EVPP 550 Waterscape Ecology and Management – Lecture 9 Professor R. Christian Jones Fall 2007

Lake Biology – Overview Habitat Regions Littoral zone –Z total < z PZ –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 – Overview Habitat Regions Pelagial zone –Z total > z PZ, z < z PZ –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 – Overview Habitat Regions Profundal zone –Z total > z PZ, z > z PZ –Open water and bottom below photic zone –Tropholytic zone: Resp > Psyn –Heterotrophs only –both suspended and substrate associated

Lake Biology – Overview Biotic 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 – Overview Biotic 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 – Overview Biotic Communities Periphyton –Attached microbial community –“slime” growing on underwater surfaces –Coats macrophytes, rocks, logs, etc. –Includes algae, bacteria, protozoa, and microinvertebrates

Lake Biology – Overview Biotic 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 –H 2 O + CO 2 + light  (CH 2 O) + O 2 –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: um picoplankton, 2-30 um nanoplankton, 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