Chapter 6 Ecology of Phytoplankton

ECOLOGY OF PHYTOPLANKTON: CHAPTER 6

MORTALITY AND LOSS PROCESSES IN PHYTOPLANKTON

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

http://www.earthlife.net/inverts/images/others/salp.jpg

http://www.amonline.net.au/fishes/fishfacts/images/salp.jpg

Tunicates

http://www.aquamarinediving.com/images/DFugitt_Bali_Tunicates.jpg

References

Blindow, I., A. Hargeby, B.M.A. Wagner, G. Andersson. 2000. How important is the crustacean plankton for the maintenance of water clarity in shallow lakes with abundant submerged vegetation? Freshwater Biology 44:185-197.

Caraco, N., J.J. Cole, S.E.G. Findlay, D.T. Fischer, G.G. Lampman, M.L. Pace, and D.L. Strayer. 2000. Dissolved oxygen declines in the Hudson River associated with the invasion of the Zebra Mussel (Dreissena polymorpha). Environmental Science and Technology 34(7): 1204-1210.

Crumpton, W. G. and R.G. Wetzel. 1982. Effects of differential growth and mortality in the seasonal succession of phytoplankton populations in Lawrence Lake, Michigan. Ecology 63:1729-1739.

Fuhrman, J. A. 1999. Marine viruses and their biogeochemical and ecological effects. Nature 399:541-548.

Landry, M. R., and R. P. Hassett. 1982. Estimating the grazing impact of marine micro-zooplankton. Marine Biology 67:283-288.

Post, D.M. 2002. Using stable isotopes to estimate trophic position: models, methods, and assumptions. Ecology 83(3):703-718.

Reynolds, C. 2006. Ecology of Phytoplankton. Cambridge University Press. Cambridge, UK.

Timms, R.M. and B. Moss. 1984. Prevention of growth of potentially dense phytoplankton populations by zooplankton grazing, in the presence of zooplanktivorous fish, in a shallow wetland ecosystem. Limnology and Oceanography 29(3): 472-486.

Vander Zanden M.J. and J.B. Rasmussen. 1999. Primary consumer d13C and d15N and the trophic position of aquatic consumers. Ecology 80(4):1395-1404.

van Donk, E. and W.J. can de Bund. Impact of submerged macrophytes including charophytes on phyto- and zooplankton communities: allelopathy versus other mechanisms. Aquatic Botany 72:261-274.

Zhu, B., D.G. Fitzgerald, C.M. Mayer, L.G. Rudstam, and E.L. Mills. 2006. Alteration of ecosystem function by zebra mussels in Oneida Lake: impacts on submerged macrophytes. Ecosystems 9:1017-1028.