Introduction to Marine Biology 4th Edition by George Karleskint,Richard Turner,James Small

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Life in the open sea is challenging because of low levels of nutrients, lack of hiding places, and the need to remain afloat. Small cell size and reliance on a small number of genes reduce the dependence of primary producers and osmotrophs on mineral and organic resources. Patchiness, large numbers, transparency, and low-nutritive quality are several ways in which organisms in the open sea deal with predation. Many plankton and nekton swim by cilia, flagella, appendages, and undulatory tails, but mechanisms of buoyancy and increasing frictional drag also prevent pelagic organisms from sinking from the surface waters.