One physiological response mechanism to high levels of sediment observed here is the production of mucus to trap sediment. Mucus production in corals is metabolically demanding and can cost corals up to 2.5 times the amount of energy that they would normally use for other physiological functions (i.e. growth and reproduction) in 24 h (Riegl and Branch, 1995). Mucus production by sponges may also be energetically demanding, however, despite visual confirmation of mucus production by sponges in response to sedimentation (Turon et al., 1999; This study) it remains unclear what energetic costs are associated with the production of mucus by sponges. It is also unclear whether the energetic cost of mucus production changes significantly when exposed to suspended sediments that differ both with size and mineralogical composition. This supports further manipulative experimentation to elucidate the differential energetic constraints of sponges exposed to contrasting grain sizes and mineralogical composition of suspended sediments, in terms of both growth and reproduction.