2. Frond-oyster puzzle
  Here are possible answers:
  1. MUTUALISM Most or all gorgonians contain photosynthesising zooxanthellae cells in their tissues. In return for a place to live these mutualistic cells provide their host with sugars, amino acids, glycerol, and other useful photosynthetic products.
  2. MUTUALISM The sponge gets a clean place to live while the frond oyster presumably benefits from the protection conferred by its sponge symbiont.
  3. PARASITISM In attaching to the gorgonian the frond oyster kills the gorgonian polyps it contacts, but the remaining colony survives.
  4. COMPETITION The two organisms are competing for space; however, because the sponge is restricted to growing on the shell of its specialised frond-oyster host and cannot move off it, the fire coral is probably the aggressor. The competition is chemical and the participants appear to be in "stand-off".
  5. COMPETITION Both the fire coral and gorgonain feed on zooplankton, so there is likely to be competition between them, at least for smaller-sized food items.
  6. PREDATION The gorgonian is primarily carnivorous, feeding on small animal-components in the water (zooplankton).