oceanography 31
Terms
undefined, object
copy deck
- Photosynthetic organisms – microscopic algae
- ⬢ Most microscopic algae are phytoplankton. ⬢ Produce food directly or indirectly for 99 % of marine animals. ⬢ We mentioned diatoms (silica shells), coccolithophores (small calcareous plates), dinoflagellates (have 2 flagellae for locomotion). ⬢ Did not mention photosynthetic bacteria.
- Photosynthetic bacteria
- The very small Prochlorococcus may form half of the ocean’s photosynthetic biomass, making it the most abundant photosynthetic organism on Earth.
- Factors affecting primary productivity
- ⬢ Availability of solar radiation. ⬢ Availability of nutrients. ⬢ Predation
- Energy flux:
- • Solar radiation – light penetrates the atmosphere, despite its thickness of over 80 km. However, very little light by 1 km depth in the ocean. • Photosynthesis restricted to the euphotic zone which extends from the surface to the compensation depth for photosynthesis. • The compensation depth for photosynthesis is where net photosynthesis is zero (i.e. gross photosynthesis = respiration) • The compensation depth for photosynthesis is approximately 100 m in the open ocean and may be less than 20 m in the coastal zone where the waters are more turbid.
- Two factors necessary for photosynthesis; solar radiation and nutrients.
- ⬢ In open ocean solar energy penetrates deeper into the water column, but the concentration of nutrients is low. ⬢ In coastal waters the light penetration is less, but the nutrient concentration is much higher. ⬢ Because the coastal zone is much more productive, nutrient availability must be the most important factor affecting the distribution of life in the oceans. ⬢ Remember coastal upwelling.
- Divide gross primary production into two components:
- • New production – generated using nutrients brought in from outside the local ecosystem by processes such as upwelling. • Regenerated production – generated using nutrients that are recycled within the system.
- Productivity in tropical Oceans
- ⬢ Solar radiation high, but nutrients low as the sunlit, surface waters are separated from deeper nutrient⬐rich waters by a permanent thermocline. ⬢ Productivity occurs at a relatively low, steady rate. ⬢ Exceptions includes areas of equatorial upwelling, coastal upwelling and coral reef ecosystems.
- Production in temperate oceans
- • Winter – nutrients concentrations highest, water column well mixed and isothermal, light relatively low. Light limited. • Spring – Compensation depth for photosynthesis increases as sun is higher in the sky, spring bloom occurs. Spring bloom becomes nutrient limited as a thermocline develops. • Summer– more solar radiation, but phytoplankton nutrient limited as a strong thermocline forms at a depth of about 15 m. • Fall – solar radiation reduced as sun gets lower in the sky, thermocline becomes unstable and breaks up. Nutrients return to surface water resulting in a fall bloom. Fall bloom becomes light limited.
- Fate of production
- • 90 % of production generated in the euphotic zone is decomposed within this zone. • 10 % sinks to deeper water. • 1 % of this accumulates on the ocean floor and may be buried. • Biological carbon pump – removal of carbon from the surface to deep waters.
- Biotic community
- assemblage of organisms that live together in a defined area.
- Ecosystem
- The biotic community and its abiotic environment, exchanging energy and chemicals.
- 3 categories of organisms
- Consumers • Herbivores – feed directly on plants or algae. • Carnivores – feed on other animals. • Omnivores – feed on both. • Bacteriovores – feed on bacteria. Produce • Detritus – waste products, dead and decaying remains of organisms. Used by • Decomposers – break down detritus for their energy requirements. Nutrients released into the environment and become available to autotrophs.
- Trophic Levels
- – Producers belong to the first trophic level (grass) – primary consumers to the second (sheep) – secondary consumers to the third (wolves)
- Conclusion:
- ⬢ It takes a lot of light to keep a killer whale going. ⬢ Can harvest more small fish (lower trophic level) than large ones.