CRAMP RAT Reference Site Model

We developed two models within the Hydrogeomorphic Model (HGM) classification. The first model the Reference Site Model (RSM) defines reef condition within six habitat classes. The RSM relies partially on subjective selection of the so-called pristine control reefs. The second model the Ecological Gradient Model (EGM) incorporates the Index of Biotic Integrity (IBI) concept. Instead of reference sites, it utilizes all sites along a continuum.

Most previous studies of coral reef condition have included reference sites. Thus, the initial modeling effort embraced this concept. In general, a “pristine” area is selected by experts to serve as a comparison to the “impacted” reef under study. Reference site selection can be troublesome due to the difficulty in determining optimal reef conditions. Sliding baselines that change over time can make determination of pristine conditions impractical. Without prior comparable historical data, this hypothetical baseline is elusive. A more pragmatic way to measure baseline conditions is to select sites unaffected by anthropogenic disturbances and compare their biological communities to other sites of interest. Sites remote from human influence or those in marine protected areas with a high degree of protection were qualitatively assumed to be reference areas. Reference sites must be determined qualitatively to avoid a circular argument where the quantified data is used both to select and analyze the sites. Although this provides an external means of defining the reference conditions used to compare against impacted areas, it is highly subjective.

Since depth and wave exposure were found to be highly influential in determining biotic communities, the first attempt at developing a model divided the reference sites into six habitat classes (3 depths and 2 wave exposures) based on these key factors. Considerable overlap between reference sites and non-reference sites prompted the expansion of the model to 12 habitat classes (3 depths and 4 wave exposures) based on depth and direction of wave exposure. The later factor is based on the work of Friedlander et al. (2003) on fish communities.

It has been suggested that anthropogenic impacts may be established for a site if variables within a habitat class deviate from the established ranges of their reference sites (USACE Coral Reef Functional Assessment Workshop 2004). Two methods were employed in testing this concept.

The simple ranking of values found few single factors that adequately described fish and coral assemblage characteristics. The environmental variables that best described biotic community factors were human population, rugosity, organic composition, and the silt/clay fraction of bulk sediments.

Quantitative analyses confirmed the factors found to be important in the variable ranking. Rugosity, organics, depth, human population and wave regimes are influential factors in both coral and fish communities, explaining a considerable portion of the variability. While the distance from a stream is also important to coral variables, fish communities are also influenced by silt, turf, coralline algae and management protection.

Two test sites were selected to represent the two ends of the spectrum, from minimally impaired to severely impaired. Kaloko/Honokōhau, Hawai‘i is under federal management protection (National Parks Service) and has relatively low anthropogenic influence, while Maunalua Bay, O‘ahu has open access and is perceived as impaired. Variable ranking determined that only three factors have ranges that are narrow enough to describe site condition. The ranges of these factors within their respective habitat classifications were used to compare with the two test sites. The values for coral cover, number of fishes, and silt/clay were expected to fall within the reference range for their respective classification for Kaloko/Honokōhau and below reference ranges for Maunalua Bay. As expected, all stations (17) at Kaloko/Honokōhau exhibited values within the reference ranges, while the majority of the stations (71%) were below reference ranges at Maunalua Bay. Thus, the RSM can sufficiently detect sites that strongly deviate from reference values for select factors in sheltered regions.

The RSM based on classification of reference sites and the use of reference values to detect degradation is effective for use in the evaluation of levels of sedimentation. However, ranges suggest that only severely degraded conditions of coral and fishes for specific habitat classes can be detected. Possible degradation can be detected by values of coral cover outside the lower reference ranges at sites with sheltered wave regimes, but not in exposed regions that typically exhibit low coral cover. Furthermore, only strong deviations of numerical fish abundance can be detected, due to high variability. Other influential factors cannot be evaluated with this model.

Following the comparison of test sites against reference values, previously surveyed non-reference sites with evidence of environmental impact were also compared to the range of reference values within each habitat class to test the validity of the model. The variables used for comparison included total coral cover, silt/clay and fish abundances that were previously found to be of merit.

Comparisons indicate that the majority of stations at Waikīkī have values for numerical fish density and coral cover that are outside the reference ranges for each station’s habitat class. Coral cover is below reference levels for their respective habitat class for all 11 transects, while the number of fishes is below reference values at over half of the stations. This concurs with the established impacts from overuse and identifies the specific area within the site where disturbance is occurring. Silt values at Waikīkī stations, where bulk sediment samples were collected, are within the reference ranges. This is in concordance with the lack of impact by sedimentation at the stations surveyed.

When comparing reference ranges to 99 stations at 26 non-reference sites, the silt/clay fraction is well above the upper range of values for sites predicted to have sedimentation impacts. The sites with established disturbance of sedimentation that far exceed the reference values include: Kakahai’a, Kamiloloa and Pālā‘au, Moloka‘i, Hakioawa, Kaho‘olawe, Pelekane Bay, Hawai‘i, and Kāne‘ohe Bay, O‘ahu. Sites that have silt values slightly higher than reference levels include Puamana Maui, Laupāhoehoe, Hawai‘i and Kamalō, Moloka‘i. This is in agreement with the US EPA’s list of polluted coastal waters showing evidence of degradation by sediments, nutrients, or bacteria. This list, revised in 2002, is based on all available water quality data. The majority of listed sites are near streams with a high level of adjacent urban and agricultural activities.

In addition to Waikīkī, numerical fish densities are well below reference levels at the majority of stations in Pelekane Bay, Hawai‘i and Kamiloloa, Moloka‘i, and at deeper sites in Kāne‘ohe Bay. One station on the shallow reef flat in Hanalei Bay, Kaua‘i is also outside the lower reference range of values. This is in concert with Friedlander and Parrish (1998a) who found the lowest biomass to occur on the reef flats, compared to other substrate types within Hanalei Bay. All sites are included in the EPA polluted coastal waters list. It appears from the low number of sites outside the reference values, that due to high variability, only extreme deviations can be detected. Attempts to quantify the effects of overfishing using numerical and biomass abundance of target food species and size distributions are difficult due to habitat differences and high variability.

Since exposed habitats may have little or no coral cover, the reference values for these sites are meaningless. Thus only sheltered sites were considered. Eight sheltered sites are outside the lower reference range. These sites where the majority of transects have low coral cover, Puhi Bay and Pelekane Bay, Hawai‘i, Kamiloloa, Moloka‘i, Waikīkī and Kāne’ohe Bay, O‘ahu and Ma‘alaea, Maui are documented to have current or historical anthropogenic impacts that affect coral coverage. Leleiwi, Hawai‘i and Puamana, Maui also deviates from the reference values. All eight sites are on the EPA polluted coastal waters list.

While the RSM is able to detect values that fall outside the reference ranges at highly impaired sites, it is not able to detect marginal degradation because of high variability within reference sites. It also cannot determine the degree of impairment or compare to other sites in the state. Only a few select variables can be used to determine impairment due to the high variability.

Since the RSM model cannot be used for other variables that may be linked to specific types of disturbance, a more efficient, parsimonious model was developed. The second approach an “Ecological Gradient Model” recognizes that all ecological factors vary over space and time. Link to EGM This alternative to the RSM is designed to establish reef condition through comparison to the same habitat class in a large number of other Hawaiian reefs in a completely objective manner.

Stations With Values Outside Reference Ranges, Indicating Impairment. Reference Values Based On Wave Exposure And Depth.
Site	Silt %	Reference Maximum	Site	Coral Cover (%)	Reference Minimum	Site	Number Of Fish/Ha x 1000	Reference Minimum
Laupāhoehoe 3 m	3.2	2.7	Pelekane Bay 6 m	0	13.0	Pelekane Bay 1, 4 & 6 m	0	4.6
Honolua S 3 m	2.2	2.7	Pelekane Bay 4 m	0.2	13.0	Pelekane Bay 5 m	0.1	4.6
Pelekane Bay	50.9	1.9	Pelekane Bay 1 m	0	13.0	Pelekane Bay 3 m	0.2	4.6
Kamiloloa 3 m	4.2	1.9	Pelekane Bay 5 m	3.2	13.0	Kamiloloa 9 m	4.4	4.6
Hakioawa 3m	9.2	1.9	Pelekane Bay 3 m	0.6	13.0	Kamiloloa 6 m	4.6	4.6
Pala’au 1 m	8.9	1.9	Pelekane Bay 2 m	4	13.0	Hanalei 3 m	1.3	4.6
Kakahai’a 9 m	50.1	1.9	Kamiloloa 9 m	6.2	13.0	Kamiloloa 7 m	1.2	4.7
Laupāhoehoe 10 m	3.2	2.5	Kamiloloa 6 m	1.4	13.0	Kamiloloa 3 m	4.5	4.7
Kakahai’a 5, 6 & 8 m	50.1	3.2	Kamiloloa 3 m	3.3	13.0	Kamiloloa 10 m	4.6	4.7
Kamalō 10 m	4.2	3.2	Kamiloloa 8 m	10	13.0	Ka’alaea 8 m	0.6	4.7
Hakioawa 10 m	14.2	3.2	Ma’alaea 3 m	5.7	13.0	Moku o lo’e 8 m	1.8	4.7
Pālā’au 10 m	8.5	3.2	Kamiloloa 7 m	3.8	21.2	Waikīkī 4 m	1.6	4.6
Kakahai’a 2 m	5.6	3.2	Kamiloloa 3 m	8.6	21.2	Waikīkī 14 m	0.1	4.6
Puamana 13 m	3.9	1.0	Kamiloloa 10 m	1.3	21.2	Waikīkī 24 m	0.2	4.6
Kakahai’a 1, 3, 4 & 7 m	5.6	1.0	Ma’alaea 6 m	0.9	21.2	Waikīkī 22 m	0.1	4.6
Kamiloloa 1, 2, 4 & 5 m	2.7	1.0	Leleiwi 10 m	20.7	21.2	Waikīkī 42 m	1.0	4.6
He’eia 2 m	55.5	1.9	Puhi Bay 1 m	4.0	21.2	Waikīkī 31 m	0.2	0.4
He’eia 8 m	59.9	3.2	Puamana 13 m	7.8	36.0
Ka’alaea 2 m	30.7	1.9	Puhi Bay 2 m	34.7	36.0
Ka’alaea 8 m	63.1	3.2	He’eia 8 m	5.3	21.2
Moku o lo’e 2 m	41.2	1.9	Ka’alaea 8 m	6.5	21.2
Moku o lo’e 8 m	31.7	3.2	Moku o lo’e 2 m	12.8	13.0
			Moku o lo’e 8 m	1.6	21.2
			Waikīkī 4 m	0.2	13.0
			Waikīkī 14 & 24 m	0	13.0
			Waikīkī 22 m	0.3	13.0
			Waikīkī 42 m	1.0	13.0
			Waikīkī 38 m	16.8	21.2
			Waikīkī 33 m	2.8	21.2
			Waikīkī 2 m	3.4	21.2
			Waikīkī 19 & 31 m	0	36.0
			Waikīkī 27 m	12.2	36.0

Coral Reef Functional Assessment Workshop. Co-sponsored by the Army Corps of Engineers and University of Hawaii Sea Grant. August 23-25, 2004.

Friedlander, A., Brown, E. K, Jokiel, P. L., Smith, W. R., and Rodgers, K.S. 2003. Effects of habitat, wave exposure, and marine protected area status on coral reef fish assemblages in the Hawaiian archipelago. Coral Reefs 22: 291-305.

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