Marine pelagic ecology
Bio 4400 spring 2009
We wish to describe and
understand:
• abundance and distribtuion of marine
organisms, both on a large and small
scale
• Vertical distribution of organisms
• Biology, behavior and life history of
important species
• Food webs; who is eating who
• Methods
Pelagic organisms live in a moving
habitat
• Plankton – drift with currents
• Nekton – may swim against currents
Currents in the Norwegian and adjacent
seas evidently of importance in
distribution of plankton
Cod
Primary production on a global
scale
•
Primary production high at high latitudes (but only a few places in
Antarctica) and nearshore; low at low latitudes and in the open ocean
•
What explains this large scale distribution of primary production?
The primary prodcution is
explained by:
• Light
• Supply of nutrients
• Stratificiation, which may be both positive
and negative for the production
• Grazing; grazers crop biomass,
regenerate nutrients
Seasonal patterns
• Higher latitudes
• Lower latitidues ?
Production of zooplankton and fish to a large extent
images primary production; highest production of fish in
upwelling regions
Production of fish depends on primary production, but
also on lenght of food chain
(Same principle Fig 17.2 The Norwegian Sea)
The vertical component is very
important in aquatic biology.
Why?
• Light for photosynthesis
• Light for vision
• Vertical gradients in temperature (temperature
usually more important than salinity; why?)
• (Currents at different depths may have opposite
directions)
The oceans are deep and dark, primary
production restricted to a thin, upper layer with
suffient light for photosynthesis
• Appart for a few exception little food available in deep
waters
Average depth in the worlds
oceans at ~4000 m
Vertical zones
Garrison
The Deep Sea
Large scale vertical distribution
• Organic matter is produced in a thin, upper layer
(often 20-50m; down to 200 m in the clearest
oceanic waters)
• Average depth of the oceans ~4000 m;
organisms throughout the water column depend
on the production of the thin, upper euphotic
zone (a few exceptions)
• The access to food governs the large scale
vertical distribution of zooplankton and fish, with
the highest abundance in upper layers
Supply of food to deep waters
• Sinking of plankton (aggregates
important), pellets and large carcasses –
only a tiny portion reaches the deep ocean
• Diel vertical migrations
• Seasonal vertical migrations
• Shortage of food explains low biomass in
deep waters
Adaptations
•
•
•
•
Ability to exploit few, but large meals
Low activity
Light sensitive eyes
Bioluminisence for protection, feeding and
matefinding
• Red, or black coloration
• ”fragility; e.g. ”watery” muscles
• Physiological adaptations to an extreeme
environment
Deep Sea fisheries
• Low biomass
• Many forms unatractive
• Production of deep sea organisms is low
• Still fisheries for some species like Orange
roughy – fishing on spawning aggregations
• Orange roughy matures at an age of ~30 years
• Such deep sea fisheries evidently not
sustainable
Adaptations: camouflage
Adaptations - camouflage
Transparency
•
Perfect camouflage by transparency requires the object to have the
same transmission characteristics as those of the surrounding medium
•
If a large volume of sea water is incorporated into tissues the animals
may get close to the ideal
•
Common in shallow water, but also some deeper-living organisms
•
Adaptations - camouflage
Silvering
•
Bodies covered in silvery ‘mirrors’.
•
A flat vertical mirror appears invisible in
symmetric down-welling light.
•
However, a reflective surface can be
disadvantageous at night, reflecting
flashes of bioluminescence.
•
Many organisms consequently have
dark colours.
Adaptations – camouflage; “silvering” common in
upper waters and partly the mesopelagic zone
Silvering
•
•
Hatchet fish, Argyropelecus,
have flattened, silvery sides
Even when an animal is
transparent or reflective, there
may be tissues that are opaque
(eyes, organs) -- organisms also
silver these tissues to achieve
camouflage
Red and black pigmentation
common in deep waters
Adaptations - camouflage
Cryptic colouration
•
In deeper layers
organisms can take on a
reddish appearance, a
colour that absorbs
incident blue light well.
•
In the bathypelagic
darkness fishes take on
a velvety black or dark
red appearance. Blue
bioluminescent flashes
are absorbed by these
colours, and if
illuminated, dark
bathypelagic animals
appear invisible against
the blackness beyond.
Adaptations
Bioluminescence – Functions?
•
Avoiding predators:
- counterillumination
- blinding and distraction
- ‘burglar alarm’
•
Finding food:
- by enhancing the visibility of a lure
- illuminating prey with a luminescent
flashlight
- emitting red light: red light rapidly
absorbed, but still may be used to detect prey
at ranges10 times that of the lateral line system
•
Attracting mates:
- species specific displays
- sexual dimorphism of signalling
Adaptations - camouflage
Bioluminescence – counterillumination
•
Organisms use photophores
amongst other for counterillumination
•
Many mesopelagic fish have batteries
of photophores along the ventral body
surface
•
These photophores produce
bioluminescence that mimics the
colour, intensity and angular distribution
of the surrounding down-welling light.
Adaptations - camouflage
Bioluminescence – counterillumination ?
Viewed from beneath, the soft glow
from the shark's many light-emitting
cells blends in with dim light filtering
from the sky and disguises the
predator's outline. Against the glow,
the dark chin patch looks like just the
sort of little fish a predator such as a
tuna is hunting
The fish darts up for the
kill—only to be bitten itself
by the predator called a
cookie-cutter shark
Adaptations
Bioluminescence – predation
•
A notable exception to the rule of blue bioluminescence is the
Malacosteid family of fishes (known as Loosejaws), which produce
red light and are able to see this light when other organisms can not
•
The light produced by these species has such long wavelengths that
it is nearly infrared and is barely visible to a human eye
•
In addition, they can produce typical blue-green light from a separate
organ
Adaptations
Bioluminescence –predation
The loosejaw fish
Malacosteus has a
blue-emitting postorbital
photophore and a
red emitting suborbital
photophore. The
photocytes in the
suborbital photophore
contain a large amount
of red fluorescent
material
Adaptations
Bioluminescence – mate finding
•Sexual dimorphism is common in the
postorbital organs of stomiatoids
and the caudal organs of myctophids.
It is suggested that the light organs
function as intraspecific markers,
although there is no evidence of
information-coding in the flash
frequencies.