Pacific Oyster Summer Mortality Disease on the US West Coast: 50
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Pacific Oyster Summer Mortality Disease on the U.S. West Coast: 50 Years Later Dan Cheney, Andrew Suhrbier, Mary Middleton and Aimee Christy Joth Davis and Benoit Eudeline Carolyn Friedman Dennis Hedgecock Research funded by: NOAA SeaGrant
Pacific Oyster Summer Mortality Disease on the US West Coast: 50
Pacific Oyster Summer MortalityDisease on the U.S. West Coast:
50 Years Later
Dan Cheney, Andrew Suhrbier, Mary Middleton
and Aimee Christy Joth Davis and Benoit
EudelineCarolyn Friedman Dennis Hedgecock
Research funded by: NOAA SeaGrant
History on US west coastHistory on US west coastHistory on US west coast
• Large scale mortalities first reported in the late 1950’s with losses of up to 50% by the early 1960’s
• Prompted a long-term study between 1965 and 1972 (summarized by John Glude)
• Paralleled observations in Japan – Matsushima Bay• Focus was on growth and mortality, reproductive
condition, diseases, and water quality• Entirely based on imported seed from high & low
mortality sites and limited local production – no hatcheries were available
History on US west coastHistory on US west coastHistory on US west coast
• Generally similar to observations from Japan• Disease organisms were rare, or were associated with
other pathologies• Elevated temperatures and turbidity appeared to be
linked to > mortalities• Seed source experiments were unclear – a low
mortality source did not lead to > survival• Thought that hatcheries could be used to select for >
survival• Mortalities declined after early 70’s
Recent WC research Recent WC research Recent WC research
• Identify environmental factors triggering a mortality- inducing stress response;
• Evaluate the relation-ships of culture practices to oyster survival;
• Assess responses to potentially harmful phytoplankton; • Begin research to determine genetic characteristics of
enhanced survival in bred and hybrid oysters; • Begin research to understand the role of reproductive
allocation with mortalities; and • Work with shellfish growers to characterize the extent
and timing of mortality events.
Presenter
Presentation Notes
West Coast US research on the diseases affecting Pacific oysters has evolved from examinations of pathology, and survival and growth to a broad assessment of the role of genetics, chromosome ploidy and aquacultural practices – focusing on these research objectives. Colleen Burge will cover herpes work in herpes infections in Tomales Bay oysters. Pathology and clearance of pathogens: Lou Burnett.
Test sitesTest sitesTest sites Totten Inlet
Willapa Bay
Coastal estuary, Willapa BayCoastal estuary, Willapa BayCoastal estuary, Willapa Bay
Taylor shellfish farms Wild stock, diploids and triploid broodstock from Willapa, tetraploid females generated from the same stocks. Hybrids – from MBP stocks, generated two lines 51 and 35, originally from Dabob Pair mated – survivors of an intense summer mortality event of MBP animals in 2004, all Cohort 9 In early summer 2006, PSI and Taylor Shellfish Farms placed 25 genetic lines with 8 replications of diploid and triploid Pacific oyster seed at 3 field sites in Washington State. These were produced from founder lines (diploid and triploid) in 2005 that survived an intensive mortality event in the summer of 2004. Variable mortality rates within these lines were reported within one month from at least one site. An additional 50 pair-mated lines of Pacific oysters from wild Dabob Bay broodstock and a labeled F2 hybrid line will be placed at the same sites in early fall 2006. Additional F2 hybrid lines are being produced for dissemination in 2007 as well. Monitoring parameters are closely matched to those of the MOREST program, in collaboration with that program, and data are being inputted into the MOREST model to fine tune our summer mortality predictive capability.
Data are available for the crosses we made for (115 and 116) as well as (140,141, 142) but we do not have data for (159 and 169). For each set of families, we chose families that differed in their yields (115 and 116, cohort 5) or survival and yield (140,141,142, cohort 7).��Families 115 and 116 were chosen and recreated for the ORDP project based on the yields of families in MBP cohort 5 that was planted in Yaquina and Totten Inlet (see attached histogram). The parental families of 115 and 116 were from MBP cohort 1.��Families 140,141 and 142 were chosen and recreated for the ODRP project based on survival of MBP families in cohort 7 that was planted in Tomales (see attached histogram). The parental families of 140,141 and 142 were also from cohort 1.��Sean may have sent details of families 159 and 169 to Andy in the past (I have been cced on several emails between them) but Sean has not records of these families now. I seem to remember that they were created as inbred families of 115 and 116 but I am not certain. The idea was that we would try to perpetuate these two families for further tests in the future.��ODRP families were produced by crossing several parents from each parental family i.e. each ODRP “family” consisted on both brother/sisters and cousins. The families were raised in MBP facilities under quarantine conditions in 0.2 micron filtered SW. The spat were reared in upwellers until they reached 5-7 mm in size before being planted at ODRP sites. There was little intentional selection for fast growing larvae or spat (although this has changed now at MBP).�
Mortality by treatment group (initial planting early June)
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ip 2003
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Water temperatures
Mortality by treatment group (initial planting early June)
Water temperatures
Presenter
Presentation Notes
Willapa 2003 – strong increase in early season water temperatures, with spikes to 35 C. Water temperature during rest of summer (except for unrecorded period) remainted low. High mortalities during the period following high spring temperatures, also was obversed in an adjacent triploid bed.
Mortality by treatment group (initial planting early June)
Water temperatures
Presenter
Presentation Notes
Mid-season period of somewhat elevated water temperatures, all exceeding 20 C, unusually warm. Very high mid-summer mortalities in some groups, especially hybrids. MBP 142 continued to exhibit poor performance.
Banas NS, Hickey BM (2005) Mapping exchange and residence time in a model of Willapa Bay, Washington, a branching, macrotidal estuary. J. Geophys. Res. 110,
Model results from test conditions based on 3 years of data
Study Site
Presenter
Presentation Notes
Results from 3 yr of hydrographic time series are shown for Willapa Bay, Washington, a macrotidal, partially mixed estuary whose river and ocean end members are both highly variable. Fluctuating ocean conditions—alternations between wind-driven upwelling and downwelling, and intrusions of the buoyant Columbia River plume—are shown to force order-of-magnitude changes in salinity gradients on the event (2–10 day) scale. Under summer, low-riverflow conditions, in fact, the effective diffusivity K is large enough to drive a net increase in salinity that is 3–6 times the seaward, river-driven salt flux.
Mortality by treatment group (initial planting early June)
Water temperatures
Presenter
Presentation Notes
02 – highest in August to Sept period. Moderate > in water temp to ~17C, with multiple spikes to 28 C at low tide. Largely affected yearlings and MBP groups. 03 – Significant elevation in mid-summer to 20C, with a gradual decline to early Sept. Increased mortalities in new MBP animals during the same period, with later mortalities in most groups.
Mortality by treatment group (initial planting early June)
Water temperatures
Presenter
Presentation Notes
04 – Higt to ~18C in late July to early August, otherwise low; however, with many sharp peaks throughout the summer. Relatively uniform mortalities with a peak in late July and early August. 05 – Moderate rise to early August at ~18 to 19C, tailing off slowly, many intense peaks to 20-35C. Maximum mortalities in same period for all groups, had an lower early mortality as well. Note overall lower mortalities in MBP animals.
We were very efficient in killing oysters in Mud Bay and Totten Inlet. In comparing oyster mortality from on bottom versus 1 foot off bottom oysters we found that oysters placed directly on the bottom suffered higher mortalities. In Mud bay it was very dramatic, as we saw a 45% increase in mortality. Totten oysters showed a 25% + increase in mortality. We consistently show lower levels of mortality in our rack plots in comparison to what local growers experience. This likely is due to the fact that our oysters are raised above bottom and theirs are not. Any differences see in longline oysters of varying heights?
30cm (130cm (130cm (1’’’) and 70cm (2.3) and 70cm (2.3) and 70cm (2.3’’’) off bottom) off bottom) off bottom
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Hybrid #1 2003 1'
Hybrid #1 2003 2.3'
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Hybrid #2 2003 1'
Hybrid #2 2003 2.3'
Presenter
Presentation Notes
In further exploring the effects of raised racks we decided to emulate culture techniques of French researchers with the use of 70cm raised racks. We compared hybrid oyster mortality on higher racks with the shorter 1 foot racks. As you can plainly see, a higher percentage of oysters died on the shorter racks even though the higher racks were subjected the oyster to more air exposure. We have yet to take end of year weight and length measurements which may prove interesting. Totten Hybrid group#1 expressed a 15% increase in mortality whereas Hybrid #2 expressed close to a 20% increase in mortality. French research, as reported in a 2003 communication, in 2002 yielded similar results when they compared racks raised 15 and 70 cm off bottom. The oysters on the lower racks experienced a higher incidence of mortality. This effect was coined the “sediment effect” by MOREST researchers.
Dominant phytoplankton taxa at summer mortality sites
• Triploid oysters showing overgrowth of flat shell (right valve) by cupped shell
• About 30% of samples (n=969) with multifocal necrosis of gill tissue
• Pathology possibly due to overheating and exposure during low tides
Presenter
Presentation Notes
Generally these were triploids with a few noted exceptions. There is a high proportion of males, suggesting loss of females, or a predisposition to form males in the triploid induction process. Triploids show substantial development. Significant lestions were found in the June 2 and July 10 samples. These consisted of multifocal necrosis of gill tissue, probably resulting from overheating and long out of water periods during low tides. Note that the live to dead size ratio does not equal 1:1 until the June 26, sample, presumably due to the losses associated with the lesions found in the June 2 samples. There were no lesions that accounted for the unequal shell size (cupped valve outgrowing flat valve) in these oysters. It is my opinion that there are a number of genotypic and phenotypic differences in triploid oysters related to poor survival and morphological differences but I cannot link the shell deformities to triploidy by histological examination. A separate report was prepared for case number O03-10.
Current research Current research Current research
• Test the hypothesis that a small number of genes control resistance to summer mortality through genomic mapping of variation in survival, growth and reproductive allocation.
• In conjunction with a breeding program focused on selecting for resistance to summer mortality, to determine how variation in reproductive allocation may interact with stress conditions associated with summer mortality.
• To evaluate selected environmental parameters and observations which appear to predict increased summer mortality risk and can be used to assess the performance of outplanted treatment groups.
• To ensure there is a timely response to oyster mortality events on commercial oyster beds, and harvest areas and provide feedback on those events to producers.
Presenter
Presentation Notes
It is proposed to create selected pedigreed populations to permit the founding of commercial summer mortality-resistant stocks in 2007 and beyond and open up avenues of future research (QTL mapping, functional genomics, proteomics) to test hypotheses about the ultimate genetic and physiological causes of this complex trait. The QTL-mapping objective will more directly and immediately test the hypothesis generated by the MOREST program that a relative small number of genes contribute additively to survival of summer mortality. It will also provide a set of linked markers that could be used to assist the commercial selection program that will be enabled by the founding of pedigreed selected stocks. QTL-mapping will further generate testable hypotheses about the genetic and physiological causes of summer mortality, by permitting identification of candidate immune or stress-response genes that co-locate to those areas in the genome contributing to variance in survival of individuals. In addition, we propose a genetic analysis of variation in reproductive allocation in pair-mated families of Pacific oysters to help resolve the influence of reproductive allocation on the timing and impact of summer mortality in oysters. The production of pedigreed lines of oysters will enable genetic selection and breeding based on reproductive traits and may lead to the development of mortality resistant lines of oysters for broodstock use by the west coast oyster industry. Additional impacts of this project will be to: Increase understanding of the etiology and pathogenesis of the summer mortality syndrome in Pacific oysters; Identify predictors of mortality and environmental stressors which may be utilized by growers to manage shellfish crops for reduced summer mortalities; Characterize impacts of longer-term changes in water quality and phytoplankton in shellfish growing areas; Reduce the present economic losses now occurring on West Coast shellfish farms and increase their operational and economic efficiencies.
