Spatial Variation in Pelagic Wildlife Assemblages in the Ascension Island Marine Protected Area
Chris Thompson| 11 June 2021
Highlights
Undersea features provide best protection targets for oceanic sharks.
Bathymetric and dynamic features in the Ascension Island EEZ have a significant influence on the distribution, diversity, abundance, size, biomass, and functional composition of pelagic wildlife assemblages within the territory.
Pelagic wildlife within the EEZ is primarily concentrated around the shallow bathymetric features of Ascension Island, and the Grattan and Young Seamounts which had the most biodiverse assemblages with the highest biomass.
The seamounts within Ascension’s EEZ differed significantly in their effect on pelagic wildlife with the southern seamounts being quite similar in their assemblage, which was more diverse, and of greater abundance and biomass than that at Harris Stewart Seamount.
The offshore locations sampled were generally depauperate, with most of the animals recorded being forage fishes.
The establishment of the Ascension Island MPA presents a substantial conservation opportunity, however effective management and enforcement is vital to the effectiveness of marine reserves (Guidetti et al., 2008) and the surveillance and enforcement of large MPAs can be challenging (Wilhelm et al., 2014).
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Ascension sampling
Map of the Ascension Island EEZ (shaded circle) showing bathymetry and sampling effort by feature, each point represents a deployment of five mid-water BRUVS.
02
Biodiversity measures
Mean taxonomic richness (A), mean total abundance (B), mean fork length (C), and mean total biomass (D) by feature for all pelagic animals observed on all mid-water BRUVS deployments from Ascension waters in 2017/2018. Shared letters indicate no significant difference (p > 0.05) based on results of pairwise comparisons from PERMANOVAs based on Euclidean distance matrices of log(x + 1) transformed data with 999 permutations. Error bars indicate one standard error.
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Functional groups
Mean total abundance (A) and mean total biomass (B) for functional groups observed per set of mid-water BRUVS deployed at each of the features sampled within the Ascension Island EEZ. Letters indicate pairwise comparisons of PERMANOVAs based on Bray-Curtis resemblance matrices of square root transformed Total Abundance and Total Biomass data by functional group. Shared letters indicate no significant difference in functional composition (p > 0.05).
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Abundance by functional groups
Principal Components Analysis of total abundance of pelagic wildlife by functional groups. Symbols indicate the feature of the sample site, vector plot indicates functional groups with a correlation greater than 0.20..
