The microbial loop
In the marine ecosystem the foregoing elementary account of the organic food cycle must be extended to take account of the significance of dissolved organic matter DOM in seawater. As mentioned earlier see Section 4.3.3 an appreciable proportion of the products of photosynthesis become released from plant cells and soon appear in the water as DOM. Although some of this component of primary production may be reabsorbed by phytoplankton, much of it is rapidly taken up by planktonic bacteria. The...
Viscosity
The viscosity of seawater decreases considerably with rise of temperature and increases slightly with increase of salinity. The coefficient of dynamic viscosity is a measure of the drag exerted on moving objects in a fluid. In seawater of salinity 35 o at 0 C the coefficient of dynamic viscosity is 18.9 X 10 9 N per cm2 per unit velocity gradient, and at 30 C is only 8.7 X 10 9. These values indicate that resistance to movement is over twice as great in the coldest parts of the sea as in the...
Dissolved organic matter DOM
Particulate organic matter is always present in seawater, but in addition, varying quantities of organic compounds are present in solution. This is referred to as dissolved organic matter DOM or dissolved organic carbon DOC Jorgensen, 1976 Williams, 1975 . The estimation of minute quantities of organic solutes is difficult, but it appears that ocean water commonly contains about 2 mg carbon per litre in dissolved organic forms, in some of which nitrogen, phosphorus, sulphur, iron or cobalt are...
Reproduction
In the sparse population of the dark levels of the sea, finding a mate must present a problem. Possession of photophores or the ability to communicate by sound or scent must greatly increase the chances of success. Light signals can provide a means of communication in social and courtship displays and in warning and territorial behaviour. An additional adaptation for this purpose has been the evolution of dwarf parasitic males. For example, in some ceratioid angler fish the male is much smaller...
Fishing methods
Even with the refinements of modern science and technology, fishing remains an essentially primitive method of obtaining food. In our exploitation of the fish stocks of the sea, we still behave mainly as nomadic hunters or trappers of natural populations of animals living in the wild state. There are broadly three ways of capturing fish they may be scooped out of the water by means of a net bag such as a trawl or seine they may be enticed to bite upon a baited hook attached to a fishing line or...
Lampitt Snow Falls In The Ocean
Bayne, B.L. 1964 . Settlement of Mytilus. J. Anim. Ecol., 33, 513-23. Bayne, B.L. 1969 . The Gregarious behaviour of the larvae of Ostrea edulis at settlement. J. Mar. Btol. Ass. UK, 49, 327. Buchanan, J.B. et al. 1978 . Variability in benthic macrofauna. J. Mar. Biol. Ass. UK, 58, 191-209. Corliss, J.B. and Ballard, R.D. 1977 . Oases of life in the cold abyss. National Geographic Magazine, 152, 441-53. Crisp, D.J. 1974 . Factors influencing the settlement of marine invertebrate larvae. In...
Sandy shores
Detailed accounts of the ecology of sandy and muddy shores and their inhabitants can be found in Bassindale and Clark 1960 , Brafield 1978 , Brown and McLachlan 1990 , Eltringham 1971 , Evans and Hardy 1970 , Hails and Carr 1975 , Hayward 1994 , Ranwell 1972 and Swedmark 1964 . The sizes of particles to which the name 'sand' is applied has been given as coarse sand 2.0-0.5 mm medium sand 0.5-0.25 mm fine sand 0.25-0.062 mm see Section 6.1.1 . Seashore sands contain particles of many types and...
Chlorophyll estimations
The quantity of chlorophyll that can be extracted from unit volume of seawater depends upon the number of plant cells present, and it is possible to calibrate a scale of pigment concentration against quantities of plant tissue Harvey, 1950 . A measured volume of raw seawater is filtered and or centrifuged to collect all cells. These are then treated with a standard volume of acetone or alcohol to extract the chlorophyll. The intensity of colour in the extract is measured colorimetrically or...
Ocean currents
The major currents of the oceans are caused by the combined effects of wind action and barometric pressures on the surface, and density differences between different parts of the sea. The density differences exist mainly because of inequalities of heat exchange between atmosphere and water at various parts of the sea surface, and also because of differences of evaporation and dilution. The course taken by currents is influenced by the rotation of the earth and by the shape of the continents and...
Pelagic deposits
Pelagic deposits occur beneath deep water beyond the edge of the continental slope, carpeting the deep ocean basins. Much of this material is of fine texture, and its nature varies with the depth and with the types of organisms that abound in the overlying water. At depths of less than about 6000 m, pelagic deposits contain a considerable proportion of material of biological origin, commonly some 30 per cent or more by weight. Although these deposits are termed 'organic', they seldom contain...
Keeping the catch
Keeping the catch fresh once the fish have been caught has always been a problem and the length of time iced fish will remain in reasonable condition effectively limits the duration of fishing for distant-water trawlers if they rely solely on ice for preservation. The development in recent years of efficient and cost-effective refrigeration and storage systems on board larger fishing boats, has made much longer fishing trips possible. If fish are stored directly in the hold, then dry...
References Bvw
Barnes, R.S.K. 1979 . Sediment preference of Hydrobia. Est. Coastal Mar. Sci., 9, 231-4. Barnes, R.S.K. and Greenwood, J.G. 1978 . Response of Hydrobia ulvae to sediments of differing particle size. J. Exp. Mar. Biol. Ecol., 31, 43-54. Barnes, W.J.P., Burn, J., Meadows, P.S. and McLusky, D.S. 1969 . Corophium volutator - An intertidal crustacean useful for teaching in schools and universities. J. Biol. Educ., 3, 283. Murphy, J. and Riley, J.P. 1962 . Analytica Chim. Acta, 27, 31.
The detritus chain
From the preceding sections we have derived several figures for energy content of various contributions to the organic detritus reaching the sea bottom. To these must be added a small amount to represent the bodies of dead pelagic predators sinking to the sea floor, which we will take to be equivalent to 20 per cent of tertiary pelagic production, giving a further 0.2 X 17 3.4 kcal-m 2-yr These energy sources in detrital form can be summarized as follows This gives us a figure of 378.4...
Surface currents
The chief surface currents and their relation to prevailing winds are shown in Figure 1.6. In the Equatorial belt between the Tropics of Cancer and Capricorn, the North-East and South-East Trade Winds blow fairly consistently throughout the year, setting in motion the surface water to form the great North and South Equatorial Currents which flow from east to west in the Atlantic, Indian and Pacific Oceans. Across the path of these currents lie continents which deflect the water north or south....
Behavioural and activity responses of mobile animals
Physiological and behavioural adaptations are necessary to withstand the fluctuating nature of the shore environment Gibson, 1969 . The wide and rapid changes of temperature and salinity that occur on the shore surface during low tide require wide eurythermy and euryhalinity in the exposed population Cornelius, 1972 Southward, 1958 . They must also be capable of making appropriate adjustments of behaviour in response to changes in their surroundings. The limpet Patella , if wetted with...
Global primary production
In Table 5.1, comparisons are made between primary production on the land and in the sea. The concept that open ocean areas have a productivity comparable to that of deserts on the land and much lower than that of coastal areas and upwelling zones, is well established. However, techniques for measuring organic production are constantly being refined and some recent data suggest that there may be two to three times as much organic matter per unit of surface area in the open ocean than previously...
Diel patterns
The study of SSLs together with data from deep-level net samples indicate that throughout the oceans, in both deep and shallow water, a numerous and varied assortment of animals perform vertical migrations with a diel rhythm. There are differences in the depths through which different species move, the speeds at which they ascend and descend, and the precise times at which they make their movements, and the same species may behave differently in different areas and at different times, but there...
Some laboratory exercises
A Salinity measurements by titration and conductimetry. B pH measurements in seawater and determination of titration alkalinity. C Estimation of a minor constituent for example phosphate Murphy and Riley, 1962 . D Elementary studies on barnacles, for example Semibalanus balanoides, B. perforatus, B. crenatus, Chthamalus stellatus, Elminius modestus. Diagnostic characters. Measurement of rate of cirral activity over ranges of temperature, salinity and pH. Comparison of the activity ranges of...
Regeneration
The processes of return of plant nutrients to the water following the degradation of organic compounds are termed regeneration. Regeneration is 'direct' when the products set free into the water by metabolism are directly utilized by plants, which is the case with most of the excretory products of marine animals. Phosphorus is excreted mainly as phosphate with some soluble organic phosphorus Marshall and Orr, 1961 . In most marine animals, nitrogen is excreted mainly as ammonia. Teleosts...
Fauna and flora
Pelagic organisms in estuaries face difficulties of maintaining position in the ebb and flow of water. The net transport of water is downstream, tending to flush pelagic organisms out to sea. On the rising tide there is some danger that they might be carried up into lethally low salinities. Some pelagic animals or larvae adjust their behaviour to reduce these dangers. Some swim mainly on the flood tide and sink to the bottom on the ebb, thereby avoiding being washed too far seawards, e.g....
Wars and fish stocks
During the first half of the twentieth century the fisheries of the north-east Atlantic were twice interrupted by war. Conditions on some of the major fishing grounds visited by British vessels have fluctuated correspondingly, with symptoms of underfishing during war years and severe overfishing in peacetime. For example, the North Sea provides an important fishery for haddock. During the years prior to 1914, the total landings of haddock from this area showed a fairly steady decline. During...
Terrigenous deposits
Terrigenous deposits are found near land, covering the continental shelf and upper parts of the continental slope. Much of this material is derived from weathering and erosion of exposed land surfaces, and consists largely of particles worn from the coast by wave action or carried into the sea by rivers or glaciers. Terrigenous deposits contain some organic material, often some 0.01-0.5 per cent of the dry weight, the finer-texture deposits usually having the greater proportion of organic...
Feeding strategies
There are broadly four ways in which benthic animals gather food they filter suspended particles from the water, they collect food particles which settle on the surface of the sediment, they obtain nutriment from the organic material which has become incorporated in the deposit, or they prey upon other animals. Many of course take food from several sources. For example, the shrimp Crangon feeds largely on surface debris but also preys on small animals the edible crab Cancer, is omnivorous,...
Energetics of a marine ecosystem
Living organisms, unlike machines, cease to exist once they stop working. All biological activity depends upon continual transfers and transformations of energy, without which any natural living system almost immediately disintegrates irreversibly. We will now draw together some of the information from preceding pages in an elementary consideration of certain energy relationships of marine life, with particular reference to shelf seas around the British Isles. Directly or indirectly the source...
Coriolis effect
Wind action on the surface does not simply blow the water in the same direction as the wind, except in very shallow depths. The earth's rotation causes a deflecting effect so that surface water is moved at an angle to the wind. This deflection, generally known as the Coriolis effect after the French engineer and mathematician who first derived an equation for it, influences any object moving on the earth's surface, and is due to the rotational movement of the earth beneath the moving body. In...
European hake Merluccius merluccius
Hake Figure 9.15 extend along the eastern side of the Atlantic from Norway and Iceland where it is only seasonally common to Morocco in North Africa. Hake are also found in the Mediterranean. It is a fish of deep water, occurring mainly at depths below 200 m, but throughout adult life it performs seasonal migrations into shallower water for spawning during spring and summer, returning to deep water in the autumn. Further south, along African and American coasts, extending down to South Africa...
Tides
Although the behaviour of tides is very complex, the underlying cause of their motion has been understood since Newton 1647-1727 accounted for tides as due to the gravitational attraction of the moon and the sun upon the oceans. A brief description is given here but fuller explanations can be found in the Admiralty Manual of Tides Doodson and Warburg, 1941, reprinted 1973 . Other useful and practical material on tides and tidal streams can be found in the RYA Manual of Navigation RYA, 1981 ....
Ocean trenches
These are the deepest parts of the ocean floor where depths exceed 7000 m. They occur mainly beneath the western Pacific Ocean close to oceanic islands for example, east of the Philippines and the Mariana Islands is the Mariana Trench, where the deepest known soundings have been made at 11 034 m. This is part of a great line of trenches extending north from the Philippines, along the east of Japan and on to the Aleutians. The bottom is also very deep in the New Britain Trench near the Solomon...
Plate tectonics
The theory of plate tectonics was formulated in the late 1960s and brings together the theories of sea floor spreading and continental drift. The continents and ocean basins are believed to have evolved over the past 200 million years or so and plate tectonics provides an explanation for the way in which this may have happened. According to current theories of plate tectonics and sea floor spreading, the outer crust of the earth the lithosphere is made up of about 20 separate lithospheric...
Nekton
Various types and sizes of midwater trawl have been designed to attempt the capture of nekton at middle depths down to 1000 m or more Harrisson, 1967 . The Isaacs-Kidd net is an elongate conical bag, usually with a mouth aperture of 8 m, and with an angled depressor plate to keep the net below the surface while towing. It can be fitted with a depth recorder, and its depth during towing can be monitored on hydrophones by attaching to the net a pressure-sensitive sound-emitter with a pulse...
Deepsea hydrothermal vent communities
In some areas of the eastern Pacific and Atlantic, hot springs or hydrothermal vents escape from volcanic fissures along the global system of mid-oceanic ridges see Section 1.2.3 where sea-floor spreading occurs. Here water emerges from cracks and crevices at temperatures of up to 250 C. Even hotter vents exist where the water flows at up to 380 C from 'black smoker chimneys', formed from precipitated minerals. In 1977, the manned submersible 'Alvin' explored one of these newly discovered...
Red tides
Certain species of dinoflagellates contain highly toxic substances which can cause the death of other marine creatures which eat them. Under certain conditions when an excess of nutrients is present and the sea is very calm, certain dinoflagellates multiply very rapidly and form a bloom. The water is often discoloured hence the name 'red tide'. Not all 'red tides' are red or toxic, but those that are occasionally cause the death of large numbers of fish. In recent years, many fish farms have...
Mangrove swamps
In tropical and subtropical areas a characteristic feature of the upper levels of estuaries and sheltered parts of the seashore is the mangrove swamp forest. This develops on mud flats which are exposed at low tide. The genus Rhizophora is a common mangrove tree which grows to large size, supported above the surface of the mud on a number of downcurving prop-roots resembling flying buttresses. These prop-roots contain air spaces which provide oxygen for the underground root system embedded in...
Oil pollution of beaches
The fate and effects of oil washed up on beaches depend not only on the variables such as oil type, mentioned above, but also on the energy level of the shore degree of exposure to wave energy and on substratum type. In general, the more exposed the shore, the quicker the biological recovery time of the littoral benthos. This applies both to rocky and sedimentary beaches. Oil does not remain long on wave-battered rocky shores, and where vertical cliffs are present the oil may never reach them...
Nutrients
In addition to dissolved carbon dioxide, which is present in seawater in ample quantities to support the most prolific naturally occurring plant growth, there are other substances, the nutrients, which plants also extract from the water and which are essential for their growth. Many of these are minor constituents of seawater, present only in very low concentration, and their supply exerts a dominant control over production. Nitrate and phosphate are of special importance. Where the quantities...
Water bottles
Before the advent of CTD probes and rosette samplers, most water sampling was done using simple water bottles such as the Nansen-Pettersson Figure 3.5 . Most such bottles take the form of an open-ended cylinder with spring-loaded valves for closing the ends. The sampler is lowered with the ends open so that water flows freely through it. When the required depth is reached, a release mechanism is operated by sending a slotted weight known as a messenger down the suspending wire, which causes the...
Elementary classification of the marine environment
Although the mixing effected by the oceanic circulation ensures that the major parameters vary but little throughout enormous volumes of water, there are nevertheless some strong contrasts between different parts of the sea. The cold, dark, slowly moving bottom layer of the deep ocean is obviously a very different Figure 1.8 Main divisions of the marine environment. Figure 1.8 Main divisions of the marine environment. environment from the well-illuminated, wave-tossed waters of the sea surface,...
Animal life
The animal population of sandy shores mainly dwells below the surface, but includes some species which at times emerge to crawl or swim. Along the upper parts of some sandy beaches is a zone where the sand dries out and air penetrates during intervals between periods of submergence. This is the littoral fringe of the sandy shore, which in the British Isles is often inhabited by the burrowing amphipod Talitrus saltator, occurring in great numbers where there is much organic debris deposited...
Marine phytoplankton
Marine phytoplankton is made up of small plants, mostly microscopic in size and unicellular. Two orders of algae commonly predominate in the larger, net phytoplankton Diatoms Bacillariophyceae and Dinoflagellates Dinophyceae . The phytoplankton often also includes a numerous and diverse collection of extremely small, motile plants collectively termed microflagellates. Floating masses of large algae are found living and growing in some areas, notably the Sargassum weed of the Sargasso area of...
Radioactive pollution
Radioactive materials may enter the sea from two main sources from weapon testing via atmospheric fallout and from atomic power industries. The main contaminants are strontium-90, caesium-137 and plutonium-239. In the UK, a major source of radiation pollution has been via the discharge of cooling water from Sellafield Nuclear Power Station. The level of discharge has been considerably reduced in recent years but caesium-137 which does not occur naturally remains in sufficient quantities for it...
Chemical composition
Estuary water is not a simple dilution of seawater. Many subtle changes in composition are involved, varying with local conditions. The relative proportions Figure 8.16 Section of Tyne Estuary showing isohalines, isotherms, percentage oxygen saturation and distribution of dominant planktonts at 2 m depth. Zone A - marine plankton containing Sagitta elegans, Nyctiphanes couchi, Calanus, Paracalanus, Pseudo-calanus, nauplii of Semibalanus balanoides, polychaete larvae, etc. Zone B - very sparse...
Mariculture requirements and methods
A primary requirement for animal farming is to keep one's stock within a protected area, where they are safe from predators and can grow under controlled conditions without severe competition for food from unwanted species. Oysters and mussels, once they have settled, remain virtually stationary, and the beds where they are grown can to some extent be protected from enemies and competitors. But fish roam about, often over considerable distances, and fish-pens cannot easily be constructed in the...
Rocky shores
Rocky shores exist where the effect of waves on the coastline is mainly erosive, wearing down the softer materials and carrying them away, leaving the hardest rocks exposed. Most of the substrate is therefore stable and permanent, forming a secure surface upon which can grow a variety of organisms requiring attachment for example, large algae, barnacles, mussels and limpets. The appearance of the shore depends largely upon the type of rock exposed. Horizontal strata often erode to a stepped...
Lemon sole Microstomus kitt
Like plaice, the lemon sole Figure 9.19 is a flatfish of shelf areas of the north-east Atlantic ranging from the Arctic to the Bay of Biscay. It does not extend as far south as plaice and generally favours a rougher sea bottom, but the two species often occur together. Lemon sole are specially abundant in the north-west part of the North Sea off the east coast of Scotland, also around the Faroes and along the south-west coast of Iceland and these are the most important fishing grounds Figure...
A field course book list
The following books are often useful during field courses General guides Barrett, J.H. and Yonge, C.M. 1972 . Pocket Guide to the Sea-Shore revised edition . London, Collins. Campbell, A.C. and Nicholls, J. 1976 . Hamlyn Guide to the Seashore and Shallow Seas of Britain and Europe. London, Hamlyn. Cremona, J. 1988 . A field atlas of the seashore. Cambridge University Press. Dipper, F.A. and Powell, A. 1984 . A field guide to the water life of Britain. Reader's Digest Nature Lover's Library....
Light and the compensation depth
In the process of photosynthesis the energy of solar radiation becomes fixed as chemical energy in organic compounds. The efficiency of the ocean surface in this energy transformation must vary with locality and conditions, but is probably on average about 0.1-0.5 per cent overall, an efficiency a little lower than that of the land surface. The ability of plants to absorb and utilize light in photochemical reactions is due to their possession of the green pigment chlorophyll and certain other...
Reproductive adaptations
The difficulties of survival on the shore have their effects on all phases of life, including reproductive processes and larval and juvenile stages. The majority of benthic organisms start life as floating or swimming forms in the plankton, and may become widely dispersed in the water before they settle on the sea bottom. Shore creatures face special risks of great losses of pelagic eggs and larvae during this phase if they drift far from the shore and settle outside the zone in which survival...
Buoyancy problems
Most protoplasm, cell walls, skeletons and shells have a density greater than seawater, and therefore tend to sink. The specific gravity of seawater is usually within the range 1.024-1.028. The overall density of much of the zooplankton is around 1.04 and of fish tissues about 1.07. Within a floating body the distribution of weight determines its orientation in the water. Therefore one of the problems facing pelagic organisms is how to keep afloat in a suitable attitude between whatever levels...
Temperature tolerances and biogeography
Water temperature exerts a major control over the distribution and activities of marine organisms Kinne, 1963 . Temperature tolerances differ widely between species, but each is restricted in distribution within its particular temperature range. Some species can only withstand a very small variation of temperature, and are described as stenothermal. Eurythermal species are those of wide temperature tolerance. Strict stenotherms are chiefly oceanic forms, and their distribution may alter...
Mackerel Scomber scombrus
Mackerel Figure 9.23 are found in warmish water on both sides of the North Atlantic. Their range extends from the south coast of Norway and northern North Sea, along the west coasts of the British Isles and into the English Channel, and as far south as the Canaries. They also occur in the Mediterranean and on the western side of the Atlantic from south Labrador to North Carolina. The life history and migrations of mackerel have been well documented by Lockwood 1976, 1978, 1989 . Two stocks of...