Behavior of Larval Butterflyfishes (Teleostei: Chaetodontidae) at Settlement on Coral Reefs
Behavior of settlement-stage (10–17 mm SL) larvae of five chaetodontid species (Chaetodon auriga, C. aureofasciatus, C. rainfordi, C. plebeius, and Chelmon rostratus) captured in light traps was investigated in open water and over coral reefs at Lizard Island, Great Barrier Reef. Average swimming speeds of all species in open water (18–26 cm s−1) were greater than average current speeds; larvae swam several meters deeper off the deeper east side of the island than off the west side, and most larvae swam directionally. Near coral reefs, about 37% of larvae swam offshore at speeds that were frequently greater than those at which they swam toward or over reefs. After a mean of 5 min, 40% of larvae reaching reefs swam away offshore, many after harassment by resident fishes. About 5% were eaten; the rest settled in a mean of 2 min. Chaetodon plebeius never settled. Non-predatory resident fishes strongly influenced the distribution of butterflyfish settlers. The three species that settled in usable numbers had species-specific settlement depths and substratum, primarily live corals. Comparing these results to studies on larger juveniles shows that individuals become increasingly selective about habitat (usually coral taxa) as they grow. Larval settlement behavior of chaetodontids is more similar to that of pomacentrids than that of lutjanids or serranids, but some features are shared by all families.
Lizard Island, northern Great Barrier Reef (14°40′S, 145°27′E). Study reefs were located off the leeward (North-West) side of the island, centered at Gully Reef in Watsons Bay (G), in the Lizard Island Lagoon at Mike's Reef (M) and Pass Reef (P), and off the windward (South-East) side at Lizard Head Reef (LH) and Coconut East Reef (CE). Base image GeoEye, used with permission.
Preserved settlement-stage larvae of the study species: (A) Chaetodon aureofasciatus, (B) Chaetodon plebeius, (C) Chaetodon rainfordi, (D) Chaetodon auriga, (E) Chelmon rostratus; scale bar = 5 mm. In life, larvae of species of Chaetodon just removed from light traps had a golden-yellow color that noticeably faded to a more silver hue in the pelagic environment. Images A, B by P. Ovenden. Images C, D, E by M. Yerman.
Vertical distributions in larvae of two chaetodontid species at leeward and windward pelagic areas near Lizard Island. (A) Chaetodon rainfordi (n = 297 observations), depth frequency distributions in the areas were significantly different (KS, P = 0.00001). (B) Chelmon rostratus (n = 199), depth frequency distributions in the areas were not significantly different (KS, P > 0.1).
Behavior of chaetodontid larvae in relation to reefs. Values are percentages of larvae released at each reef (ignoring those eaten or still swimming over the reef at the end of the observation period). Offshore indicates larvae that swam away from the reef without ever reaching it; Settled indicates larvae that settled on the reef; Away indicates larvae that swam over the reef, and then away from it. (A) C. auriga, released only at Gully and Lizard Head reefs; (B) Chaetodon aureofasciatus; (C) C. plebeius, released only at Gully, Lizard Head, and Pass reefs; (D) C. rainfordi.
Contributor Notes
Associate Editor: J. F. Schaefer.