Shallow water and intertidal marine sediments are often heterogeneous. This heterogeneity has led to a definition of microenvironments and their associated biological species. The definition encompasses habitat and species size, species behaviour and physiology, stability and environmental interfaces. We distinguish between open and closed interfaces, and suggest an associated topological structure. Examples are given from the intertidal zone. Three of these are discussed in detail.

(i)Sand grains. The occurrence of periphytic micro-organisms on sand grains is considered. The topography of the sand grain surface is closely related to the distribution of microbial colonies some of which contain a range of species. Bacteria, blue-green algae and diatoms have been identified. Species interactions and micro-variation in sediment physico-chemistry are likely to affect the constituents, distribution and abundance of the colonies. The activities of periphytic micro-organisms change the bulk properties of sediments.

(ii)Banding in sediments. Characteristic banding patterns are described from a sandy and muddy intertidal shore. Marked discontinuities in the microbial flora and physico-chemical properties occur at interfaces between the bands. For example, Eh, chlorophyll levels, and sulphide can all change dramatically over a few mm. The significance of these alterations for the meiobenthic and interstitial fauna is discussed.

(iii)Invertebrate burrow linings.Bioturbation structures including invertebrate burrows change local properties of sediments. The microbial and chemical properties of Nereis diversicolor burrow linings are described in detail. Sediment from the burrow lining closely resembles the sediment surface in many of its attributes. The sediment/water interfacial zone with its associated microbial and chemical properties is therefore extended vertically into sediments by these structures. Attention is drawn to the stabilising function of burrows and to their palaeoecological significance.

Radioactive species, in the dissolved state in sea water, can serve to define rates and directions of water movement. The requirements for such applications are that tracer species be soluble, chemically conservative, of half-life compatible with the process timescale under study and have non-uniform inputs. Boundary and point source inputs generate concentration gradients induced by the known-rate kinetics of radioactive decay. Advection-diffusion and box-model treatments are widely used in data interpretation and examples of a range of applications, based on 14C, 222Rn, 228Ra and fallout nuclides, are presented. Reactive radionuclides such as 228Th and 210Pb can, on the other hand, be used to trace the fate of many heavy metals introduced into the marine environment. The release of waste from the nuclear industry provides a very convenient source of tracers for coastal waters. This application is illustrated by several studies of Windscale-derived radiocaesium in Scottish waters.

The Hansen and Rattray (1966) procedure for classifying estuary circulation pattern is applied to the estuaries of the Dornoch and Cromarty Firths, and the Tay, Forth, and Clyde. All are found to be partlymixed, with the Cromarty Firth and Clyde approaching the stratified condition. The ability of the method to forecast stratification and circulation is examined by comparing predictions and field measurements in the five estuaries. Acceptable results are obtained in cases of better mixing, but some significant departures occur with low range tides and with irregular depth.

One dimensional dispersion coefficients are calculated for the five systems and vary from 70 to 1285 m2s−1. Values increase both as mixing diminishes and with distance seaward along the estuary. Comparison with the table relating values to contributing mechanisms given by Cox and Macola (1967) shows in these cases density-driven circulation to produce higher coefficients than storage basin effect. The results also suggest that transverse circulation induced by Coriolis force produces a further order of increase in dispersion coefficient, values then exceeding 500m2s−1.

The highest carbonate values are associated with exposed coasts of Lewisian gneiss, reaching 95% CaCO3 in SW Tiree: around Iona average values are 80 to 85% CaCO3. Maximum values of 60 to 70% on Islay indicate a regional gradient which reflects a reduced fetch southwards, and a greater input from reworked glacial drift and fluvial material.

High energy carbonate deposits are distinguished by the low diversity of their components, nearly all coming from fragmented molluscs and barnacles. Low energy carbonates have diverse components, with foram and echinoid values each reaching 10%. The ratio most easily separates the two facies (high energy mean = 18-5: low energy mean = 2-1).

In the immediate offshore tidal-swept zones such as the Sound of Iona barnacles are the most important contributors to the sediment.

Most of the carbonate is fresh and by its relationship to contemporary shore ecology can be shown to be of present-day origin. Offshore, however, relict grains are widespread. Their pitted surfaces are inhabited by very abundant diatoms, and it is tentatively suggested that local carbonate dissolution may be caused by them. Additionally they represent a much more abundant source of silica for eventual silicification of the carbonate than do sponge spicules, which are rare.

Recent studies of the unexpectedly diverse assemblages of ainimals living either in, or on, deep sea sediments have revealed a community of extremely low standing crop—seemingly directly attributable to the low fallout of utilisable organic matter onto the bottom. This benthic community is also characterised by small organism size and probable low rates of biological activity measured as respiration or reproduction.

Strictly comparable sampling methods demonstrate a close similarity between Rockall Trough (NE Atlantic) and the central N Pacific in terms of the proportions of major faunal groupings present, even if the constituent species are different, despite considerable differences in standing crop. Therefore the relative proportions of the wide spectrum of small, but not necessarily simple, forms of life that comprise the deep sea benthos may vary, but little, over wide areas of the world ocean. Moreover, considerable affinity of this fauna in Rockall Trough to that of the soft muds of Scottish sea lochs is suggested, even to species common to both habitats.

The deep sea fauna seems homogeneously dispersed over large areas, the major variability occurring at the smallest possible scale—that of the size Of the organisms themselves: by structuring their habitat into a myriad of microniches these animals probably have evolved a biologically highly complex type of community, characteristically vulnerable to, and slow to recover from natural and anthropogenic perturbation. The effect on this fragile and still obscure natural community, in realizing proposals to harvest deep sea minerals, is thus likely to be local extinction of the community followed by extremely slow recovery by means of larval recruitment and immigration from surrounding areas.

This paper reviews the knowledge of deterioration processes which occur when steel and concrete structures are situated in seawater. The basic corrosion mechanisms of steel, together with possible methods of protection, are outlined briefly. With regard to coatings and cathodic protection, recent developments to counteract the increasingly severe conditions encountered by oil-production platforms in the North Sea, are discussed. Concrete structures usually provide a naturally-inhibitive internal environment to confer protection from corrosion to encased steel reinforcements, but mention is made of the possibilities of such protection becoming ineffective during long service in severe offshore conditions.

The basic features of corrosion fatigue are described in the light of recent research but some aspects, which are of great importance for the performance of steel structures, are shown to be not well documented or understood. Corrosion fatigue of concrete structures has not been studied extensively, a particularly neglected area being the elucidation of the fundamental mechanisms of deterioration.

This paper considers the background, philosophy and desirability of the use of used automobile tyres in the construction of floating breakwaters for wave attenuation problems in general and their application to fish farm protection in particular. The method of construction and the assessment of performance are discussed.

Model tests using one quarter scale tyres in a hydrodynamics laboratory towing tank are described. By computerised data collection and processing, the wave attenuation characteristics were deduced for twentyfive breakwater designs made up from the two most commonly used tyre groups or modules. Wave induced loads on the catenary mooring system were also analysed for extreme values. This data forms part of a systematic study of scrap tyre breakwater design parameters and some conclusions can be drawn.

The implications of these model results are scaled to apply to the environmental requirements of fish farms and the relevance of the local topography is discussed.

The Clyde Estuary is recovering from gross pollution inherited from the age of the Industrial Revolution.It is necessary now to establish the degree of recovery and determine any subsequent effects of future planning consents. Documentation on water quality was subjective until the 1960's when quantitative studies on pollution levels commenced.

Much attention has been paid to dissolved oxygen (DO) levels in the estuary. The changes in the DO regime over the last ten years have been quantified with the help of multiple regression techniques. The use of these techniques in establishing the changes resulting from improvements to Dalmarnock and Paisley sewage treatment works is described. Deterministic models, based on the diffusion-convection equation, have been used to predict future DO conditions. The theoretical base of these models is outlined and examples are given of the use of the models in predicting the effects of possible developments on the estuary.

Biological monitoring has also been utilised to assess estuarine recovery. Benthic data has been accumulated since 1967. Regular surveys highlight improvements in species richness, diversity and stability. Spatial and temporal population variation was investigated and the salinity tolerances of the species considered. Fish life is increasing and is now present for much of the year, although salmon are still excluded from the upper Clyde system. The lower estuary remains an important overwintering feeding ground for wader populations.

The effects of changing scale on ships and semi-submersibles are explored in this paper. In the early part attention is drawn to the wide differences in design practice which exist for large ships with, in particular, a tendency for a lower length to breadth ratio as size is increased. Theoretical reasons for this are given, the principal ones being that this leads to a reduction in steel weight per ton displacement without any large increase in power. It is suggested that this tendency will continue until the weight of the transverse material in the hull approaches that of the longitudinal material. Many other characteristics of the ships improve with lower L/B ratios but manoeuvrability declines and in order to reap the benefit of low L/B designs greater research should be applied to improving this aspect of large ships.

Much greater flexibility in design exists for semi-submersibles since there are no draft restrictions. The paper examines the effects of geometric variations in semi-submersibles and concludes that the stability, dynamic motions and wind and hydrodynamic drag all improve with increasing size but that structural steel weight may not be a significantly lower percentage of the displacement unless design changes are made with changing scale. Attention is drawn to the big improvements in rolling (pitching) performance which would enable large floating platforms to have a very low level of motion. This could have great significance for the siting of petrochemical and other plants at sea.

Under the Offshore Installations (Construction and Survey) Regulations 1974 all structures established or maintained in UK waters must possess a valid certificate of fitness. To obtain this certificate annual visual inspections of parts of the structure must be carried out both above and below water. A major survey of the complete structure or platform is required every five years.

Underwater inspections may be carried out down to 50 m by divers on surface demand. Below 50 m when divers are involved it is essential to use either a diving bell or lock-out submersible. To avoid saturation diving and reduce diving hazards, the unmanned submersible has been developed as an underwater inspection tool.

Various navigation systems have been developed for offshore position fixing. Deepwater navigation and surveying relies on a combination of surface radio stations and seabed underwater acoustic transponders. Platform navigation for underwater inspection and maintenance is a major problem due to poor diving access and few underwater reference points.

The inefficiency of the present diver operated navigation and survey systems round platforms is now being investigated by a research team from the University of Strathclyde. Preliminary tests of equipment have already been carried out in a diving tank and at sea.

This is a brief review intended to supply bases for prediction of future changes in the North Sea Benthos. It surveys long-term changes which are affecting the benthos. Any prediction must take into account change in temperature, depth, bottom type, tidal patterns, current patterns and zoogeography of the sea and the history of these is briefly touched on from late Tertiary times up to the present. From a prediction of changes in the benthos, certain information concerning the pelagic and planktonic biota could also be derived.

Maps are shown to be the most striking way of displaying the distribution of marine species on a geographical scale. They have been used to indicate not only the presence or absence of a species, but also its abundance. A single map only records the distribution pattern at a particular moment in time, but repeated mapping clearly demonstrates temporal fluctuations. Many ecological insights have been derived from distribution maps especially when they are compared with records of environmental factors such as substratum type, current velocity or temperature. Moreover maps actually stimulate experimental work which seeks to explain the distribution patterns displayed.

Aquaculture now makes a considerable contribution to world supplies of aquatic products for human consumption. Economic forces frequently have a more crucial bearing on the techniques adopted in particular regions than can be explained simply by the natural resources involved. The progress which has been made already is reviewed in the context of the main biological, economic and institutional problems which must be overcome to ensure further rapid expansion of aquaculture.

Evidence is presented to show that the dominant mode of temperature change of the last 25 years, in the North Atlantic, has recurred throughout the last 100 years. Temperatures in the NE Atlantic, where this mode is especially prominent, tend to be inversely related to the strength of the Trade and Westerly Winds. The mode of temperature change, which extends through the top 250 m and involves corresponding salinity changes in the NE Atlantic, is interpreted as resulting from a shift in the North Atlantic Current system, wind-induced increases in the transport of the North Atlantic Gyre being accompanied by a radial shrinkage of the current system and a reduction of the warm water discharge to the north. A theoretical analysis, relating this current change to a shift in the separation of the Gulf Stream from the North American coast, is attempted to examine the consequences of this interpretation