Transcript EVPP 550 Waterscape Ecology and Management – Lecture 11

EVPP 550
Waterscape Ecology and
Management – Lecture 11
Professor
R. Christian
Jones
Fall 2007
Lake Biology – Benthos
Profundal Benthos
• Profundal habitat can
be very challenging in
lakes
– Cold for most of the
year due to summer
stratification
– Anaerobic in
mesotrophic and
eutrophic lakes
– Poor food quality: no
resident primary
producers, all food is
imported and “stale”
Lake Biology – Benthos
Profundal Benthos
• A few groups have
been able to adapt to
this environment
• Those which have can
prosper if conditions
are not too severe
• Examples are
chironomids (midges),
chaoborus (phantom
midges) and
oligochaetes
Lake Biology – Benthos
Profundal Benthos
• Chironomids have been
extensively studied
• Some species can
maintain constant
respiration even at low DO
• Some can withstand no
oxygen for up to 4 months
at 10oC
• Food supply of profundal
chironomids is surface
sediment particles
ingested in bulk with algae
and bacteria selectively
assimilated
Lake Biology – Benthos
Profundal Benthos
• Adaptations
– Hemoglobin
• Helps to bind and store
limited amounts of O2
– Anaerobic glycolysis
• Can split carbohydrates
to produce energy with
using oxygen
• Similar to what happens
in your muscles under
strenuous activity
• Accumulate an oxygen
debt that must later be
satisfied
– Stop growth, become
dormant
Lake Biology –
Profundal Benthos
• Life History of
Chironomus anthrocinus
in L. Esrom
– Egg mass deposited at
night in May on lake
surface near shore
– Water currents spread the
eggs throughout the lake
as they sink to the bottom
– By June, hatching occurs,
food is abundant and
larvae double in size by
early July
– Oxygen is depleted in
summer and growth stops
Lake Biology –
Profundal Benthos
• Life History of
Chironomus anthrocinus
in L. Esrom
– Fall overturn brings
oxygen to the bottom
satifying the oxygen debt
and allowing fresh growth
to occur based on food
still in the water column
– Animals are quiescent
during winter, but perk up
again the following spring
with onset of new food
Lake Biology –
Profundal Benthos
• Life History of
Chironomus anthrocinus
in L. Esrom
– Some have grown large
enough to emerge after
one year, but many need
a little more growth and
emerge the second year
– Emergence occurs at the
surface, mating occurs,
eggs are laid, and adults
die within a few days
– Highly synchronized
pop’n
Lake Biology –
Profundal Benthos
• Chaoborus
– Phantom midge
– Alternates between
plankton and benthos
– Prey mostly on
zooplankton and are
preyed upon by fish
– Migrates daily from
sediment surface to
photic zone
– Under anaerobic
conditions, may stop
downward migration at
the thermocline
Lake Biology –
Profundal Benthos
• Oligochaetes
– Development is
unsynchronized
– Burrow through surface
sediment, digesting
bacteria, mixing
sediments, and recycling
nutrients
Littoral Zone
• Portion of lake
where photic
zone includes
the bottom
The Littoral Zone Macrophytes
• Macrophytes
– Plants whose overall
structure is visible to the
naked eye
– Distribution in lakes is
subject to two basic
constraints:
• Water must be shallow
enough for light to reach
the bottom (= littoral
zone as we have
defined)
• Physical stability
sufficient to allow plants
to grow to the bottom
The Littoral Zone Macrophytes
• Characteristics
– General Morphology
• 4 basic
morphological
types typically
occupying “zones”
of increasing depth
• Emergent
• Floating-leaved
• Submersed
• Unrooted
The Littoral Zone Macrophytes
• Emergent macrophytes
– Occupy the transition
zone between land and
water
– Rooted in sediment or
saturated soils
(anaerobic)
– Shoots and leaves extend
into the air so, like
terrestrial plants, they
must be self-supporting &
get CO2 from air
– Mostly angiosperms
– Ex.: cattails, wild rice
The Littoral Zone Macrophytes
•
Floating-leaved macrophytes
– Root in sediment, leaves float on
surface
– Connections are via stems or
petioles
– 0.5 m < z < 3 m
– Need to have some standing
water, but limited by petiole or
stem length
– In case of water lilies, both root
and stem are underwater and
petioles (leaf stem) extends
through water to surface leaves
– A patch of water lilies may
actually be one plant
– Ex: yellow water lily (Nuphar),
white water lily (Nymphaea)
The Littoral Zone Macrophytes
• Submersed Macrophytes
– Whole plant is underwater
– 0.5 < z < 10 m (angiosperms), up to 100 m for
mosses, Chara
– No supporting tissue, rely on
turgor pressure and
buoyancy to maintain erect
form
– Underwater leaves often
finely dissected, but may be
laminar
– May have heterophylly
(different underwater vs.
surface leaves)
– Ex: Myriophyllum (milfoil),
Potomogeton (pondweed),
Chara (stonewort), Isoetes
(water fern)
The Littoral Zone Macrophytes
• Unrooted macrophytes
– Floating
• Lemna (duckweed)
• Eichornia (water
hyacinth)
– Submersed
• Ceratophyllum (coontail)
The Littoral Zone Macrophytes
• Taxonomy
– Charaphytes
(stoneworts)
• Algal group related
to green algae
• Macroscopic form
• Ex: Chara, Nitella
– Bryophytes
(mosses, liverworts)
• Plants with some
tissue and
reproductive
specialization, but
no vascular tissue
(xylem, phloem)
• Ex: Sphagnum
The Littoral Zone Macrophytes
• Taxonomy
– Ferns and Fern
Allies
• Plants with
vascular tissue,
but no flowers
• Ex: Isoetes
(submersed
macrophyte found
in soft water)
• Ex: Equisetum
(horsetail)
(emergent
macrophyte)
The Littoral Zone Macrophytes
• Taxonomy
– Gymnosperms
• Vascular tissue
• Reproductive:
“cones”
• Ex: Bald Cypress
(emergent)
– Angiosperms
•
•
•
•
•
•
•
•
Vascular tissue
Flowers
Ex: Cattail (Typha)
Ex: Water Lilies
(White and Yellow)
Ex: Myriophyllum
(milfoil)
Ex: Hydrilla
Ex: Potamogeton
(pondweed)
Ex: Vallisneria
(water celery)
Macrophytes – Factors
Affecting Growth
• Low oxygen levels
around roots
– Sediments are usually
anoxic, but roots need
oxygen or growth will be
inhibited
– Some species have
vertical air tubes called
lacunae which extend
from the shoots down
into the roots to help
aerate
– Root cells may be able to
withstand oxygen debt
Macrophytes – Factors
Affecting Growth
• Inorganic carbon supply
– Low rate of diffusion of
CO2 through bulky
macrophyte tissue could
lead to carbon shortage
– Plants can also use CO2
and in very soft water,
uptake can occur through
roots
Macrophytes – Factors
Affecting Growth
• Depth – Pressure
– Vascular macrophytes do
not grow to a depth of
more than 10 m
(representing 1 extra
atmosphere of pressure)
– This seems to be related
to the effect of this extra
pressure on the xylem
and phloem
– However, mosses have
been found at up to 165
m and Chara to 64 m in
Lake Tahoe, for example
Macrophytes – Factors
Affecting Growth
• Depth - Light
– Two effects: Light &
Pressure
– Water transparency is
highly correlated with
depth to which
macrophytes can grow
– Note that maximum
depth of colonization is
less than photic zone
depth which is about
double Secchi disc depth
Macrophytes – Factors
Affecting Growth
• Depth - Light
– One way that
macrophyte communities
respond to potential light
limitation is to favor
species that develop a
canopy as opposed to
those the grow near the
sediment surface
(rosettes)
Macrophytes – Factors
Affecting Growth
• Nutrients
– N&P can be taken up by
roots and shoots
– Relative importance of
root vs. shoot uptake
depends on sediment vs.
water concentrations
– Ex: Lake Wingra, WI
• 73% of P by roots
• 27% of P by shoots
– Root uptake is then
translocated to shoots to
fuel growth
Macrophytes – Factors
Affecting Growth
• Sediment Stability
– Texture is important
• Need fine particles: fine
sand, silt or clay
• Course sand, cobble,
boulders are not good
rooting medium
– Stability is also important
• If sand is moving, like
on a beach plants will
not become established
Macrophytes – Patterns of
Abundance & Production
• Seasonal
– In temperate areas,
macrophytes are very
seasonal in their growth
– Maximum development
in late summer
– However, some dieback
over much of the year
– In fact, plants create and
shed shoots continuously
Macrophytes – Factors
Affecting Growth
• Productivity determination
– Maximum standing crop
• But this ignores biomass that was shed building up to maximum
– C-14 approach
• Measure C-14 uptake by actively photosynthesizing parts of plant
– Cohort analysis
• See previous page
Macrophytes – Spatial
Patterns
• Within lake
– Macrophytes generally cover only
those parts of the right habitat
(light, substrate, etc.)
• Between lakes
– Great differences between lakes
Littoral Zone Periphyton
• Characteristics
– General Morphology
• Algae: unicells,
filaments, colonies
• 2 general types of
attachment
– Adnate: cells in close
contact with substrate,
hard to dislodge
– Loose: cells only
loosely attached,
easily dislodged
– Taxonomy
• All groups of algae
represented, esp
– Cyanobacteria,
diatoms, greens
Littoral Zone Periphyton
• Factors affecting
development
– Substrate Availability
• The amount of surface
habitat obviously influences
the abundance of periphyton
• Could be fairly static like
bottom area in photic zone
or very dynamic like annual
plant surfaces
– Light
• Have a very similar
photosynthesis-light
relationship as
phytoplankton
Littoral Zone Periphyton
• Factors affecting
development
– Nutrients
• Can periphyton get
nutrients from their host
substrate?
• Results seem to
suggest this is not a
major factor
• Label P in sediments,
grow macrophytes, less
than 5% of P in
epiphytes comes from
sediment
• High correlation with
lake water P
Littoral Zone Periphyton
• Patterns of Abundance
and Productivity
– Epiphytic periphyton vary
both with depth and
seasonally
– These variations are a
combination of:
• Changes in the density
of epiphytes on the
macrophyte
• Changes in the amount
of macrophyte substrate
available at different
depths and times
Littoral Zone Periphyton
• Productivity would also need to take into account
variations in light and P-I response
Littoral Zone - Periphyton
•
•
•
•
Resulting productivity could vary seasonally and from one year to the
next
Note day-to-day variation in production (light driven)
Note different seasonal pattern (substrate availability driven)
Note rough equivalence of 10 mg C produced per mg Chl a present
per day
Littoral Zone – Littoral
Invertebrates
• Characteristics
– Include a much larger
suite of organisms than
found in the profundal
benthos
– Some of the dominant
groups include:
• Flatworms
• Oligochaetes
• Molluscs
– Snails
– Bivalves
• Arthropods
– Crustaceans
– Insects
Littoral Zone – Littoral
Invertebrates
• Characteristics
– A wide variety of feeding
strategies including:
• Grazers/herbivores (due
to presence of primary
producers in the littoral
zone)
• Detritivores
• Predators
– Littoral grazers tend to
focus on periphyton as it
is much more digestable
– Macrophyte production
tends to get utilized as
detritus
Littoral Zone – Littoral
Invertebrates
• Characteristics
– Type of predators
• Lurking
–
–
–
–
Dragonflies
Sit in a concealed position
Attack prey as they come by
Concealed, but dependent
on prey movement
• Hunting
– Water bugs
– Actively search for prey
– Often well-armoured, taste
bad, and move quicky to
avoid predators
– Can capture both moving
and stationary prey
Littoral Zone – Littoral
Invertebrates
• Characteristics
– Littoral zone can be an
area of great physical
and chemical complexity
– Allows a very high
diversity, but also
presents some significant
sampling problems
– Heterogeneous
distribution
– Difficulties in capturing
organisms within
vegetation, rocks, logs,
etc.
Littoral Invertebrates –
Patterns of Abundance
• Seasonal and spatial patterns
• Examine results from a study of littoral invertebrates
in the tidal freshwater Potomac River
– Organisms captured by dropping nets over 0.5 m2 of weedbed
– Nets closed by diver at bottom and brought to surface where
organisms were removed from vegetation and preserved
• Study design
– 3 bed types: open water, Hydrilla, mixed
– 2 months (July, August)
– 5 replicates each
Littoral Zone –
Littoral
Invertebrates
•
Results
– Macrophytes harbored much higher
abundance of macroinvertebrates
than open water
– Taxa list was similar at all sites, but
relative abundance differed both
with plant type and month
Littoral Zone – Littoral
Invertebrates
• Cluster
analysis
– Confirmed
differences
between veg
and open
water
– Suggested
that variation
between
months was
more
important that
variation
between plant
types
Littoral Zone – Littoral
Invertebrates
• PCA
– Reinforced
importance of
plants
– And the effect of
month over plant
type