NORTHWESTERN HAWAIIAN ISLANDS CONNECTIVITY STUDIES

Connectivity among coral reef invertebrates across the Hawaiian Archipelago

We are continuing our survey of fish and invertebrate species across the NWHI to assess the level of connectivity between the isolated reef habitats of the NWHI and the Main Hawaiian Islands (MHI). Our research seeks to answer the questions: How connected are populations of invertebrates 1) among the NWHI?; and 2) between the MHI and NWHI? An ongoing debate exists as to whether the NWHI is a series of relatively fragile (isolated) ecosystems, or whether it is a single large and robust ecosystem that can withstand anthropogenic influences such as debris accumulation, pollution and global climate change (Selkoe et al. in prep). There is also a direct management concern about whether the NWHI serves as a source or a sink for the Main Hawaiian Islands. By using assays of population connectivity, we hope to settle this issue in a format that has statistical power and scientific credibility.

Figure 1: The ‘opihi ‘alinalina or Cellana sandwicensis, a prized limpet species found throughout the Hawaiian archipelago. (Click on the image to open a larger version.)

Figure 2: Calcinus haigae commonly found in colonies of Porites meandrina. Photo by Iliana Baums. (Click on the image to open a larger version.)

We have assembled an outstanding team of scientists, including: Iliana Baums (Ph.D., coral genetics); Kim Selkoe (Ph.D., ecosystem management and threat analyses); Kim Weersing, Chris Bird, Greg Concepcion, Joe O’Malley, Matt Iacchei (graduate students); Van Nicholas Velasco and Carly Allen (undergraduate student assistants). These researchers have participated in three research cruises to the NWHI using the newly-outfitted Hi‘ialakai to visit eight locations throughout the NWHI. On these cruises we have collected non-lethal tissue specimens (coral fragments, and small tissue clips) from over 2,000 invertebrates of 30 different species from throughout the Hawaiian archipelago. The multi-species approach to assess population connectivity in the Hawaiian archipelago will be incorporated into a broader framework (funded by the National Science Foundation) to put population structure within the Hawaiian archipelago into context using samples from elsewhere in the Indo-Pacific.

To date, our preliminary results suggest that there are large differences among taxa in their degree of connectivity throughout the archipelago. Some species appear to move between the NWHI and MHI with relative ease (e.g., the opihi species Cellana exarata and C. sandwicensis), while others (e.g., C. talcosa) do not (Bird et al. in review; see Figure 1). Among both opihi (Hawaiian endemic limpets; Bird et al., in review) and hermit crabs (Baums et al., in prep), we find that some closely related species show significant population structure across the archipelago while other species show no significant population structure within Hawai‘i. Our results thus far suggest that population structure across the Hawaiian archipelago does not fit a simple isolation by distance model, and broad-scale generalizations based on oceanographic currents are poorly supported. Also, closely-related species with similar ecology and reproductive biology (such as opihi and hermit crabs as outlined above) appear to have significantly different patterns of gene flow. Together, these results suggest that species-specific differences in reproductive biology or larval behavior may dominate patterns of connectivity in Hawai‘i.

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