BIO3082 Lecture Notes - Lecture 16: Lake Tanganyika, Climate Change Scenario, Diatom
Lecture 16 – Aquatic Food Webs
Effects of Climate Change on Aquatic Primary Production
• Marine primary production is changing
o Greenhouse gas emissions are decreasing oceanic planktonic primary
production (∆pp) – trends vary
o Outlooks vary depending on whether low emissions or high emissions
scenarios
o Overall decrease in primary production
o Increases of CO2 and stratification
• Global change → causes warming, carbonation and stratification of water
systems
o Effects can be stimulatory or inhibitory to primary producers
Effect
Stimulatory Effect
Inhibitory Effect
Increased water temperature
Faster metabolism
Critical thermal limits
Increased CO2 levels
Increased carbon fixation
Potential acidification
Increased stratification
Greater light penetration -
Can increase photosynthesis
Reduced nutrient mixing →
phytoplankton aren’t getting
nutrition → reduction in
biomass and diversity
Case Study: Lake Ecosystem
• Temperatures in Lake Tanganyika increased by 0.9˚c at surface and 0.2˚c at
bottom
o Difference in densities: surface less dense, bottom more dense →
increase stratification of lake → reduce fertile mixing and slowed
vertical mixing
• Significant decreases in abundance and diversity of planktonic primary
producers
• Other marine and freshwater systems, phytoplankton abundance have
increased
o E.g. warming in northeast Atlantic has resulted in net primary
production increase – more northern regions
o Previously cold regions have had increase in primary production
o Warm regions decreasing in primary production
• Effects at Bottom of Food Chain
o Warming has disrupted trophic interactions between phytoplankton
and zooplankton species
▪ Asterionella Formosa (diatom)
▪ Keratella chochlearis
• Feed on diatom
• Populations peak 21 day earlier
• Largely synchronous with diatoms
• Population remain stable as they consume diatoms
during peak bloom
▪ Daphnia pulicaria
• Populations expected to decrease due to lack of food
availability
• Feed on diatom
Not all Producers Respond to Warming Equally
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Document Summary
Reduced nutrient mixing phytoplankton aren"t getting nutrition reduction in biomass and diversity. Not all producers respond to warming equally: different primary producers respond in different ways to global change, due to timing, distribution, phenology. Includes species responsible for toxic blooms: effects on producers filter through food webs, specialist vs. generalise species. Increased warming local extinction as fish move to more suitable conditions in deeper waters and nearer the poles: biggest problem: overexploitation in combination with climate change loss of marine biodiversity at an alarming rate. Exam long answer: one major ecological effect of climate change is the remodelling of food webs. Summarise how climate change will effect trophic interactions in such systems. Structured answer: climate change is expected to cause large-scale changes in the distributions of fish species in marine ecosystems and in turn the fisheries that depend on them: fisheries are defined as a provisioning service".
