Effects of Sea Level on Reef Habitats of Papahanaumokuakea Marine National Monument During the Last Glacial Maximum

Date
2011
Authors
Lopes, Keolohilani
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Fletcher, Charles
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Oceanography
Global Environmental Science
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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Friedlander, 2004) while several dives in MCE habitat on Midway atoll recorded endemic fish rates above 90% (NOAA 2010, Unpublished).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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