Deep Sea, part II

V. Mesopelagic zone
    A. Little known about ecology of organisms
    B. Species composition and distribution --

zooplankton -- some of the same species as in the epipelagic

fishes -- generally small (2-10 cm)
    bristlemouths (one species, Cyclothone signata is thought to be the most abundant fish on earth!)
    also other fishes: hatchetfishes, viperfishes… all long, eel-like fishes with large mouths and eyes

    C. Deep scattering layers (DSL) --vertical migration like in the epipelagic, but to even deeper water during the day

        1. some do not migrate
            a. fish - tend not to have a swim bladder, weaker bones; fewer spines and scales; not as streamlined
            b. zooplankton - filter detritus (including fecal pellets)
            c. tend to be sit-and-wait predators
        2. some migrate -- interzonal fauna
            fish tend to have swim bladders, well-developed bones and muscles
            gain energy from the production of the surface waters

    D. Food and Feeding -- partitioning by depth and by food size
    E. Life History Patterns
        1. most mesopelagic organisms are short-lived (mature at 1-3 years; live 2-4 years)
        2. may have seasonal reproductive patterns

VI. Community Ecology of the Benthos -- patchy environment
    A. Faunal composition --
        1. functional groups
            a. few filter/suspension feeders
            b. many deposit feeders (feed on sediment)
            c. some predators

            d. epifauna – live on the surface
            e. infauna – live within the sediments
        2. taxonomic diversity -- continually finding new species
            a. crustaceans (~30-50% in the Atlantic abyssal) – isopods, amphipods,
            b. polychaetes (~40-80% in the Atlantic)
            c. echinoderms -- large sea cucumbers, brittle stars
            d. sponges (Porifera) -- glass sponges
            e. cnidarians – include sea anemones, sea pens, sea fans
            f. fishes – lack of more derived fish; common: Rat tails, Cusk eels, Bythidids (brotulas)
            g. foraminifera are ubiquitous but often ignored; may be involved in benthic microbial loop
        3. common characteristics
            a. small infauna
            b. fragile (lack of CaCO3)
            c. patchy
            d. may not be seasonality in reproduction or abundance

    B. Diversity of the benthos
        1. high – are many species, although each is rare
        2. unusual for any one species to be >10% of the total abundance
        3. species diversity versus depth
            a. increases with depth until 1500-3000 m, then levels off and declines
            b. high variability
        4. hypotheses to explain high diversity
            a. hypothesis versus theory (misuse in text)
            b. stability-time hypothesis (Sanders)
                i. stable environment; long period of time for species to specialize (competitive niche partitioning)

                ii. BUT many benthic species do not seem to specialize
            c. Cropper/disturbance hypothesis (Dayton and Hessler 1972)
                i. intense feeding or ‘cropping’ from all types of animals prevents any species from reaching high population sizes and reduces competition

                ii. BUT most deep-sea organisms do not appear to have adaptations to avoid predation
            d. Area hypothesis
                i. Species number is positively correlated with area;
                ii. diversity is higher in the deep sea because it is big

                iii. BUT both species density and abundance are actually highest at intermediate depths
            e. Newer ideas -- deep sea is actually dynamic on the time scale relevant to organisms living there
                i. local spatial heterogeneity (patchiness)
                ii. small scale disturbance – communities not at equilibrium
                iii. recruitment limitation – low fecundities and densities mean that potential competitive dominants can’t colonize all favorable patches

                iv. really need more data and experiments

    C. Feeding -- food scarce and patchy; bacterial decomposition is slower (~3X slower) at low temperature and high pressure

    D. Life history patterns
        1. poorly studied
        2. most are slow growing
        3. most have delayed sexual maturity
        4. hermaphrodism may be common in fish
        5. some organisms (fish and many gastropods) have planktotrophic larvae (but not all)

    E. Human impacts
        1. mining of manganese nodules – suspends sediments
        2. orange roughy

        3. waste disposal – dredge spoil, sewage sludge, industrial waste, radioactive waste, excess CO2
        4. deep sea drilling

VII. Hydrothermal vent communities
    A. History of study
        1. predicted hot springs at seafloor spreading sites
        2. discovered in 1977
        3. now about 30 sites have been studied at many rift areas, most on mid-ocean ridges at depths of 1500-4000 m
    B. What are hydrothermal vents?
        1. mixture of hydrothermal water and icy cold waters of the deep
        2. several types –
            a. black smokers
                i. very high temperature (~400 oC);
                ii. rich in metals and sulfides that precipitate to form particle rich black smoker plumes
            b. white smokers
                i. intermediate temperatures (100-300 oC);
                ii. white particles precipitate at these temperatures

            c. more diffuse fluids leaking from other areas
        3. very different than the rest of the deep sea
            a. steep gradients of chemistry and temperature

            b. high frequency of disturbance
    C. How do organisms live there?
        1. rich in reduced sulfur compounds
            sulfide is toxic to most organisms

        2. chemosynthesis by bacteria (chemolithoautotrophic) –
            a. use the oxygen in the seawater and the reduced compounds from the vents; can only live in a narrow band near the vents
            b. high microbial biomass at vents

        3. Some animals filter bacteria or graze on bacterial mats
        4. Some have symbiotic relationships with the bacteria
            a. vestimentiferan worms; large clams and mussels
            b. blood has special hemoglobin that binds to both oxygen and sulfide; oxygen used for the organism's own
                respiration and sulfide for the bacteria (prevents poisoning of the worm)
            c. vestimentiferan worms
                i. don't even have digestive tracts as adults
                ii. specialized organ, a 'feeding body' or trophosome -- is filled with symbiotic chemosynthetic bacteria
            d. some of the clams and mussels also can filter-feed
            e. some shrimp have episymbionts
        5. other organisms prey on the grazers or the symbiotic animals
    D. Who lives there?
        1. many unique organisms
            a. 443 species recovered, 82% of which are endemic
            b. 1 new class, 3 new orders, 22 new families
        2. Who are they? -- large clams, mussels, crabs, snails, polychaete worms, benthic siponophore, five new fish species and vestimentiferan worms
        3. Diversity of organisms is low
        4. Many of the organisms appear to be ‘ancient’ members of their lineages
    E. Life history
        1. grow rapidly and attain maturity quickly
        2. some reproduce synchronously (cued by tides?), but most do not
    F. Zonation around vents – temperature
        1. high temperature flows (>50 oC) - community dominated by alvinellid polychaetes
        2. moderate temperature (<30 oC) flows have vestimentiferan worms
        3. low temperature (<5 oC) flows have bivalves
        4. areas with no measurable flow that have suspension-feeders (polychaetes, barnacles, anemones) and no symbiont fauna
    G. Temporary habitat
        1. each vent may only last for decades

        2. have drastic changes in species composition during that time
        3. high rates of mortality (44% in 26 days) observed for vestimentiferan worms (collapsing chimneys and fish predation)
        4. how are they colonized?
    H. Human impact and use
        1. vent shrimp -- two light-sensitive patches on their dorsal sides that can detect the 'glow' of the vents
            -- may help them disperse or prevent from getting cooked; may have been harmed by the lights of the subs
        2. economic interest in mining minerals at these sites -- iron, copper, zinc, gold  -- not yet viable
        3. bacterial bioremediation of waste sulfides from industrial processes already operating on a laboratory scale with deep sea bacteria

VIII. Other unique deep water communities
    A. Cold seep communities
        1. especially on the continental slope and in sediment-rich areas
        2. only discovered in past 15 years or so
        3. not associated with hydrothermal vents
        4. hydrocarbon seeps
        5. cold hypersaline brines
        6. also chemosynthetic based community – either sulfide or methane based
        7. often the animals there are different than those at hot vents (211 seep species, only 13 shared between vents and seeps)
        8. may be longer-lived than vent systems

    B. Dead whales and other 'baitfalls'
        1. whale carcasses rare: ~1 per 25 km2
        2. estimated that it would take ~5000 years for that many calories to accumulate over a similar area of the seafloor
                by the sinking of material from the euphotic zone
        3. found quickly by many organisms (amphipods, fish); rapidly devoured by specialized, opportunistic faunas (e.g., grenadierfish [rattail fish])
        4. decomposed by bacteria
        5. unique communities develop that consume the bacteria

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