LAPID, E.; CHADWICK, N. E. *; Bar Ilan University; Auburn University : Coral sweeper tentacles as probes to remotely detect competitors

Inducible elongated tentacles in sea anemones (catch tentacles, fighting tentacles) and corals (sweeper tentacles) have been proposed to function in prey capture, sexual reproduction, and damage to competitors. We add here a possible function as probes for the remote detection of advancing competitors. Nocturnal field surveys on the Red Sea brain coral Platygyra daedalea showed that most colonies directed sweeper tentacles toward nearby corals (< 5cm distant) and appeared to inflict unilateral tissue damage, but that some extended sweepers in random directions (21% of N=100 colonies). Laboratory experiments revealed that feeding tentacles transformed into extremely elongated sweeper tentacles at about 30 days following contact with coral competitors. Throughout the study year, brain corals also spontaneously developed sweepers on areas not facing competitors and eventually transformed them back into short feeding tentacles at a rate of 15�7 (mean�STD) tentacles colony^-1 year^-1. This rate appears sufficient to remotely detect most slow-growing coral neighbors and for maintenance of a wide coral-free zone around brain corals in the field. This behavior also may prevent faster-growing acroporid table corals from overtopping brain corals at some distance above the colony. Random morphogenesis of sweeper tentacles as pre-emptive probes to detect and damage advancing competitors may contribute to the persistence of some massive corals on Indo-Pacific coral reefs. Random development of elongated probe-like tentacles also may serve a similar function in other sessile cnidarians.