Biological factors controlling primary production

1. cilia Biological factors controlling primary production • Primary production, as well as being controlled by light, nutrients and temperature, is also controlled by grazing • Grazers on phytoplankton include:zooplankton, benthic filter-feederssuch as clams, as well as larger herbivores (e.g. blue whale) Tiny hairs (cilia) surround the mouth of this organism shown in the background, beating to capture food and to aid movement. When the cilia move, they give the impression of a rotating wheel—hence the term, rotifer, used to describe this group of zooplankton

2. Zooplankton grazing • Zooplankton grazing is a selectiveprocess—phytoplankton species are not grazed equally • Copepods* for example, discriminate between slow and fast-growing diatoms to maximize their protein intake • Some phytoplankton contain toxins which make them unpalatable to some zooplankton (i.e., grazers tend to avoid them) *The organism shown in the background is one type of copepod.

3. Phytoplankton diversity • Phytoplankton are very abundant in the ocean (approximately 10,000 cells per liter) • They have a huge variety of forms • Two major groups are: diatoms and dinoflagellates Shown as a background to this slide is adinoflagellate. Can you see its flagellum?

4. Some phytoplankton have smooth edges, and are shaped like pill boxes

5. Other phytoplanktonspecies have spineswhich project fromthe cell

6. Others are shaped like long columns or form chainsor both

7. Together, they are a diverse group of organisms!

8. Non-motile forms of phytoplankton have a tendency to sink out of the well-lit surface layers of the ocean.

9. Spines may slow down sinking by increasing the resistance of cells. Spinesmay also act asgrazing deterrents.

10. Vertical migration • Just as some phytoplankton are motile, zooplankton can swim • Some zooplankton rise to the ocean’s surface at night, and return to deeper layers during the day Q: Why do you think they do this?

11. A: To avoid predators and to feed on phytoplankton in the upper layer Vertical migration has also been shown to increase the residence time of some zooplankton in estuaries, because their movement partly counteracts the transport of water due to tides.

12. Cost:benefit for vertical migration • Vertical migration is energetically expensive, because although zooplankton can take advantage of warm surface layers with abundant food for part of the day, they also swim into deeper, colder water • Deeper water has less food, and its temperature slows down egg development and reduces birth rate • Overall, there must be an advantage to doing it.