Effects of anemonefish on giant sea anemones

[ThRoewer]

Effects of anemonefish on giant sea anemones: expansion behavior, growth, and survival

The symbiosis between giant sea anemones and anemonefish on coral reefs is well known, but little information exists on impacts of this interaction on the sea anemone host. On a coral reef at Eilat, northern Red Sea, individuals of the sea anemone Entacmaea quadricolor that possessed endemic anemonefish Amphiprion bicinctus expanded their tentacles significantly more frequently than did those lacking anemonefish. When anemonefish were experimentally removed, sea anemone hosts contracted partially. Within 1–4 h in most cases, individuals of the butterflyfish Chaetodon fasciatus arrived and attacked the sea anemones, causing them to contract completely into reef holes. Upon the experimental return of anemonefish, the anemone hosts re-expanded. The long-term growth rate and survival of the sea anemones depended on the size and number of their anemonefish. Over several years, sea anemones possessing small or no fish exhibited negative growth (shrinkage) and eventually disappeared, while those with at least one large fish survived and grew. We conclude that host sea anemones sense the presence of symbiotic anemonefish via chemical and/or mechanical cues, and react by altering their expansion behavior. Host sea anemones that lack anemonefish large enough to defend them against predation may remain contracted in reef holes, unable to feed or expose their tentacles for photosynthesis, resulting in their shrinkage and eventual death.

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 mM 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.