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Explaining Spatial Variation in Coral Size Structure in American Samoa.

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Title:Explaining Spatial Variation in Coral Size Structure in American Samoa.
Authors:Ferguson, Marie H.
Contributors:Oceanography (department)
Date Issued:Dec 2017
Publisher:University of Hawaiʻi at Mānoa
Abstract:Coral size structure distributions (i.e. the distribution of individual colony sizes within a
population) have been shown to vary between and among populations exposed to different
environmental regimes and disturbance histories. Subsequently, assessing size structure spatiotemporal
variability in relation to biogeophysical factors can provide insight into underlying
mechanisms driving spatial patterns observed in coral populations. A total of 22 species of coral
are now listed as threatened under the U.S. Endangered Species Act (ESA); however species
level data on demographic processes and responses of corals to threats needed for effective
management is deficient. This includes: 1) quantitative assessments of population status, and 2)
identification of potential environmental drivers that influence the status of a given species.
Here, analysis of a rare ESA-listed species, Isopora crateriformis (Isopora spp. used as a proxy),
and an abundant species, Montastrea curta, from a 2015 NOAA Ecosystem Sciences Division
(ESD) survey across five islands in American Samoa (within 0 – 30m depth range) was used to
determine spatial variation in population size structure patterns across two spatial scales (siteand
strata-level resolution). Using co-located data available, a range of environmental (e.g.
benthic geomorphology), oceanographic (e.g. temperature, wave energy), biological (e.g. benthic
cover), and anthropogenic impact covariates were collated and synthesized at comparable spatial
scales to the coral population data. Generalized modeling and multi-model inference were used
to evaluate the strength and magnitude of the relationship between biogeophysical/anthropogenic
covariates (explanatory covariates) and size distribution parameter estimates (response variable)
for each coral species. Due to its versatility and effectiveness, the Weibull distribution was used
to characterize the observed size spectra and the distribution shape parameter, k, was used as the
size spectra response metric in statistical modeling. Analyses reveal that i) size structure spatially
varied among and between species and ii) modeled biogeophysical relationships varied
significantly between species. Mean net carbonate accretion rate and net carbonate accretion rate
variability (i.e. net carbonate accretion rate coefficient of variation), in addition to
geomorphological slope and slope variability, accounted for a large proportion of spatial
variation in the Isopora spp. site-level size spectra (R2 = 58%). For Isopora spp. strata-level
analysis, wave energy and mean accretion rate explained a large proportion of spatial variation
(R2 = 46%). In contrast, for Montastrea curta site-level analysis, irradiance (photosynthetically
active radiation), percent coral cover, wave energy, mean depth, M. curta juvenile abundance,
and SST explained a large proportion of spatial variation in the size spectra (R2 = 45%). For M.
curta strata-level analysis, irradiance, mean accretion rate, SST, and wave energy explained a
large proportion of spatial variation (R2 = 57%). Our results suggest that the Weibull shape
parameter, k, is a reliable metric that captures variability in the coral size distribution and that
species-specific biogeophysical factors explain coral size structure variability across space.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2017.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Oceanography

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