ECOSYSTEMS MANAGEMENT STUDIES

Evaluating ecosystem “health and value”

During the fourth quarter we continued to gather and compile existing data, develop methods comparisons, and synthesize available information. Our ranking scheme comparing the health and value of islands in the Northwestern Hawaiian Islands (NWHI) with islands in the Main Hawaiian Islands (MHI) was accepted for publication in the journal Pacific Conservation Biology with very favorable reviews:

Jokiel, P. L. and K. S. Rodgers. (in press). Ranking coral ecosystem “health” and “value” for the islands of the Hawaiian Archipelago. Pacific Conservation Biology.

This paper forms an important basis for an expanded future ecosystem evaluation in the NWHI which will be expanded as we increase the data base. This report describes the development and evaluation of what is essentially an index of biological integrity (IBI). Sufficient data on five vitally important biological indicators were developed for both the NWHI and the MHI. These include: reef fish biomass; reef fish endemicity; total living coral cover; population of the endangered Hawaiian monk seal (Monachus schauinslandi); and number of female green sea turtles (Chelonia mydas) nesting annually on each island. The index of relative biological “health” and “value” of the coral reefs of the NWHI was developed in the context of the entire Hawaiian Archipelago. The resulting index showed that the “worst” of the NWHI is better than the “best” of the MHI. Only five metrics were used, but a sensitivity analysis revealed that all five metrics are qually significant in defining relative health and value. The same pattern emerges when we use any four of the five metrics (see Figure 1). Thus all five biological metrics show essentially the same pattern, suggesting that numerous biological characteristics of ecosystems are impacted in a similar manner under anthropogenic stress.

Figure 1. Results of sensitivity analysis with index of biological integrity (i.e. “health” or “value“) ranking recalculated using only 4 of the 5 metrics. From left to right in the figure: the first bar (black) is the index calculated with all 5 metrics for use as a reference; the second bar was calculated with no turtle data; the third bar with no seal data; the fourth bar with no fish biomass data; the fifth bar with no fish endemism data; and sixth bar with no live coral cover data. The same pattern emerges even if we eliminate one of the metrics. (Click on the image to open a larger version.)

The composite scoring developed using these data shows that the ecological status of the MHI is poor compared to the NWHI. A growing body of information demonstrates that the reefs of the NWHI are an integral component of the Hawaiian Archipelago ecosystem and are an extremely valuable ecological resource. Thus the proper management of the NWHI is important to the ecological vitality of the Hawaiian Archipelago as a whole. The NWHI should not be viewed as a separate entity from the MHI because the two areas are clearly interdependent. The migration of turtles from feeding grounds in the MHI to nesting grounds in the NWHI provides an excellent example of the interdependence of the two areas. Movement of large fish and endangered Hawaiian monk seals provide other examples. The fact that the same species of fish, corals and other marine organisms occur along the entire Archipelago with high rates of endemism provides evidence that the NWHI and the MHI represent a single ecosystem with a long evolutionary history.

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