NORTHWESTERN HAWAIIAN ISLANDS CONNECTIVITY STUDIES

Connectivity among coral reef fishes and bottomfishes across the Hawaiian Archipelago

This research component seeks to assess the level of connectivity among isolated reef habitats through a survey of fish species across the NWHI. The survey includes samples of 20+ fish species collected at the major islands and atolls of the NWHI. This research is conducted with advanced molecular genetic methodologies, using the genetics core facility at HIMB.

Ultimately, our work will determine whether reef ecosystems of the NWHI are isolated management units or components of a large interactive ecosystem. In the former case, each reef ecosystem will have to recover from environmental insults (whether human or natural) without significant input from other reef ecosystems. A corresponding conservation mandate would be that each ecosystem is an independent management unit.

Our multi-species approach to assessing population connectivity in the Hawaiian archipelago will be incorporated into a broader framework (funded by the National Science Foundation) to examine the phylogeography of many of these same species throughout the Indo-Pacific. This will provide a comparative framework to bolster the scientific foundations for implementing the NWHIMNM. The information provided by our connectivity studies is critical to assessing the patterns and magnitude of connection between the NWHI and the Main Hawaiian Islands; knowledge required by decision makers formulating management plans for the NWHI.

Progress in the field

Two previous Hawaiian research cruises using the Hi‘ialakai (May–June 2005 and September–October 2005) allowed our personnel to visit eight locations in the NWHI. In May–June 2006, we participated in an additional cruise with HIMB personnel collecting over 1,000 fish specimens at Nihoa, French Frigate Shoals, Gardner Pinnacles, and the isolated Johnston Atoll. The collections at Johnston Atoll, approximately 1,000 km south of French Frigate Shoals, will allow us to test for a possible connection to the middle region of the NWHI.

In addition to reef fish collections in the NWHI and at Johnston Atoll, NSF funding was used to make parallel collections at island groups to the west and south of Hawai‘i. These include: the Marshall Islands (March 2006); Fiji (April 2006); and Christmas Island (June 2006).

The snappers that inhabit the deep reefs are of special concern due to the ongoing bottom-fishery. In collaboration with Chris Kelley, we have contracted fishermen in the MHI as well as the NWHI to collect specimens in support of microsatellite DNA and mtDNA surveys of ehu (Etelis carbunculus), onaga (Etelis coruscans), and opakapaka (Pristipomoides filamentosus). We have procured independent funding from the NMFS and Western Pacific Fisheries Management Council to advance these projects.

Progress in the lab

As noted in previous reporting periods, we have sequenced mitochondrial DNA from three fish species; the flame angelfish (Centropyge loriculus), large-scale squirrelfish (Myripristis berndti), and yellow tang (Zebrasoma flavescens). The first two are known to disperse on ocean currents as larvae and appear to have widespread Central Pacific populations (Schultz et al. 2007; Craig et al. 2007), while the yellow tang shows statistically significant genetic structure (Eble et al. In prep), indicating that the Hawaiian Archipelago is not a single highly-connected ecosystem.

Figure 1. These parsimony networks shows the relationship among mtDNA haplotypes for the endemic butterfly fishes Chaetodon miliaris (top) and Chaetodon fremblii (above), as well as the geographic distribution of haplotypes. Note that the common haplotypes are distributed across the entire Hawaiian archipelago. (Click on the images to open larger versions.)

Hawaiian endemic species require special attention in terms of wildlife management due to the greater risk that accompanies a restricted distribution. In the current research period, we began to examine population structure in three species of endemic Hawaiian butterflyfishes (Chaetodon miliarsi, C. fremblii, and C. multicinctus). Thus far, we have collected and sequenced 170 C. fremblii and 229 C. miliaris (Figure 1), and have made significant progress in collections of C. multicinctus from throughout the Hawaiian Islands. Each of these species plays a distinct role in the coral reef ecosystem, based on feeding habits and social behavior. Hence these three species can provide a unique example of how these factors may alter the degree to which populations are connected over meso-scale distances.

Bottomfish surveys are still in the development stage. Currently, Ph.D. students Tonatiuh Trejo and Michelle Gaither are screening microsatellite loci to determine the most robust and dependable loci.

Introduced Species

The blueline snapper (ta‘ape; Lutjanus kasimira) was introduced to O‘ahu from two locations: French Polynesia and the Marquesas. Previous work by Sergio Planes has demonstrated diagnostic mtDNA markers for these two locations. Using these markers, Ph.D. student Michelle Gaither is surveying across the Hawaiian archipelago, to resolve the pattern of colonization for this introduced species. Her initial results demonstrate that both Polynesian and Marquesan lineages survived the colonization, and occur at proportions close to the size of the initial introductions. Additional specimens from the NWHI are needed to characterize the invasion of this isolated habitat.

Summary

An ongoing debate about the NWHI is whether it is comprised of a series of relatively fragile (isolated) ecosystems or a single robust ecosystem that can sustain extraction of resources. There is also a direct management concern about whether the NWHI serves as a source or a sink for the Main Hawaiian Islands. Our assays of population connectivity will resolve this issue in a format that has statistical power and scientific credibility. To accomplish this, our greatest bottleneck lies in sample acquisition, and it is here that we will focus our efforts in the coming year.

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