Seamounts

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Seamounts

• Jessica Arbour and Rowan Meyer-Macaulay

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• Seamounts are defined as circular or elliptical
  features of volcanic origin, regardless of size.
  (Epps et al. 1989)

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Hot Spot Hypothesis

• As a plate passes over a magma source that is
  fixed with respect to the mantle, islands will
  form like plumes of smoke.
• 3 interrelated aspects
• Kinematics
• Plate Interaction
• Chemistry

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Assumptions

• Kinematics
• Magma sources are securely anchored in the deep
  mantle and therefore can be used as a reference
  point
• Plate Interaction
• Little mechanical interaction between the plume
  and oceanic lithosphere

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Chemistry

• Isotope ratios show a gradual change from normal
  mid-ocean basalt values to more radiogenic
  values as hotspot islands were approached
• Link between geophysical plumes and the idea of
  mantle heterogeneity

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Flow around seamounts

• Depends on
• Current Speed
• Stratification
• Latitude
• Morphology of seamount or seamount chain.

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Flow around seamounts

• Seamounts effect
• Internal wave generation
• Eddy formation
• Local up welling
• Taylor columns

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Flow around seamounts

• Taylor columns
• Closed, streamlined anticyclonic vortex
• Remain trapped above seamounts
• Transport nutrients into the euphotic zone

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Flow affects on primary productivity

• Residence time
• Days affects only primary producers
• Several weeks may affect zooplankton
• Months micronekton

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• Significant differences in abundances and species
  composition in waters above seamounts and the
  surrounding waters.
• Southeast Hancock Seamount
• Maurolicus mulleri and Gnathophausia longispina
  dominant in upper waters around seamount, squid
  Iridotenthis iris dominant in deeper waters.
  (Boehler and Seki, 1984)

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Cobb Seamount (Dower et al. 1991)

• Measures of Chlorophyll a above seamount were
  0.1-1.3 mg m-3
• Measures in surrounding waters were gt0.28 mg
• m-3

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Stratification

• Reduces topographic effect on flow
• Seamounts extending into stratified parts of the
  ocean give rise to intricate fluid dynamics

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Stratification

• Direction of flow in each layer
• Increased Stratification decreases the heights of
  the Taylor columns
• Different affects depending on number of seamounts

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Flow around seamounts

• Variety is due to
• Difference in shape
• Difference in size/height
• Interaction with impinging flows

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Biogeography

• Provincial
• Species restricted to the region in which the
  seamount is located
• Widespread/Cosmopolitan
• Species occur both beyond the immediate region
  and worldwide
• Exotic
• Species are rarely or never before found in the
  immediate region
• Endemic
• Species confined to a particular seamount or
  several of the same chain

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• Over 596 species of invertebrates in 16 phyla
  from sampled from 60 different seamounts
• 92 (15.4 ) were new species
• 55 species of plants on 4 seamounts
• 3 were new species

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Diversity

• Heights extend sometimes from abyssal plains to
  the euphotic zone
• Composition of substrata
• Feeding grounds

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• Kaufman et al
• 2 seamounts, Horizon Guyut and Megellan Rise
• Found 52 megafaunal morphytes, 46 invertabrets
  and 6 species of teleost fish on Megellan
• Xenophyophores were most common on both with
  densities as high as 189 individuals per 1000m2

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• Shallow seamounts summit depth lt1000m tend to
  support equal numbers of provincial and
  widespread/ cosmopolitan species
• Deep seamounts summit depth gt1000m are typically
  dominated by widespread/cosmopolitan species
• Degree of endemism does not seem to have a depth
  correlation

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Factors affecting distribution

• Substrate availability
• Hydrodynamic factor
• Nutrient availability
• Bioturbation
• Depth

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Distribution and Abundance of Seamount Fauna

• Several factors influence the species composition
  and relative abundances of seamount fauna
• Recirculation patterns
• Taylor cap formation
• Local water currents
• Dispersal from other seamounts or coastal
  environments
• Seamount distribution
• Stepping stone hypothesis
• Topographic features of seamounts
• Enhanced flow, turbulence

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Recirculation patterns and larval dispersal

• Retention and residence time
• Important for maintenance of local populations
• Closed circulation patterns increase the
  residence time of water masses and retention of
  larvae.
• Mullineaux and Mills, 1997
• Examined retention of larvae over Fieberling
  Guyout (E Tropical Pacific)

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• Larvae dominated by cnidarians, polychaetes and
  gastropod
• Species composition differed from typical abyssal
  Pacific sediment dwelling fauna
• Colonization of polycarbonate plates highest on
  summit
• Consistent with retention within circulation cell

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Larval strategies

• Types of development
• Direct development
• Lecithotrophy
• Planktotrophy

• Traditional view long planktonic duration
  broader geographic range
• Parker and Tunnicliffe (1994) studied larval
  strategies on the Cobb Seamount
• Defined short term (lt2 weeks), medium term
  (2-8weeks) and long term (gt8 weeks) pelagic
  larvae

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Parker and Tunnicliffe (1994)

• Determined of each larval strategy from
  seamount fauna (top)
• 26.5 direct releases
• 37.6 short lived larvae
• 15 of 89 sp. - larval periods gt2 weeks
• Differed from typical composition (bottom)
• Cobb Seamount was an island
• Is the composition of larval strategies a relict
  of a coastal ecosystem?

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Water flow patterns near Cobb seamount

• Recirculating water current over Cobb seamount
• Circulating water is replaced every 17 days
• Explains dominance of species with larval periods
  shorter than 14 days
• How do direct developers reach Cobb Seamount?

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Kelp Rafting

• Kelp forests are abundant along western North
  America
• Kelp dislodged in storms form rafts
• Adults of epiphytic species may survive 100 days
  on a raft

• Most epifaunal species from the Cobb seamount are
  known from kelp forests
• Migration vector for direct developers and
  species with short larval periods

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Global Seamount Species Distributions

• Seamounts may provide stepping stones across
  vast expanses of deep basin habitat
• Temporal scales
• Species from subsiding islands transfer to
  younger islands, slowly migrating across deep
  basins scale of millions of years
• Seamounts may act as waystations for species
  dispersing across deep basins in steps tens to
  hundreds of generations

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• Many Indo-Pacific species are allied with distant
  seamounts from the central Pacific and Eastern
  South Pacific.
• Laemonema rhodochir (Codling fish)
• Absent from the Western South American Shelf
• Stepped across the Pacific

Adapted from FishBase
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• Spotted Gunard (Pteryoptrigla picta)

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Endemism on Seamounts

• Endemism on seamounts
• 12-15 up to 22-36
• May relate to longevity of habitat
• Circulation patterns
• Reinforce local populations, partially restrict
  dispersal off seamount
• Geographic barriers
• Vertical barriers to dispersal

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Geographic Barriers

• Amphipod Eurythenes gryllus
• Found deeper than 3500m in Atlantic and Pacific
• Recently identified from 3 seamounts
• Brooder with no planktonic larvae
• Bucklin et al (1987) - Horizon Guyout
• Unusual habitat for this species (water flow
  17cm/s basin currents lt6cm/s)
• E. gryllus would have to have swum up the seamount

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• Bucklin et al 1987
• Seamount E. gryllus were larger and less abundant
  than basin E. gryllus
• Populations from seamount crest genetically
  distinct from nearby basin populations
• High genetic distinctiveness of crest population
• Either differential selection or
• Low interbreeding
• Reproductive barrier
• Migration to crest infrequent event
• Vertical barrier to reproduction

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Local Flow Effects on Abundance

• Seamounts possess complex topographic features
  which effect water flow patterns
• Current acceleration favored for recruitment and
  growth
• Higher flow -gt more larvae moving past a spot
• Higher flow -gt increased food access for young
  recruits
• Jasper Seamount multipeaked summit
• Dominated by sedimentary suspension feeders

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• Genin et al. (1986) - Black coral Stichopathes
  sp. on Jasper Seamount
• Colonies 500-1150m, up to 20 colonies/m2
• Abundance higher near peaks than mid-slope sites
  from similar depths
• High density on pinnacles

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Flow effects on infauna

• Levin and Thomas, 1989
• Horizon and Magellan Seamounts
• Both summits capped by calcareous ooze
• Horizon perimeter exhibited highest flow
  velocities
• Infauna dominated by polychaetes
• 66-67 of cap sites
• 47 perimeter site

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• Levin and Thomas (1989)
• Cap polychates
• 80 motile
• 41 carnivores (M cap)
• Perimeter polychaetes
• 47 motile, 23 sessile
• Deeper vertical distribution
• Lower infaunal activity
• Soft and hard substrate fauna have opposite
  responses to increased flow

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Conservation of Seamount Fauna

• Short-lived, high intensity seamount fisheries
• Deep sea fish - high energy efficiency strategy
• low locomotion
• 25-50 energy available to growth/reproduction
• Seamount fish species
• Large muscle mass
• 5 energy available to growth and reproduction
• Seamount fish aggregate in large schools other
  deep sea fish disperse over large areas

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Targeted Fish Species

• Extreme Longevity
• Orange Roughy (100 years), Sebastes spp. (75
  years)
• Low fecundity
• Infrequent, episodic recruitment
• Dependant on flow of food past seamounts
• Pelagic Armorhead
• Soviets and Japanese (1967)
• 200 000mt landed annually
• from Emperor Seamounts
• 1982 commercially extinct

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• Orange Roughy (Hoplostethus atlanticus)
• Metabolic demands 10X higher than available
  through primary production above seamounts
• Sustainable catch is 1-2 of biomass
• Serial depletion of stocks to maintain fishery
• Tasmanian stock 50 year average age

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Seamount Coral Conservation

• Seamount benthic ecosystems are often dominated
  by corals
• Trawling on seamounts destructive to coral
  populations
• Coral harvests for jewelery
• Tangle netting
• Removal of coral reefs reduces habitat
  heterogeneity
• Biomass of unfished seamounts was 106 greater
  than fished
• sp 46 greater on unfished

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Seamount Conservation

• Highly sensitive ecosystems
• Slow recovery
• Many reside within international waters
• Management is difficult
• Some management programs and marine reserves
• Bowie Seamount a Canadian Marine Protected Area
  as of April 2008

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Future Research

• Species composition and abundances are effected
  by a range of biological and physical gradients
• Comprehensive sampling of seamount fauna
• Life histories of endemic species are unknown
• A greater understanding of seamount ecosystems is
  essential to conservation