6.4 Pressure/response relationships: sponges

Description

The identification of cause-effect pathways and derivation of dose:response relationships are essential for effective dredging management and impact-prediction. For this purpose, and in order to avoid confounding interactions of stressors, light attenuation, suspended sediment concentrations and sediment smothering were tested in isolation.

Results of these individual experiments contributed to the derivation of trigger values that can be used to interrogate models for impact prediction and in water quality monitoring programs to alert dredging proponents to levels of stressors that, if continued, could detrimentally impact sponge populations.

However, during dredging operations these three pressures occur in combination which may have additive or synergistic negative effects on sponges under realistic field conditions. Therefore, a final experiment which investigated the combined effects of these stressors under different dredging scenarios was also performed.

Aims

• To investigate responses of different sponge morphologies to a range of controlled sedimentation treatments simulating conditions associated with dredging activity.
• To examine the effects of environmentally realistic light reduction over an extended period (30 d), with a particular focus on changes in sponge symbiosis.