Deep Sea Ecosystems, Part 1

I. Zonation -- Figure 1.22 review
    deep sea >200 m deep
    dysphotic zone -- still receives some light (no PS)
    aphotic zone -- no light

II. Sampling the deep sea
    A. Long cable and sampling gear
    B. Dredges - often not 'quantitative'; box cores or multicores
    C. Trawl avoidance by midwater fish
    D. New technology – submersibles; ROV; deep sea cameras; acoustical devices
    E. Still poorly sampled
    F. Lack of natural history data

III. Environmental Characteristics – temporal constancy
    A. Light

    B. Pressure
        1. increases one atmosphere for every 10 meters depth
        2. difficulties bringing deep sea organisms to the surface
        3. pressure-dependent physiology
                a. deep-sea bacteria
                b. enzyme properties in fish
                c. homeoviscous adaptation – deep-sea bacteria construct their membranes from more fluid lipids
                d. protein synthesis
                e. solubility of CaCO3 increases at greater pressure
                f. fish lack a functional swim bladder in the deep-sea
    C. Salinity

    D. Temperature

    E. Oxygen
        1. generally high but does decrease in the 20 m or so just above the bottom
        2. oxygen minimum zone (500-1,000 m)

    F. Food
        1. allochthonous -- comes from elsewhere (no photosynthesis)
            a. some particles (e.g., marine snow and fecal pellets) are not directly edible by animals; animals feed on decomposer bacteria
            b. patchy and limiting –
                i. restrict the abundance and size of most deep-sea organisms
                ii. more food available under areas of high surface primary production or near terrestrial habitats
                iii. only about 20% of the epipelagic production makes it to the mesopelagic
                iv. only about 5% makes it to the abyssal
                v. typically are 5-10X fewer organisms at 500 m than at the surface, and perhaps 10X fewer again at 4,000 m
            c. particles accumulate on bottom
 
        2. autochthonous -- hydrothermal vents
            a. chemosynthesis
            b. higher abundance and diversity of life than elsewhere in the deep sea

IV. Adaptations of Deep Sea Organisms
    A. Color
        1. mesopelagic
            a. fish generally silvery-gray or deep black
            b. invertebrates purple and bright red

        2. deep sea --
            a. no countershading
            b. often colorless; whitish; black (fish) – lack pigment

    B. Eyes/Sensory adaptations
        1. mesopelagic
            a. (<2000 m) have large eyes
            b. some fish have tubular eyes – two part retina; great sensitivity to low light; yellow filter to distinguish
                between natural light and bioluminescence

            c. bilobed eyes in invertebrates
            d. twilight vision -- enhancement of vision of some fish in mesopelagic

            e. dimorphic eyes – some mesopelagic squids; small eye oriented downward and
                    large eye upward -- match downwelling light with its photophores and is camouflaged
        2. >2000 m -- reduced or no eyes
        3. bottom dwellers -- may have no eyes
        4. mesopelagic fishes often have well-developed lateral lines
    C. Food scarcity --
        1. huge mouths
        2. backpointing teeth
        3. bioluminescent lures
    D. Low oxygen
        1. problem in oxygen minimum zone
        2. fishes, krills and shrimps have large gills
        3. tend to be less active
        4. some have hemoglobin that is very efficient at low oxygen
    E. Problems finding mates
        1. low population densities
        2. many deep-sea fishes are hermaphrodites
        3. signals to attract mates -- bioluminescence, pheromones
        4. male parasitism
        5. invertebrates aggregate into breeding groups, although the cues aren't known

    F. Body Size --
        1. Most deep-sea benthos and mesopelagic organisms are small
         2. Abyssal gigantism -- some invertebrates

    G. Bioluminescence –
        1. common
            a. in general emits light of 460-480 nm (blue)
            b. most prevalent in mesopelagic and upper bathypelagic

        2. Structure – light can be produced by the animal's own tissue or by    bioluminescent symbiotic bacteria
            a. simple – glandular cells or cups with bacteria that produce light
            b. may have lenses to focus, color filters, or adjustable diaphragms
            c. squids often combine photophores with skin that contains chromatophores and can alter the color/intensity of the bioluminescence

        3. function
            a. counterillumination -- preventing silhouette production
            b. luring prey (e.g., angler fish)
            c. lighting an area to see prey
            d. mate recognition
            e. burglar alarm hypothesis -- startles the predator; may attract other predators;
                deep-sea squids
                


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