EVPP 550Waterscape Ecology and Management – Lecture 9

Professor R. Christian

JonesFall 2007

Lake Biology – OverviewHabitat Regions

• Littoral zone– Ztotal < zPZ

– Bottom is within photic zone

– Trophogenic: Psyn>Resp– Autotrophs and

heterotrophs– Supports benthic algae,

rooted macrophytes which add structure

– Substrate-associated plants and animals are characteristic

Lake Biology – OverviewHabitat Regions

• Pelagial zone– Ztotal > zPZ, z < zPZ

– Open water within photic zone

– Trophogenic: Psyn>Resp

– Autotrophs and heterotrophs

– Species that can suspend in water column or actively swim are characteristic

Lake Biology – OverviewHabitat Regions

• Profundal zone– Ztotal > zPZ, z > zPZ

– Open water and bottom below photic zone

– Tropholytic zone: Resp > Psyn

– Heterotrophs only– both suspended

and substrate associated

Lake Biology – OverviewBiotic Communities

• Plankton– “wanderers”– Suspended in the water column– May demonstrate limited mobility, but location

chiefly controlled by currents– Found principally in the pelagic region, but

sometimes also in littoral or profundal– Phytoplankton: “plant”-like/photoautotrophs

• Algae, cyanobacteria

– Zooplankton: “animal”/heterotrophs• Rotifers, cladocera, copepods

Lake Biology – OverviewBiotic Communities

• Benthos– Organisms associated with the bottom &

sediments– Found in both littoral and profundal– Phytobenthos

• Includes aquatic macrophytes and benthic algae

– Zoobenthos• Invertebrates of many groups• Most diverse in the littoral

Lake Biology – OverviewBiotic Communities

• Periphyton– Attached microbial community– “slime” growing on underwater surfaces– Coats macrophytes, rocks, logs, etc.– Includes algae, bacteria, protozoa, and

microinvertebrates

Lake Biology – OverviewBiotic Communities

• Nekton– Organisms controlling their own

movements– Can move freely and inhabit all lake

zones– Includes fish and larger invertebrates

Lake Biology - Phytoplankton

• Characteristics– “plant” component of the plankton– Primary producers– All have chlorophyll a– Conduct standard photosynthesis– H2O + CO2 + light (CH2O) + O2

– All require N, P, trace elements– Some also can utilize DOM or even may feed

suplementally on bacteria

Lake Biology - Phytoplankton

• Characteristics– Vary in taxonomy and morphology– All divisions of eukaryotic algae represented

• Greens, diatoms, dinoflagellates, cryptophytes, euglenoids

• Cyanobacteria (blue-green algae) can be very important

• Range from very small unicells (<1 um) to large colonies and filaments (up to 1 mm or more)

• Size categories: 0.2-2 um picoplankton, 2-30 um nanoplankton, 30-200 um microplankton

Lake Biology - Phytoplankton

• Adaptations– Avoid sinking

• General morphology: hairs, projections, anything to increase friction

• Flagella: can swim against gravity• Lower density: gas vacuoles, lipids

– Nutrient uptake• Sinking: breaks down boundary layer facilitation

diffusion• Small size: higher surface area/volume

Lake Biology - Phytoplankton

• Adaptations– Predation avoidance

• Colonial habitat• Projections• Indigestable muscilage

– Reproduction• Mostly asexual: binary fission, autocolony

formation• Sexual: When stressed some produce zygote,

diatoms use zygote to restore size

Lake Biology - Phytoplankton

• Factors affecting growth– Light

• Light energy required for photosynthesis• Light varies with latitude, season, time of day,

cloud cover, attenuation coefficient, depth• Photosynthesis shows an assumptotic relationship

to light• To estimate photosynthetic production in the field,

need to account for time of day and depth variations in light

Lake Biology - Phytoplankton

• Factors affecting growth– Light

• Photosynthetic rate/primary production quantified by measuring either: O2 production or C-14 uptake

• Can use either:– Bottle string in situ– P-I curve in lab extrapolated to field condition using light

extinction and ambient light data

Lake Biology - Phytoplankton

• Factors affecting growth– Nutrients

• N required for proteins, amino acids• P required for ATP, nucleic acids• Si for diatom frustules• Trace metals in enzymes• Vitamins by some algae• Nutrients can be taken up in excess of current

need for future use (luxury uptake)

Lake Biology - Phytoplankton

• Factors affecting growth– Nutrients

• P generally limiting in most fw systems, but sometimes N

• Si for diatoms, Mo for N fixers• Relationship between P and:

– Cell size– Chl a– Pico biomass– Group biomass

Lake Biology - Phytoplankton

• Factors affecting growth– Grazing

• Spines and projections may increase effective size and inhibit grazing

• Cladocerans esp Daphnia are most efficient grazers• Heavy grazing may reduce abundance and productivity of

phytoplankton• Light to moderate grazing may actually stimulate production

by increasing nutrient availability• Differential grazing may favor certain cyanobacteria and

colonial green algae by removing their competitors since they are resistant to grazing

• Nanoplankton vs. Daphnia

Lake Biology - Phytoplankton

• Factors affecting growth– Parasites

• Chytrid and biflagellate fungi– Infect desmids and diatoms

• Viruses– Can infect cyanobacteria

– Sedimentation

Lake Biology - Phytoplankton

• Factors affecting growth– Washout

• Important in lakes receiving large inputs of water– Mainstem reservoirs, urban lakes

• Washout processes may not be simple– Displacement without mixing - Linear decrease in

plankton with time– Complete mixing – exponential decline in plankton with

time

• Washout may keep plankton low even when nutrients are available