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The material in this slide show is provided free for educational use only. All other forms of storage or reproduction are subject to copyright please contact the National Marine Aquarium www.national-aquarium.co.uk Science Training & Education Partnership The slide show was designed and produced for the NMA by STEP, the Science Training & Education Partnership www.step-up-to-science.com Plant growth in the oceans: Resources and controls Plant growth Resource limitation Grazing control Summary Plant growth Resource limitation Grazing control Summary The most important plants in the ocean are phytoplankton These tiny, single-celled plants grow simply by dividing into two new cells If the conditions are good for growth, the number of cells will double each day DAY 1 1 cell DAY 2 2 cells DAY 3 4 cells DAY 4 8 cells Population (number of cells) Starts with one cell, one cell division per day This growth is exponential, and is described by a model of the type: Nt 2 Nt1 exp(k.(t2 t1)) where N is number of cells and t is time, and the constant k is related to the doubling time: ln(2) k doublingtime The exponential model is obviously correct in describing the process of continuous cell division, but it predicts an unrealistic ever-increasing biomass DAY 30 535 million cells In reality, there is a limit to the amount of phytoplankton biomass that a habitat will support, so the rate of population increase starts to decline Population (number of cells) Same initial rate as the exponential model, but reaches an equilibrium value This logistic model is more complex, but makes a more realistic prediction P Pequil.Pstart Pstart ((Pequil Pstart)exp( K.t) Starting population Equilibrium population Rate constant Time Plant growth Resource limitation Grazing control Summary What can limit phytoplankton growth? Too little light Lack of materials to build new cells Like all plants, phytoplankton algae grow by photosynthesis LIGHT CARBON DIOXIDE WATER CARBOHYDRATE OXYGEN They build complex organic materials from carbon dioxide and water, using light as an energy source STEP Light decreases as you go deeper into the ocean The decrease in light with depth is also described well using an exponential model, this time a decay: Lz 2 Lz1 exp(K(z2 z1)) Light at depth ‘z2’ Light at depth ‘z1’ Absorption coefficient Difference in depths Photosynthesis is dependent on light Depth (metres) Depth (metres) There is more photosynthesis where water is clear than where it is turbid Photosynthetic rate Photosynthetic rate surface Enough light here for growth 100 m 500 m 1000 m Too dark for growth 3500 m So phytoplankton will grow well when they are close to the surface ... … but phytoplankton that are deeper down will not receive enough light for growth The light available for phytoplankton is controlled by a number of different environmental factors LIGHT ENERGY Phytoplankton production Phytoplankton biomass Ocean circulation Climate Weather Incident solar radiation Ice cover Wind mixing Average light in surface mixed layer Turbidity Mixed layer temperature Phytoplankton production Phytoplankton biomass In addition to light, phytoplankton need a wide range of chemical elements to build organic material Carbon is the most abundant element in organic material However, carbon is in plentiful supply in the surface oceans Carbon dioxide is readily soluble in water, and can diffuse in from the atmosphere Other elements are needed to build phytoplankton biomass Some elements are required in large amounts, whilst others are needed only in minute quantities These elements are usually called nutrients Nutrients needed in large amounts include nitrogen, silicon and phosphorus Ocean circulation Climate Weather CHEMICAL NUTRIENTS Incident solar radiation Ice cover Wind mixing Average light in surface mixed layer Turbidity Mixed layer temperature Phytoplankton production Phytoplankton biomass Again, there are complex environmental controls on the amount of nutrients available to phytoplankton Ocean circulation Climate Chemical nutrient supply Weather Incident solar radiation Ice cover Average light in surface mixed layer Turbidity Mixed layer temperature Nutrient availability Wind mixing Phytoplankton production Phytoplankton biomass Biogenic regeneration Trace elements are elements that are needed in very small amounts Many are metals, such as iron, zinc and cobalt. They may form parts of enzymes, so that trace elements can be important controls on growth and uptake of nutrients Ocean circulation Climate Chemical nutrient supply Weather Trace elements Incident solar radiation Ice cover Average light in surface mixed layer Turbidity Mixed layer temperature Nutrient availability Wind mixing Phytoplankton production Phytoplankton biomass Biogenic regeneration Plant growth Resource limitation Grazing control Summary So far, we have looked at controls on phytoplankton growth rates Removal of phytoplankton is an important control on both biomass and production Ocean circulation Climate Chemical nutrient supply Weather Trace elements Incident solar radiation Ice cover Nutrient availability Wind mixing Average light in surface mixed layer Phytoplankton production Phytoplankton biomass Turbidity Mixed layer temperature BIOMASS LOSSES Biogenic regeneration Herbivorous animals that graze phytoplankton are small, ranging in size from fractions of a millimetre to a few centimetres These animals grow and reproduce rapidly, so that their population increases fast when phytoplankton biomass increases This means that grazing is an effective control on phytoplankton The overall picture of control on phytoplankton involves many factors, often inter-related Ocean circulation Climate Chemical nutrient supply Weather Trace elements Incident solar radiation Ice cover Nutrient availability Wind mixing Average light in mixed layer Phytoplankton production Phytoplankton biomass Turbidity Biogenic regeneration Grazing Mixed layer temperature Sedimentation Plant growth Resource limitation Grazing control Summary You have seen that Cell division gives rapid population increase Phytoplankton does not increase exponentially in nature You have seen that Light decreases with depth Photosynthesis is determined by light, so decreases with depth and turbidity You have seen that Chemical nutrients are also important for phytoplankton growth Grazing by herbivores can control the abundance of phytoplankton Ocean circulation Climate Chemical nutrient supply Weather Trace elements Incident solar radiation Ice cover Nutrient availability Wind mixing Average light in mixed layer Phytoplankton production Phytoplankton biomass Turbidity Biogenic regeneration Grazing Mixed layer temperature Sedimentation NOTES for USERS The material in this slide show is designed to support the teaching of science at Key Stage 4 A full description of the slide show, and linked activities for students, can be found on the National Marine Aquarium (NMA) web-site: www.national-aquarium.co.uk Teachers are free to amend the slide show in whatever way they feel fit, or to use slides in other contexts. However, please note that neither the NMA nor the designers will accept responsibility for modifications, and original material remains copyright of the NMA Individual images used in the slides are copyright of NMA or STEP, except where acknowledged separately The slides have been set up to display as A4 landscape format. If they are incorporated into other slide sequences with different display settings, change in aspect ratio and text location will occur The slide sequence contains the minimum of effects and transitions. However, there are some automated animations, and teachers will wish to make sure that they are familiar with the sequence before use in class Use the PowerPoint notes viewer to obtain additional information for some slides Science Training & Education Partnership
