An Investigation of Environmental Drivers of Crown of Thorns Starfish Outbreaks on Guam
Date
2020
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Abstract
One of the least understood and prevalent threats to Guam’s reefs is Acanthaster
planci, more commonly known as Crown-of-Thorns Starfish (COTS). COTS are
prolific corallivorous asteroid echinoderms. At high population densities, COTS
can rapidly decimate coral reef ecosystems in a matter of months. Several
devastating COTS outbreaks in Guam dating back to 1967 brought the
understanding that COTS outbreaks are a real threat to Guam’s coral reefs.
Considerable research has been done on COTS biology and several hypotheses
have been put forward to explain the occurrence of outbreaks but the cause(s) still
remain contentious. This study aims to relate the physical environment to COTS
outbreaks in order to find supporting evidence that COTS outbreaks are linked to
environmental conditions. We hypothesized that precipitation and low wave
events were the two factors that set the stage for the occurrence and proliferation
of COTS outbreaks in Guam. To investigate this, we calculated and mapped
COTS populations to assess spatio-temporal variability. A seasonal climatology
was constructed and surface mapped from regional model data to determine the
mean seasonal environmental conditions. An event-based analysis was then
performed on two sites, Gun Beach and Uruno Point, to discover any
consistencies between the presence of COTS and environmental parameters at the
sites. Overall, we were unable to find any consistent or significant spatio-temporal
relationships that support our hypothesis. This study highlights the data
sparseness of Guam and sets the stage for future research into COTS outbreak
ecology in Guam. Further research and long-term fine-scale data will be necessary
to accurately pinpoint the relationship between the physical environment and
COTS outbreaks on Guam.
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crown of thoms starfish, guam, invasive species, coral reef, ecosystem
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61 pages
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Curley, Zoe
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