Week 9

• Chlorophyll-a sensor observing the oceans from space measures blue, red absorbed, green, and IR reflected.
• Prochlorococus and Synechococus are different groups that dominate in different regions.
• Different groups, including small eukaryotes, diatoms, and others, dominate in different regions.
• Phytoplankton are at the base of the oceans food chains.
• Ocean Phytoplankton are responsible for half the Earth’s total primary production.
• Learning outcomes: Be aware of the major groups of phytoplankton in the ocean and appreciate how we observe these organisms (including from space).
• Global primary production is the fixation of gaseous or dissolved CO2 to produce organic matter.
• The oceans contribute around half of global primary production.
• Vascular plants dominate terrestrial production with only minor contributions from other groups.
• In contrast, oceanic primary production is dominated by unicellular organisms collectively termed phytoplankton.
• Phytoplankton form the basis of all major oceanic food webs.
• Macroalgae, also known as seaweed, do not proportionately contribute to global primary production.
• Phytoplankton and Ocean Primary Production are observed from space.
• The origins of modern phytoplankton involve multiple endosymbiotic events, often referred to as 'a bug, that ate a bug, that ate a plant'.
• Dinoflagellates are smaller than the largest diatoms and are weakly motile, with many having a readily decomposable cellulose cell wall but none having hard parts.
• Dinoflagellates may dominate the phytoplankton when silica is unavailable for diatom growth.
• Coccolithophores have a mosaic of calcite (CaCO3) plates covering the cell wall and can form massive summer blooms once diatom blooms have subsided.
• Phytoplankton is biomass dominated by three groups of larger eukaryotes: diatoms, dinoflagellates, and coccolithophores.
• Diatoms have a cell wall made from opal (SiO2) with a nano-scale structure, and are the ocean's main primary producer, growing at a rate of 3 div./day.
• Diatoms are often colonial and can form large tangled masses, dominating production in spring bloom and upwelling zones.
• Diatoms have a fossil record since 185 Ma and are believed to have evolved 250 Ma.
• Diatoms are used as a model for nanotechnology and attempts are being made to bioengineer smaller silicon chips.
• Diatoms have chloroplasts and oil filled "vacuoles" and can be autotrophic, heterotrophic, or "mixotrophic", combining photosynthesis with phagotrophy - ingestion of prey.
• Dinoflagellates have an organic cellulose wall and may be autotrophic, heterotrophic, or "mixotrophic".
• Dinoflagellates may contain toxins and concentrations may kill fish.
• Phytoplankton are numerically dominated by three small groups: Prochlorococus, the smallest known photosynthetic organism (prokaryotic), Synechococcus, a widely distributed cyanobacteria in oceans and freshwater systems (prokaryotic), and Pico-eukaryotes, a highly diverse and widely distributed group.
• Diatoms have a siliceous frustule (hard external "shell") made of opal (SiO2.n H2O), include the largest phytoplankton and are desirable as food for larger zooplankton and small herbivorous fishes.
• Phytoplankton and Ocean Primary Production
• Dinoflagellates, some species generate bioluminescence
• Bioluminescence as an alarm call, predator is illuminated
• Cover the predator in bioluminescence and the predator itself is eaten by something bigger
• Coccolithophorid algae, secrete CaCO 3 calcite
• Unicellular algae secrete tiny calcite platelets (1 - 5 μm) or “coccoliths” about a single cell in a “coccosphere”.
• Coccolithophorid algae are widespread but rare in T < 2 ° C; fastest growth – 1.5 div./day.
• Coccolithophorid algae are abundant in ancient warmer seas (e.g Cretaceous).
• Coccolithophorid algae may have problems with ocean acidification.
• Coccolithophorid blooms give a distinct pale “chalky” colour, spectacular from space.
• Coccolithophorid algae are abundant in ancient warmer periods (e.g Cretaceous).
• Chalk also contains opaline flints, remains of siliceous algae.
• Vast deposits of chalk in Europe from warm Cretaceous-age shelf seas.