Currents in the Lizard Island region of the Great Barrier Reef Lagoon and their relevance to potential movements of larvae

112

105

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.

Section: Currents and Swimming Speedsupporting

confidence: 82%

Orientation of pelagic larvae of coral-reef fishes in the ocean

Leis¹,

Carson-Ewart²

2003

112

105

“…Correlations between the wind field and larval supply suggest that, counter-intuitively, inter-annual replenishment into the front-reef habitat increases as onshore winds decrease in intensity. Considering that current flow in this region is primarily wind driven (Wolanski & Ruddick 1981, Frith et al 1986, it is hard to envisage how such inter-annual trends could be explained by simple hydrodynamics. Does this mean that the physical model discussed earlier is invalid as a n explanation for inter-annual changes in larval supply?…”

Section: Discussionmentioning

confidence: 99%

“…This peculiarity means that currents in the region are minimally affected by the EAC. Although shifts in the exact position of the bifurcation may alter influence of the EAC at Lizard Island, a 2 yr study by Frith et al (1986) suggested that non-tidal currents at all depths in this area are primarily wind driven (Wolanslu & Ruddick 1981, Frith et al 1986). …”

Section: Introductionmentioning

confidence: 99%

Dynamic coupling of reef fish replenishment and oceanographic processes

Milicich¹

1994

Oceanographic processes have been shown to play a pivotal role in the control of recruitment variability in some commercial, northern temperate fish populations. This study investigates the link between inter-annual changes in larval supply and wind stress for unexploited reef fish populations at Lizard Island, northern Great Barrier Reef. For the first time, this relationship is analysed separately for front-reef and back-reef habitats and results for 3 major reef fish familes (Pomacentridae, Apogorudae, Blenniidae) reveal that the link between wind stress and larval supply appears to be habitat-dependent, In the back-reef habitat, there appears to be a positive correlation between interannual changes in the frequency of onshore winds and the level of larval supply. This phenomenon is associated with large-scale changes in weather systems, suggesting that the relationship may be predictable at a region-wide scale. Results for the front-reef habitat suggest that the effect of wind stress on inter-annual levels of larval supply is less important. Survival and advection of earlier larval stages may be more influential in determining fluctuations in the magnitude of replenishment to this habitat. Although not helpful in predicting inter-annual changes In larval supply, a local retention mechanism may keep larval supply lnto thls habitat elevated above that of the back-reef side. Comparison of these results with a non-reef mixed-age group of schooling pelagic fishes suggests that these patterns are a unique feature of the replenishment process.

“…If they use their swimming capabilities to modify dispersal, genetic evidence suggests that they are using them to retard rather than enhance dispersal (Doherty et al 1995). There is considerable evidence from hydrodynamic studies suggesting that young larvae will not necessarily be transported very far from reefs (Black et al 1991, Black 1993, particularly in the summer months (Frith et al 1986). Local retention, along with the early development of swimming ability in some demersal-spawning reef fishes, suggests that many populations of reef fishes may have a significant potential for self-seeding 1 .…”

Section: Implications For Dispersalmentioning

confidence: 99%

Development of swimming abilities in reef fish larvae

Fisher¹,

Bellwood²,

Job³

2000

219

189

Recent studies have revealed that reef fish larvae have excellent sustained swimming capabilities and considerable potential for modifying their dispersal patterns by active swimming. However, these studies concentrate solely on the late pelagic phase. We examined the development of swimming abilities from hatching through to settlement in 3 reef fish species (Pomacentrus amboinensis, Sphaeramia nematoptera, Amphiprion melanopus). Larval rearing provided larvae at all stages of development. Experiments were conducted in flow chambers designed for measuring the critical and sustained swimming capability of young larvae. In all 3 species, critical swimming ability increased steadily with age, size, relative propulsive area and developmental stage of the larvae. In contrast, sustained swimming ability showed a marked inflection during development. Differences among species throughout development appear to reflect variations in the developmental patterns of the 3 species. Propulsive area was highly correlated with swimming ability and may prove useful for estimating swimming capabilities among species. The results suggest that some species have the potential to actively modify their dispersal patterns from an early age.