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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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Size-class frequency distribution (mm) of juvenile corals ≤50 mm from the three main taxa: (A, B, and C) Acropora, (D, E and F) Pocillopora, and (G, H and I) Porites sp, at the northern (white), central (light grey ) and southern (dark grey) sectors of the GBR.Juveniles <10 mm have been added to the size class 10–14 mm.
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pone-0057788-g004: Size-class frequency distribution (mm) of juvenile corals ≤50 mm from the three main taxa: (A, B, and C) Acropora, (D, E and F) Pocillopora, and (G, H and I) Porites sp, at the northern (white), central (light grey ) and southern (dark grey) sectors of the GBR.Juveniles <10 mm have been added to the size class 10–14 mm.

Mentions: The size structure of juvenile Acropora, Pocillopora, and Porites corals differed significantly among latitudinal sectors (Chi-square contingency Table 3A, Fig. 4). Juvenile Acropora were relatively evenly distributed among size classes in the northern and central sectors (Fig. 4a, b), whereas in southern sector the highest frequency of individuals was in the size-class 30–34 mm (relative proportion: 22%) with few individuals in the smallest (7.9%) and largest (2.8%) size classes (Fig. 4c). The size distribution of juvenile Pocillopora and Porites displayed some similarities among sectors. In the northern sector juvenile Pocillopora and Porites peaked in the 25–29 and 30–34 mm size classes (25–29 mm: 17.2% and 19.2% respectively; 30–34 mm: 20.7% and 17.6% respectively), and the relative proportion of individuals decreased with size (Fig. 4d, g), while in the central sector frequencies were highest in the smallest size class (18.5% and 21.6%, respectively) and generally decreased with size (Fig. 4e, h). In the southern sector juvenile Pocillopora and Porites were relatively evenly distributed among size classes up to 40 mm, with few individuals in the two largest size classes (3.8% and 1.5% respectively; Fig. 4f, i).


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)

Size-class frequency distribution (mm) of juvenile corals ≤50 mm from the three main taxa: (A, B, and C) Acropora, (D, E and F) Pocillopora, and (G, H and I) Porites sp, at the northern (white), central (light grey ) and southern (dark grey) sectors of the GBR.Juveniles <10 mm have been added to the size class 10–14 mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0057788-g004: Size-class frequency distribution (mm) of juvenile corals ≤50 mm from the three main taxa: (A, B, and C) Acropora, (D, E and F) Pocillopora, and (G, H and I) Porites sp, at the northern (white), central (light grey ) and southern (dark grey) sectors of the GBR.Juveniles <10 mm have been added to the size class 10–14 mm.
Mentions: The size structure of juvenile Acropora, Pocillopora, and Porites corals differed significantly among latitudinal sectors (Chi-square contingency Table 3A, Fig. 4). Juvenile Acropora were relatively evenly distributed among size classes in the northern and central sectors (Fig. 4a, b), whereas in southern sector the highest frequency of individuals was in the size-class 30–34 mm (relative proportion: 22%) with few individuals in the smallest (7.9%) and largest (2.8%) size classes (Fig. 4c). The size distribution of juvenile Pocillopora and Porites displayed some similarities among sectors. In the northern sector juvenile Pocillopora and Porites peaked in the 25–29 and 30–34 mm size classes (25–29 mm: 17.2% and 19.2% respectively; 30–34 mm: 20.7% and 17.6% respectively), and the relative proportion of individuals decreased with size (Fig. 4d, g), while in the central sector frequencies were highest in the smallest size class (18.5% and 21.6%, respectively) and generally decreased with size (Fig. 4e, h). In the southern sector juvenile Pocillopora and Porites were relatively evenly distributed among size classes up to 40 mm, with few individuals in the two largest size classes (3.8% and 1.5% respectively; Fig. 4f, i).

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