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31 Cards in this Set
- Front
- Back
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What is the epipelagic zone?
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Thin top layer of ocean where photosynthesis occurs
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Logistical Contraints of Studying the Epipelagic Zone
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01: Experimentation Difficult
- Hard to study because life is in moving fluid - Organisms are plankton (transported by current flow) or nekton (can transport themselves) - Constantly changing location 02: Sampling Challenging a. Done remotely - Many devices sample selectively - Many organisms are delicate crushed or killed b. Local environment is constantly changing - No boundaries, except shores - Orgs constantly shift position due to currents, upwelling, mixing - Shifts can be rapid c. Spp Composition highly variable at any locality - Difficult if aim is to study particular species 03: |
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How is the epipelagic zone studied?
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1. Field Experimentation
2. Extrapolate From Fresh Waters 3. Extrapolate from Lab to Field 4. Correlation Approach |
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Field Experimentation
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1. Manipulate whole water masses
- ex. does iron limit prod in epipelagic zone? --> Dispense iron granules via ship in patches and measure diatom production in enriched vs. control patches 2. In Situ Mesocosm Expts - Giant containers that capture portion of water column that can be manipulated --> Alter trophic composition, nutrient regimes, etc. - Can have replicates of many different treatments |
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Extrapolate From Freshwater Systems
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- Easier to manipulate an entire lake
- Extrapolate with caution however because some processes occur in the ocean that do not in lake and vice versa |
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Extrapolate From Lab to Field
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- Done in all ecological fields
- Problematic: a. Realism: difficult to keep epipelagic orgs alive as well as behaving and functioning normally in a lab b. Scaling Up: spatial and temporal scales very different from lab study and real world |
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Correlation Approach
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Explore relationship between variables using observational data, no manipulation
Correlation does NOT mean causation |
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Trophic Structure: Food Webs
( x --> y --> z)? |
short and simple
phytoplankton --> zooplankton --> nekton relatively few secondary consumers |
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Food Web is Microbe Based
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- one drop seawater contains 1 mil bact, 10 mil viruses
a. Viroplankton - Poorly understood, <30 nm to 3 microm - bacteriophage for reproduction - require hosts - recycle nutrients by lysing bacteria - killed by UV light b. Bacteriopankton - 50% C in marine food webs goes through bacteria - 10% marine bacterial spp cultures |
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Trophic Forms of Bacteria in Food Web
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Autotrophic: photosynthetic (ex. blue green algae)
Heterotrophic: take up DOM or other bacteria Mixotrophic: can photosynthesize and feed |
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SAR 11 clade
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pelagibacter ubique
most abundant bacterium in world, worldwide distribution, smallest cell replicating cell known |
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Phytoplankton: Purpose and limitations?
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- Fix lots of CO2
- Poduce 90% of Earth's O2 - Help make clouds - Limited by: P, N, silica (diatoms), iron, trace elements |
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Can phytoplankton be harnessed to control greenhouse gases?
SOIREE Expt |
- phytoplankton consume CO2 when fixing C
- iron limited - try seed ocean with iron to create phytoplankton blooms to take CO2 out of atmosphere? - Southern Ocean Iron Release Expt: released iron tracer over 100 km^2 - monitored 2 weeks - got large bloom but C not transferred to deep ocean --> Seeding ocean with Fe will NOT help sequestetr CO2 |
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How do phytoplankton help create clouds?
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- damaged by UV light
- produce chemical antioxidant dimethylsulfoniopropionate (DMSP) as protection - DMSP breaks down to dimethylsulfide (DMS) - DMS goes into air and serve as nuclei for water droplets that form clouds |
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Trophic Structure: Abundance of epipelagic zone
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- abundance is largely controlled by physical processes, esp those influencing nutrient flux
- strong bottom up control by nutrients (primarily N, P, Fe) - nutrientys --> phytoplankton -->zooplankton --> nekton |
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What controls nutrient flux in epipelagic zone?
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Nutrient source: deeper waters where remineralization occurs
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What is the pattern of abundance?
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very high primary production but relatively low phytoplankton standing stock
Reason: most primary production consumed by epipelagic animals |
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Abundance -- Plant: Animal Biomass Ratio
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1. Terrestrial Systems: I gr plant biomass : 0.001 gr animal biomass
2. Epipelagic Systems: I gm plant biomass : 20 gm animal biomass - High animal biomass sustained by high primary production (most eaten) - High primary production sustained by high nutrient flux - High nutrient flux results from microbial activity and physical transport processes |
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Trophic Structure: Distribution
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- Distribution is tied closely to physical and chemical processes
- Set mostly by physiological tolerances - Co-occurring species have similar tolerances to abiotic conditions - Species have generalized niches (specialists and highly co-evolved biological interactions rare – i.e. mutualism and parasitism) |
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Movement Patterns of Epipelagic Organisms
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- Phytolankton, bacterioplankton, protists: move horizontally, stay in upper layers
- Larger zooplankton and smaller fish: move horizontally with current - Larger fish and mammals: cruise long distances, nekton go virtually anywhere they want |
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Movement Patterns: Horizontal Distributions
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- Varies widely because different water masses have different physical / chemical attributes
- Water masses moved by currents - Assemblage of organisms moved with its water mass |
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Movement Patterns: Diel Vertical Migrations
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- Zooplankton stay in depth during day to avoid predators
- Travel to surface at night to feed on similar plankton - So many vertically migrating organisms (can be tracked by sonar) |
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Trophic Structure: Species Diversity
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- Low, yet not incredibly low
- Epi Zone covers > 70% Earth’s surface but # of spp is low - By comparison, millions of spp of terrestrial insects ~ 4000 spp zooplankton worldwide - Same number of fish spp in entire epi zone as in Amazon River Basin |
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Why is Species Diversity so low?
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- 3 Main Reasons:
1. Low Speciation Rate (due largely to gene mixing) - Spp have high dispersal abilities and rates - Geographic boundaries are rare – little opportunity for local adaptation - Many hermaphroditic spp – results in lower genetic diversity 2. Relatively little niche space (decr. Dimensionality) - Virtually no physical structure - Environment very homogeneous (few microhabitats) 3. Spp have broad, generalized niches - Environment unpredictable – favours generalists - Most spp have generalized diets - Specialized spp rare (very few mutualists) |
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Epipelagic Diversity Conundrum
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Given the attributes of the epipelagic zone (structureless, homogeneous), why are there as many spp as there are?
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The Paradox of Plankton
G.E. Hutchinson |
Why so many spp and why isn't competitive exclusion operating?
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Potential Explanations to the Paradox of Plankton /Epipelagic Diversity Conundrum
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1. Succession
2. Contemporaneous Disequilibrium (Horizontal Heterogeneity 3. Thin Layer / Vertical Partitioning Hypothesis 4. Intermediate Turbulence Hypothesis |
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Succession
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- community assemblages in a water mass changes predictably through time
- most spp are probably present most of the time - big shift in which spp groups are most abundant among successional stages |
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Contemporaneous Disequilibrium
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Much patchiness in assemblage compositions because:
- many water masses at any given time - Dif patchiness at dif successional stages -- dif assemblies - Mixing reintroduces spp and nutrients, resettling patch to earlier successional stage |
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Thin Layer / Vertical Partitioning Hypothesis (Vertical Heterogeneity)
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- get sharp temp and salinity discontinuities with depth
- abundances of spp highest at discontinuities - Dif spp at dif continuities (vertical partitioning) - Reduced spatial overlap means reduced interspecific competition |
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Intermediate Turbulence Hypothesis
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- Major source of disturbance: turbulence
- incr turbulence, incr disturbance, decr spp - What would happen if turbulence --> 0 - Plankon require turbulence to remain in the epipelagic zone - If turb --> 0, number of epipelagic spp --> 0, spp that depend on phytoplankton starve and die |
