1Deep--Sea Fauna,Zonation and Biogeography

Who Lives in the Deep Sea?Bacteria/ArchaeaProtozoa Meiofauna (42-500 m)Macrofauna (>300 m)Megafauna (visible, >1 cm)Giants

2Bacteria

heterotrophic,autotrophic

aerobic anaerobic

sulfate reducersulfide oxidizermethane oxidizerFe, Mn oxidizers

in sedimentin gutson detrituson carcassesas symbiontson hard surfaces

BACTERIA AND ARCHAEA

Protozoa

ForaminiferaKomokiacea (superfamily)

Xenophyophores

3MetazoanMeiofauna

Nematodes Ostracods

Harpacticoid copepods

Gnathostomulida

Kinorhynchs

Oligochaetes

Loricifera

MacrofaunaPeracarid crustaceans

Brachiopoda

Bryozoa

Mollusca

Annelida:polychaetes Priapulida

Amphipods, isopods tanaids, cumaceans

4Megafauna - Echinoderms

Asteroids

Crinoids

Ophiuroids

Holothurians

Echinoids

Megafauna

Cnidarians

Mollusca

Annelida

Sponges

HagfishEnteropneust

Crustaceans

Echiura

5Humongofauna (Giants)giant squid

Munopsis

Kinetoskias

Colossendeis

Culeolus

Eurythenes

pycnogonids

ascidians

bryozoan

Site Depth (m) Substrate % Polychaetes Dominant

N. Carolina Margin I. 850 34% sand 43 ScalibregmaNC II. 20% sand 74 ChrysopetalidNC III. 31% sand 66 DorvilleidHorizon Guyot 1840 Foram Sand 47 ParaonidSanta Catalina Basin 1130 Mud 77 ParaonidCentral Pacific Seamounts 1480-3150 Calcareous muds 66-67 CirratulidSan Diego Trough 1230 Mud 76Rockall Trough 2200 ? 59HEBBLE 4820 90% mud 67 AmpharetidPorcupine Abyssal Plain >4500 35 Spionidae Central North Pacific 5500 Red Clay 55Aleutian Trench 7298 49

Polychaetes often comprise half or more of the macrofauna

6Key Zoogeographic FeaturesOriginal view - 1 province, cosmopolitan species

(no geographic boundaries)

Ekman 1953 - 4 zoogeographic zones:Atlantic, Indo-Pacific, Arctic, Antarctic.

Vinogradova - 1959, 62, 79. Species have limited distributionsOnly 15% of species occur in > 1 oceanOnly 4% of species occur in all ocean

Genetic methods reveal cryptic species; cosmopolitanism rare(France & Kocher 1996) Eurythenes gryllus is many species

But there is great similarity among oceans at the generic level.Genera are cosmopolitan

Of 143 isopod genera in the Pacific , 134 are present in the Atlantic

Desmosomatidae (Isopods): North vs South Atlantic - same 12 generaNorth Pacfic vs Atlantic - Pacific is missing 2 genera and=77% similarity has one not in the Atlantic

Asellote isopodsPoore et al. 94 - 67% of 98 genera on the SE Australian slope arein the Atlantic

Ophiomusium (brittle star) worldwide at mid to slope depths.

7Vinogradova, 1979. Zoogeographic divisions of the

abyssal and hadal zones of the world

Distinct hadal fauna (Belyaev 1959, 1989)more amphipods, polychaetes, bivalves, echiurids, holothurians

Origins of Deep-Sea FaunaAntarctic or shallow water origins thensubmergence

Deep origins and Antarctic emergence(Ilyarachnid isopods) in taxa withdiversity centers in the deep sea.

Isolated basins have endemics only atspecies level, suggestinginvasion from shelves and recentevolution.

Red Sea and Sea of Japan haveeurybathic species from Indian& Pacific oceans.

A. High latB. EquatorC. Mid lat

8What is Zonation?Pattern of uniform change in species

Step-like boundaries between regions ofhomogeneous composition.

Current usageNon-repeating, sequential pattern of species replacement

measurable as changes in the overall rate of changein faunal composition.

Why should we care about zonation?Resource exploitation is increasing (fisheries, petroleum)

Sound management demands understanding of distributions

Zonation Terminology

Shelf

Upper Slope

Lower Slope

Continental Rise

Abysssal

meters200

500

1000

3000

4000

6000

Epipelagic (euphotic)

Mesopelagic (disphotic)

Bathypelagic (aphotic)

Benthopelagic

Bathyal

Hadal

9Zonation in the PastSince Challenger Expedition:

Scientists have recognized that species change much more rapidly with depth down the continental margin than horizontally.

Depth-related changes in the ocean are considered one of the greatest environmental gradients on this planet (Gage and Tyler ).

What can generate zonation in the Ocean?

What can generate zonation in the Ocean?

TemperatureSalinity

Bottom typeFood levels

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Challenger/Sars expeditionsMurray and Hjort (1912)

3 ZONES:

Shelf (to 200/300 m)

Archibenthic transition (600/800 - 2000/3000) (bathyal)(based on megafauna, topography, temperature)

Abyss(upper boundary set at 4oC isotherm - Bruun 1957)(lower boundary at 6000 m - topography)

There is little areabetween 1000 & 2500 m

Yet, this is the zone of highest diversity

shelf

transition

abyss

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Controlling Gradients: LightLight: present to 1000 mChildress 1995: the use of vision by fishes, crustaceans, squidabove 1000 m elevates metabolic rate and affects forms present

Controlling Gradients: Hydrostatic pressureonly variable directly related to depth (10 m = 1 atm)

pressure accelerates reactions in which the molar volumeof the products are less than the molar volumes of thereactants.

Pressure retards reactions in which there is a volumeexpansion (Le Chatelier effect)

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Increased dissolution of calcium carbonateIncreasing metabolic cost associated with maintainingcarbonate structures at depth (molluscs,foraminiferans, echinoderms show effects)Influence on chemosynthesis based on H2S? Stabilityof gas hydrates (>450 m)Protein structure, membrane fluidity, lipid contentDifferent propreties of gellatinous/membranousmegafauna?

A piezo barrier to downward colonization: 500-1000m, 2000-3000m

Effects of pressure in the deep sea

Controlling Gradients: Temperature55oN to 55oS - Warm, low density upper layerThermocline may form a barrier. Much of the deep sea is 2-4oC

Increasing temperature increases chemical reaction rates.2 to 3 x rate increase with 10o C temperature increase.

Adaptations to cold: increasing concentrations of enzymes adopting enzymes effective at low temperatures incorporating modulator compounds that help maintain

enzyme reactions over a range of temperatures

Are water mass effects the result of temperature (?)

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Controlling Gradients: Organic FluxSince Forbes (1859) - importance of food recognized.Decreasing food input with depthDifferent rates of mixing within sediment with depth

Food effects on zonation may be modified by competitors.Effects of OM flux include changes in sediment geochemistry.

High flux depletes oxygen. .

TROX model -

foraminifera distributions based on oxygen and food

TROX model-applied toforaminifera

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Controlling Gradients: Oxygen

Oxygen minima at 100-1000 m (

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Pelagic Zonation

Governed largely by light but in some places temperature.

Evidence of the importance of competition comes from non-overlapping distributions of related species

Ontogenetic zonation is commonOften larvae are found shallowest and gravid females deepest(Tradeoffs between food and mortality from predation)

Zonation may be forced by physiographyof the ocean floor

SHELF BREAK - Boundary between shelf and deep-sea fauna.Referred to as the mud line by John Murray (1895) = upper limit for muddy bottom, deep-sea conditionsmay occur at 200 m (W. Europe), 500 m ( Antarctic)or few m (fjords)

HEMIPELAGIC VS PELAGIC SEDIMENTS Ekman (1953)Break between hemipelagic (with considerable terrigenous input)and pelagic sediments is a key zoogeographic boundary.

ANTARCTIC - Little difference between shelf and deep-sea faunas

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Bathyal (200-3000 m) vsAbyssal (4000 - 6000 m)

Bathyal has shallow and deep faunasAbyssal with true deep faunas.

But new data by Rex for molluscs suggests that most abyssal species also occur in the bathyal realm and few are endemic. (Rex et al. 2005; Am. Nat. 165).

Menzies:Greater continuity of shelf and bathyal faunas at high latitudes and of bathyal and abyssal faunas at low latitudes. Why?

Means of Evaluating ZonationMultivariate Classification Procedures - rely on similarity matrices

similarity coefficients: Percent Similarity Coefficient, Bray Curtis coefficient, Normalized Expected Species Shared [NESS]

Cluster Analysis -highly dependent on parameters chosen(can achieve multiple forms of clustering with same data set)

Ordination - employs linear models, best when only a smallpart of the depth gradient is being examine.

Vertical ranges of species zonal breaks are thosewhere greater number of upper and lower depth limits occur(requires large data set)

Cumulative species curves

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Porcupine Seabightzonalbreaksarethosewheregreaternumberofupperandlowerdepthlimitsoccur

Cascadia Basin

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What Changes with Depth? Taxonomic composition Diversity Density, Biomass Body Size Trophic structure

Megafauna - New England Margin(Hecker 1990- Photographic survey)

(284,692 indiv. 94,380 m2 of seafloor)

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Upper slope: to 700 m Dasmosmilia lymani, Flabellum alabastrum Upper-middle slope: (1100-1200 m)Geryon quinqueidens, SynaphobranchusNezumia, Phycis chesteri, Glyptocephalus

Transitional Lower Middle Slope: 1500-1700Distichoptilum gracile + Anemones

Lower Slope: Ophiomusium lymani, Cerianthid anemone,Distocptilum gracile, Echinus affinus

Hecker, 1990

Species replacement with depth was gradual in flat areas and abrupt in steep areas.

Geographic variation was observed related to glacial inputs/hard substrate.

Lowest densities on middle slope

Depth ranges are narrow on upper slope and broad on lower slope

Hecker, 1990

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HECKER, 1990

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ExamplesAlong Gayhead Bermuda Transect Gastropods and cumaceans show narrower depth ranges than polychaetes and brittle stars.

In N. Atlantic, sharpest changes are at shelf, and a zone of 400-1000 m is reflected in megafaunal changes (Sanders, Grassle, Haedrich, Rex).

N. Atlantic studies support a step model, with biggest changes at 200 m, 400-600 m, 1000 m, 1400 to 1600 m, 2000 m.

Echinoderms 800-1200 m and 1800 m - Rockall Trough. Agree with Bay of Biscay (Sibuet).

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Pacific ExamplesIn North Pacific Fish (Oregon/Washington) (Pearcy et al. 1982)

New species appear at: 400-700 correspond to OMZ boundary. 1900 to 2000m.

Species disappear at500-900 m2800-3100 m (floor of Cascadia Plain)

Holothurians show only gradual replacement (Carney & Carey 1977)

Mediterranean - (Emig 1997)Expression of upper bathyal zone is directly related to slopephysiography, thus slope profile should be given in studies.

Upper bathyal - belts of suspension feeders related to flow structure

Maximal density in upper bathyal (higher than shelf)

Zones: 100-600 m, 600-1300 m, 1400-1600 m, 1600-2000, > 2000

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Carneys OverviewCarney 2005

Upper BoundaryBiota Shelf to

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Compositional Zonation

MACROBENTHOSShallower Taxa -Amphipods, molluscs, polychaetes

Increasing in deep water --tanaid and isopod (peracarid) crustaceans-aplacophorans (mollusca)-sipunculans, priapulids

MEGABENTHOSSponges more common on the slope, echinoderms(holothurians, asteroids,brittle stars) below

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Zonation of Body SizeWITHIN TAXALarger size species found at deep end of taxon range

Asellote isopods - smallest genera < 250 m, largest > 1000 mTanaids,GastropodsForaminifera.

ACROSS TAXADecrease in average body size with depth - replacement of large by small species(except fish in NW Atlantic)

Lampitt et al. 1986 -Porcupine Seabight

At shallow depths large species dominate biomassAt deeper depths small species dominate biomass

***** Small species - shallow:deep

11% vs 34% of biomass 93% vs 98% of numbers

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Zonation of Feeding ModeReduction in suspension feeding &increase in deposit feeding with depth

Replacement of sedentary deposit feeders with mobile deposit feeders at deeper depths. (Fauchald and Jumars 1979)

50:50 surface and subsurface-deposit feeders at depth.

Taxon Rates of Species Change with DepthDo big and little animals show similar zonation?

Is zonation pattern taxon specific?

Rex 1977

Megafauna changed most rapidly with depthbut holothurians changed slowly (Carney and Carey 1982)

Predatory gastropods changed at an intermediate rate

Infaunal polychaetes changed slowest

Higher trophic levels have narrower bathymetric zones

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Testing Causes of ZonationBarnacle Manipulative Experiments

Dayton et al. 1982

-transplanted 250 Bathylasma coroliforme from 400 m to 25-40 m. Normally live > 100 m

Individuals survived for 2 y and produced larvae

Authors argued water movement restricted distribution.

Faunal Age Change with DepthOriginal belief :

the deeper the zone the more ancient the fauna(primitive protobranch bivalves, brotulid fishes)

primitive generalists do best

For holothurians and starfish,bathyal forms are most primitive,

abyssal and hadal forms are specialized

Radiation of diversity in the deep sea occurs for few taxaIlyarachnidae (isopods)

Early belief - diversification in Antarctic then submergence to deep

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Horizontal/Lateral ExtentDo vertical zonation patterns persist over wide horizontal ranges?

Wide lateral ranges off S. Australia (bathed in homogeneous Antarctic intermediate water).

Atlantic margin - more restricted lateral rangesAssociated with eastern, western boundary water masses

And strong gradients in productivity

Gayhead-Bermuda transect bivalves (Allen and Sanders 1996)Fauna more similar between adjacent basins than depthsIncreasingly cosmopolitan than depth.