Northwestern Hawaiian Islands Status and dynamics of the - - PDF document

Western Society of Naturalists Monterey-Seaside, CA 11/14/2009 1

Status and dynamics of the black-lipped pearl

• yster, 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

Northwestern Hawaiian Islands Black-lipped Pearl Oyster (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

Midway Atoll: 28°12’N 177°21’W

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

• f the most northwestern reefs near the end of

the chain. Black-lipped pearl oysters (Pinctada margaritifera) were heavily harvested at Pearl and Hermes Atoll in the late 1920s to make

• buttons. Over 150 tons (or 150,000 individuals) were removed.

A survey in 1930 concluded the population was extremely 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 this species because it is an important filter feeder. Although we know more about the past population at PHA, Midway is much more accessible and has more infrastructure so we worked at Midway, about 60 miles away. Kristin McCully

Western Society of Naturalists Monterey-Seaside, CA 11/14/2009 2

Questions

• Recruitment

– Where in Midway Atoll is recruitment highest? – At what time of year is recruitment highest?

• Recruit Growth

– Where in Midway Atoll do recruits grow fastest? – At what time of year do recruits grow fastest?

• Adult Distribution

– In which habitats and areas are Pinctada found? – In which habitats and areas are other large bivalves found?

• Juvenile Survival and Growth

Questions

• Recruitment

– Where in Midway Atoll is recruitment highest? – At what time of year is recruitment highest?

• Recruit Growth

– Where in Midway Atoll do recruits grow fastest? – At what time of year do recruits grow fastest?

• Adult Distribution

– In which habitats and areas are Pinctada found? – In which habitats and areas are other large bivalves found?

• Juvenile Survival and Growth

Spat collector Buoy Attached to substrate Eartag

Recruitment: Methods

0.5 1 1.5 2 2.5 3 3.5 4 4.5 Hook Flats 188 PP RB FB 163 172 187 Average number of new Pinctada recruits per 2 week period and spat collector ±SE Site

Recruitment: Spatial Variation

East Backreef Patch Reefs West Backreef

In order to restore this species, using members of the same population, it is necessary to understand spatial and temporal variation in recruitment, juvenile survival, and growth, as well as adult distribution. First, we asked where in Midway Atoll and at what time of year are recruitment highest. We study recruitment in this species using "spat collectors," which are basically black plastic shadecloth folded like an accordion. This design is modified from pearl farms in the South Pacific. 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. We measured over 2000 individual recruits in our 2009 field season. As you can see, recruitment is highly variable between sites, but highest at a site on the SE backreef. Kristin McCully

Western Society of Naturalists Monterey-Seaside, CA 11/14/2009 3

Recruitment: Temporal Variation

0.5 1 1.5 2 2.5 3 3.5 4 1 5/28-6/1 2 6/11-6/15 3 6/26-7/3 4 7/15-7/17 5 7/30-8/5 Average number of new Pinctada recruits per 2 week period and spat collector ±SE Time Interval (end date of 2 week period)

Questions

• Recruitment

– Where in Midway Atoll is recruitment highest? – At what time of year is recruitment highest?

• Recruit Growth

– Where in Midway Atoll do recruits grow fastest? – At what time of year do recruits grow fastest?

• Adult Distribution

– In which habitats and areas are Pinctada found? – In which habitats and areas are other large bivalves found?

• Juvenile Survival and Growth

Recruit Growth: Spatial Variation

East Backreef Patch Reefs West Backreef

10 20 30 40 50 60 70 Hook Flats 188 PP RB FB 163 172 Percent Growth ±SE Site

Recruit Growth: Temporal Variation

5 10 15 20 25 30 35 40 45 1 5/28-6/1 2 6/11-6/15 3 6/26-7/3 4 7/15-7/17 5 7/30-8/5 Percent Growth ±SE Time Interval (end of 2 week period)

However, there is an interesting temporal pattern. In 2009, we measured recruitment in 5 2-week 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. Now, we'll focus on the question of where in Midway Atoll and at what time of year do recruits grow fastest. Percent growth is (final size at end of 2 week period minus initial size) divided by initial size. We have

• ver 400 growth measurements of over 200
• individuals. As you can see, recruit growth is also

highly variable between sites. But again, there is an interesting temporal pattern. Recruit growth increases through the summer. Kristin McCully

Western Society of Naturalists Monterey-Seaside, CA 11/14/2009 4

Annual Variation in Temperature

18 20 22 24 26 28 30 Jan Mar May Jul Sep Nov Average Daily Temperature (°C) Day of Year 2006 2007 2008

Questions

• Recruitment

– Where in Midway Atoll is recruitment highest? – At what time of year is recruitment highest?

• Recruit Growth

– Where in Midway Atoll do recruits grow fastest? – At what time of year do recruits grow fastest?

• Adult Distribution

– In which habitats and areas are Pinctada found? – In which habitats and areas are other large bivalves found?

• Juvenile Survival and Growth

Adult Distribution: Habitats

Legend Forereef Backreef Patch reef Sand

N NW Deep S SE E SW

Based on: NOAA.

• 2003. Atlas of the

shallow-water benthic habitats of the NWHI.

Legend Forereef Backreef Patch reef Sand

Adult Distribution: Survey Sites

N NW Deep S SE E SW

Both the temporal patterns in recruitment and recruit growth may be related to the drastic annual variation 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

• ver this period. We hypothesize that the observed

decrease in recruitment and increase in growth are due to this rapid temperature increase. But where are adult pearl oysters and other large bivalves found? We used a NOAA benthic habitat classification based on IKONOS remote sensing imagery to divide Midway's shallow marine habitat into four broad habitat categories: forereef, backreef, patch reef, and

• sand. We also divided the atoll into 7 sectors based
• n field experience to ensure the surveys covered the

entire atoll. We used ArcGIS to randomly select 5 survey sites in each habitat-sector combination. Each survey was a 25 m x 4 m belt transect, in which we measured and identified all bivalves > 5 cm. We completed 59 surveys in 2009, about half of our goal. We hope to finish in 2010. Kristin McCully

Western Society of Naturalists Monterey-Seaside, CA 11/14/2009 5

Baggy pen shell Streptopinna saccata Cliff oyster Spondylus violacescens Black-lipped pearl oyster Pinctada margaritifera Jewel oyster Chama iostoma

Bivalve Distribution: Abundance

2 4 6 8 10 12 Streptopinna Spondylus Chama Pinctada Average number of individuals per transect ±SE Habitat Forereef Backreef Patch reef Sand

Bivalve Distribution: Pinctada

500 m

Questions

• Recruitment

– Where in Midway Atoll is recruitment highest? – At what time of year is recruitment highest?

• Recruit Growth

– Where in Midway Atoll do recruits grow fastest? – At what time of year do recruits grow fastest?

• Adult Distribution

– In which habitats and areas are Pinctada found? – In which habitats and areas are other large bivalves found?

• Juvenile Survival and Growth

Although we focused on pearl oysters, we measured and identified all bivalves > 5 cm. The main 3 species we observed were pen shells (Streptopinna saccata), cliff oysters (Spondylus violacescens), and jewel

• ysters (Chama iostoma).

As you can see, we found very few pearl oysters. In fact, we found only 1 pearl oyster at one site. The other three species were most common at forereef sites, but also present on patch reefs. We observed no bivalves at sand sites, which we expected since all species live on hard

• substrate. However, we wanted to check our

habitat classification. Spondylus is also common

• n artificial substrate, such as seawalls and

pier pilings. So, where are adult pearl oysters found? In 3 years of looking, we've found exactly 11 adult pearl oysters. 8 are on patch reefs in the central lagoon with high Porites compressa coral cover, as you can see in this photo. 2 are on the seawall in the harbor. The only one we found on our surveys is

• n the SE forereef.

Since we've found so few adults and yet relatively high recruitment, we hypothesized that juvenile mortality is very high, possibly due to predation. We just started an experiment to test this hypothesis at the end of the summer and will have more information next year. Kristin McCully

Western Society of Naturalists Monterey-Seaside, CA 11/14/2009 6

Juvenile Growth and Survival

Site: WB No Mesh Large Mesh Small Mesh X 5 tiles X 5 tiles X 5 tiles X 6 juveniles X 6 juveniles X 6 juveniles Site: PP No Mesh Large Mesh Small Mesh X 5 tiles X 5 tiles X 5 tiles X 6 juveniles X 6 juveniles X 6 juveniles PP WB

Conclusions

• Recruitment

– Recruitment is highly variable across sites – Recruitment decreases through the summer

• Recruit Growth

– Recruit growth is highly variable across sites – Recruit growth increases through the summer

• Adult Distribution

– Adult P. margaritifera are extremely rare, but found primarily on patch reefs in center of atoll with high Porites compressa coral cover – Other bivalve species are most common on the forereef and also found on patch reefs

• Juvenile Survival and Growth

– In progress

Acknowledgments: People

• Advisor: Don Potts
• Statistics and planning help: Marm Kilpatrick
• Labmates

– Wendy Cover, Helen O’Brien, Anne Warner, Rachel Fabian

• Field Assistants

– Kate Schoenrock, Jamie Barlow

• Mitsubishi Volunteers

– 2008: Connie Claggett, Eric Conard, Debbie Conway, Joe Nichols – 2009: Tom McDermott, Beverley Parker, Sylvia Ni, Tsurumi Seeichi, Guido Fernandez

• John Klavitter and Matt

Brown, USFWS

Acknowledgments: Funding

• Mitsubishi Corporation Global Coral Reef Conservation

Program

• Midway Atoll National Wildlife Refuge
• U.S. Fish and Wildlife Service
• Friends of Long Marine Lab
• UCSC Center for the Dynamics and Evolution of the Land-Sea

Interface (CDELSI)

• Department of Defense National Defense Science and

Engineering (NDSEG) Fellowship

Performed under Permit PMNM-2008-056B

We deployed 15 sets of tiles at 2 sites in 3 cage treatments: No mesh, Large mesh, and Small mesh, designed to keep out different levels of predators. We epoxied about 6 juveniles from our spat collectors to each tile. We will return in 2010 to determine growth and survival. We hope to show that it is possible to restore this species using some of these methods in the Northwestern Hawaiian Islands. i'd like to thank many wonderful people, including my advisor, labmates, field assistants, volunteers, and colleagues at USFWS, as well as several funding sources. Kristin McCully