attached Includes 98% of all marine species

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1 The Benthos By definition: organisms (animals and plants) that live on, in or attached to the sea floor Includes 98% of all marine species Coral Reefs alone contain 25% of all marine species! Community composition determined by benthic composition

2 Benthic vs. Pelagic Benthic organisms are not adapted to wide ranges in pressure There are very few transparent organisms Generally stay to a smaller spatial area (they don t move around as much) We classify them in relation to the type of shoreline or bottom structure

3 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 adult invertebrates cling to the bottom, but babies are at the mercy of the currents.

4 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 survive or not is largely dependent on the availability of food or suitable habitat (subtrate) in that environment.

5 Benthic Substrates Rocky, sandy, or muddy intertidal Muddy deposits or hydrothermal deposits in the deep sea Biomass is closely related to surfacewater primary production

6 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

7 Primary Production Benthic Biomass

8 Many marine species have bipartite life histories 1. Planktonic dispersive early stage 2. benthic or site attached adult stage PLANKTONIC LARVAE SETTLEMENT *Larva: an independent, often free-living, developmental stage that undergoes changes in form and size to mature into the adult; especially common in insects and aquatic organisms. (From a Latin word meaning "ghost" or "mask.") REPRODUCTION BENTHIC ADULTS

9 More facts of nature: you don t see the bipartite lifestyle often on land

10 Marine organisms: complex life cycles

11 Sea urchin Starfish Sea cucumber Bryozoa Phoronid Polychaete Gastropod crabs barnacle nemertean

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14 Bipartite Lifestyles A major component of benthic ecology deals with recruitment The larvae are often very different from the adult life stage While planktonic, many larvae do not consume food (they rely on internal reserves) Some larvae utilize the DOM, acting as (essentially) very large bacteria

15 Demographically closed Retention Pelagic fisheries perspective Hjort (1914) Stock-recruitment relationships

16 Demographically closed Retention Benthic ecology perspective Thorson (1950) For organisms with multi-phase life histories, understanding the biotic and physical mechanisms that regulate abundance/distribution of adults requires integrating the dynamics and distributions of several aspects of the life cycle. Dispersal Larval pool Demographically open

17 Demographically closed Retention Tagging Studies Swearer et al Jones et al (Nature) Genetic pop. structure: Barber et al (Nature) Larval pool Larval pool Mixture of larval inputs Dispersal Demographically open

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21 Larger reserves may eliminate fisheries benefits

22 Reserves and Species Persistence Reserves can meet conservation goals in two ways: Large Individual Size > mean dispersal distance 2-3x mean dispersal distance with advection Large Total Network Area From Botsford, Hastings, and Gaines Ecology Letters

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24 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 m 2 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

25 Abundance and diversity The main determinant of spatial and temporal patterns variation in vent flow Results in variations in: Temperature Chemical composition of the fluid Bacterial production

26 Spatial patterns Within 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 H 2 S and O 2 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

27 East Pacific Rise 9 ºN Tubeworm zone Bivalve zone Serpulid zone Periphery

28 Spatial patterns Between 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

29 Temporal (successional) patterns East Pacific Rise 9 ºN (Shank et al. 1998) April 1991: eruption Diffuse flow 22-55ºC Increased H 2 S (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 m 2, separated by m) Associated Lepetodrilus Bythograea thermydron; amphipods; zoarcids 32 months Diffuse flow 16-35ºC Reduced H 2 S (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

30 East Pacific Rise 9 ºN (continued) 42 months Diffuse flow 20-32ºC Reduced H 2 S ( mmol kg -1 ) Cessation of flow in some fissures Riftia doubled in density Tevnia colonization continued Mussels 1-5 ind m months Diffuse flow 10-20ºC Reduced H 2 S ( 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

31 Shank et al. (1998) Microbial material 11 months: Tevnia 32 months: Riftia overtaking Tevnia 42 months 55 months

32 Larval dispersal and supply Larval retention (ephemeral habitat) vs. larval dispersal (dilution) JdFR separated from EPR by > 2000 km

33 Larval dispersal and supply 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)

34 Mesoscale hydrodynamic processes (km s 100s km s) Larvae near the bottom can travel between vents (100s m s) within a 6-h tidal excursion Larval entrainment in the hydrothermal plume diluted 10 4 x by volume vertical velocities = 10 cm s -1 vertical volume fluxes = 500 m 3 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

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