Temporal and Spatial Distribution of the Harmful Diatoms Chaetoceros concavicornis and Chaetoceros c

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Temporal and Spatial Distribution of the Harmful
Diatoms Chaetoceros concavicornis and Chaetoceros
convolutus along the British Columbia Coast

• L. J. Albright, S. Johnson, and A. Yousif

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Chaetoceros concavicornis
Nomarski differential interference contrast
Phase contrast
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Chaetoceros concavicornis line drawings
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Chaetoceros convolutus
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Chaetoceros convolutus line drawings
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Apparent goals

• Determine a minimum lethal concentration of
  harmful Chaetoceros spp.
• Determine safe areas for penned salmon based on
  local harmful Chaetoceros spp. concentrations

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How they harm fish

• Barbed spines get caught in fish gills
• Cause excessive mucus production
• Limit gas exchange over gills

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1998 Harmful Chaetoceros spp. first reported in
early March Only Hotham Sound reached lethal
concentrations
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Harmful Chaetoceros spp. concentrations were
greatest in Jervis Inlet Lethal concentrations
also found in Call Inlet (Stations 39-40) in
October cruise
Jervis Inlet
Call Inlet
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Effect of salinity
Experimental cultures
Natural seawater
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Discussion

• Areas of phytoplankton-related penned salmon
  kills coincide with areas of high concentrations
  of harmful Chaetoceros spp.
• Cochlan et al. subsurface chlorophyll maximum
  12-14m possible that harmful diatoms lay below
  0-10m depth samples
• Seawater bodies with salinity over 26 are most
  prone to containing harmful Chaetoceros spp.
• Possibility stratification of Strait of Georgia
  more susceptible to blooms than turbulent
  Johnstone
• Further study needed regarding temperature,
  nutrients, grazing, and latitude

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Sub-lethal concentrations of the harmful diatoms,
Chaetoceros concavicornis and C. convolutus,
increase mortality rates of penned Pacific salmon

• L. J. Albright, C. Z. Yang, and S. Johnson

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Goals

• Determine if apparently sub-lethal concentrations
  of harmful Chaetoceros spp. increased mortality
  rates of penned salmon
• Noticed that mortalities increased due to
  apparent vibriosis or bacterial kidney disease
  (BKD) epizootics after sub-lethal
• epizootic affecting a large number of animals at
  the same time within a particular region or
  geographic area. Used of a disease.
• Attempt to recreate a Chaetoceros-bacterial
  pathogen-salmon mortality interaction under
  laboratory conditions

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6 fish pens
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Bloom 1 mid-March to mid-April Bloom 2 mid-May
to late May Bloom 3 mid-July
Mortality rates increase coincided with 2
harmful Chaetoceros spp. Blooms No harmful
Chaetoceros spp. bloom in mid-July no fish
mortality increase in mid-July
Mean harmful Chaetoceros spp. concentrations
during two blooms were 0.49 and 0.37
cells/ml Apparent cause of death in most cases
vibriosis
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Bloom 1 mid-March to late March 1.55
cells/ml Bloom 2 mid-April to late April
3.13 cells/ml Likely causes of death BKD and
vibriosis
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Bloom 1 mid-March 0.060 cells/ml Bloom 2 late
April 0.024 cells/ml No increased fish
mortality during blooms
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Laboratory experiment methods

• Tank 1 untreated
• Tank 2 Vibrio anguillarum added on day 3
• Tank 4 C. concavicornis added daily
• Day 1-2 21-37 cells/ml
• Day 3-7 14-21 cells/ml
• Tank 3 same as Tank 4, but V. anguillarum added
  on day 3
• Fish sampled from Tanks 2, 3, and 4
• after 6 hours, and every day for 5 days

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Tank 4 all fish dead in 7 days
Tank 3 38 mortality in 10 days
No deaths in Tanks 1 and 2
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Discussion

• Possible that the fish immuno-protective system
  is compromised
• Dominant pathogen (Vibrio, BKD, other) is the
  cause of death when weakened fish encounter
  harmful Chaetoceros spp.
• Fish recovering from bacterial infection are more
  susceptible
• Concentration as low as 0.4 cells/ml can cause
  sub-lethal effects (lethal gt 5 cells/ml)

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Pictures and links

• http//thalassa.gso.uri.edu/HABChaet
• http//thalassa.gso.uri.edu/plankton/diatoms/gener
  a/chaetoc/genus/chaet.htm
• http//www.hmsc.orst.edu/classes/MB492/Gregchaetoc
  eros