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
Both morphology and behaviour develop during the pelagic larval stage of demersal teleost fishes. Demersal perciform fishes from warm-water habitats begin their pelagic larval stage as plankton but end it as nekton, with behavioural capabilities (including swimming, orientation and sensory abilities) that can influence, if not control, dispersal trajectories. The ontogeny of these behaviours, and the gradual transition from plankton to nekton, are central to understanding how larval fishes can influence dispersal and how behaviour can be integrated into dispersal models. Recent behavioural research shows that, from about 5 to 8 mm standard length, larvae of warm-water perciform fishes can directly influence dispersal, because they swim in an efficient inertial hydrodynamic environment, can swim for kilometres at speeds that heuristic models show will alter dispersal trajectories, can swim faster than ambient currents before settlement, can orientate in the pelagic environment and can detect sensory cues (light, sound, odour) that allow orientation. Fish larvae also control their vertical position (which may change temporally, spatially and ontogenetically), allowing indirect influence on dispersal. Most research on larval behaviour relevant to dispersal (i.e. swimming, orientation and sensory abilities) has been done with warm-water perciform species. This invites the question: Will the same be found in cool water or in species of other orders? The hydrodynamic and physiological effects of temperature indicate that larvae in warm water should swim more efficiently and initially at smaller sizes than larvae in cool water. Limited evidence suggests that larvae of perciform fishes are more behaviourally competent and attain morphological and behavioural milestones when smaller (and probably younger) than do larvae of clupeiform, gadiform and pleuronectiform (CGP) fishes. Perciform fishes dominate demersal fish communities in warm water, whereas CGP fishes dominate in cooler waters. These hydrodynamic, physiological, ontogenetic, phylogenetic and biogeographic factors imply that larval fish behaviour may have more influence on dispersal in warm seas than in cool seas. This hypothesis requires testing. Additional factors that should be taken into account when using behaviour of larvae to produce biophysical models of dispersal are discussed.
LETTERSUndercover. Many Alpheidae shrimps live deep in the reef and are impossible to collect nonlethally. Published by AAAS
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.
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