Lecture 11 - Buoyancy, Chemical composition Flashcards
Only animals with ________ have lower metabolic rates at depths beyond the effect of lower temps
Image forming eyes
Lower metabolic rates reflect what
Reduction in locomotor abilities of sighted animals (relaxation of selection for locomotion)
Buoyancy
Density = weight/volume
Seawater density
1.026 g/ml at 20C
1.028 g/ml at 5C
(decreases at higher temps)
Negatively buoyant
sinks (higher density than fluid)
Positively buoyant
floats (lower density than fluid)
Neutral buoyancy
neither sinks nor floats (same density as fluid)
Major factors determining composition
- Effect on density of whole animal
- swimming costs, patterns of behavior - Physical strength
- strong skeleton and connective tissue require muscles and high activity - Energy values of material
- high value = more food input and E storage required
Buoyancy of gelatinous species
Near neutral at all depths
Buoyancy of non-gelatinous inverts
Negatively buoyant at shallow depths
Neutral at greater depths
(crustaceans, squids)
Buoyancy of fishes (expect mackerels and sharks)
Neutral at all depths
Ways of staying up in the water column
- Swim to stay up ( - buoyant)
- Achieve or approach neutral buoyancy
a. reduction of heavy materials (increase water content)
b. Lower density of the body fluids
c. Add light materials - lipids
d. Gases or spaces
How does reducing heavy materials change animals?
Increases water content and decreases skeleton and proteins (gelatinous animals)
Limits strength and activity
What are the two ways to lower the density of body fluids?
- Lower the concentration of solutes (teleost fishes)
2. Replace ions in body fluids
Two mechanisms for replacing ions to reduce density of fluids
- Lower molecular weight ions replace heavier ones (lower density due to less weight)
- Greater partial molal volumes of replacing ions (lower density since the volume of solution for a given weight is increased)
Usually ions used to replace other ions
NH4+
Na+
3 major subgroups of lipids
- Phospholipids - Major component of cell membranes
- Triglycerides - storage fat
- Wax Esters - long chain fatty alcohol esterified to a long chain fatty acid
What animals add lipids to become less dense?
Sharks, teleosts, whales, shrimps, nemertean worms
What lipid do portuguese sharks use to become less dense?
Squalene
Two ways to uses gases/spaces to decrease buoyancy
- rigid walls/hard boxes
2. flexible walls/soft boxes
Rigid walls
Internal pressure does not need to equal external pressure
Don’t need to be filled to work
Used by cuttlefish, Nautilus, Spirula, Sepia
Flexible walls
Internal pressure = external pressure
Need to be filled with gas to work
Examples - fish bladders, siphonophore bladders, kelp gas bladders
Disadvantage of hard boxes
Depth limited by crushing of structure
Reverse osmosis can force water into the chamber against osmotic gradient
Disadvantages of soft boxes
Vertically migrating animals must remove gas to rise due to danger of embolism
Energetic costs of refilling the bladder limit migrators to shallow depths
Swim bladders are absent in pelagic fishes below _____ but are present in _____.
1000 m
near-bottom fishes
Elevated lipid in midwater crustaceans and fishes are found only in species from where
Regions of high seasonality (Antarctic, California, Indonesia)
Hypothesis for lower lipid content at depth
A. Low food supplies
B. Lack seasonality, variability in food supply
- higher lipids are reserved for seasonal changes in food availability
