Underwater vision

Question 1

how is light attenuated at diff depths?

Answer 1

surface - broadly same absorption of different WLs
deeper - shifted to blue.
100m blue dominates
1500m - monochromatic too dim for deep sea fish, to see, max transition at 460nm.

Question 2

what was the first link to measuring Chl a in oceans?

Answer 2

described by Jerlov, Categorised transmission spectra. first link to measuring Chla in oceans.
1, 1A 1B, 2, 3 oligotrophic,
2, 3, 5, 7, 9- more euthrophic. peak transmission spectra 570nm.

Question 3

now, how is ocean chl a measured?

Answer 3

satellites, greater resolution of both water properties and spatial resolution.

Question 4

which photoreceptor cells are usually found in marine creatures?

Answer 4

single cone - 450nm
Rod - 500nm
Double cone - 540nm

Question 5

some basic adaptations of deep sea visual systems

Answer 5

very large eyes
upwards facing eyes - catch down welling light.
animal colour changes - more transparent.
however, optimal sensitivity of photoreceptors and WL which are actually present don’t match up - closer to bioluminescence.

Question 6

how does coastal marine photoreceptors differ from FW

Answer 6

marine more blue shifted sensitivity of photoreceptors.

Question 7

how is bioluminescence used?

Answer 7

emission centered around 480nm
finding food, communication, predator defence, disruptive camouflage eg hatchet fish.
diurnal migrators use photophores for camouflage against downwelling illumination.
Photoreceptors tuned to bioluminesence instead of downwelling light.

Question 8

why do some animals in deep ocean use red bioluminescence?

Answer 8

dragon fish can see red, which many prey species cannot. therefore can illuminate prey in light which is invisible to prey.

Question 9

what is a camouflage strategy in epipelagic waters?

Answer 9

silver mirrors - deeper, light is absorbed and scattered more symetrically. amount of light reflected is the same from light from behind, when viewed from any direction. silvery fish form a flat mirror.
use guanine crystals 100nm thick, arranged to form mirror under the skin.
scales as , even on a curved surface.ertical as poss.

Question 10

how is transparency adaptive?

Answer 10

dont form a silhouette, although can still cause reflections.
deeper, switch from transparency to red/black, when there is no risk of silhouettes. dark pigments will absorb bioluminescence.

Question 11

how do vertically migrating species cope?

Answer 11

eg squid, can be transparent in shallow water, and then dynamic change using chromatophores to red pigmented.