Zooplankton Ecology

Zooplankton Feeding

    A. Ingestion
        1. ml of water cleared per animal per time (F) versus density of food (D)
Zooplankton filtering rate versus phytoplankton cell density
                F = filtering rate or clearance rate
                Decreases at high cell density because filtering apparatus clogs
                Increased filtering rate for larger zooplankton (especially Daphnia)

        2. ingestion I = F * D
                D = cell density

Zooplankton ingestion versus phytoplankton density
                Ingestion increases as cells get more concentrated
                Curve levels off due to saturation/clogging

    B. Selection during feeding
        1. specialization of feeding types
            a. raptorial (copepods)
            b. filter feeding (cladocera)
            c. ciliary mucus (rotifers)
        2. size of food particles that can be taken
            a. can depend on size of filtering combs
            b. experiments
                i. beads of different size
                ii. coulter/particle counter – measure the size range of particles in natural assemblages before and after grazing
            c. varies with the size of the zooplankton
        3. effect of polysaccharide coatings and of spines
            a. Shape of algae
            b. Spines increase the effective length of the algal cells
            c. Algae with polysaccharide/mucilaginous coatings may be resistant to digestion even when they are consumed

        4. species-specific feeding rates on different algae
            a. Some mechanical effects – spines
            b. Some behavioral (selection) – taste (soaked beads)
        5. differences in selectivity between different zooplankton species
            a. copepods more selective than cladocera
            b. herbivorous calanoid copepods do better at low food quantities and low food qualities

Differences between (Diaptomus) calanoid copeopod and Daphnia growth in low versus high food quality
Competition between Daphnia and Diaptomus based on food quantity and food quality

    C. Utilization of food
        1. some algae not digested
        2. nutritional effects – vitamins, etc.
            a. energy (total amount of food)
            b. 'food quality' -- amino acids, lipids (fatty acids, 'fish oils'), vitamins, phosphorus

Sterner and Schulz, 1998, Food Quantity/Quality Definition Figure
            c. often get best growth and reproduction with a mixed diet
        3. assimilation –
            a. the part of the ingested food that an organism can actually uses
            b. key to how well organisms can grow and reproduce
            c. not 100% -- generally is ~30-80%
            d. measure with radioactively labeled food
            e. Use for energy budgets to help determine zooplankton production
                i. ingestion
                ii. assimilation
                iii. growth
                iv. reproduction
                v. excretion – dissolved form
                vi. egestion – bulk material in fecal pellets
                vii. respiration
                viii. molts
        4. use of detritus
            a. some organisms can grow on detritus
            b. often most of the nutrition comes from grazing on the decomposers on detrital surface (bacteria and fungi)
                and not the refractory (hard to digest/poor quality) food
        5. antibiosis
            a. when fed the cyanophyte Microcystis or Oscillatoria, Daphnia reduces its filtering rate (F)
            b. Keratella (rotifer) dies when confined with Eudorina (green)
            c. Chlorella (green) is toxic to Brachionus
            d. Some Anabaena strains are toxic to Daphnia
        6. regeneration of nutrients
            a. nutrients  ---> algae --->  zoop  ---> fish
            b. the supply of nutrients is external to the lake or stream, BUT, zooplankton excrete nutrients back into the lake – recycle nutrients
            c. complex feedbacks
           d. remineralization of nutrients – primary excretory products
                i. PO43- (phosphate)
                ii. NH4+ (ammonium)
                iii. Also there is DOP and DON
        7. Source of zooplankton food is sometimes not algae, but terrestrial
            a. Autochthonous production – C fixed within the lake by phytoplankton, macrophytes, benthic algae
            b. Allochthonous production – C fixed outside of the system (in this case terrestrial)

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