I conducted laboratory experiments at the UC Berkeley Gump South Pacific Research Station and field activities along the north shore of Moorea, French Polynesia. A barrier reef encloses a lagoon ranging 0.8-1.3km in width and 2-6 m in depth, with patch reefs interspersed with coral rubble and sand (for a detailed description of the lagoon see Galzin and Pointier 1985). I conducted surveys in the Tiahura (17°29'20.76"S, 149°54'0.30"W), Vaipahu (17°28'49.02"S, 149°50'12.36"W), Maharepa (17°28'57.48"S, 149°49'41.70"W) and Teharoa (17°28'26.70"S, 149°47'12.36"W) sectors of the lagoon (Fig. 1). I collected coral colonies from the Vaipahu, Maharepa and Teharoa sectors of the lagoon, crown-of-thorns stars (Acanthaster planci) from the Vaipahu and Maharepa sectors of the lagoon, and pin-cushion stars (Culcita novaguineae) on Gump Reef, a fringing reef adjacent to the research station (Figure 1).
Tube-dwelling amphipods (Gammaropsis sp.) induce the formation of fingers on Montipora spp. corals. All finger-forming amphipods in Moorea appear to belong to a single undescribed species (Bergsma 2009). No other species of amphipod has been described as associating with living scleractinian corals.
Montipora is one of the dominant genera of corals in the northern lagoon of Moorea, but its taxonomy is poorly resolved and species level identifications could not be made with certainty (see Bergsma 2009 for a list of Montipora species that may associate with amphipods). For the laboratory studies, I used a single morphospecies of Montipora (possibly M. aequituberculata). Colonies of the selected morphospecies are typically encrusting or plating when not associated with amphipods. When amphipods are present, however, the colonies form fingers that extend up to 20 cm, and resemble branching corals in morphology (Plate S1a).
For the prey preference experiments, I paired Montipora with colonies of Acropora digitifera. Crown-of-thorns sea stars (Acanthaster planci) preferably prey on Acropora corals (De’ath and Moran 1998; Pratchett 2007), and I selected A. digitifera because it is common in the lagoons of Moorea, and its branching morphology is most similar to the morphology of Montipora sp. colonies with fingers (Plate S1b). For all field surveys, I treated corals at the generic level because of the difficulty of identifying many corals to species.
For the laboratory studies, I used A. planci and pin-cushion stars (Culcita novaguineae), both common coral predators in the lagoons of Moorea. Recently attacked colonies were identified by the feeding scars and denuded coral skeletons left among otherwise healthy corals (Plate S1c, S1d). It was difficult to attribute coral damage to C. novaguineae in the field, so for field surveys I focused solely on A. planci, whose foraging damage was easily detectable.
Bergsma G (2009) Tube-dwelling coral symbionts induce significant morphological change in Montipora. Symbiosis 49:143-150
De'ath G, Moran PJ (1998) Factors affecting the behaviour of crown-of-thorns starfish (Acanthaster planci L.) on the Great Barrier Reef: 2: Feeding preferences. J Exp Mar Biol Ecol 220:107-126
Galzin R, Pointier JP (1985) Moorea island, Society archipelago. 5th Int Coral Reef Congr: 73-102
Pratchett MS (2007) Feeding preferences of Acanthaster planci (Echinodermata : Asteroidea) under controlled conditions of food availability. Pac Sci 61:113-120