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Deep Sea Ecosystems

Bioluminescence on Camera03:57

Bioluminescence on Camera

On a volumetric basis, ~90% of the ocean (79% of the entire biosphere) is cold and dark -- the deep sea

No photosynthesis

Most of the food used by organisms comes from out of this zone

Expensive and difficult to sample

I. Zonation -- Figure 1.22 review -- SHOW THIS FIGURE

deep sea -- >200 m deep (below depth of continental shelves)

dysphotic zone -- still receives some light (no PS)

aphotic zone -- no light (begins at ~600 m in the tropics and ~100 m in the temperate zone)

II. Sampling the deep seaEdit

Sampling the deep sea is very difficult!!Edit

A. Long cable (2-3X the required depth) and sampling gear; often doesn't collect properly -- requires a long time to take a single haul; also has great weight and chance for snagging the cable or fouling the gear; deep trawl in the trenches may take 24 hours

B.   Dredges are often not 'quantitative' -- now use (in soft sediments) box cores or multicores that sample a known bottom area

C. Midwater fish can often avoid the nets used -- midwater trawls

Underwater inspection by Remotely Operated Vehicle (ROV) at 153m deep01:55

Underwater inspection by Remotely Operated Vehicle (ROV) at 153m deep

1.  submersibles

2.ROV (remotely operated vehicles)

3.deep sea cameras

4.acoustical devices

E.Still poorly sampled – Gage (1996) estimated that <500 m2 of the deep ocean floor has been sampled quantitatively (out of 270 million km2)

F.Lack of natural history data for organisms

III. Environmental Characteristics -- at any point the characteristics remain constant for long periods of time

A. Light --

1.nearly absent in upper mesopelagic; absent below that

2.no photosynthesis

3. some light produced by the animals themselves

B. Pressure -- part of why it is difficult to study the deep sea

1. increases one atmosphere for every 10 meters (33 ft) depth (weight of the overlying water)

2.deep sea pressure 20->1000 atmospheres

3. now have traps that can maintain pressure to bring deep-sea organisms to the surface in good condition (but this is REALLY expensive)

4.pressure-dependent physiology -- enzymes and lipid membranes depend on high pressure

a. example of deep-sea bacterial growth at different pressures

b.enzymes from closely related fish living at different depths indicated that pressure differences as small as 100 atm can alter enzyme properties

cmuscle enzymes are less efficient at depth and in low cellular concentrations -- may explain the abundance of 'float and wait' predators

d. homeoviscous adaptation -- more fluid lipids in membranes of deep-sea bacteria to maintain membrane fluidity

e. effects on protein synthesis

f. solubility of CaCO3 increases at greater pressure and lower temperature -- more difficult to make shells -- are fewer shell-forming organisms in the deep sea, and they often have thin shells

g.   fish lack a functional swim bladder in the deep-sea

C. Salinity -- often uniform

D. Temperature -- it is below the main thermocline, so the temperature is often uniform (often 1-2 oC at depth) except around vents (where may be 400oC); not seasonal

E. Oxygen

1. generally high (oxygen rich cold water sinking and flowing along the bottom from the Arctic and Antarctic -- are so few deep sea organisms that their metabolism doesn't use up all of the oxygen; does decrease in the 20 m or so just above the bottom [most respiration])

2. oxygen minimum zone (500-1,000 m) -- oxygen may fall to less then 0.5 ml/liter -- due to respiration and lack of replenishment

3. some areas of low oxygen -- Carioca Trench (off Venezuela in the Caribbean); Santa Barbara basin (off CA)

F. Food

1. allochthonous -- comes from elsewhere (no photosynthesis in the deep ocean)

a.   dominant food source in deep sea – must sink from the upper water column

b.  sinking dead phytoplankton and other organisms

c.  some particles (e.g., marine snow and fecal pellets) are not directly edible by animals and are decomposed by bacteria that are then eaten by other organisms

d.  patchy and limiting –

lack of food is thought to restrict the abundance and size of most deep-sea organisms

more food is available under areas of high primary production or near terrestrial habitats

only about 20% of the epipelagic production makes it to the mesopelagic

only about 5% makes it to the abyssal

typically are 5-10X fewer organisms at 500 m than at the surface, and perhaps 10X fewer again at 4,000 m

  particles accumulate on bottom, so there are more bacteria and other organisms on the bottom than in the deep water column (and causes lower oxygen levels there)

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-grey or deep black

b. invertebrates purple and bright red -- absorb blue bioluminescent light produced by predators (decrease probability of detection)

2. deep sea --

    1. countershading absent

    1. often colorless; whitish; black (fish) – lack pigment

  1. Eyes/Sensory adaptations
    Sandalops2

1. mesopelagic

a. (<2000 m) have large eyes

b. some fish have tubular eyes – two part retina -- acute vision in the direction that the eyes are pointed and laterally -- almost like having 2 pairs of eyes -- give acute vision in the direction that the eyes are pointed (up or forward), but not good for lateral vision -- the retina continues up the side of the eye that gives lateral vision; eye is a short black cylinder; each eye has 2 retinas (one at cylinder base, one on cylinder wall) – give binocular vision; seems to have greater sensitivity to low light; the eyes have a translucent lens; some have a yellow filter that allow the fish to distinguish between natural light and bioluminescence

c. eyes similar to tubular eyes are also seen in one octopus (Amphitretus) and some krill (Stylocheiron) -- bilobed eyes

d. twilight vision -- enhancement of vision of some fish in mesopelagic

presence of the photopigment rhodopsin

increased density of rods in the retina

e. dimorphic eyes – squids (family Histioteuthidae); also have many photophores (light-producing organs); live in mesopelagic between 500 and 700 m; small eye oriented downward and large eye upward; matches downwelling light with its photophores and is camouflaged

2.>2000 m -- reduced or no eyes

3.>     bottom dwellers --

often have no eyes

4. mesopelagic fishes often have well-developed lateral lines

  1. Food scarcity --

1. huge mouths -- swallow anything (larger relative to their size than fish in other oceanic realms)

2. backpointing teeth (prevent escape of prey)

3. mouth and skull may be hinged to open wider than the body (viperfish, Chauliodus and rattrap fish, Malacosteus)

4. bioluminescent lures (angler fish; stomiatoids)

5. black linings in coeloms – prevent bioluminescence from prey in gut from escaping

  1. 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

  1. Problems finding mates

1. low population densities -- difficulty in finding mates

2. many deep-sea fishes are hermaphrodites (have both male and female gonads)

3. signals to attract mates -- bioluminescence, pheromones

5.male parasitism -- males reduced and attached to females (angler fish, Ceratias); when the male finds the female he bites into her side and remains there for the rest of his life; in some species the male's modified jaws fuse with the female's tissue, their circulatory systems join and the female nourishes the male

6.invertebrates in the deep-sea seem to aggregate into breeding groups, although the cues aren't known

  1. Body Size --

1. but most deep-sea benthos and mesopelagic organisms are small (less food available?) -- average organism size decreases with increasing depth

 2. Abyssal gigantism

a. some invertebrates (but not most; some amphipods, isopods, ostracods, mysids and copepods); not vertebrates  look up isopod, Bathynornus giganteus (42 cm), amphipod, Alicella gigantean (15 cm), ostracod (Gigantrocypris) and copepod (Gausia princeps)

b. what is the explanation for this increased size at depth?

(1) metabolism under high pressure

(2) low temperature and low growth (due to low food) increases longevity and delays sexual maturity)

(3) larger animals may be more mobile and more able to find patchy food and mates

(4) increase size to avoid predation?

  1. Bioluminescence – widespread in the sea

1. common

    1. in general emits light of 460-480 nm (blue) lots of luminescent colors are possible -- may be b/c blue light travels the farthest

    1. most elaborate light producing organs – photophores – are in deep sea organisms

    1. most prevalent in mesopelagic and upper bathypelagic

2. Structure of photophores (light organs) -- can be produced by the animal's own tissue or by bioluminescent symbiotic bacteria

a.similar to firefly luminescence – luciferin is oxidized by the enzyme luciferase to produce a molecule that emits light

b. simple – glandular cells that produce light or glandular cups with bacteria that produce light; surrounded by black pigment cells

c. also may have lenses to focus the light, color filters, or adjustable diaphragms

d. 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 – mimics the downwelling light

experiment with midwater shrimp (Sergestes similis) -- with eyes covered with blinders, didn't produce light; with clear blinders they matched the downwelling light (SCAN PAGE 341 MARINE BIOLOGY TEXT; SCIENCE VOL 20: 1979, J.A. WARNER ET AL.)

b.   luring prey (e.g., angler fish)

Angler-Fish

c. lighting an area to see prey (some fishes have photophores that produce red light that is invisible to most other midwater organisms, but the fish can see it and may use it to spy undetected on potential prey)

d.  mate recognition -- pattern of photophores is different among different species and even different sexes of the same species

e.  burglar alarm hypothesis -- startles the predator; attracts other predators, so is dangerous; some deep-sea squids (Histioteuthis dispar) produce a luminescent cloud instead of a black ink cloud to escape predators

V. Mesopelagic zone -- more known about benthic deep-sea fauna than about midwater pelagic, but we do know about some mesopelagic organisms; 'world of twilight'; at upper part is enough light to see by (about enough to read by, but not enough for PS); this region extends to the absence of lighted area -- about 200-1000 m

A. Little known about their ecology

B. Species composition and distribution -- lantern fish (Myctophidae) and other small fish (Gonostomatidae and Sternoptychidae -- hatchet fish -- look up Argyropelecus affinus), krill (euphausids), shrimp (sergestid and pasaphaeid), squids, deep floating siphonophores (Cnidarians)

zooplankton -- some of the same species as in the epipelagic -- krill, copepods, shrimp, ostracods (generally small [several mm] although one group, Gigantocypris, can reach 1 cm), amphipods; also predators such as chaetognaths, jellyfish, siphonophores, comb jellies, larvaceans, pteropods, squids; vampire squid (Vampyroteuthis)

fishes -- generally small (2-10 cm); bristlemouths (Cyclothone signata is thought to be the most abundant fish on earth!) and lanternfishes (blunt heads, large mouths and large eyes) are the most abundant (may be 90% of the midwater trawl haul); generalist feeders; are also other fishes -- marine hatchetfishes (unrelated to FW hatchetfishes), viperfishes, dragonfishes, barracudinas, sabertooth fishes, lancetfishes, snake mackerels and cutlassfishes -- all long, eel-like fishes with large mouths and eyes; many have photophores on ventral surface and are less than 30 cm long; largest mesopelagic fish may be one of the lancet fishes (Alepisaurus ferox) that grows to ~2 meters. 

C. Deep scattering layers (DSL) -- observed on sonar -- often two or three deep layers in the day, and one shallow layer at night -- vertical migration like those in the epipelagic, but to deeper water during the day; found in all but the arctic ocean; more animals involved in the migration in areas of high surface productivity

1. some do not migrate -- some fish (Cyclothone, Sternoptyx), mysids, some shrimps (sergestids [look up Sergestes similis], penaeids, carideans), a few euphausids, amphipods, cephalopods, cnidarians – these non-migrating mesopelagic fish tend not to have a swim bladder, have weaker bones and fewer spines and scales and not be as streamlined; the non-migrating zooplankton filter detritus (including fecal pellets); the fishes, shrimps and squids tend to be sit-and-wait predators

2. some migrate -- interzonal fauna -- generally from 300-500 m in day to surface at night) most mesopelagic fish (Myctophidae, look up Tarletonbeania crenularis, Gonostomatidae look up Cyclothone pallida), most euphausids (look up Euphausia pacifica)  and decapods; -- these fish tend to have swim bladders, well-developed bones and muscles -- these organisms 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 (e.g., sediment -- much of the abyssal plain floor is MUD, rock, manganese nodules)

A. Faunal composition --

1.   functional groups

    a.few filter/suspension feeders (are more in the rocky areas of the deep-sea that have higher flow rates, but these environments are rare compared with soft sediment low-flow areas)

b. many deposit feeders (feed on sediment)

c. some predators -- sea stars, brittle stars, crabs, fishes, squids, sea spider (pycnogonids), tripod fishes

  d.  epifauna – live on the surface

e. infauna – live within the sediments

2. taxonomic diversity -- continually finding new species often related to shallow Antarctic region species (where water originates and where deep water ends up)

a. crustaceans (~30-50% in the Atlantic abyssal) – giant scavenging isopods, amphipods, (tanaids, cumaceans)

b. polychaetes (~40-80% in the Atlantic)

c.echinoderms -- often the most conspicuous fauna

i.large sea cucumbers (Holothuroidea); some have leg-like appendages that use to walk across the seafloor

ii. brittle stars (Ophiuroidea)

iii.some less common – starfish (Asteroidea), sea lilies (Crinoidea), sea urchins (Echinoidea)

                 d.sponges (Porifera)

Imgres

i.  includes rare glass sponges (Hexactinellida)

                              e.sea anemones (Anthozoa), sea pens (Pennatulacea), sea fans (Gorgonacea), hydroids (Hydrozoa) and zoanthids (Anthozoa)

  f. molluscs -- primitive members of Neopilina; gastropod and bivalve mollusks in the infauna

g. Fishes – lack of more derived fish - tripod fish

i. Rat tails (Macrouridae)

ii. Cusk eels

iii. Bythidids (brotulas)

iv.  Liparids (snailfishes)

v. Eels (Synaphobranchus, Cyema)

  h. Foraminifera are ubiquitous (seamounts, hydrothermal vents, manganese nodules, sediments…) but often ignored; may be involved in benthic microbial loop; fist sized Rhizopodia

3.common characteristics

a. small infauna

b. fragile (lack of CaCO3)

c. patchy

d.may not be seasonality in reproduction or abundance

{C}


B. Diversity

"In any one square meter of mud, more than 100 species of small worms, mollusks and crustaceans might be found.  An adjacent square meter of mud may hold just as many different species." -- van Dover 2000

1. relatively high – long considered a biological desert; actually are many species, although each is rare; it is still argued how many species there are -- scientists are extrapolating from relatively few samples; may rival the richest terrestrial and shallow-water ecosystems

2. unusual that any one species is >10% of the total abundance; over 90% of the species are <2% of the total abundance.  In shallow-water the numerically dominant species is often >10-25% of total individuals

3. there are more rare species (one individual in a sample) in deep-sea versus shallow water samples

4. species diversity versus depth -- diversity increases with depth until 1500-3000 m and then levels off and declines -- high variability in these patterns

5. hypotheses to explain high diversity

hypothesis versus theory

hypothesis – a statement that might be true; must be testable – possible to prove that the hypothesis is false if it really is false – e.x. hypothesis that whales have gills; sometimes can’t test the hypothesis – somewhere in the world there are mermaids – difficult to prove false; then this isn’t a valid scientific hypothesis;

in general, you can’t prove a hypothesis true – all hypotheses up for falsification at all times; if you conditionally accept this as ‘true’ – consistent with all available information and lots of attempts to reject it have failed, then it may be elevated to a theory – but this is still open to falsification and can be overturned at any time by new evidence)

In other high diversity environments, such as tropical rain forests and coral reefs, obvious structural complexity is often implicated.

Older hypothesesEdit

a. stability-time hypothesis (Sanders 1968)

unusual physical stability over evolutionary time allowed for greater competitive niche partitioning

the deep sea is a highly stable environment; there has been a long period of time for species to specialize (e.g., on different particle sizes); BUT it is not clear that any benthic species really specialize on specific particles, and this hypothesis has been falsified in other environments

b. cropper/disturbance hypothesis (Dayton and Hessler 1972)

Predation by megafauna enhances diversity by alleviating competition

Food is limiting, but space isn’t, in the deep-sea.  Most organisms are generalists and feed on anything smaller than themselves; propose that diversity is maintained because intense feeding or cropping from all types of animals prevents any species from reaching high population sizes and reduces competition (not really logical); BUT most deep-sea organisms do not appear to have adaptations to avoid predation  and heavy predation should select for large numbers of young, short lifespan and fast growth, the opposite of the deep-sea pattern (still theoretically possible for this to happen if predation is selective against certain age groups).  PROBLEMS

c. area hypothesis

Species number is correlated with area (more area equals more species); diversity is higher in the deep sea because it is big; both diversity and area of sea bottom decrease with decreasing depth (Abele and Walters 1979); BUT applies only to Atlantic, not Pacific; both species density and abundance are actually highest at intermediate depths; this is unlikely (Rex 1983)

Deep sea is patchy

Grassle and Morse-Porteos (1987) propose that diversity is maintained by three factors:

(1) patchy distribution of food

(2) small scale disturbance (for example disturbance of the sea floor by polychaetes or other organisms or slumping) allows diversity – patches vary in their stage of succession

(3) no dispersal barriers

4 major current hypotheses: -- deep sea is actually dynamic on the time scale relevant to organisms living there

1.     local spatial heterogeneity (patchiness)

                                                        i.     spatial patchiness and nonequilibrial dynamics

                                                      ii.     small spatial scale and long temporal scale – polychaete mudballs, protozoan tests, sponge spicules, burrows, pits and mounds persist for long periods of time and provide distinct microhabitats

                                                     iii.     patchiness within the sediments (particle-size distributions) – grain size diversity is correlated with macrofaunal diversity

                                                     iv.     patches can persist for long periods (not disturbed by tides and currents) – often 2-5 years, but still less than the life span and reproductive age of many deep-sea species

                                                      v.     in areas of high hydrodynamic flow there is less diversity, greater abundance, and greater dominance – more like shallow-water communities – so flow may be important

2.     nonequilibrium dynamics – small scale disturbance

                                                        i.     balance between rates of competitive exclusion (related to growth rate) and frequency of disturbance

                                                      ii.     growth rate is a function of POM, which declines exponentially with depth

                                                     iii.     predation higher in shallow than deep waters

                                                     iv.     bioturbation and physical disturbance thought to decrease linearly with depth

                                                      v.     recent disturbance experiments in the SE Pacific abyssal (Borowski and Thiel 1998) depressed diversity for more than 3 years – somewhat inconsistent with this – in abyssal where disturbance is infrequent, should be near competitive exclusion, and disturbance should increase diversity (may just be slow recovery); seems as if colonization is LOW in much of the deep sea

3.     interactions among 3+ trophic levels

4.     recruitment limitation

                                                        i.     low fecundity and low density

                                                      ii.     can’t colonize all favorable patches

                                                     iii.     theoretical models show that this increases diversity by decreasing biotic interactions and competition

really need more data!  More manipulative experiments to resolve this problem

C. Feeding -- food scarce and patchy, but isn't sinking away as in the pelagic; bacterial decomposition is slower at low temperature and high pressure (story of the lack of decomposition of the bologna sandwich in the Alvin after submerged and filled with water for 11 months in 1968); does seem as if the microbial activity is 1-3 X slower in the deep sea benthos than in shallow water benthos; food limited environment

D. Life history patterns

1. poorly studied

2. most are slow growing and not active -- deep sea clams may be 50-100 years old, but some recent evidence shows that some bivalves are fast growing (mature in ~ 1 year) and other mollusks, echinoderms and amphipods may have lifespans of ~10 years)

3. most have delayed sexual maturity and slow embryological development

4.     hermaphrodism may be common in fish

5.     some organisms (fish and many gastropods) have planktotrophic larvae – the early life stages are spent in the surface waters feeding, and the juveniles migrate down as they mature/metamorphose (some angler fish, myctophids, stomiatids, gastropods, some squids); others, especially very deep-sea organisms do not migrate (cephalopod Vampyroteuthis infernalis and some prawns)

E. Human impacts

1. Mining of manganese nodules – suspends sediments

2. Not immune from human impacts – orange roughy, benthopelagic fish that has been trawled from seamounts around New Zealand and Australia; this mining has also removed deep-water corals and other invertebrates

3. Waste disposal – dredge spoil, sewage sludge, industrial waste, radioactive waste, excess CO2

HOT SPRINGS, COLD SEEPS AND DEAD BODIES

VII. Hydrothermal vent communities

A.   History of studyEdit

1.     discovered in 1977 -- first seen in the Galapagos Rift Vent (2700 m) [Bob Ballard, discoverer of the Titanic];

2.     predicted that there would be hot-water springs at seafloor spreading sites, but it was a complete shock to find productive exotic invertebrate communities in the abyssal.

3.     now about 30 sites have been studied at many rift areas; most sites are on mid-ocean ridges at depths of 1500-4000 m

B.    what are they?

1.     warm water or VERY hot water -- mixture of hydrothermal water and icy cold waters of the deep

2.     several types -- black smokers, chimneys…

                              a.     columnar chimneys and black smokers

                                                      i.     columnar chimney typical of E. Pacific rise

1.     form early at hydrothermal site, after a volcanic eruption

2.     400 degree C fluids in bare basalt or new chimneys

3.     can grow to 10-20 meters

                                                    ii.     black smoker

1.     metal and sulfide-rich high temperature, acidic fluids mix with cold alkaline seawater, causing the metal sulfides to precipitate and form particle-rich 'black smoker' plumes

2.     calcium sulfate anhydrite

3.     orifice is typically 10 cm diameter or less

4.     most extreme temperature gradients anywhere on biosphere (greater than 350 degrees per cm in places)

5.     rise heights of plume typically 150-200 m

                              b.     white smokers

                                                      i.     fluids of intermediate temperatures (100-300 degrees C) are emitted

                                                    ii.     silica, anhydrite and barite (BaSO4) precipitate white particles at these temperatures

                              c.     beehives and flanges -- horizontal layering with diffuse ~350 degree C fluids

                              d.     complex sulfide mounds

3.     very different than the rest of the deep sea -- steep gradients of chemistry and temperature; high frequency of disturbance (more like the intertidal zone ecologically); alvinellid polychaetes live in tubes bathed by 30-70 degrees C and routinely experience a thermal gradient of as much as 60 degrees C
often live in areas of extreme temperature gradients – from bottom ocean water (only a few degrees) to up to 350 oC at black smokers

a.     many animals live in areas where get exposed to warm and then cold water

b.     may have huge gradients across their bodies

C.    How can organisms live there?Edit

1.     rich in reduced sulfur compounds (hydrogen sulfide, H2S) and icy cold seawater

a.     sulfide is toxic to most organisms – inhibits anaerobic respiration enzymes and competes with oxygen for binding with hemoglobin at concentrations 1,000 – 1,000,000 X LESS than those found at vents, so how can anything live there?sulfide is toxic to most organisms -- inhibits cytochrome c oxidase systems at micro to nanomolar concentrations

b.     these organisms thrive at millimolar concentrations

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

a.     {C}S2- + CO2 + O2 + H2O                   SO42- + [CH2O] chemosynthesis in shallow marine sediments (coupled with sulfate reduction)

b.     inorganic sulfide and oxygen yield the energy and sulfide serves as the electron donor

c.     can also get chemosynthesis under anaerobic conditions at the vents; then the principle electron donor is hydrogen; nitrate, sulfate, sulfur and carbon dioxide all serve as electron acceptors

d.     microbial biomass at vents can be 4X that of photosynthetic heterotrophic microorganisms in the overlying surface waters and 4000X those of other deep-sea microbial populations

                              e.     may also be bactgerial photosynthesis if there is a long-wavelength capturing bacteriopigment -- photon flux emitted by high temperature fluids at vents

3.     Some animals filter bacteria or graze on bacterial mats

4.     some have symbiotic relationships with the bacteria (vestimentiferan worm, Riftia pachyptila; large clam, Calyptogena magnifica and mussel, Bathymodiolus)

                                a.     generally sulfide is a poison – binds to the cytochromes and the hemoglobin and interferes with oxygen binding and respiration (poisons aerobic metabolism)

                                b.     the blood of these organisms has special hemoglobin that binds to both oxygen and sulfide; oxygen used for the organism's own respiration and sulfide for the bacteria (the cytochromes of Riftia are no less susceptible to sulfide poisoning)

                                c.     the bacteria get carbon dioxide both from the respiration of the Riftia and from the environment

                                d.     the worm Riftia doesn't even have a digestive tract as an adult -- have a specialized organ, a 'feeding body' or trophosome -- that is filled with symbiotic chemosynthetic bacteria; this organ fills much of the worm's body cavity; some of the clams and mussels also can filter-feed, although now known that some have degenerate feeding grooves

                                e.     some shrimp have episymbionts

                                 f.     worms get bacteria from environment when they are juveniles, before the gut closes; clams and mussels have it passed down from mother in eggs

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 (over 500 new species, more than 12 new familes; more than 90% of the species known only from vents)

b.     debated where they fit into the taxonomic scheme

                                                      i.     1 new class, 3 new orders, 22 new families (Tunicliffe 1992)

2.     large clams, mussels, crabs, snails, polychaete worms, benthic siponophore, enteropneust worms, five new fish species and vestimentiferan worms

3.     Vestimintiferan worms (Pogonophora) are a new Farmily of Polychaetes

                                                    ii.     Have no digestive tract

                                                   iii.     Have symbiotic sulfide utilizing bacteria (chemosynthesis)

                                                   iv.     Are absent from the W. Pacific vents

4.     Gastropod mollusks, Alvinoconcha hessleri are common in the W. Pacific

5.     unlike in the deep sea mud environments, the diversity of organisms is low

6.     Many of the organisms all appear to be ‘ancient’ – old members of their lineages

                                                    v.     suggested that these may be the areas in which life evolved -- archaea are there; thermophilic organisms may be most ancient; chemosynthesis (possibly pyrite forming energy flow)

                                                   vi.     sea lilies (crinoids) previously only known from fossils before found in the deep sea; monoplacophoran is a living fossil and a missing link between chitons and unsegmented gastropods (Neopilina) -- these are deep sea, not vent

                                                 vii.     barnacle Neolepas zevinae is a relict barnacle; along with the most primitive living genera of all 3 major barnacle suborders found at deep sea vents

                                                viii.     several ancient mollusks -- limpet Neomphalus fretterae.

                                                   ix.     may have been refuges from major planetary extinctions

E.    life history -- many vent organisms grow rapidly and attain maturity quickly; some tube worms measured to grow >85 cm/yr on East Pacific Rise; some polychaetes and vesicomyid clams may have synchronous gemetogenesis and discontinuous recruitment -- may be cued by tidal pumping at the vents; most species seem to have asynchronous gametogenesis

F.    several types of zonation at the vents

1.     high temperature flows (>50 oC) from sulfide chimneys that have a community dominated by alvinellid polychaetes

2.     moderate temperature (<30 oC) flows that have vestimentiferans

3.     low temperature (<5 oC) flows that have bivalves

4.     areas with no measurable flow that have suspension-feeders (polychaetes, barnacles, anemones) and no symbiont fauna

this zonation is not just due to physical characteristics, but to balance of larval settlement, predation and competition

initial vent succession (E. Pacific Rise):

bacteria grow

vestimentiferans grow (3 species – Tevnia jerichomana, Riftia pachyptila, Oasisa alvinae), in that order

mussels displace vestimentiferans – either divert the hydrothermal fluids or inhibit larval settlement

G.   each vent may only last for decades (although can last for several hundred years) and have drastic changes in species composition during that time -- how are they colonized?  Is there succession?

1.     most of the gastropod mollusks studied at the vents actually have nonplanktonic development -- low dispersal

2.     high rates of mortality observed for vestimentiferan worms (collapsing chimneys and fish predation) (44% in 26 days)

3.     some species on seamounts have larvae with lifespans of weeks to months, but recent study of unique currents around these seamounts showed that the larvae may be retained at the same seamount

4.     genetic differentiation – often not much within a ridge system, but more between ridge systems

H.   human effects -- some of the shrimp have 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

I.      economic interest in mining minerals at these sites? (iron, copper, zinc, gold); also use of bacterial bioremediation of waste sulfides from industrial processes already operating on a laboratory scale

VIII. Other unique deep water communities

A. Cold seep communities – 24 deep-sea locations in the Atlantic (off the gulf coast of florida), E and W Pacific and Mediterranean; especially on the continental slope and in sediment-rich areas; only discovered in past 15 years or so

1. not associated with hydrothermal vents

2. cold hypersaline brines

3. hydrocarbon seeps

4. also chemosynthetic based community – either sulfide or methane based (intracellular bacteria in the mollusks) -- so the endosymbionts are methanotrophic some have both types of endosymbionts

5. often the animals there are different than those at hot vents (211 seep species, only 13 shared between vents and seeps)

6. in the brine pools, a salt diapir pressurizes a shallow methane reservoir and release of gas excavates a brine pool

7. may be longer-lived than vent systems

B. Dead whales and other 'baitfalls'

1. whale carcasses rare: ~1 per 25 km2

2. another food patch in the deep sea -- estimated that it would take ~5000 years for that many calories to accumulate over a similar area of the seafloor by the sinking of photosynthetically derived organic material from the euphotic zone

3. decomposed by bacteria

4. unique communities; almost like at vents – specialized deep-sea mollusks

5. found quickly by many organisms (amphipods, fish); rapidly devoured by specialized, opportunistic faunas; grenadierfish can locate a food fall within minutes of its arrival on the seafloor


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