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Spatial variation in abundance, size and orientation of juvenile corals related to the biomass of parrotfishes on the Great Barrier Reef, Australia.

Trapon ML, Pratchett MS, Hoey AS - PLoS ONE (2013)

Bottom Line: Size-class structure, orientation on the substrate and taxonomic composition of juvenile corals varied significantly among latitudinal sectors.The abundance of juvenile corals varied both within (6-13 ind.m(-2)) and among reefs (2.8-11.1 ind.m(-2)) but was fairly similar among latitudes (6.1-8.2 ind.m(-2)), despite marked latitudinal variation in larval supply and settlement rates previously found at this scale.While numerous studies have advocated the importance of parrotfishes for clearing space on the substrate to facilitate coral settlement, our results suggest that at high biomass they may have a detrimental effect on juvenile coral assemblages.

View Article: PubMed Central - PubMed

Affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, Australia. melanie.trapon@my.jcu.edu.au

ABSTRACT
For species with complex life histories such as scleractinian corals, processes occurring early in life can greatly influence the number of individuals entering the adult population. A plethora of studies have examined settlement patterns of coral larvae, mostly on artificial substrata, and the composition of adult corals across multiple spatial and temporal scales. However, relatively few studies have examined the spatial distribution of small (≤50 mm diameter) sexually immature corals on natural reef substrata. We, therefore, quantified the variation in the abundance, composition and size of juvenile corals (≤50 mm diameter) among 27 sites, nine reefs, and three latitudes spanning over 1000 km on Australia's Great Barrier Reef. Overall, 2801 juveniles were recorded with a mean density of 6.9 (±0.3 SE) ind.m(-2), with Acropora, Pocillopora, and Porites accounting for 84.1% of all juvenile corals surveyed. Size-class structure, orientation on the substrate and taxonomic composition of juvenile corals varied significantly among latitudinal sectors. The abundance of juvenile corals varied both within (6-13 ind.m(-2)) and among reefs (2.8-11.1 ind.m(-2)) but was fairly similar among latitudes (6.1-8.2 ind.m(-2)), despite marked latitudinal variation in larval supply and settlement rates previously found at this scale. Furthermore, the density of juvenile corals was negatively correlated with the biomass of scraping and excavating parrotfishes across all sites, revealing a potentially important role of parrotfishes in determining distribution patterns of juvenile corals on the Great Barrier Reef. While numerous studies have advocated the importance of parrotfishes for clearing space on the substrate to facilitate coral settlement, our results suggest that at high biomass they may have a detrimental effect on juvenile coral assemblages. There is, however, a clear need to directly quantify rates of mortality and growth of juvenile corals to understand the relative importance of these mechanisms in shaping juvenile, and consequently adult, coral assemblages.

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Map of Eastern Australia showing the Great Barrier Reef region with the three sectors chosen for this study.At each sector, three mid-shelf reefs with three sites each on the reef crest have been surveyed.
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pone-0057788-g001: Map of Eastern Australia showing the Great Barrier Reef region with the three sectors chosen for this study.At each sector, three mid-shelf reefs with three sites each on the reef crest have been surveyed.

Mentions: Surveys of juvenile corals were conducted in three distinct locations on the Great Barrier Reef (GBR) from north to south, separated by at least 500 km: i) northern GBR, in the vicinity of Lizard Island (14°41′S, 145°28′E), central GBR, in vicinity of Trunk Reef (18°25′S, 146°47′E), and southern GBR, in the vicinity of Heron Island (23°27′S, 155°55′E) (Fig. 1). Within each location, sampling was conducted at three reefs, and three sites per reef, giving a total of nine sites per location. Only mid-shelf reefs were sampled to minimize any effects of cross-shelf variation, and all sampling was constrained to a single habitat type, the exposed reef crest. The exposed reef crest was selected as this habitat is characterised by hard substratum covered by i) short sparse turf algae with a conglomeration of detritus, microbes, small invertebrates and microalgae, also referred as “epilithic algal matrix” (EAM, see [38]), with underlying CCA (crustose coralline algae), making the distinction between turf algae and CCA very difficult, ii) high cover of adult corals [39] and iii) high rates of coral recruitment [14]. The biotic and abiotic processes that may influence the distribution of juvenile corals operate across a range of spatial scales [13]. Therefore, this hierarchical nested sampling design facilitates the examination of local and regional variation in juvenile coral assemblages, and provides greater insight into the processes that may be structuring these populations on the GBR.


Spatial variation in abundance, size and orientation of juvenile corals related to the biomass of parrotfishes on the Great Barrier Reef, Australia.

Trapon ML, Pratchett MS, Hoey AS - PLoS ONE (2013)

Map of Eastern Australia showing the Great Barrier Reef region with the three sectors chosen for this study.At each sector, three mid-shelf reefs with three sites each on the reef crest have been surveyed.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585139&req=5

pone-0057788-g001: Map of Eastern Australia showing the Great Barrier Reef region with the three sectors chosen for this study.At each sector, three mid-shelf reefs with three sites each on the reef crest have been surveyed.
Mentions: Surveys of juvenile corals were conducted in three distinct locations on the Great Barrier Reef (GBR) from north to south, separated by at least 500 km: i) northern GBR, in the vicinity of Lizard Island (14°41′S, 145°28′E), central GBR, in vicinity of Trunk Reef (18°25′S, 146°47′E), and southern GBR, in the vicinity of Heron Island (23°27′S, 155°55′E) (Fig. 1). Within each location, sampling was conducted at three reefs, and three sites per reef, giving a total of nine sites per location. Only mid-shelf reefs were sampled to minimize any effects of cross-shelf variation, and all sampling was constrained to a single habitat type, the exposed reef crest. The exposed reef crest was selected as this habitat is characterised by hard substratum covered by i) short sparse turf algae with a conglomeration of detritus, microbes, small invertebrates and microalgae, also referred as “epilithic algal matrix” (EAM, see [38]), with underlying CCA (crustose coralline algae), making the distinction between turf algae and CCA very difficult, ii) high cover of adult corals [39] and iii) high rates of coral recruitment [14]. The biotic and abiotic processes that may influence the distribution of juvenile corals operate across a range of spatial scales [13]. Therefore, this hierarchical nested sampling design facilitates the examination of local and regional variation in juvenile coral assemblages, and provides greater insight into the processes that may be structuring these populations on the GBR.

Bottom Line: Size-class structure, orientation on the substrate and taxonomic composition of juvenile corals varied significantly among latitudinal sectors.The abundance of juvenile corals varied both within (6-13 ind.m(-2)) and among reefs (2.8-11.1 ind.m(-2)) but was fairly similar among latitudes (6.1-8.2 ind.m(-2)), despite marked latitudinal variation in larval supply and settlement rates previously found at this scale.While numerous studies have advocated the importance of parrotfishes for clearing space on the substrate to facilitate coral settlement, our results suggest that at high biomass they may have a detrimental effect on juvenile coral assemblages.

View Article: PubMed Central - PubMed

Affiliation: ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, Australia. melanie.trapon@my.jcu.edu.au

ABSTRACT
For species with complex life histories such as scleractinian corals, processes occurring early in life can greatly influence the number of individuals entering the adult population. A plethora of studies have examined settlement patterns of coral larvae, mostly on artificial substrata, and the composition of adult corals across multiple spatial and temporal scales. However, relatively few studies have examined the spatial distribution of small (≤50 mm diameter) sexually immature corals on natural reef substrata. We, therefore, quantified the variation in the abundance, composition and size of juvenile corals (≤50 mm diameter) among 27 sites, nine reefs, and three latitudes spanning over 1000 km on Australia's Great Barrier Reef. Overall, 2801 juveniles were recorded with a mean density of 6.9 (±0.3 SE) ind.m(-2), with Acropora, Pocillopora, and Porites accounting for 84.1% of all juvenile corals surveyed. Size-class structure, orientation on the substrate and taxonomic composition of juvenile corals varied significantly among latitudinal sectors. The abundance of juvenile corals varied both within (6-13 ind.m(-2)) and among reefs (2.8-11.1 ind.m(-2)) but was fairly similar among latitudes (6.1-8.2 ind.m(-2)), despite marked latitudinal variation in larval supply and settlement rates previously found at this scale. Furthermore, the density of juvenile corals was negatively correlated with the biomass of scraping and excavating parrotfishes across all sites, revealing a potentially important role of parrotfishes in determining distribution patterns of juvenile corals on the Great Barrier Reef. While numerous studies have advocated the importance of parrotfishes for clearing space on the substrate to facilitate coral settlement, our results suggest that at high biomass they may have a detrimental effect on juvenile coral assemblages. There is, however, a clear need to directly quantify rates of mortality and growth of juvenile corals to understand the relative importance of these mechanisms in shaping juvenile, and consequently adult, coral assemblages.

Show MeSH
Related in: MedlinePlus