ANSWER IN FULL Most marine organisms have a density greater than seawater (for e

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ANSWER IN FULL

Most marine organisms have a density greater than seawater (for example, cocolithophores secrete a calcium carbonate covering). Consequently, most are not neutrally buoyant (they sink). The sinking rate can be conceptualized as:

SR (sinking rate) = (w1 - w2) / (R * Vw) where w1 is the density of an organism, w2 is the density of seawater, R is the surface resistance and Vw is the viscosity of water (related to temperature and salinity). Plankton frequently display surface or body modifications that alter their surface resistance (e.g., long spines or other odd body shapes that spread their mass over a large surface area, see Figure 1). How does body shape affect this relationship and how does body shape affect sinking in plankton? Nekton achieve buoyancy by altering density by for example, having gas filling sacs such as a swim bladder. Why don’t nekton have similar long spines and odd shapes compared to plankton?

Explanation / Answer

The spines and long projections seen in plankton gives resistance to the plankton to prevent sinking. These projections increase surface area and increase resistance to the water. The R or surface resistance is increased.

In Nekton, the body is streamlined to propel itself through the water. These need to search for food in the water. Plankton need not search much for food, they just need to stay afloat. The debris of dying fish is enough for their food. Hence, their shapes vary

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