The Benthos

• By definition: organisms (animals andplants) that live on, in or attached tothe sea floor

• Includes 98% of all marine species• Coral Reefs alone contain 25% of all

marine species!• Community composition determined by

benthic composition

Benthic vs. Pelagic

• Benthic organisms are not adapted towide ranges in pressure

• There are very few transparentorganisms

• Generally stay to a smaller spatial area(they don’t move around as much)

• We classify them in relation to the typeof shoreline or bottom structure

DIFFERENCES BETWEEN LAND AND OCEAN:

Ocean currents move ocean animals around.

Small animals in the ocean can be pushed around by currents, and may not be able to choose where to go. Adult fish and mammals can swim strongly, and adultinvertebrates cling to the bottom, but babies are at themercy of the currents.

Standard ecological theory (land):Animals are found in comfortable environments

Marine ecological theory:Animals may be found where the currents put them.Depends on animal’s lifestyle. Whether they surviveor not is largely dependent on the availability offood or suitable habitat (subtrate) in thatenvironment.

Benthic Substrates• Rocky, sandy, or muddy intertidal• Muddy deposits or hydrothermal

deposits in the deep sea• Biomass is closely related to surface-

water primary production

Benthic Diversity, Biomass

• Benthic diversity is largely controlled by– Temperature (more in warmer waters)– Currents (this affects the benthic structure)– Wave Energy (infauna vs. epifauna)

• Benthic Biomass is largely controlled by– Water column primary productivity

Primary Production

Benthic Biomass

Many marine species have ‘bipartite’ life histories

1. Planktonic dispersive early stage

2. benthic or site attached adult stage

BENTHIC ADULTS

REPRODUCTION

SETTLEMENT

PLANKTONICLARVAE

*Larva: an independent, often free-living, developmentalstage that undergoes changes in form and size to matureinto the adult; especially common in insects and aquaticorganisms. (From a Latin word meaning "ghost" or"mask.")

More facts of nature: you don’t see the bipartite lifestyle often on land

Marine organisms:complex life cycles

Seaurchin Starfish Sea cucumber

crabs

BryozoaPolychaete

Gastropod

Phoronid

barnacle

nemertean

Bipartite Lifestyles

• A major component of benthic ecology dealswith recruitment

• The larvae are often very different from theadult life stage

• While planktonic, many larvae do notconsume food (they rely on internal reserves)

• Some larvae utilize the DOM, acting as(essentially) very large bacteria

Retention

Demographically closedPelagic fisheries perspective

Hjort (1914)

Stock-recruitment relationships

Retention

Demographically closed

Larval pool

Dispersal

Demographically open

Benthic ecology perspective

Thorson (1950)For organisms with multi-phase lifehistories, understanding the biotic andphysical mechanisms that regulateabundance/distribution of adults requiresintegrating the dynamics and distributionsof several aspects of the life cycle.

Larval pool Mixtureof larvalinputs

Tagging Studies

Retention

Demographically closed

Larval pool

Dispersal

Demographically open

Swearer et al. 1999Jones et al. 1999 (Nature)

Genetic pop. structure:Barber et al. 2000 (Nature)

Largerreserves may

eliminatefisheriesbenefits

Reserves and SpeciesPersistence

From Botsford, Hastings, and Gaines. 2001. Ecology Letters

• Reserves can meetconservation goalsin two ways:– Large Individual

Size• > mean dispersal

distance• 2 - 3x mean

dispersal distancewith advection

– Large TotalNetwork Area

Abundance and diversity

The vent fauna comprises a list of mainly new and undescribed species 1991: 223 of the 236 species listed were new to science 1998: 443 species were listed Preponderence of three phyla: molluscs, arthropods and annelids

The list of species is still growing deep sea: 85 spp. on 61 manganese nodules at 2 sites vents: 236 spp. from ~30 dives intertidal boulder field: 214 invertebrate spp. in 9 0.01 m2 samples temperate corals: 309 spp. on 8 coral heads

most species are endemic to vents

some deep-sea taxa are absent from vents

most species are sessile with a few highly mobile ones

~75% of species only occur at one site

The main determinant of spatial and temporal patterns variation in vent flow

Results in variations in:• Temperature• Chemical composition of the fluid • Bacterial production

Abundance and diversity

Spatial patternsWithin vent fields

Diffuse flows: density and composition decrease concentrically

e.g. EPR (e.g. 9 ºN)

Tubeworms at vent openings: the obturaculum has to be exposed to absorb H2S and O2 in big clusters or small tufts

Mussels grow everywhere form patches or beds (100s-1000s of individuals)

Clams in cracks (for ideal positioning of foot and siphon) between lava pillows or on sheets away from high temperatures in areas of low fluid flux;

Crabs and fish very motile within or near animal clumps to distances of up to 500 m

East Pacific Rise – 9 ºN

Tubeworm zone Bivalve zone

Serpulid zone Periphery

Spatial patternsBetween vent fields

EPR, 21 ºN (Hessler et al. 1985) Two fields separated by few km One Calyptogena-dominated The other (higher flow) Riftia-dominated

Galapagos Rift (Hessler and Smithey 1984) Sites within 500 m of one another Rose Garden: dense vestimentiferan and mussel beds Garden of Eden: few vestimentiferans and mussels, no clams Mussel Bed: few vestimentiferans, mussels very abundant

MAR: no great spatial variability Broken Spur (29 ºN), TAG (26 ºN) and Snake Pit (23 ºN): dense assemblages of shrimp and few mussels Lucky Strike (37 ºN): single-taxon assemblages of mussels Logatchev: the only known vent field with live clams

Temporal (successional) patterns

East Pacific Rise – 9 ºN (Shank et al. 1998)

April 1991: eruption Diffuse flow 22-55ºC Increased H2S (1.9 mmol kg-1) and Fe (0.151 mmol kg-1) White filamentous bacterial mats, 1-10 cm thick, “snowstorms”

11 months Reduced vent emissions Reduced thickness of bacterial mats Patches of Tevnia (1-4 m2, separated by 2-340 m) Associated Lepetodrilus Bythograea thermydron; amphipods; zoarcids

32 months Diffuse flow 16-35ºC Reduced H2S (0.98 mmol kg-1) and Fe (0.024 mmol kg-1) Great spatial variability in diffuse flow Dead tubeworms in areas of ceased flow No bacterial mats Colonies of Riftia, over colonies of Tevnia, and elsewhere Increase in faunal diversity

East Pacific Rise – 9 ºN (continued)

42 months Diffuse flow 20-32ºC Reduced H2S (0.4-0.8 mmol kg-1) Cessation of flow in some fissures Riftia doubled in density Tevnia colonization continued Mussels 1-5 ind m-2

55 months Diffuse flow 10-20ºC Reduced H2S (0.19-0.3 mmol kg-1) and Fe (0.011 mmol kg-1) Some re-openings of flow Great increase in abundance of Riftia; no change in Tevnia Increased complexity (microhabitats), increased abundance of limpets Great increase in mussels (covering tubeworms and cracks) Great increase in serpulids Some anemones

Shank et al. (1998) Microbialmaterial

32 months:Riftia overtakingTevnia

11 months:Tevnia

42 months

55 months

Larval dispersal and supply

JdFR separated from EPR by > 2000 km

Larval retention (ephemeral habitat) vs. larval dispersal (dilution)

Stepping stone model A population divided into discrete subpopulations Dispersal occurs primarily between neighboring subpopulations Gene flow decreases as the number of steps between subpopulations increases

Island model All subpopulations are equally accessible to dispersing larvae Long-range dispersal among subpopulations predominates No relationship between genetic divergence and geographic distance

Examples SS: tubeworms and shrimp at Galapagos and EPR (Riftia pachyptila, Tevnia jerichonana, Oasisia alvinae, Ventiella sulfuris) IM: tubeworms at JdFR (Ridgeia piscesae) mussels, clams and limpets at EPR (Bathymodiolus thermophilus, Calyptogena magnifica, Eulepetopsis vitrea, Lepetodrilus pustulosus)

Larval dispersal and supply

Larvae near the bottom can travel between vents (100s m’s) within a 6-h tidal excursion

Larval entrainment in the hydrothermal plume diluted 104x by volume vertical velocities = 10 cm s-1

vertical volume fluxes = 500 m3 s-1

When plumes become neutrally buoyant they spread laterally they form vortex pairs

retention of larvae within the plume

vortex shedding

delivery of a concentrated patch of larvae

Mesoscale hydrodynamic processes (km’s – 100s km’s)