Vibrio tubiashii : disease and pathogenicity to

Pacific oyster larvae

Pacific Coast Shellfish Growers Association Annual Meeting

September 26, 2012

Elene Dorfmeier, Carolyn Friedman, Steven RobertsUniversity of Washington | School of Aquatic & Fishery Sciences

Pacific Northwest Shellfish Industry

• USD100 million industry (~3000 jobs)

• Large-scale production reliant on shellfish hatcheries

• Oysters account for ~76% of shellfish production

Photo: OSU

Google Maps

Aquaculture and Bivalve Larvae

Declines in larval settlement

Re-emergent disease

Seawater chemistry changes

Photo: Norbert Dankers

Regional Problems

The Pathogen:Vibrio tubiashii (Vt)

Gram-negative, facultative anaerobe

Causative agent of vibriosis in early stage shellfish

Pathogenic to a variety of marine invertebrates, including Pacific oyster

Photo: Phetsouvanh et al. 2008

Disease

Vibriosis: Characterized by bacterial swarming, loss of

motility, soft tissue necrosis, and mortality

Larval mortality within 24 hours of exposure to the most pathogenic strains

Management of bacterial disease has been historically problematic

Re-emergent in the NorthwestLarvae Photo: Lisa Crosson

Bacteria Photo: Dartmouth EM Facility

Environmental Change:Ocean Acidification

The chemical changes associated with the increase

of CO2 in the oceans.

• increases aqueous CO2

• lower seawater pH

• decreased carbonate ion (aragonite, calcite)

availability

Acidification of Northwest WatersSUMMER 2009:

Dabob Bay

Totten Inlet

Map: R. Jacobsen Graphs: Simone Alin et al. NOAA

Impact of Ocean Acidification on Marine Calcifiers

Effects of ocean acidification on calcifying organisms:

Growth and development

Energy allocation

Metabolic depression

Photo: Emma Timmons-Shiffman

Environmental Shifts and Shellfish Aquaculture

1. Re-emergent bacterial disease

Vibrio tubiashii

2. Host response to environmental shifts

high pCO2 and temperature

Photo credit: Steve Ringman, Seattle Times

Research Goals

Investigate the influence of elevated pCO2

on Vibrio tubiashii growth

Determine the impact of elevated pCO2 on

Pacific oyster larval susceptibility disease

Photo: Norbert Dankers

Investigate the influence of

elevated pCO2 on Vibrio tubiashii

growth

Photo: Dartmouth Electron Microscope Facility

Vt Growth CurvespCO2:

Ambient (7.9 pH)

750 ppm (7.8 pH)

2000 ppm (7.4 pH)

Temperature:

16°C

Photo: Ghent University

Establish growth curvesStandard bacterial enumeration

Error Bars = 95% CI

Growth Rate

Error Bars = 95% CI

Growth Rate

p = <0.001*

p = 0.1

Error Bars = 95% CI

Growth Rate

Error Bars = 95% CI

Total Abundance

Stationary Phase

p = <0.001*

*

*

Total Abundance

Error Bars = 95% CI

Summary: Vt Growth At 16°C, Vt grew faster and reached higher

abundance at elevated pCO2

Enhanced Vt growth under acidified conditions may lead to outbreaks of vibriosis in hatcheries

Why? / How? Enhanced gene expression of cell division when exposed to lower

pH (cadA, toxR, rpoS)?

Photo: Dartmouth Electron Microscope Facility

Determine the impact of elevated

pCO2 on Pacific oyster larval

susceptibility disease

Photo: Virginia Sea Grant

Vt Disease Challenge

pCO2:

Ambient (7.9 pH)

750 ppm (7.8 pH)

2000 ppm (7.4 pH)

Temperature:

16°C

Disease agent:

V. tubiashii

RE22

Photo: Ghent University

Vt doses (102 – 106 CFU/ml) LD50 at 24, 48, and 72 hrs

Overview: Vt Disease Challenge

Photo: FAO

Early stageD-veliger3 days old

Prodissoconch I veliger

10 days old

Error Bars: 95% CIp-values >> 0.05

Results: Larval Disease Challenges

Early stageLate Stage

Larval survival after 48 hours Vt exposure

ND ND

LD50 Results

LD50 reported in CFU/ml of V. tubiashii

Late Stage

Early stage

Logistic curve: Pi = 1 / (1 + e –(a + b * x))

LD50 Results

LD50 reported in CFU/ml of V. tubiashii

Late Stage

Early stage

Logistic curve: Pi = 1 / (1 + e –(a + b * x))

LD50 Results

LD50 reported in CFU/ml of V. tubiashii

Late Stage

Early stage

Logistic curve: Pi = 1 / (1 + e –(a + b * x))

Larval Disease Challenge

No detectable difference in Pacific oyster susceptibility to vibriosis at elevated pCO2.

Considerations:

• Length of exposure to experimental conditions

• Conditions throughout early shell development is important to overall survival

• Vt culture conditions

Summary: Disease and OA Elevated pCO2 does not affect Vt pathogenicity, but Vt

growth under acidified conditions may facilitate outbreaks of vibriosis

Higher temperature exacerbates growth

Still many unanswered questions

Rearing oysters at lower temperatures when higher pCO2 levels exist may have lower risk of vibriosis

Trade-off less disease / slower oyster growth

Saltonstall-Kennedy Program (NOAA)

UW School of Aquatic & Fishery Sciences

Generous student support provided by NOAA

NSA – Pacific Coast Section

Ed and Vicky Jones

Taylor Shellfish Hatchery

Washington Sea Grant

NOAA PMEL

Joth Davis - Taylor Resources

Emma Timmons-Shiffman

Mackenzie Gavery

Sammi Brombacker

Robyn Strenge

Alex Rutherford