Effects of anemonefish on giant sea anemones: Ammonium uptake, zooxanthella content and tissue regeneration

Zooxanthellae symbiotic with stony corals utilise ammonium excreted by resident fish populations. However, the contribution of ammonium produced by anemonefishes to host sea anemones has not been examined. In split-pair laboratory experiments with the giant sea anemone Entacmaea quadricolor, one half of each sea anemone was maintained with two individuals of the endemic anemonefish Amphiprion bicinctus, and the other half was maintained without anemonefish. Sea anemone fragments maintained with anemonefish regenerated significantly faster than those without anemonefish. After 8 weeks of regeneration, there were more endosymbiotic algae (zooxanthellae) in the tentacles of sea anemones with anemonefish than in those lacking fish. Adult anemonefish (8 cm total length) each excreted ammonium at a rate of about 0.97 µM h−1. Sea anemones that had been maintained without anemonefish for 4 weeks took up ammonia from enriched water at a faster rate than those that had been maintained with anemonefish, which absorbed very little ammonium. We conclude that anemonefishes provide ammonia for their host anemones and zooxanthellae, enhancing rates of tissue growth and regeneration.