Effects of combined dredging-related stressors on sponges: a laboratory approach using realistic scenarios

Mari-Carmen Pineda,Nicole S Webster,Ross Jones,Jasmine Kamp,Brian Strehlow,Alan Duckworth

doi:10.1038/s41598-017-05251-x

Abstract

Dredging can cause increased suspended sediment concentrations (SSCs), light attenuation and sedimentation in marine communities. In order to determine the combined effects of dredging-related pressures on adult sponges, three species spanning different nutritional modes and morphologies were exposed to 5 treatment levels representing realistic dredging scenarios. Most sponges survived under low to moderate turbidity scenarios (SSCs of ≤ 33 mg L−1, and a daily light integral of ≥0.5 mol photons m−2 d−1) for up to 28 d. However, under the highest turbidity scenario (76 mg L−1, 0.1 mol photons m−2 d−1) there was 20% and 90% mortality of the phototrophic sponges Cliona orientalis and Carteriospongia foliascens respectively, and tissue regression in the heterotrophic Ianthella basta. All three sponge species exhibited mechanisms to effectively tolerate dredging-related pressures in the short term (e.g. oscula closure, mucus production and tissue regression), although reduced lipids and deterioration of sponge health suggest that longer term exposure to similar conditions is likely to result in higher mortality. These results suggest that the combination of high SSCs and low light availability can accelerate mortality, increasing the probability of biological effects, although there is considerable interspecies variability in how adult sponges respond to dredging pressures.

Highlights

Sediments released into the water column by natural resuspension, river runoff and human activities such as dredging pose a potential risk to sensitive ecosystems such as coral reefs, seagrass meadows and sponge gardens[1,2,3,4]
All tanks returned to control conditions and no significant differences were retrieved between treatments (Fig. 1, Table 1, Table 2)
The results from this study show a range of responses from three sponge species to the combined effects of elevated suspended sediment concentrations (SSCs), light attenuation and sedimentation, with sponge health being negatively affected by moderate to high turbidity scenarios (≥10 mg L−1, ≤0.8 mol photons m−2 d−1)

Summary

Introduction

Sediments released into the water column by natural resuspension, river runoff and human activities such as dredging pose a potential risk to sensitive ecosystems such as coral reefs, seagrass meadows and sponge gardens[1,2,3,4]. Sponges are sessile filter-feeding organisms that play important roles in marine ecosystems, including substrate consolidation, habitat provision, seawater filtration and bentho-pelagic energy transfer[7,8,9] Despite their abundance and ecological importance, our understanding of how sponges respond to turbidity is still very basic[10, 11]. Some species have active cleaning mechanisms to remove sediments such as the production of mucus-like substances and tissue sloughing, selective rejection of inhaled particles and the use of water jets to unblock inhalant pores[10, 11, 24] These ‘active’ mechanisms (requiring energy expenditure) work in conjunction with more ‘passive’ mechanisms that reduce sediment accumulation such as the existence of self-cleaning surfaces, and micro and macro morphology and orientation that promotes sediment rejection under gravitational forces[11, 31]. The removal of sediment by epibionts is a passive mechanism for self-cleaning that has been reported in some sponges[11]

Methods

Results

Conclusion