Question

Ls4208_midsem_2017

7. What is the link between ecological stoichiometry and primary production in a coastal ecosyaystem? How net primary production can be measured in a coastal ecosystem?What is the link between net primary production and secondary production? [2+2+2=6 marks]

The question is from previous year question paper

Answer 1

Link between ecological stoichiometry and primary production:---
This is a pressing issue in many coastal waters, where anthropogenic activities have caused large changes in riverine nutrient inputs. Here we investigate variation in the biochemical composition and synthesis of amino acids, fatty acids (FA), and carbohydrates in mixed phytoplankton communities sampled from the North Sea.
✓The communities were cultured in chemostats supplied with different concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) to establish four different types of resource limitations. Diatoms dominated under N-limited, N+P limited and P-limited conditions. ✓Cyanobacteria became dominant in one of the N-limited chemostats and green algae dominated in the one P-limited chemostat and under light-limited conditions. Changes in nutrient availability directly affected amino acid content, which was lowest under N and N+P limitation, higher under P-limitation and highest composition to different degrees when experiencing shifts in nutrient availability. This will have implications for phytoplankton growth, community structure, and the nutritional quality of phytoplankton as food for higher trophic level.

Link between primary production and secondary production:----
It involve processes that occur in food webs. Controls may be top down (predator control) or bottom up (nutrient limitation), and separating them may be difficult.
✓Predator-prey interactions have been examined for both macro organisms and micro organisms, but total food webs that include both have only rarely been described. It is apparent that both kinds of controls have effects that may be direct, indirect, or interactive.
✓ Nutrient limitation affects plants primarily and the whole food web secondarily.
✓Nutrient limitation takes several forms. Nutrient supply may limit the currently dominant population; it may limit the potential net primary production, or it may limit gross primary production in excess of respiration. While nutrient supply may limit total ecosystem production, it also influences community structure in ways that can have far-reaching consequences.
✓ Even in communities lacking significant inputs of nutrients, some organisms may be well supplied. Microzones in the plankton probably expose phytoplankton to nutrient concentrations that vary by orders of magnitude.
✓The ocean contains a number of mesoscale and regional inputs of nutrients that produce localized, transitory blooms of phytoplankton in an otherwise oligotrophic sea. Because of their short-term nature, blooms tend to be out of synchrony with zooplankton and are limited by depletion of the nutrient supply rather than by grazing. The ocean is thus bottom-up controlled in localized blooms and may be top-down controlled elsewhere. As in most terrestrial systems, only a small fraction of the production of seagrass beds and salt marshes is utilized directly by grazers. However, the major producers on coral reefs, macroalgae growing between the corals, are heavily grazed. This affects community structure but not community productivity.