Calanus spp
Four species in the northern Atlantic
• C. helgolandicus: Mediterranean, Atlantic
(central i Bay of Biscay), North Sea
(common in the Oslofjord during autumn)
• C. finmarchicus: Norwegian Sea
• C.hyperboreus: Greenland Sea
• C. glacialis: Arctic shelf regions
• (Three northernmost species also along
the eastern coast of Canada/USA)
Relative size C. glacialis, C.
hyperboreus (+Metridia sp; left)
*
C. glacialis and C. finmarchicus
Our local hero - Calanus finmarchicus
Calanus finmarchicus
• Main Calanus-species in the Norwegian
Sea
• Primarily feed on phytoplankton
• Microzooplankton occurs in diet; exact
proportion uncertain, partially described as
a herbivore, partially as an omnivore
• Very important prey organism e.g. fish
Large scale distribution C. finmarchicus
• Calanus needs access to deep water for
overwintering (overwinters at ~500 - 1000 m;
somewhat shallower in fjords), thus are confined
to deep regions for completing its life cycle
• Calanus at the shelf are expatriates, ocean-shelf
interactions essential for ”seeding” the shelf
• Calanus overwinters in deep fjords, yet probably
are expatirates in these environments,
dependent on new seeding each year
Timing of life history events and
number of generations
• C. finmarchicus ascends in ~February off
western Norway (i.e. well ahead of the spring
bloom). Spawning seems to be timed so that
their offspring can take benefit of the spring
bloom (although the bloom also fuels extra
spawning). Ascent/spawning progressively later
towards west and north in the Norwegian Sea
• C. finmarchicus starts descending for
”overwintering” already in June; one generation
being the rule
Driving forces life history
• Food – spring bloom, length growth
season
• Predators – timing of life history events,
selection of overwintering habitat
(horizontally migratory fish/resident
mesopelagic fish)
• Temperature? (selection overwintering
depth)
• (advection)
Since Calanus are mainly
restricted to oceanic regions,
major planktivorous fish stocks
carry out horizontal feeding
migrations
Distribution of herring May 2002, blue arrows indicate migrations of
herring in April/May and red arrows mirgations in June 2002
Distribution of herring August 2002. Red arrow indicates migrations of
herring in July; blue arrows migration August 2002
The herring life history is adapted to Calanus
finmarchicus life history (and vice versa?)
• Calanus develops progressively later from east
to west, and from south to north
• Herring is following this progression, exploiting
Calanus ascending from overwintering and their
progenies
• As Calanus descends for overwintering, herring
return to their own overwintering areas (fjords in
northern Norway).
• The herring migrations imply a vast wave
of potential mortality – spawning ahead of
their arrival might represent a selective
advantage
• Predation pressure is at a maximum in
mid-summer (herring, blue whiting and
mackerel peak abundance in the
Norwegian Sea).
• Driving force for seasonal descent?
Copepod life cycles:
6 nauplii stages (NI – NVI)
6 copepodite stages;
(CI-CVI), C6 are the adults
May diapause in different stages
Calanus finmarchcus:
* Spawning peak around spring bloom
* Diapause in deep water (C5 mostly, C4-C6)
* Descent variable, autumn/late summer
* Adult about 3.5 mm prosome
* 1 – more generations per year
Calanus finmarchicus
Calanus finmarchicus stn M
Differences between Calanus
species
• Size
• Number of yearly generations (although
related to habitat)
• Timing of life history events
• Spawning based on internal (C.
hyperboreus), vs primarily external
resourses (C. finmarchicus)
• Habitat requirements
Number of generations
• C. finmarchicus normally one generation
year-1 in the Norwegian Sea
• C. helgolandicus normally 2? generations
year-1 (North Sea)
• C. glacialis normally needs 2 year to
complete the life cycle
• C. hyperboreus >2 years to complete life
cycle
Timing of spawning and habitat
requirements
• In co-occurring poulations, C. glacialis
spawns first, then C. finmarchicus and
then C. helgolandicus
• Habitat requirements often explained in
terms of temperature (e.g. C. glacialis
confined to waters colder than 2 ºC)
• Overwintering of C. finmarchicus in cold
Norwegian Sea water rather than in
overlaying warm Atlantic water
”Match-mismatch” theory
• Fish spawn at at rather fixed time
• Successful recruitment of copepods (nauplii) is related to
the spring bloom, which varies with weather conditions
• So while fish larvae are present in a rather fixed time
window (although temperature affects developmental
time), their food occurs during a more variable, and more
weather-dependent time window (also related to
transport of Calanus onto the shelf).
• To find food at time of first feeding (i.e. when the yolk
sack is used) is critical for the larvae.
• If this coinsides with present of copepod eggs and
nauplii, there is a ”match”; if these young copepod
stages are scarse during the period for first feeding,
there is a ”mis-match”; leading to mass mortality of
larvae (according to the theory)
Potential food chain impacts of
climate change
• Changes in temperature, wind and light will
impact timing of the spring bloom, and thus
timing and magnitude of zooplankton production
• C. finmarchcius is very important prey for fish
larvae and juvenile fish of most commercially
important species (as well as for larger herring
and mackerell)
• Spring the most critical period for fish larvae/(0group)
Possible effects climate change; shifts between
C. finmarchicus and C. helgolandicus
C. Helgolandicus and C. finmarchicus display
opposite climate responses
Conclusion:
• Substitution of C. finmarchicus with C.
helgolandicus will seriously alter timing of
the presence of important prey for fish,
causing serious ”mis-match”
• C. helgolandicus spawns considerably
later, and will not be present at time when
first-feeding larvae occur.
• Increased temperature increases
metabolic strain when food is limited