EVPP 550 Waterscape Ecology and Management

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EVPP 550Waterscape Ecology and Management
Lecture 10

• Professor
• R. Christian Jones
• Fall 2007

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PhytoplanktonPatterns of Abundance

• Seasonal - Winter
• In temperate lakes, phytoplankton are generally
  greatly reduced during winter due to low
  temperature and ice cover which impedes light
  transmission
• However, over the winter nutrient concentrations
  increased due to decomposition and sediment
  release

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PhytoplanktonPatterns of Abundance

• Seasonal - Spring
• With abundant nutrients in place, rapid growth
  occurs in spring when light and temperature again
  become favorable
• In shallow lakes, increase in ambient light alone
  is sufficient to start the bloom
• In deeper lakes, may need to get stratification
  before light and temperature reach their optima
• In most lakes, spring bloom is dominated by
  diatoms

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PhytoplanktonPatterns of Abundance

• Seasonal - Spring
• Spring bloom may continue for several weeks, but
  is eventually ends when nutrients become
  exhausted which for diatoms may be either P or Si
• Grazing may also play a role in cropping back the
  large phytoplankton populations

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PhytoplanktonPatterns of Abundance

• Seasonal - Summer
• In many oligotrophic and mesotrophic lakes a
  decline occurs in summer as nutrients become
  limiting
• Smaller algae such as small flagellates and
  cyanobacteria dominate as they are better able to
  utilize low nutrient levels

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PhytoplanktonPatterns of Abundance

• Seasonal - Fall
• In these lakes a second bloom often occurs in the
  fall as nutrients start to be remixed into the
  epilimnion
• Diatoms are again often dominant, but other
  species can also occur
• In late fall, light and temperature decline,
  stratification breaks down and phytoplankton
  populations collapse

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PhytoplanktonPatterns of Abundance

• Empirical Data
• A study compiled data from many lakes and found
  that the bimodal pattern we just described held
  very well for eutrophic lakes (here I would use
  the term mesotrophic/eutrophic
• However, oligotrophic lakes did not show as clear
  a seasonal pattern

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PhytoplanktonPatterns of Abundance

• Seasonal-Hypereutrophic Lakes
• In highly productive systems (hypereutrophic)
  growth may continued unabated through the summer
  forming a single large peak in late summer
• Often dominated by cyanobacteria

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PhytoplanktonPatterns of Abundance

• Interannual
• Cycles are fairly predictable in a given lake
• Some variability due to climatic variation
  including flushing
• In this graph the different lines represent
  different diatom species in Lake Windermere, UK

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Zooplankton - Characteristics

• Taxonomy
• Protozoa
• Single-celled, heterotrophic, eukaryotic
• Feed on bacteria and small algae
• Ciliates
• Amoebae
• Zooflagellates

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Zooplankton - Characteristics

• Rotifers
• Small invertebrates
• Multicellular, heterotrophic, eukaryotic
• Suspension feeders
• Rythmically beating rotating cilia near mouth
  creating a feeding current, also moves organism
  through water
• Relatively small (0.2-0.6 mm)
• Generation time 1 wk

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Zooplankton - Characteristics

• Rotifers
• Life History
• Have both sexual and asexual (parthenogenetic)
  reproduction
• Asexual during favorable periods
• Stressful conditions induce sexual reproduction
  which produces resting eggs
• Resting eggs are resistant to drying, cold, heat,
  etc. and can hatch when favorable conditions
  return

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Zooplankton - Characteristics

• Cladocera
• Small invertebrate arthropods
• Multicellular, heterotrophic, eukaryotic
• Use jointed appendages for swimming and feeding
• water fleas
• Very characteristic of freshwater

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Zooplankton - Characteristics

• Cladocera
• Most are herbivorous filter feeders
• Filter algae from the water as they swim in a
  rather passive fashion
• Some are raptorial predators, mainly on other
  cladocera
• Adults range from 0.3 mm up to 3 mm except
  Leptodora up to 10 mm
• Generation time as low as 2 weeks when asexual

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Zooplankton - Characteristics

• Cladocera
• Like rotifers, have both asexual and sexual
  reproduction
• During favorable conditions, there can be many
  generations of asexual reproduction (eggs that
  dont need fertilizing)
• When stress occurs, males are produced and sexual
  females, meiosis occurs to produce gametes
• Male gametes fertilize eggs in brood chamber
  producing sexual (epphipial) eggs

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Zooplankton - Characteristics

• Copepods
• Small invertebrate arthropods
• Multicellular, heterotrophic, eukaryotic
• Use jointed appendages for swimming and feeding
• Found in freshwater, estuaries and the ocean
• Very characteristic of marine zooplankton

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Zooplankton - Characteristics

• Copepods
• Some are passive filter feeders, but most go
  after individual particles
• Take algae and small invertebrates
• Adults range from 0.5 mm to 5 mm
• Calanoid cyclopoid common in plankton

Calanoid
Cyclopoid
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Zooplankton - Characteristics

• Copepods
• No asexual reproduction
• Fertilized egg hatches into a larva called a
  nauplius
• Nauplius undergoes a series of molts (6) before
  changing into a form that looks like an adult
  (copepodid)
• Copepodid undergoes 6 further molts before
  becoming an adult (sexually mature)
• Males and females look similar, but males have
  clasper
• Generation time months to one year

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Zooplankton Factors Affecting Growth

• Two methods have been used to measure zooplankton
  performance
• Population growth rate (r)
• N(t) N(0) ert where r is the growth rate of the
  population in units of 1/time
• Filtration rate
• Filtration rate volume of water cleared of
  particles per unit time, mL or per unit time

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Zooplankton Factors Affecting Growth

• Food concentrations and Temperature
• Zooplankton growth often seems to be limited by
  food and temperature
• In the study cited below, r increased with
  temperature at each food concentration and with
  food concentration at each temperature
• Growth rate at the highest T and food was over 7x
  that at the lowest combination

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Zooplankton Factors Affecting Growth

• Food quantity and quality
• Both the quantity and quality of food are
  important
• r b d (birth rate death rate)
• At the lowest food concentration, birth rate was
  very low and death rate quite high
• As food concentration increased, birth rates
  increased and death rates declined strongly
• The green alga Chlamydomonas supported highest
  birth rates and lowest death rates

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Zooplankton Factors Affecting Growth

• Filtering rates are a function of temperature and
  body size
• In the data shown below, larger individuals
  filter much more water than smaller ones
• For this species, filtration rates increase to
  20oC and then decline

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Zooplankton Factors Affecting Growth

• Food concentrations and Temperature
• Zooplankton growth often seems to be limited by
  food and temperature
• In the study cited below, r increased with
  temperature at each food concentration and with
  food concentration at each temperature
• Growth rate at the highest T and food was over 7x
  that at the lowest combination

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ZooplanktonPatterns of Abundance and Activity

• Some zooplankton populations grow in a
  synchronized pattern
• This is particularly true in the temperate and
  polar areas with strong seasonality
• In these areas there may be only one or two
  generations per year
• Graph on the right shows a copepod population in
  a Norwegian lake which has one well synchronized
  cohort per year

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ZooplanktonPatterns of Abundance and Activity

• Here is a second one with two synchronized
  populations and a resting stage
• This is most common in copepods which require
  sexual reproduction
• In the cladocerans and rotifers, there is less
  synchrony generally partially due to continuous
  asexual reproduction under favorable conditions
• Its also harder to discern the different stages
  in cladocerans

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ZooplanktonPatterns of Abundance and Activity

• Other factors affect zooplankton abundance and
  acitivity in the field such as predation
• Here is a data set which found that predation by
  Leptodora was a major controlling factor on
  Daphnia populations
• Note the very high birth rate (b) in July meaning
  they were producing lots of eggs
• But r was near 0, implying a high death rate
• The period of high death rate corresponded with
  the maximum for the predaceous cladoceran
  Leptodora

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ZooplanktonPatterns of Abundance and Activity

• Predation by fish is also an important regulatory
  factor
• It has strong effects on behavior
• In a lake with fish present, a strong diel
  migration of zooplankton was observed with
  zooplankton exiting the top layers during the
  day, presumably to avoid fish predation
• In a similar nearby lake without fish,
  zooplankton remained in the upper layers all day
  which presumably allows them to feed longer

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ZooplanktonPatterns of Abundance and Activity

• In addition to these depth patterns of avoidance,
  there seem to be other behaviors for avoidance of
  fish predation
• Zooplankton cluster within macrophyte beds during
  the day, but venture into open water at night

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ZooplanktonPatterns of Abundance and Activity

• Presence or absence of fish in a lake has a
  strong effect on the species and sizes of
  zooplankton
• An important early study looked at the size
  structure of lakes in Connecticut with and
  without anchovy
• This study led to the concept of top-down
  control of food webs by which predators as
  opposed to food sources control biological
  communities

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ZooplanktonPatterns of Abundance and Activity

• While top-down control seems to regulate the
  types and sizes of zooplankton, the total biomass
  of zooplankton is strongly related to food supply
• Here, we see a graph showing a positive
  correlation between TP vs. zooplankton
• The inference is that P fuels phytoplankton
  growth which fuels zooplankton growth, a bottom
  up pattern

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ZooplanktonPatterns of Abundance and Activity

• A typical seasonal pattern of zooplankton
  activity involves a late spring-early summer
  maximum (see phytoplankton seasonal pattern
  earlier in lecture)
• Note that all 4 groups of zooplankton can play a
  role during the year
• The numbers attained tend to be inversely
  proportional to the size of individuals

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ZooplanktonPatterns of Abundance and Activity

• Zooplankton can exert heavy grazing pressure on
  phytoplankton and create their own top-down
  effect
• Their effect varies strongly with seasonal and
  depth patterns in abundance

Grazing/filtering rates above 50/day would exert
a major control over phytoplankton. That would
imply that 50 were removed on a daily basis.