EEMB 142A Exam 2 study Guide.docx

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Ecology, Evolution & Marine Biology

I) The Epipelagic Zone- life in a constantly moving medium  Thin top layer of ocean where photosynthesis occurs  Know comparatively little and difficult environment to study B) Studying the Epipelagic zone i) Logistical constraints  Organisms transported by current flow(plankton) or can transport themselves(nekton)  All are constantly changing location (a) Experimentation Difficult  Limited types of experiments that can be done (b) Sampling Challenging  Done remotely  Many devices sample „selectively‟  Many organisms delicate- crushed or killed  Local environment constantly changing  No boundaries(except shores)  Organisms constantly shift position(currents, upwelling, mixing)  Shifts can be rapid(day/night, even hourly)  Species composition highly variable at any locality  Frustrating if goal is to study a particular set of organisms  Approaches to studying the Epipelagic (a) Field Experimentation  Possible to perform certain kinds of experiments  Manipulate whole water masses(defined by temperature and salinity)  Ex: does iron limit production in the epipelagic  Iron granules dispensed by ship in patches several kms in size  Diatom production followed in enriched and control patches  In situ mesocosm experiments  Giant containers that capture portion of water column that can be manipulated (after trophic composition, nutrient regimes etc.)  Can have replicates of many different treatments (b) Extrapolate from Freshwater Systems  Easier to manipulate entire lakes( lakes with and without planktivores)  Extrapolation has value but done with caution(processes controlling epipelagic zone not necessarily the same as in lakes) (c) Extrapolate from Lab to Field  Done in all ecological fields but also problematic  Realism and issue: difficult to keep epipelagic organisms alive much less behaving and functioning normally in lab  Scaling-up an issue: spatial and temporal scales very different between lab study and real world (d) Correlation Approach  Explore relationship between variables using observational data  Use caution: correlation does not imply causation B) Trophic Structure i) Food webs  Phytoplankton Zooplankton Nekton  Relatively few secondary consumers (a) Microbe based  One drop of seawater contains: 1million bacteria, 10 million viruses  Genetics and microscopy accelerate understanding of microbe world (b) Viroplankton poorly understood  Most use bacteria to reproduce(bacteriophages), require hosts  Help recycle nutrients by lysing bacteria  Many killed by UV light (c) Bacterioplankton  ½ of all carbon in marine food webs goes through bacteria  10% of marine bacterial species have been cultured  Trophic forms  Autotrophic(photosynthetic) (e.g. blue green algae)  Heterotrophic(take up DOM or other bacteria)  Mixotrophic (can photosynthesize or feed)  Pelagibacter ubique(SAR11 clade) most abundant bacterium in world is the smallest self- replicating cell (d) Phytoplankton rule the world  Fix lots of CO2, produce 90% of earth‟s O2, and help create clouds  Limited by: phosphorous, nitrogen, silica(diatoms), iron, trace elements  Factoid 1: Harness phytoplankton to control greenhouse gas?  Phytoplankton consumes CO2 when fixing carbon  Phytoplankton is iron limited  Seed ocean with iron to create phytoplankton blooms to take CO2 out of the atmosphere?  Southern Ocean Iron Release Experiment(SOIREE):  Released iron and a tracer over 100km^2  Monitored for 2 weeks  Got large phytoplankton bloom but carbon not transferred to deep ocean  Factoid 2: How phytoplankton helps create clouds  UV light damages phytoplankton  Phytoplankton produce chemical dimethylsulfonioproprionate(DMSP) as protection(antioxidant)  MMSP breaks down to Dimethylsulfide(DMS)  DMS goes into air and serve as nuclei for water droplets that form clouds ii) Abundance  Largely controlled by physical processes(particularly those that influence nutrient flux)  Strong bottom-up control by nutrients(primarily N, P, Fe)  Nutrients: huge role in shaping abundance and community structure  NutrientsphytoplanktonzooplanktonNekton  What controls nutrient flux in the epipelagic zone?  Nutrient source: deeper waters where remineralization occurs  Mixing, upwelling and turbulence move/inject nutrients into surface water  Pattern: very high primary production but relatively low phytoplankton standing stock  Reason: most primary production consumed by epipelagic animals  Plant: Animal biomass ratio  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 iii) Distribution: 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)  Movement patterns  Phytoplankton, bacterioplankton, protists- move horizontally by currents, stay in upper layers  Larger zooplankton and smaller fish- move horizontally with current, diel vertical migration(DVM)  Larger fish and mammals- cruise long distance  Horizaontal Distrtributions  Varies widely because different water masses have different physical and chemical attributes  Water masses moved by currents  Assemblages of organisms moves with water mass  Diel Vertical Migrations  Zooplankton stay at depth during day to avoid predators  Travel to surface at night to feed on smaller plankton  So many vertically migrating organisms(can be tracked by sonar) iv) Species Diversity: low(yet not incredibly low)  Epipelagic zone overs > 70% of earth‟s surface but number of species is low  By comparison, millions of species of terrestrial insects  4,00- species of zooplankton (~1,200 are copepods)  Same number of fish species in the entire epipelagic as in the amazon river basin  Why is Species Diversity so low?  Low speciation rate  Species have high dispersal abilities and rates(lots of gene mixing)  Geographic boundaries rare- little opportunity for local adaptation  Many hermaphroditic species- results in lower genetic diversity  Relatively little niche space  Virtually no physical structure  Environment very homogeneous (few microhabitats)  Species have broad, generalized niches  Environment unpredictable (favors generalists)  Most species have generalized diets  Specialized species rare(e.g. very few mutualisms)  Epipelagic Diversity conundrum  Given attributes of the Epipelagic Zone (structureless, homogenous), why are there as many species as there are?  „The Paradox of Plankton‟ G.E. Hutchinson- why so many species and why isn‟t competitive exclusion operating?  Potential explanations  Succession: community assemblage in a water mass changes predictably through time  Most species probably present most of the time  Big shift in which species groups are most abundant among successional stages  Contemporaneous Equilibrium(horizontal heterogeneity)  Much patchiness in assemblage composition because: i. Many water masses at any given time ii. Different patches at different succession stage iii. Exclusion does occur within a patch iv. Mixing reintroduces species and nutrients, resettling patch to earlier successional stage  „Thin Layer‟ or Vertical Partitioning Hypothesis  Reduced spatial overlap means reduced interspecific competition  Intermediate Turbulence Hypothesis  Major source of disturbance is turbulence  Plankton require turbulence to remain in Epipelagic zone  If turbulence=0, number of pelagic species=0 II) Kelp/coral A) Why do coral reefs and giant kelps occur in certain parts of the world? i) Biology of Kelp and of Reef-forming Corals (a) The environmental conditions needed for survival, growth and reproduction ii) Ocean-Atmospheric Coupling (a) Determines abiotic conditions where kelp forests and coral reefs can and cannot form iii) Giant Kelp requires: (a) High light (b) Cool temperatures (c) High nutrient flux(N,P)  Cool, nutrient rich waters are found closer to Equator on eastern margins of ocean basins  Kelp forests most extensive on eastern margins of ocean basins  Related to occurrence of cool, nutrient-rich surface water  upwelling  oceanic circulation patterns (d) Sufficient water motion (e) Hard substratum B) Biology of Reef forming corals  Phylum Cnidaria  Almost all are Scleractinia-stony corals  Colonial animals(polyps)  Secrete calcium carbonate to form reef structure  Reef-forming corals termed hermatypic-contain symbiotic dinoflagellate called Symbiodinium(zooxanthellae)  Hermatypic corals are functional mixitrophs- fix CO2 to create organic  Polyps capture zooplankton  Symbiodinium(symbiont) photosynthesizes to create photosynthetic food for coral; needed for corals to grow enough to form reefs. (b) Reef-forming corals require 4 abiotic conditions be met; 1. Annual Mean Water Temperature >18C  High enough calcification rate requires warm water for CaCo3 deposition>erosion 2. High Light Levels  Reef growth can be limited( need nutrition from Symbiodinium via photosynthesis)  No active reef formation at depth >25-50m 3. Clear Water  Need low turbidity/ low sedimentation  Turbidity reduces light and hinders photosynthesis  Sediments smother coral polyps  Reason why coral reefs rare directly adjacent to large land masses 4. Constant Marine Salinity  Corals cannot survive at lower or higher salinities  Reason why there are no estuarine or freshwater coral reefs  Another reason why no large coral reefs near river mouths (c) Corals generally occur in the tropics: between Tropic of Cancer and Tropic of Capricorn  Where annual mean surface temperatures >18C  Ocean-Atmospheric Coupling  Solar radiation makes water warm  Earth‟s curve makes water warmer at the equator  Because earth‟s axis is tilted relative to the sun, there is little variation between 23.5N & S of the equator- why we have seasons  Reefs outside tropics at western margins  Reefs only very close to equator at eastern margins  Solar radiation heats surface air  Warm air rises  Air moves along Earth surface to replace rising air  Rising air cools, sinks to replace air surface  Air moves toward low pressure areas from high pressure areas- creates surface winds with characteristic directions  Direction of winds alternates every 30 of latitude  But these are not the directions we perceive on Earth because of the Coriolis effect  An effect whereby a mass moving in a rotating system experiences a force acting perpendicular to the direction of motion and to the axis of rotation. On the earth, the effect tends to deflect moving objects to the right in the northern hemisphere and to the left in the southern.  Earth‟s rotation makes winds appear to veer  Wind moves surface of ocean  Because Ekman Transport and Coriolis Effect, surface water moves at 45 angle from apparent wind direction- 90 from original wind direction before Coriolis Effect  General pattern(working inward)- warm water flowing west, cool water flowing east, cold water flowing west  Land masses deflect warm water away from Equator at western margin of ocean basins  Deflects cool water toward equator at eastern margin  Forms major gyre system  Determines where conditions for growth, survival and reproduction are met (d) Temperate Reef Comparison 1. Predominant Biogenic Structure  Temperate reefs- macroalgae- more dynamic  Tropical reefs- stony coral- less dynamic 2. Coral Reefs: lower standing crop of macroalgae  Despite macroalgae grows > 50times faster than corals 3. Coral reefs: greater number and diversity of herbivores(particularly herbivorous fishes) 4. Coral reefs: detritus-based food wen less important( little algal material left unconsumed by herbivores) 5. Coral reefs: low nutrient concentrations in water(bluer the water, rarer the phytoplankton)  Oligotrophic- refers to bodies of water or soils with very low nutrient levels 6. Coral reefs: more constant and benign environmental conditions 7. Coral reefs: higher species diversity III) Coral reefs A) What is a Coral Reef?  Coral reefs : wave resistant features built by hermatypic corals that are cemented together  Form when CaCO3 deposition rate= erosion rate B) Two Major Divisions of Coral reefs 1. Coastal reefs: elongate structures that border a continental coast from anywhere where conditions are favorable 2. Atolls: ring-shaped reefs around volcanoes in the open ocean; have unique origins  Darwin‟s Subsidence Theory of Atoll Formation  A balance between upward coral growth of corals and seafloor sinking  Slow accumulation of coral limestone moves living surface upward and seaward  Step 1: formation of fringing reed  Step 2: formation of barrier reef(creates lagoons)  Step 3: Atoll forms as island subsides completely  Darwin proposed theory in 1860”s; proven correct 100yrs later when scientist drilled holes in atolls and hit volcanic rock under 100ms of limestone  Habitats within a Barrier reef/Lagoon system C) Primary production of Coral Reef Ecosystem  Primary productivity of coral reef ecosystems: coral reefs among most productive environments in world  Total primary production:  On reef ~5,000gC/m/yr  Adjacent phytoplankton ~50gC/m/yr.  The benthic organism responsible for extraordinary primary productivity:  Symbiodinium  Turfing and filamentous algae~ cyanobacteria 1. Incredibly efficient nutrient recycling  Particularly between coral and Symbiodinium  Symbiodinium provide organic compounds to coral host and receive N, P in return(tight recycling)  Further nutrient inputs when coral digest zooplankton/ POM 2. Nitrogen-fixation by blue-green algae(Cyanobacteria)  Nitrogen fixation=conversion of inert molecular version of nitrogen (N2) into biologically useful compounds such as ammonia and nitrate  Pathways nitrogen fixation by cyanobacteria transferred to coral reef community: o Algal fragments break off and become detritus o Algae releases DOM(including dissolved organic nitrogen) o Grazing and herbivores and resulting release of nitrogen by excretion 3. Herbivore-algal interaction  Grazing(mostly by fishes) favors turfing algae and cyanobacteria that: o Have very high nutrient-uptake efficiency o Efficiently convert photosynthetic products to growth o Trap sediment particles remineralized by microbes to yield nutrients  Remineralization= transformation of organic molecules to inorganic forms by biological activities 4. Nutrient flux can be high due to high water flow  Flux=concentration delivery rate  Nutrient concentrations in water can be low, but delivery rates can be high due to high water flows  Nutrient flux is what drives primary productivity 5. Nutrient-laden water can enter coral reef systems  Terrestrial runoff to coastal reefs  Internal waves can break on oceanic reefs, bringing deep nutrient-rich water to reef o Internal wave= gravity wane that oscillates within - instead of on the surface - of the ocean, often at a thermocline) D) Diversity of Corals and Coral Reef fishes  Species richness of corals and fishes extraordinarily high:  >80 coral genera containing hundreds of species in same geographic region  C
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