S\~lmrnlng speeds of the late-stage, pelaglc larvae of coral-leef flshes were measured in situ near Llzard Island on Australia's Great Barrler Reef, and Ranglroa Atoll, Tuamotu Islands, French Polynes~a d u n n g 1995-96 Larvae were captured w~t h llght traps and crest nets, and released indiv~du-ally In open water They were then followed by SCUBA d~v e r s , normally for 10 mm, and their speed was measured w~t h a m o d~f~e d plankton-net flow meter and a stop watch Swlmmlng speeds of 260 lalvae of 50 specles In 15 famll~es of mostly perclform reef f~s h e s are presented Most measurements were for pomacentnds (8 genera 16 specles, 127 ~n d~v i d u a l s ) , apogonids (1 genus, -5 specles, 18 1nd1-vlduals), chaetodontids (3 genera. 8 specles, 49 ~ndlviduals), lethrlnlds (1 genus, -4 specles, 11 lndivlduals), nemipterlds ( l genus, 2 specles, 10 ~ndlvlduals), serranlds (2 genera, 2 specles, 14 md~vlduals) and acanthurlds (2 genera, -4 specles 13 ~n d~v l d u a l s )Numbers of lndlvlduals per specles ranged from 1 to 25 Speeds were remarkably hlgh for such small flshes ( 0 7 to 5 5 cm) Average speed was 20 6 cm S ' (ranqe 2 to 65), or 13 7 body lengths s ' (range 2 to 34) SE fol specles wlth n > 4 ranged from 0 8 to 5 3 cm s ' 14 1 to 25 0 " 0 of mean speed), but speed of the fastest lndlvldual ot each specles averaged 144 "/o of mean speed A taxonom~c component was evident, with apogonlds the slowest (2 to 13 cm S l ) , followed by nemipterlds (10 cm s ') Speed of pomacentr~ds and chaetodontlds varled wldely among specles (7 to 35 cm s '), whereas acanthunds, lethrlnlds and s e r r a n~d s were fast ( l 9 to 55 cm S-') Except for apogonlds and nem~ptel-lds, nearly all specles had mean swlmming speeds greater than average ambient current speeds In the L~zard Island area Mean speed was positively correlated wlth size (slope 8 2, r2 = 0 43) when all taxa were lncluded but was not correlated wlth slze for the Pomacentndae and Chaetodontidae when each were considered alone The speeds reported here combined wlth data on swimming endurance recently reported by Stobutzk~ & Bellwood (1997. Mar Ecol Prog Ser 149 35-41) reveal remarkable swlmnling a b l h t~e s for late-stage pelaglc larvae of coral-reef flshes whlch could e~t h e r gleatly enhance d~spersal or eliminate it
During the day, we used settlement-stage reef-fish larvae from light-traps to study in situ orientation, 100 to 1000 m from coral reefs in water 10 to 40 m deep, at Lizard Island, Great Barrier Reef. Seven species were observed off leeward Lizard Island, and 4 species off the windward side. All but 1 species swam faster than average ambient currents. Depending on area, time, and species, 80 to 100% of larvae swam directionally. Two species of butterflyfishes Chaetodon plebeius and Chaetodon aureofasciatus swam away from the island, indicating that they could detect the island's reefs. Swimming of 4 species of damselfishes Chromis atripectoralis, Chrysiptera rollandi, Neopomacentrus cyanomos and Pomacentrus lepidogenys ranged from highly directional to nondirectional. Only in N. cyanomos did swimming direction differ between windward and leeward areas. Three species (C. atripectoralis, N. cyanomos and P. lepidogenys) were observed in morning and late afternoon at the leeward area, and all swam in a more westerly direction in the late afternoon. In the afternoon, C. atripectoralis larvae were highly directional in sunny conditions, but nondirectional and individually more variable in cloudy conditions. All these observations imply that damselfish larvae utilized a solar compass. Caesio cuning and P. lepidogenys were non-directional overall, but their swimming direction differed with distance from the reef, implying the reef was detected by these species. Larvae of different species of reef fishes have differing orientations and apparently use different cues for orientation while in open, pelagic waters. Current direction did not influence swimming direction. Net movement by larvae of 6 of the 7 species differed from that of currents in either direction or speed, demonstrating that larval behaviour can result in non-passive dispersal, at least near the end of the pelagic phase.
Settlement-stage pelagic larvae of the coral-reef damselfish Chromis atripectoralis consistently swam to the south at 24 to 25 cm s -1 in day-time ambient conditions off Lizard Island, Great Barrier Reef. This was true on both the windward and leeward sides of the island, 100 to 1000 m from the nearest reef. Larvae released during the day 25 to 100 (mean 58) m from an underwater speaker broadcasting nocturnal reef sounds had no overall swimming direction. This was true on both windward and leeward sides of the island, 500 to 1000 m from the nearest reef. The broadcast sounds resulted in an alteration of behavior indicating that the larvae heard them. In the presence of the nocturnal reef sounds, swimming speed increased about 5 cm s -1 off the leeward side but not the windward side. Larvae released 50 to 150 (mean 78) m from a speaker broadcasting artificial sound (pure tones) at the leeward location swam to the south at 30 cm s -1 . This shows that larvae of C. atripectoralis can distinguish between a sound with potential biological significance and one devoid of biological significance. Larvae did not swim in any particular direction relative to the speaker when nocturnal reef sounds were broadcast; therefore, we have no evidence that the larvae can localize these sounds. We conclude that settlement-stage larvae of this damselfish can hear reef sounds, and can distinguish between reef sounds and an artificial sound, but we have no indication that they can localize the sound. We speculate on the reasons for altered swimming behavior in the presence of reef sounds.
At Lizard Island, Great Barrier Reef, catches of fish larvae by light traps that broadcast nocturnal reef sounds (noisy traps) were compared with catches by quiet traps over two 2·5 week new‐moon periods in November (XI) 2000 and January (I) 2001. Three areas were sampled: near‐reef (NR, 500 m from the shore) in I, middle (M, 650 m) in I and XI and offshore (O, >1000 m) in XI. The most abundant taxa captured were Apogonidae, Blenniidae, Chaetodontidae, Lethrinidae, Mullidae and Pomacentridae. Significant differences in catch were found between areas, and a position effect was found at the O and M areas. At the NR and M areas, no taxa had significantly greater catches in quiet traps, but larvae of five taxa had significantly greater catches in noisy traps. These were (areas and times of greater catches): Apogonidae (NR; M XI), Mullidae (M I & XI), Pomacentridae (NR; M I & XI), Serranidae (M I) and Sphyraenidae (NR). At the offshore area, five taxa (Apogonidae, Blenniidae, Chaetodontidae, Mullidae and Pomacentridae) had significantly greater catches in quiet traps and only Lethrinidae had significantly greater catches in noisy traps. Thus some taxa (particularly apogonids and pomacentrids which had catches up to 155% greater in noisy traps, but also lethrinids and mullids, and perhaps others), were attracted to reef sounds at night, but this apparently varied with location and time. The sound‐enhanced catches imply a radius of attraction of the sound 1·02–1·6 times that of the light. More than 65 m from the speaker,the broadcast sound levels at frequencies typical of fish hearing were equivalent to background levels, providing a maximum radius of sound attraction in this experiment.
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