The early life history of labroid fishes at Lizard Island, Northern Great Barrier Reef

Green, Alison Lesley (1994) The early life history of labroid fishes at Lizard Island, Northern Great Barrier Reef. PhD thesis, James Cook University.

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Abstract

Adult labrids showed distinctive patterns of distribution and abundance among habitat zones at Lizard Island, which were consistent in space (among sites) and time (annually and seasonally). Patterns of labrid abundance and diversity among habitats were not clearly influenced by substrate characteristics such as percent live cover, substrate diversity and complexity. However depth was an important factor influencing habitat use, with 7 abundant species present in higher densities in either shallow (Halichoeres spp., Stethojulis bandanensis, Thalassoma hardwicke and T. jansenii) or deep habitats (Cons schroederi, H. melanurus, T. lunare). Only one abundant species, Labroides dimidiatus was ubiquitous at all depths. Most species used the same habitat zones at different life history stages (adults and recruits), suggesting that patterns of distribution and abundance of adults were determined by recruitment patterns at this scale. In contrast, two species (Labroides dimidiatus and Thalassoma lunare) showed ontogenetic shifts in habitat use, indicating that their recruitment patterns were modified by post-settlement processes.

Labroid recruits (labrids and scarids) also showed distinctive patterns of distribution and abundance among microhabitats within. 2 zones (Reef Base and Sand Flat). Three abundant taxa: 2 labrids (Coris schroederi and Halichoeres melanurus) and a group of scarids (Scares spp.), were present in significantly higher densities within stands of macroalgae in territories of two herbivorous damselfish (Dischistodus prosopotaenia and D. perspicillatus) than they were in adjacent microhabitats (reef matrix and rubble/sand patches). The territories provided excellent replicate units of habitat for studying the early life history of these species. Many rare species were also most abundant in the territories.

Each damselfish species facilitated the growth of macroalgae within their territories by excluding trophic competitors and disruptive carnivores. The territories of D. prosopotaenia were established on the reef matrix/sand interface at the bottom of the slope, and were characterised by multispecific stands of green, red and brown algae. D. perspicillatus territories were established on sand on the sand flat, and were characterised by a monospecific stand of blue-green algae. In contrast to the territories, adjacent microhabitats were almost devoid of macroalgae. Both damselfish species were abundant and occurred in large aggregations ( >20 individuals), where territories covered > 20% of large areas ( > 250m²). The result was that recruitment of these labroids to large areas with damselfish aggregations, was significantly higher than to adjacent areas without aggregations.

C. schroederi and Scarus spp. used both types of territories in high densities, while H. melanurus was only present in high densities in D. prosopotaenia territories. A manipulative experiment using artificial territories indicated that H. melanurus may have discriminated between the territories on the basis of their microhabitat characteristics, rather than their location on the reef profile. However further manipulative studies are required to test this hypothesis.

Labrids which used the territories heavily as recruits did so at different times of the summer. Scarids used them most heavily in the early summer, C. schroederi used them in mid-summer and H. melanurus used them in late summer. These recruitment patterns were spatially (among sites) and temporally (between years) consistent, and probably decreased the possibility of inter-specific interactions between labroid recruits during, the first few weeks of benthic life.

Scarid recruits used the territories for only a few weeks before they were evicted by the resident damselfish. This coincided with the size at which they became herbivores and trophic competitors to the damselfish. In contrast, the carnivorous labrids continued to use territories heavily throughout their lives, with adults of one species (C. schroederi) spending >50% of their time within territories. This behaviour appeared to be tolerated by the resident damselfish, which only attacked them on rare occasions.

Living within territories had no negative effects on diet, growth or survivorship of C. schroederi and H. melanurus recruits during the first 2 months of benthic life, despite their high densities. This was probably because resources (food and shelter) were also much higher in territories than in other microhabitats. The result was that patterns of higher overall recruitment to areas with damselfish aggregations were either reinforced or unchanged by early post-settlement processes, which suggested that sizes of adult populations of these species should have been higher in the vicinity of territories than in adjacent areas without territories. However this was not the case, suggesting that processes operating after the first 2 months of benthic life modified spatial patterns of recruitment. One possibility was that some individuals may have moved out of areas with damselfish aggregations onto adjacent areas where aggregations were absent. These results suggest that damselfish aggregations act as focal sites for labroid recruitment, which may result in higher local abundances of some labroids, both in areas with damselfish aggregations and adjacent reefal areas.

Item ID: 27393
Item Type: Thesis (PhD)
Keywords: labrid abundance; distribution pattern; abundance pattern; territory diversity; labroid recruitment patterns
Date Deposited: 25 Jun 2013 03:59
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 49%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060399 Evolutionary Biology not elsewhere classified @ 51%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 49%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 51%
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