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Structural support
Regulating body fluids
Flotation (buoyancy)
Success of planktonic "plants"
All organisms (land or sea) must adapt to environment
o Obtain food or nutrient resources
o Minimize energy requirements
o Reproduce successfully
o Escape from predators
Energy requirements must be minimized!
Adapt to life in seawater?
o Dense and saline fluid
o Sparse food/nutrient resources
Adaptations to consider
o STRUCTURAL SUPPORT
o REGULATING BODY FLUIDS
o FLOTATION (BUOYANCY)
STRUCTURAL SUPPORT
Density of tissue/skeltons density of seawater.
Gravity is counteracted effectively
Marine organisms do not require the structural strength of land
organisms. Marine animals can attain great size (e.g., whales)
REGULATING BODY FLUIDS
All organisms must maintain constant (±) ionic conc.
in internal body fluids ("electrolyte balance"). How
does this work in marine animals?
Invertebrates and sharks -- no problem. Salinity of body fluids (Sbf) is similar to sea-water salinity (Ssw): Sbf Ssw
Bony fish -- a problem because Sbf < Ssw
Why? .. Body-fluid chemistry inherited from cartilagenous
ancestors (adapted to brakish esuarine environments).
Consequence? .. Water diffuses out of cells to more saline sea
water --> dehydration of fish.
Compensation? ...
Drink a lot of sea water
Excrete salt ions preferentially through ...
... gills
... highly concentrated urine
Migratory marine fish in fresh water -- reverse the process:
Absorb salt ions from specialized gill slits
Excrete large amounts of dilute urine
Marine mammals -- same problem as bony fish.
Compensation? ... Obtain water from their food.
FLOTATION (BUOYANCY)
Plankton & nekton tend to sink from prefered habitat
... away from source of food, nutrients, sunlight. Adaptations
to retard sinking ...
Gas retention: . . (usually O2 or respired CO2)
Flexible internal chambers or "floats" (jellyfish, sargassum)
More rigid gas chambers in invertebrates: Nautilus, cuttlefish
Flexible swim bladders (most fish)
Must compensate for pressure changes with depth.
Active swimmers (some tuna, sharks) and bottom-dwelling fish have
no swim bladders.
Store low-density oils:
Whales, seals: blubber, oily and "light" (energy
source as well)
Fish and sharks: oil stored in organs, e.g. sharks liver
Plankton: store oils in their cells (energy source as well)
Appendages . . (especially in plankton)
Spines, ruffles, feathery extensions
Increase frictional resistance in water and retards sinking
Used also in food gathering and to provide some mobility
Adaptations of phytoplankton -- why are they the dominant marine
"plants" ?
Requirements ..
Sunlight -- must maintain themselves in the photic zone.
Nutrients (N & P) -- low concentration in surface waters,
so "plants" must be dispersed.
These stratagies for success are best met by very small and simple plants: phytoplankton!
Flotation: Adaptations allows phytoplankton to remain
in surface waters
Appendages, oil storage (noted above)
Small size increases frictional resistance to sinking.
Frictional resistance depends on surface area.
Surface area - to - Volume ratio increases with decreasing size.
Nutrition: Small size is a real advantage in
nutrient-poor waters.
Nutritional requirements are proportional to size (volume)
Ability to satisfy requirements is proportional to surface area
Phytoplankton obtain nutrients and excrete wastes by direct exchange
with sea water across the cell wall.
Large area and small volume favors this simple mode of existence.
(WITH PARTICULAR FOCUS ON PLANKTON AND NEKTON)
Structural support
Regulating body fluids
Flotation (buoyancy)
Success of planktonic "plants"
All organisms must adapt to their environment (land or ocean)
in order to:
o Obtain food or nutrient resources
o Reproduce successfully
o Escape from predators
Organisms must achieve these objectives with a minimum expenditure
of energy.
How do marine organisms adapt to the specific conditions of
sea water?
o Dense and saline fluid
o Sparse food or nutrient resources
Adaptations that we shall consider
o Structural support
o Regulating body fluids
o Flotation (Buoyancy)
Structural support
o The density of tissue and skeltons are just slightly greater
than the density of seawater.
o Thus, gravity is conteracted effectively in the oceans, and
marine organisms do not require the structural strength to resist
gravity like life on land does
o Marine animals can attain great size (e.g., whales)
Regulating body fluids
All organisms must maintain a realtively constant concentration of ions in their internal body fluids; this is termed the "electrolyte balance." How is this "electrolyte balance" maintained by different types of marine organisms?
Invertebrates and cartilagenous fish (e.g., sharks). Not a problem, because the salinity of their body fluids (Sbf) is similar to seawater salinity (Ssw)
Bony fish. They have a problem, because the salinity of body fluids (Sbf) is less than seawater salinity (Ssw). Why this salinity difference? The body-fluid chemistry of modern bony fish was inherited from cartilagenous ancestors who were adapted to brakish esuarine environments. What is the consequence of Sbf < Ssw? Water diffuses out of cells to more saline sea water, causing dehydration of the animal. How do bony fish compensate for this loss of water? By drinking a lot of sea water, and by excreting salt ions preferentially through their gills and highly concentrated urine.
Marine bony fish that migrate into fresh water (e.g., salmon) must be able to reverse this process while they are in fresh water. They absorb salt ions from specialized gill slits, and excrete large amounts of dilute urine.
Marine mammals . . have the same salinity imbalance as bony fish (Sbf < Ssw). They compensate for water loss by relying on food to provide for their water requirements.
Flotation (Buoyancy)
Pelagic organisms (plankton, nekton) tend to sink from their prefered habitat, and hence their source of food, nutrients, sunlight. Numerous adaptive mechanisms have evolved to retard sinking.
Gas retention. Many organisms retain gas (usually O2
or respired CO2) in their bodies
Flexible internal chambers, or "floats" (e.g., jellyfish,
Sargassum).
Rigid gas chambers in invertebrates (e.g., Nautilus, cuttlefish)
Flexible swim bladders (most fish). Fish with swim bladders must
compensate for pressure changes as they move up and down in the
water column. Active swimmers (like some tuna and sharks) have
no swim bladders; they maintain their position by ..... swimming
actively! Bottom-dwelling fish have no need for swim bladders.
Store low-density "oils." Whales and seals make and store "blubber" to serve as an energy reserve and for buoyancy. Fish store oils in their organs, e.g., liver. Plankton also store oils in their cells for energy and for buoyancy.
Appendages. When you look at pictures of plankton, you should notice that they typically have spines, ruffles, and feathery extensions from their bodies. These extensions retard sinking by increasing frictional resistance in water. Appendages are also used food gathering and to provide some mobility.
Adaptations of phytoplankton -- why are they the dominant
marine "plants" ?
Consider the requirements of "plants" in the marine
environment: They must receive solar radiation, and they must
be able extract enough nutrients (remember that N and P are the
limiting nutrients) from surface sea water where nutrients are
in short supply. How do marine "plants" cope with these
requirements
Sunlight: Marine "plants" must maintain themselves in
the photic zone.
Nutrients: Marine "plants" must be widely dispersed
to utilize the low concentration of nutrients in surface waters.
These strategies for success are best met by very small and simple photosynthetic organisms: the phytoplankton.
Flotation: Adaptations allows phytoplankton to remain in surface
waters.
Appendages, oil storage (considered above)
Small size increases frictional resistance to sinking.
Frictional resistance depends on surface area
Surface Area: Volume ratio increases with decreasing size.
Nutrition: Small size is a real advantage in nutrient-poor
waters.
Nutritional requirements are proportional to size (volume) of
the organism.
The ability to satisfy requirements is proportional to surface
area.
Phytoplankton obtain nutrients and excrete wastes by direct exchange
with sea water
across the cell wall. The larger the surface area and smaller
the volume, the better
this simple mode of existence works
Sphere Disk (like a diatom)
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