From our assessment of 400 kcal-m-2-yr-1 of food energy available on the sea bottom, we must now deduct 47 kcal • m-2 • yr-1 directly utilized by benthic fauna, leaving 353 kcal-m-2-yr-1 for bacteria. We have estimated the consumption of bacteria by benthic animals to be 140 kcal-m-2-yr-1 and for the stock of bacteria to remain constant this must be the annual production. This implies a high conversion efficiency of 140/353 = 0.4 approximately, and a respiratory loss of 213 kcal-m-2-yr-1.
The biomass of benthic bacteria is obviously very small compared with larger organisms. It varies greatly with the grade of deposit, being much greater in muds than in coarse substrates. Because the English Channel bottom is mainly of a gravelly texture, we will take a low figure of 0.025 g dry wt-m-2 for benthic bacteria. Assuming a calorific value of 4 kcal-g-1 dry wt for bacteria, this gives an energy content for the stock of 4 X 0.025 = 0.1kcal-m-2. For an annual production of 140 kcal • m-2 • y-1 this stock must reproduce itself over 1400 times, which is certainly not a very high rate of multiplication for bacteria (Zhukova, 1963).
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