these sponge-microbe associations are highly stable under environmental stressors, including elevated temperature (33)(34)(35), eutrophication and sedimentation (36), and some symbionts are spongespecific, meaning they occur negligibly in the environment (37). Stable sponge-microbe associations were also found across large geographic distances (38).…”

Bioeroding sponges in a time of change: insights into the physiology and cellbiology of a photosymbiotic coral-eroding sponge

“…Experimental loss of symbionts in C. orientalis as a result of thermal stress has been observed before, and can cause longer-term energetic deprivation and mortality to the holobiont (Fang et al, 2013a(Fang et al, , 2014; Chapter 4 of the present thesis). Cnidaria that are symbiotic with Symbiodinium may compensate for the loss of phototrophic capacity by increasing their heterotrophic potential (Grottoli et al, 2006;Dove et al, 2013), but the presence of such plasticity in photosymbiotic sponges is debatable and could not be confirmed here (Fang et al, 2014(Fang et al, , 2017(Fang et al, , 2018Pineda et al, 2017b; Chapter 4 of the present thesis). In our experiment, heterotrophic uptake of carbon was generally higher by day than by night regardless of the treatment, which is in accordance with higher pumping rates of C. orientalis by day .…”

“…A handful of studies have shown that bioeroding sponges that host Symbiodinium erode faster when exposed to sunlight (Rosell and Uriz, 1992;Hill, 1996;Schönberg, 2006) and that decreases in light availability affect the holobiont negatively (Pineda et al, , 2017a(Pineda et al, , 2017b, but the mechanism behind such observations remains elusive. In such bioeroding sponges, one may ponder on the intriguing possibility that photosynthetic products may stimulate bioerosion.…”

“…Trade-offs between heterotrophy and autotrophy within single individuals however remain debatable (Fang et al, 2014(Fang et al, , 2017(Fang et al, , 2018Pineda et al, 2017b). Future experiments addressing the feeding plasticity of photosymbiotic sponges are clearly of need.…”