The functional capabilities of reef fish larvae: implications for dispersal during the pelagic phase

Fisher, Rebecca (2002) The functional capabilities of reef fish larvae: implications for dispersal during the pelagic phase. PhD thesis, James Cook University.

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Abstract

This thesis examined the extent to which tropical reef fish larvae are capable of influencing their dispersal and settlement patterns by quantifying swimming performance and behavioural characteristics throughout their pelagic phase. The provision of food to late stage Amphiprion melanopus larvae increased average sustained swimming distances from 6.9 km to 12.2 km, and the maximum swimming distances from 11.8 to 28.7 km. There was also a significant relationship between sustained swimming time and experimental swimming speed, with fish at slower speeds swimming longer and covering greater total distances. Results for Amphiprion melanopus suggested that larvae could sustain swimming at speeds of 8.5 bls-1 and 50% of their U-crit. This was supported by observations on late stage larvae of nine species (from the families Apogonidae, Lethrinidae and Pomacentridae) captured in light traps off Lizard Island. These data on swimming ability were used to estimate the swimming speeds that other reef fish taxa should be able to maintain for significant lengths of time (12 - 48 hours). The results suggest that many reef fish families are able to sustainably swim 2 - 3 times faster than previously estimated. The feeding and swimming speed studies suggest that previous flume-based estimates of sustained swimming underestimate the potential abilities of reef fish larvae. Consequently, sustained swimming behaviour by reef fish larvae could have a much greater impact on modifying larval dispersal than previously thought.

The intrinsic swimming speeds and nocturnal swimming activity of five reef fish species were quantified throughout their larval phase. Video techniques were used to obtain undisturbed observations of swimming behaviour in captive bred larvae. Larvae were found to maintain relatively high swimming speeds throughout development. Speeds were consistent among three anemonefish species (Amphiprioninae), which swam an average of 3.9 and a maximum of 8.4 body lengths per second. The results support short duration experimental and in-situ evidence of high sustained swimming speeds. However, the most striking aspect is that larvae routinely swim at such speeds without external stimuli. The proportion of time larvae spent swimming at night increased rapidly towards the end of the larval phase in all the species examined. In addition, the relative swimming speeds of larvae were significantly greater at night than during the day. Patterns of nocturnal activity appear to relate to the active nocturnal settlement behaviour of larvae. The pattern of swimming, and speeds achieved, suggest that an active behavioural mechanism for self-recruitment is well within the capabilities of the reef fish larvae examined.

Knowledge of the extent of differential water column use by larvae is essential to assess the extent to which they are capable of influencing their dispersal patterns using active behaviour. An experimental light trap was designed to enable the discrete depth sampling of late stage reef fish larvae in the field. This design was used to describe the vertical distribution of late stage larvae off Lizard Island on the Great Barrier Reef in Australia. The largest numbers of late-stage reef fish larvae were found in the upper layers suggesting they migrate into surface waters at night, possibly as part of the settlement process. Several reef fish families were found throughout the water column. This distribution was not attributed to species-specific depth preferences within these families. There were, however, consistent size-specific vertical distributions among families, with larger individuals near the surface and smaller individuals in the middle of the water column, suggesting subtle differences in water column use within species. Some families appear to occur solely near the bottom, indicating family level differences in vertical distributions. The presence of highly structured vertical distributions in late stage reef fish larvae, both among and within species, provides evidence of differential water column use by settlement stage reef fish larvae. The findings of this study emphasise the potential importance of water column use in the overall dispersal and settlement strategies of reef fish larvae.

Overall, the results of this thesis show that tropical reef fish larvae are capable of exerting considerable control over their dispersal patterns during the larval phase, as well as modifying patterns of recruitment and levels of self-recruitment on reefs. It is clear that tropical reef fish larvae are not passive particles. For benthic or brooded species this applies throughout the larval phase. These abilities need to be taken into consideration when constructing oceanographic models of dispersal. If the full potential of larvae behaviour is realised, it may be that reef fish populations of some families are maintained primarily by self-recruitment. If this is true our current understanding of reef fish population dynamics will change dramatically.

Item ID: 27396
Item Type: Thesis (PhD)
Keywords: reef fish larvae; sustained swimming ability; vertical distribution composition; dispersal control; settlement pattern control; self recruitment level
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Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Fisher, R., and Bellwood, D.R. (2001) Effects of feeding on the sustained swimming abilities of late-stage larval Amphiprion melanopus. Coral Reefs, 20 (2). pp. 151-154.

Chapter 2: Fisher, R., and Bellwood, D.R. (2002) The influence of swimming speed on sustained swimming performance of late-stage reef fish larvae. Marine Biology, 140 (4). pp. 801-807.

Chapter 3: Fisher, Rebecca, Bellwood, David R., and Job, Suresh (2000) Development of swimming abilities in reef fish larvae. Marine Ecology-Progress Series, 202 . pp. 163-173.

Chapter 3: Bellwood, David R., and Fisher, Rebecca (2001) Relative swimming speeds in reef fish larvae. Marine Ecology-Progress Series, 211 . pp. 299-303.

Chapter 4: Fisher, R., and Bellwood, D.R. (2002) A light trap design for stratum-specific sampling of reef fish larvae. Journal of Experimental Marine Biology and Ecology, 269 (1). pp. 27-37.

Date Deposited: 25 Jun 2013 02:50
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 51%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060201 Behavioural Ecology @ 49%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970105 Expanding Knowledge in the Environmental Sciences @ 51%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 49%
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