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Modeling Mesophotic Coral Distributions in the Au’au Channel, Hawaii


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Objectives

To develop a spatially-explicit model of mesophotic scleractinian coral presence for 30 to 150 meter depths in the Au’au Channel, Hawaii using readily-available bathymetry and optical validation data. This work is designed to: (1) support the management plan review process currently underway at the Hawaiian Islands Humpback Whale National Marine Sanctuary (HIHWNMS); (2) provide baseline data for management decision making; and (3) identify gaps in our knowledge about mesophotic corals inside the HIHWNMS boundaries.

Estimated  project area for modeling mesophotic coral presence in the Au’au Channel.
Figure 1. Estimated project area for modeling mesophotic coral presence in the Au’au Channel.

Project Summary

Mesophotic coral ecosystems (MCEs) are light-dependent communities comprised of corals and other associated organisms found between approximately 30 to 150 m in depth (Figure 2; Hinderstein et al. 2010). Mesophotic corals are thought to have some special adaptations, including flattened morphologies and lower metabolic demands, which allow them to live in low light environments (Kahng et al. 2010). In the Hawaiian archipelago, Kahng and Kelley, 2007 and Rooney et al. 2010 found that different types of MCEs dominated specific depth ranges.  In 30 to 50 m of water, Upper MCEs were dominated by a low diversity of hard corals found in shallower reefs (Pocillopora meandrina, P. damicornis, Montipora capitata, and Porites lobata).  In 50 to 80 m of water, Branching/Plate Coral MCEs were dominated by hard corals with a singular morphology.  In 80 to 130 m of water, Leptoseris Coral MCEs were dominated by the coral species, Leptoseris hawaiiensis, giving MCEs at this depth their name. Several physical factors are assumed to influence the distribution of these MCEs, including temperature, hard substrate availability and the availability of photosynthetically active radiation at depth (Kahng and Kelley, 2007).

Figure 2.  MCE dominated by colonies of Leptoseris hawaiiensis at a depth of 90 m in the Au’au Channel.  Adapted from Rooney et al. 2010.  Photo credit: Hawai’i Undersea Research Laboratory.
Figure 2. MCE dominated by colonies of Leptoseris hawaiiensis at a depth of 90 m in the Au’au Channel. Adapted from Rooney et al. 2010. Photo credit: Hawai’i Undersea Research Laboratory.

Mesophotic coral distributions are important for resource managers to understand because they play a pivotal role (separate from their shallow-water counterparts) in shaping ecological communities, including providing habitat for reef fish and invertebrate species, refugia for certain shallow-water species and residence for some species not seen outside the mesophotic zone (Glynn 1996; Riegl and Piller 2003; Bak et al. 2005; Boland and Parrish, 2005; Armstrong et al. 2006; Kahng and Kelley, 2007). Despite this unique ecological role, there has been limited exploration of these moderate-depth ecosystems because they are difficult and expensive to access using traditional underwater sampling techniques (Pyle 1996; Menza et al. 2008). Additional research is needed to better understand these mesophotic communities (Kahng and Maragos, 2006), as they are increasingly threatened by numerous anthropogenic stressors (Wilkinson, 1999; Klyepas and Eakin, 2007). In the interim, spatially explicit predictive models maybe used to fill these informational gaps, and provide valuable baseline data on MCE distributions for unexplored regions.  This baseline data may then be used to more effectively plan and refine future research efforts in support of ecosystem based management.

The primary objective of this study is to produce a spatially explicit model of mesophotic scleractinian coral presence for 30 to 150 meter depths in the Au’au Channel.  Other live benthic cover, including azooxanthellate assemblages, are beyond the scope of this project and will not be included in this modeling effort. The model will be developed using readily-available bathymetry and optical validation data for the Au’au Channel.  These datasets will be the primary inputs for all subsequent analysis. A suite of predictor variables will be developed from the bathymetry surface, including mean depth, standard deviation of depth, rugosity, plan curvature, profile curvature, curvature, slope, slope of slope and other environmental variables, as needed. These predictors will used to model the potential distribution of mesophotic scleractinian corals in the Au’au Channel. The predictor variables will be quantitatively linked with the response variable (i.e., mesophotic scleractinian coral presence) extracted from the optical validation data to develop a spatially explicit predictive model. A range of modeling approaches will be evaluated early in the project.  The optimum modeling approach will be selected based upon an evaluation of input data, exploratory analysis and consultation of project partners.  Cross validation techniques will be used to assess the quality of the final model output. This mesophotic coral distribution model will expand the Hawaiian Islands Humpback Whale National Marine Sanctuary’s (HIHWNMS) assessment capabilities and support ecosystem-based management practices within the Sanctuary.

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Time Frame

January 2011 – March 2012

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Project Manager:
1305 East West Highway
SSMC-IV, N/SCI-1
Silver Spring, MD 20910
301-713-3028 x146



1305 East West Highway
SSMC-IV, N/SCI-1
Silver Spring, MD 20910
301-713-3028 x144



1305 East West Highway
SSMC-IV, N/SCI-1
Silver Spring, MD 20910
301-713-3028 x164