Standing stock measurements

The earliest attempts to measure organic production in the sea were indirect, being based on estimates of the total amount of plant material in the water, i.e. the standing stock. This does not give a direct indication of the rate of production because account must be taken of the rate of turnover. If the plants are being very rapidly eaten, high production may maintain only a small standing stock. For example, on a well-lit coral reef, as much as 1-5 kg of seaweed can grow on every square metre in a year. However, at any one time, only a few small pieces may be seen because herbivorous fish and urchins quickly graze the growths down (Shepard, 1983). Alternatively, where the consumption rate is very low and the plants are long lived, a large standing stock is not necessarily the result of a rapid production rate. A large standing stock may itself limit production by reducing the penetration of light through the water and diminishing the supply of nutrients.

The size of the standing stock depends upon the balance between the rate of production of new plant cells and the rate at which they are lost by animal consumption and by sinking below the photosynthetic zone. To determine production rates from standing stock measurements it is therefore necessary to estimate both the rate of change in size of the population and also the rate of loss, the latter being particularly difficult to assess with any certainty. The following methods have been used for measuring the standing crop.

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