Effects of Sea Level on Reef Habitats of Papahanaumokuakea Marine National Monument During the Last Glacial Maximum
Date
2011
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Abstract
Mesophotic Coral Ecosystems (MCE) (50-100m) are not as well understood as their
shallower counter-part, the Photic Reef Ecosystem (PRE) (0-50m). The disparity in the
level of understanding between the two regions is mainly due to the difficulty in getting
observations from these depths. This study used Geographic Information System (GIS)
software to calculate habitat increases of 88.53% (5605.34 km2) in the PRE from the Last
Glacial Maximum (LGM), when the sea level was 120m below the present day sea level.
A statistically similar amount of habitat gain was found between the MCE and PRE
(Show stat values). Understanding habitat changes will allow scientists to deduce causes
of important differences in ecosystem characteristics between these two environments,
such as endemism rates. PRE endemism rates for fish in Papahānaumokuākea Marine
National Monument (PMNM) are 20.6% (DeMartini, Friedlander, 2004) while several
dives in MCE habitat on Midway atoll recorded endemic fish rates above 90% (NOAA
2010, Unpublished). Similar changes in area between PRE and MCE, coupled with
drastically different fish endemism rates suggests a continuous MCE habitat regime
while the PRE experienced dramatic changes inducing extinctions or sever loss of biota.
Rate of sea level rise may have had the most detrimental impact on the PRE, increasing
as much as 25mm/yr during meltwater pulse episodes which lasted as long as 1000
years (Fletcher, Sherman, 1995). These relatively rapid rates are faster than the
accretion rate of corals in PMNM, subsequently leading to drowning of the ecosystem.
As MCE are not heavily light dependent and probably cover a wider depth range than
PRE, likely exhibit more continuity and habitat stability. A stable and long lasting
isolated habitat is required for the evolutionary processes to produce unique animals
that are found nowhere else in the world. The Continuous Marine Habitat (CoMaH)
hypothesis explaining MCE endemism rates looks like the most plausible explanation of
the historic events that shaped the current marine environments of the PMNM. CoMaH
hypothesis supports the idea that the MCE habitat is able to endure the large
fluctuations and rapid increase of sea level providing a continuous habitat for marine
organisms to evolve into endemic species.
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corals, coral reef ecology, sea level rise
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49 pages
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