The food supply of the benthic macrofauna derives, directly or indirectly, almost entirely from living and dead particulate matter sinking from the overlying water. There is very little primary production of food on the sea-bed because plants can grow only where there is sufficient light for photosynthesis. Vegetation on the sea bottom is therefore limited to shallow water. Large algae produce a lush growth on and near the shore, especially in middle latitudes, and form a primary food source which supports many omnivorous and vegetarian animals, and contributes quantities of organic debris to the local sediments. This vegetation seldom extends deeper than some 40-60 m and is confined to areas of rocky bottom, or stones large enough to provide secure attachment for the plants. Rock and sediment in shallow water may also be covered with a thin microfloral film, mainly diatoms and other unicellular algae. Surface layers of sediments contain large numbers of bacteria, and traces of food are also produced by chemosynthetic species capable of metabolizing inorganic compounds.
Particulate food sinking through the water reaches the bottom in great variety. There is sometimes an appreciable amount of vegetable matter derived from the land, and even in very deep water dredging has disclosed a surprising quantity of terrestrial material in the form of fragments of wood and leaf. Much of this may be carried into the deep ocean basins by turbidity currents (see Section 5.7) flowing down the continental slope. However, in most areas the greater part of the food supply consists of the remains of pelagic organisms. In shallow water, the major component is usually planktonic diatoms and other microscopic plants, and the abundance of this food depends upon the rate of surface production. Seasonal changes in the quantity of phytoplankton produce fluctuations in the supply of food to the benthos (see Section 5.4.3). In temperate latitudes the numbers of planktonic diatoms reaching the bottom may be over a hundred times greater during the summer months than in winter, and there are associated changes in the weight of benthic populations.
The movement of food particles from the surface to deeper levels is not solely a matter of passive sinking. Active transport downwards is effected by vertically migrating organisms which ascend to feed at the surface and then move downwards, where they may be devoured by deeper-living predators or where their faecal pellets may be used as food by other organisms. Faecal pellets are often rich in organic matter, some of which may be material that was not digested during passage through the gut, and some is bacterial protoplasm rapidly multiplying on this organic substrate (Harding, 1974).
There is a tendency for planktonic micro-organisms, fragments of organic debris (e.g. discarded 'houses' of larvaceans) and inorganic particles to become aggregated by both physical and biological processes into larger clumps. These provide micro-habitats which harbour numerous and diverse communities of bacteria, algae and protozoa (Fowler and Knauer, 1986). Such material sinking through the water as particles greater than 0.5 mm in size, is referred to as 'marine snow' (Lampitt, 1996) and is sometimes observed to carpet the sea bottom as a layer of 'marine fluff'. This is probably one of the main ways in which biogenic material reaches the sea-bed. The protoplasmic content of this snow undoubtedly contributes significantly to the food web of deeper levels, especially by enabling animals to obtain food from micro-organisms which, though too small to be directly consumed individually, can be readily ingested in this aggregated state. This is also an important route whereby atmospheric CO2, after solution in the sea surface and fixation by photosynthesis, is rapidly transferred to deep levels and eventually released, probably mainly as bicarbonate and dissolved CO2. This has obvious implications for our understanding of the interactions between atmosphere and ocean with respect to the 'greenhouse effect' (see Section 10.2.1).
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Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.