Kevin Kapuscinski and Katie Woodside

6.1 Introduction

Principle Loss Processes

·  Hydromechanical dispersion (wash-out, downstream transport, dilution)

·  Sedimentation

·  Consumption by grazers

Other Loss Processes

·  Parasitism

·  Physiological death

·  Wastage

Rate of Population Change

rN = r’ – rL (Eqn. 5.1) where rN = increase rate, r’ = replication rate, rL = instantaneous rate of loss to all mortalities

rL = rw + rs + rg + .... where rw = loss due to wash-out, rs = loss due to sedimentation, rg = loss due to grazing, etc

If rL > r’ than rN < 0 and the population is declining.

6.2 Wash-out and dilution

6.2.1 Expressing dilution

rw = qs / V where qs = volume of particle free water that enters the impoundment (magnitude of hydraulic replacement rate), V= volume of the impoundment (if particles are evenly distributed/ there is no patchiness)

6.2.2 Dilution in the population ecology of phytoplankton

·  Sensitivity to flushing increases with slow growth rate

6.2.3 Phytoplankton population dynamics in rivers

·  Larger rivers (3rd or 4th order) support populations of river plankton (potamoplankton) in non-flowing water

·  Non-flowing water

·  Boundary friction between banks and bed

·  Fluvial ‘deadzones’ (little ponds within the river) sensitive to changes in discharge, fluid exchange, and turbidity

·  C-strategists and CR-strategists do well in rivers

·  Consumption by filter-feeding zooplankton and zoobenthos

·  Macrophytes in headwaters and lateral dead-zones act as shelters and substrata

6.3 Sedimentation

6.3.1 Loss by sinking

·  Turbulent entrainment slows sinking

·  Non-motile organisms vulnerable to variations in mixed depth

·  Small, motile, or minimization of density helps reduce sinking rates (Stokes eqn.)

6.3.2 Mixed depth and the population dynamics of diatoms

·  Colony formation and siliceous exoskeletons provide increased form resistance and entrainability

·  Dependent on turbulence and absolute mixed-layer depth for dispersal and population recruitment (intensity and extent of vertical mixing)

·  Lack of nutrients = heavy sinking losses

·  Onset of stable thermal stratification = higher sinking losses

·  Shortening mixing depth = accelerated rate sinking rate = accelerated sinking loss

·  Accelerated sinking rate could be positive mechanism used to escape near-surface insolation, could allow for population re-establishment upon better conditions

·  Large phytoplankton succumb more to sedimentation than colonial phytoplankton

·  Sedimentation main loss of limnetic (open-water) phytoplankton

·  Sedimentation leads to seasonal succession of other phytoplankton

6.3.3 Accumulation and resuspension of deposited material

·  ‘Seed banks’ need to survive and escape back into water column

·  Resting stages with independent capacity for germination, regrowth, and reinfection

·  Resting cysts and stages that depend on still-suspended or resuspended propagules encountering tolerable conditions

·  As sediment builds up, materials are compacted and lost from semifluid layer, water and biominerals are lost upon compaction

·  Filaments and chains exist in semifluid layer longer than centric unicells

·  Resuspension dependent on:

·  Sufficient turbulent force

·  Depth of sediments

·  Borrowing of invertebrates, fish, etc

6.4 Consumption by herbivores

6.4.1 The diversity of pelagic phagotrophs and their foods

·  Zooplankton – feed on live or detrital organic particles for most/all energy and carbon

·  Protistan microzooplankton

·  <200 mm heterotrophic protistans and metazoans

·  Many photoautotrophs with phagotrohpic capabilities

·  Planktic ciliates can ingest long filaments by coiling them intracellularly

·  Feeding largely depends on encounter/chance

·  Multicellular microzooplankton

·  Marine - larval crustaceans, rotifers, larvaceans, larvae of other groups (molluscs and echinoderms)

·  Marine - feeding largely depends on encounter, cilia around mouth, mandibular mouthparts

·  Lakes – rotifers, copepod nauplii

·  Freshwater mesozooplankton

·  0.2 – 2 mm

·  Can exploit currents and turbulence

·  Common adaptations – transparency, ability to propel self

·  Copepods (cyclopoids and calanoids)

·  Cyclopoids – short biramous antennules, pear-shaped, thoracic legs

·  Calanoids – long antennules, cylindrical shape, can filter feed via currents created by appendages or actively capture larger algae and ciliates

·  Branchiopods (Cladocera)

·  Specialized filter-feeders drawing water through carapace

·  Short abdomen and thorax covered by carapace, 4 to 6 pairs limbs with setae, large biramous antennae

·  Daphniidae

·  Marine mesozooplankton

·  Calanoids, cladocerans, thaliacean tunicates (salps)

·  Calanoids are more efficient carbon harvesters than cladocerans

·  Cladocerans can filter more water, harvest more food, faster metabolism and growth than calanoids in nutrient rich environments

·  Tunicates – gelatinous, barrel-shaped, low body mass filter-feeders

·  Planktivorous macroplankton, megaplankton and nekton

·  Trophic cascades with zooplanktivorous fish

·  Macroplankton (2 to 20 mm), Megaplankton (>20 mm) – polychaetes, amphipods, larval decapods, larval hemipterans

·  Swimming nekton (fish, squid) and their juvenile hatchlings

6.4.2 Impacts of filter-feeding on phytoplankton

·  Means to sieve and concentrate particles

·  Filtration rates versus Feeding rates

·  Food availability

·  Depends size of filter, leakage

·  Size and texture of food

·  Chemoreception

·  Kairomones (undigestable cells)

·  Production of toxic substances by phytoplankton

·  Mucilage decreases successful ingestion

·  Algal removal and grazer nutrition

·  Without predators it depends on temperature and food availability

·  Food thesholds and natural populations

·  Larger filter-feeders have larger resource base than smaller filter-feeders

·  Algal food resource supplemented by detritus and bacteria

·  Larger zooplankton more vulnerable to predation

·  Feeding pressure on zooplankton varies (fish switch between benthic and planktic resources)

6.4.3 Selective feeding

·  Filter-feeding plus active capture through chemoreception, scraping, fragmenting food

6.4.4 Losses to grazers

·  Filter-feeding more damaging than selective feeding

6.4.5 Phytoplankton-zooplankton interactions (zooplankton don’t control phytoplankton in predictable way)

·  Competitive interactions

·  Cladocerans select against small algae leaving large indigestible algae for daphniids

·  Feedbacks

·  Excretory wastes, sloppy eating (recycled nutrients)

·  Bottom-up and top-down processes in oligotrophic systems (resource restraints)

·  Bottom-up and top-down processes in enriched systems

·  Control of system can switch from top-down to bottom-up and vice versa

·  Seasonal, temperature influences who has control

·  Intervention in food-web interactions

·  Catastrophic events (fish kills, toxic substances)

·  Invasions of exotics

·  Food-chain length

·  Determined by stability of key components, availability of resource base, usable energy influx. (Overall transfer of energy through trophic levels important)

·  Stable isotope analyses of food webs show that size of ecosystem and totality of resources more important determinants

6.5 Susceptibility to pathogens and parasites

6.5.1 Fungal parasites

·  Difficult to distinguish except based on host

·  Host cells almost always killed

·  Under low light, low infection rates

6.5.2 Protozoan and other parasites

·  Often wrap around algae or suck out contents through holes made in cell walls

5.5.3 Pathogenic bacteria and viruses

·  More common in lakes than oceans

·  Viruses may be dormant for years

6.6 Death and Decomposition

·  Failure of organism to maintain basic metabolic functions

·  Programmed cell death (apoptosis)

6.7 Aggregated impacts of loss processes on phytoplankton composition

·  Seasonal succession, succession of different phytoplankton species

Salps Class Thaliacea



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