Western Society of Naturalists 11/14/2009 Monterey-Seaside, CA Kristin McCully Northwestern Hawaiian Islands Status and dynamics of the black-lipped pearl oyster, Pinctada margaritifera , at Midway Atoll, Northwestern Hawaiian Islands Kristin McCully* and Donald Potts *mccully@biology.ucsc.edu Ecology and Evolutionary Biology Department, University of California, Santa Cruz http://bio.research.ucsc.edu/people/potts/midway/ http://sanctuaries.noaa.gov/science/condition/pmnm/images/fig1_lg.jpg The NWHI are the islands, reefs, and atolls northwest of the main Hawaiian Islands, which now comprise the Papahanaumokuakea Marine National Monument. This talk will focus on Midway Atoll and Pearl and Hermes Atoll, two of the most northwestern reefs near the end of the chain. Black-lipped Pearl Oyster Midway Atoll: 28°12’N 177°21’W ( Pinctada margaritifera ) • Heavily harvested at Pearl & Hermes Atoll in late 1920s • 1930 survey resulted in ban of harvest in Hawai’i • Recent NOAA surveys show no recovery since then (Keenan et al. 2006) • Harvesting also likely at Midway, but no historical record • USFWS is interested in restoration Although we know more about the Black-lipped pearl oysters (Pinctada margaritifera) were heavily past population at PHA, Midway is harvested at Pearl and Hermes Atoll in the late 1920s to make much more accessible and has more buttons. Over 150 tons (or 150,000 individuals) were removed. infrastructure so we worked at Midway, A survey in 1930 concluded the population was extremely about 60 miles away. depleted and resulted in ban on its harvest throughout Hawaii, which still stands today. NOAA surveys in the last 10 years have found less than 1000 individuals and concluded that the population has not recovered. US Fish and Wildlife Service is interested in restoring 1 this species because it is an important filter feeder.
Western Society of Naturalists 11/14/2009 Monterey-Seaside, CA Kristin McCully Questions Questions • Recruitment • Recruitment – Where in Midway Atoll is recruitment highest? – Where in Midway Atoll is recruitment highest? – At what time of year is recruitment highest? – At what time of year is recruitment highest? • Recruit Growth • Recruit Growth – Where in Midway Atoll do recruits grow fastest? – Where in Midway Atoll do recruits grow fastest? – At what time of year do recruits grow fastest? – At what time of year do recruits grow fastest? • Adult Distribution • Adult Distribution – In which habitats and areas are Pinctada found? – In which habitats and areas are Pinctada found? – In which habitats and areas are other large – In which habitats and areas are other large bivalves found? bivalves found? • Juvenile Survival and Growth • Juvenile Survival and Growth In order to restore this species, using members of the First, we asked where in Midway Atoll and at what same population, it is necessary to understand spatial time of year are recruitment highest. and temporal variation in recruitment, juvenile survival, and growth, as well as adult distribution. Recruitment: Methods Recruitment: Spatial Variation 4.5 Average number of new Pinctada recruits per 2 week period and spat collector ±SE Spat collector 4 3.5 Buoy 3 2.5 2 1.5 1 Eartag 0.5 Attached to 0 substrate Hook Flats 188 PP RB FB 163 172 187 Site West Backreef Patch Reefs East Backreef We study recruitment in this species using "spat We measured over 2000 individual recruits in our collectors," which are basically black plastic 2009 field season. As you can see, recruitment is shadecloth folded like an accordion. This design highly variable between sites, but highest at a site on is modified from pearl farms in the South Pacific. the SE backreef. Every two weeks, we measure and mark all new and recurring individuals. We deployed 10 spat collectors at each of 9 sites throughout the atoll. 2
Western Society of Naturalists 11/14/2009 Monterey-Seaside, CA Kristin McCully Questions Recruitment: Temporal Variation 4 • Recruitment Average number of new Pinctada recruits per 2 3.5 – Where in Midway Atoll is recruitment highest? week period and spat collector ±SE – At what time of year is recruitment highest? 3 • Recruit Growth 2.5 – Where in Midway Atoll do recruits grow fastest? 2 – At what time of year do recruits grow fastest? 1.5 • Adult Distribution 1 – In which habitats and areas are Pinctada found? 0.5 – In which habitats and areas are other large bivalves found? 0 1 2 3 4 5 • Juvenile Survival and Growth 5/28-6/1 6/11-6/15 6/26-7/3 7/15-7/17 7/30-8/5 Time Interval (end date of 2 week period) Now, we'll focus on the question of where in However, there is an interesting temporal pattern. Midway Atoll and at what time of year do recruits In 2009, we measured recruitment in 5 2-week grow fastest. intervals between early May and early August. We observed a decrease in recruitment through the summer. This is particularly interesting because this species has been shown to spawn and therefore recruit in times of rapid temperature change in spring and fall. Recruit Growth: Spatial Variation Recruit Growth: Temporal Variation 45 70 40 60 35 Percent Growth ±SE 50 Percent Growth ±SE 30 40 25 30 20 15 20 10 10 5 0 0 Hook Flats 188 PP RB FB 163 172 1 2 3 4 5 Site 5/28-6/1 6/11-6/15 6/26-7/3 7/15-7/17 7/30-8/5 West Backreef Patch Reefs East Backreef Time Interval (end of 2 week period) But again, there is an interesting temporal pattern. Percent growth is (final size at end of 2 week period Recruit growth increases through the summer. minus initial size) divided by initial size. We have over 400 growth measurements of over 200 individuals. As you can see, recruit growth is also highly variable between sites. 3
Western Society of Naturalists 11/14/2009 Monterey-Seaside, CA Kristin McCully Annual Variation in Temperature Questions • Recruitment 30 Average Daily Temperature (°C) – Where in Midway Atoll is recruitment highest? 28 – At what time of year is recruitment highest? 26 • Recruit Growth – Where in Midway Atoll do recruits grow fastest? 24 – At what time of year do recruits grow fastest? 22 • Adult Distribution – In which habitats and areas are Pinctada found? 20 – In which habitats and areas are other large 18 bivalves found? Jan Mar May Jul Sep Nov • Juvenile Survival and Growth Day of Year 2006 2007 2008 Both the temporal patterns in recruitment and recruit But where are adult pearl oysters and other large growth may be related to the drastic annual variation bivalves found? in temperature at this high-latitude reef. Midway's sea temperature is coldest in March and April and warmest in August and September, with an 8-degree change over this period. We hypothesize that the observed decrease in recruitment and increase in growth are due to this rapid temperature increase. Adult Distribution: Habitats Adult Distribution: Survey Sites Legend Legend N N Forereef Forereef Backreef NW NW Backreef Patch reef E E Patch reef Sand Deep Deep Sand Based on: NOAA. SE SE SW SW 2003. Atlas of the shallow-water benthic habitats of the NWHI. S S We used a NOAA benthic habitat classification We used ArcGIS to randomly select 5 survey sites in each habitat-sector combination. Each survey was based on IKONOS remote sensing imagery to divide Midway's shallow marine habitat into four broad a 25 m x 4 m belt transect, in which we measured and identified all bivalves > 5 cm. We completed habitat categories: forereef, backreef, patch reef, and sand. We also divided the atoll into 7 sectors based 59 surveys in 2009, about half of our goal. We hope on field experience to ensure the surveys covered the to finish in 2010. entire atoll. 4
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