Chapter 4 - Underwater Light and Sound

Notes for Chapter 4:
Use of Underwater Light and Sound

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Case History: Eye in the Sky
CZCS animated image source

        Make your own custom satellite images from 1978 to 1986 at the
         Coastal Zone Color Scanner website (SeaWiFS)
           or check out Nasa's Image Wall or Earth Observatory

I. Sunlight in the Sea

    a) The Quality of Underwater Light
        terms: photons, absorption, scattering, light wavelength, infrared,
            visible light, ultraviolet, white light, spectrum of solar energy

RQ4.1: Why is the ocean blue?

b) The Quantity of Underwater Light

RQ4.2: Under what conditions can a marine plant live relatively
deep underwater and still photosynthesize?

c) The Effect of Darkness on Life in the Sea
terms: euphotic vs. dysphotic vs. aphotic zone

RQ4.3: Explain why most oceanic habitat is fundamentally
less hospitable to organisms than land habitat.

II. The Uses of Light by Marine Organisms

a) The Capture of Solar Energy by Photosynthesizers
terms: chlorophyll a

        1) Marine algae use pigment molecules to capture light
            that chlorophyll misses
        terms: red algal pigments phycoerythrin and phycocyanin,
            brown algal pigment fucoxanthin

RQ4.4: Why are land plants and green algae green in color?

2) Does the quality of light determine the depths at which
algae grow most profusely?

RQ4.5: Why does one find red and brown algae successful
at relatively greater depths than green algae

b) Using light to See and Be Seen

        1) Many marine animals have excellent vision
        terms: fishes and squids have cameralike eyes with
            lens and retina, crustaceans (and other arthropods) have
            compound eyes with multiple ommatidia, other animals
            have simple eyespots or can sense light all over body

Image (L) as seen through a bee's eye (R)

         2) Animals use transparency, camouflage, and
              countershading as ways of avoiding notice by
              predators or prey that use eyesight
        terms: chromatophores, visual predators, countershading

        RQ4.6: Many animals use chromatophores for camouflage. Explain
            how other animals use light coloration (e.g., fish), or even have light
            organs with symbiotic bacteria that "glow in the dark" (see squids
            below) to brighten their undersurface (ventral side), while their top
            (dorsal) side is dark in coloration?

c) The Production of Light by Organisms
terms: bioluminescence, luciferase, luciferin

RQ4.7: If the sun's light doesn't penetrate very deep, explain
how there can still be quite a bit of light in the deep sea.

        1) The reasons for bioluminescence are diverse and not all understood.
           It occurs in diverse, mostly marine, organisms.
               More Links: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - (10 or 11: Harbor Branch sites - not responding 2/17/02)

                      Featured Organisms:
                            p. 91: dinoflagellates or here (incl. red tide)
                            p. 92: ctenophores (comb jellies)

        RQ4.8: The advantage of bioluminescence sometimes seem
            obscure, if there are indeed always advantages, but what are
            some alternative hypotheses that might explain why animals
            such as the tiny dinoflagellates or walnut-sized ctenophores
            appear to make themselves more visible to predators?

2) The lights of some animals confuse predators

3) The lights of some predators attract or spotlight prey
terms: photophores

                     Featured Organisms:
                            p. 92: flashlight fish (Photoblepharon palpebratus)
                            p. 92: Pachystomias (loosejaws or black dragonfish)

        RQ4.9: Why does the loosejaw fish, Pachystomias, have a
            particularly striking adaptative use of light organs for its
            success as a deepsea hunter?

4) Ventral lights hide the silhouettes of many midwater animals

                     Featured Organisms:
                            p. 92: lantern fish
                            p. 93: squids with photophores for countershading

RQ4.6: See above.

5) Light can be used for species recognition

d) The Use of Light Cycles to Initiate Daily and Seasonal Activities

        1) Organisms that migrate to the sea surface and back each
            night often control their movements by tracking sunlight
        terms: diurnal (or diel) migration

Featured Organism p. 94: copepod
(see also RQ 1.14, p. 14, 114, Tab. 5.1)

RQ4.10: Explain how a planktonic organism such as a copepod
can benefit from diurnal migration.

        2) Long nights change the reproductive activities - and even the
            shape - of some algae
       terms: photoperiodism

III. Underwater Sound
terms: wavelength, frequency, hertz, SOFAR

Featured Organism:
Why do narwhals have an 8 foot long tooth? (Click here to find out)
Image source

IV. Sound Detection and Production by Marine Animals

a) Incidental Noise - An Unavoidable Side Effect of Movement
in Water

b) The Detection and Production of Sounds by Fishes

        1) The lateral lines of fishes detect vibrations and low-
            frequency sounds
        terms: lateral line, romasts

RQ4.11: What advantage is there to be able to detect
vibrations or low-frequency sounds as a fish?

        2) The inner "ears" of fishes detect high-frequency sound;
            their swim bladders both help with detection and produce
            sounds
        terms: otoliths

c) Sound as a Weapon of Offense and Defense

d) Animal Sonar
terms: melon

    The beluga whale has an especially pronounced melon.
    See one at Chicago's Shedd Aquarium in Jessica Ruck's
    Beluga QuickTime movie

1) Most toothed whales use echolocation
terms: toothed vs. baleen whales

        RQ4.12: Where and how do toothed whales (including
        dolphins) generate sounds for echolocation? What are
        these sounds used for?

2) Echolocation is a sensitive way of seeing the world

e) Sound as a means of Communication

1) Dolphin whistles don't seem to resemble human language

Apple Computer has some cool online Quicktime videos on
studies of dolphin intelligence or here

RQ4.13: What evidence is there that dolphin clicks might
or might not be analogous to our use of language?

2) Humpback whales "sing" complex "songs" during mating
season

RQ4.14: Which humpbacks sing and when do they sing? Are
there regional differences in the song sung?

3) Do whales "talk" over long distances?

RQ4.15: What is the evidence that whales may be able to
communicate over great distances?

Listen to a sperm whale song here

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or Lecture Notes by Chapter
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