Rich assemblages of acid-resistant microfossils occur in intertidal sediment from the British Isles and are here reported, for the first time, to contain large numbers of dino-flagellate cysts. These cysts provide evidence to show that the distribution of certain dino-flagellate cysts is different from that of the motile stage, that the coastal distribution of cysts appears to be controlled by currents and that their occurrence within bays is possibly related to localized temperature and salinity conditions. Further, they present evidence that potential conditions for a red tide of Gonyaulax polyedra Stein may be present in the east Irish Sea.

The visual pigments in the retinal rods of 17 species of deep-sea fish were examined by microspectrophotometry or visual pigment extract spectrophotometry. In 15 species single visual pigments were found with peak sensitivities between 470 and 490 nm, typical of deep-sea fishes. However, in one species, Stylephorons cordatus, two visual pigments were found with λ values at 470 and 481 nm. In another species, Scopelarchus analis, three visual pigments were found with mean λ values of 444, 479 and 505 nm. The short-wave pigment of this species was found both in main and accessory retinae. It was present both in single rods and in outer segments which had the most long-wave sensitive pigment in their distal parts. It is argued that these two-pigment rods are in the process of changing their visual pigment from a ‘juvenile’ VP505 pigment to an ‘adult’ VP444 pigment. The VP479 was found only as a single pigment in rods in the accessory retina.

Little is known of the biochemistry of diatoms, although many workers have reported growth experiments with the unicellular algae of the marine phyto-plankton. Experiments have often been performed without due regard for the appropriate control of physical and chemical conditions. Many reports contain only incomplete data of the growth under a given set of conditions, and it is often impossible to say whether the effects recorded are upon the growth rate, the total crop, or both. Other studies have been reported which included the addition of organic matter to cultures which were only uni-algal and not bacteria-free. At the present time even the mere maintenance of stock cultures of the marine unicellular algae is perforce an empirical matter. Results in replicate cultures often show gross differences in growth that are apparent on inspection by eye alone, and insufficient information is available regarding the nature of these variations in growth to allow the rational development of improved culture media. Due therefore to a lack of suitable techniques, most of the results available are difficult, if not impossible, to interpret in terms of the biochemical activities of the algae.

1. Vertical traverses down the shore were worked at four localities in the Isle of Man, with varying degrees of wave-exposure, for which factor a coefficient is given.

2. The upper limit of distribution is high water neaps in a sheltered place, and up to high water of extreme spring tides at greater waveexposure. The lower limit similarly drops with increasing exposure.

3. Barnacles are largest and most abundant in a wave-exposed locality. The effect of wave-exposure may be reproduced by a current.

4. In sheltered localities the optimum level for growth, mean size, etc., is at low water for newly settled barnacles, but moves progressively up to high water as they grow older. In a very exposed situation, however, the optimum is always at low water.

5. In an exposed situation the gonads mature in their first year below about half-tide level, and in their second year above this level. With decreased wave-exposure the age of maturation rises, especially at high water until in a very sheltered place few barnacles mature at all.

The turbot Scophthalmus maximus L. is a large teleost flatfish of the family Bothidae. Its range extends from the Adriatic (Faber, 1883) and Mediterranean (Morgan, 1956) northwards to the Norwegian coast, and includes the Baltic Sea and waters surrounding the British Isles. It has been recorded as far north as the Lofoten Islands (Fulton, 1905), and is taken occasionally at Faroe, Iceland and Rockall.

This paper embodies various observations which were made from time to time while the author was a member of the staff of the Plymouth Laboratory. It also outlines certain generalisations based on the author’s previous published work and that of other recent workers in the field of comparative physiology of feeding and digestion.

In the course of some 4 years′ work on the biology of fouling organisms, observations have been made on aspects of the general biology of Balanus balanoides, B. crenatus and Verruca stroemia.

Observations on the state of development of the ova within the mantle cavity of B. balanoides and of the occurrence of the larvae in the plankton indicate that hatching takes place during the first fortnight in March, that the later-stage nauplii are abundant during the second half of that month and that the cyprid larvae may become abundant during April. The larval sequence is not always completed successfully; conditions which seem inimical are discussed.

Factors which seem to be of importance in affecting settlement of B. balanoides are discussed. The presence of other organisms is an adverse factor, though the potency of this factor is probably not the same for all organisms; the presence of slime can prevent settlement and, though evidence can be quoted in support of heavier settlement on shaded surfaces, it is emphasized that the operation of other factors may have brought about this result. The proportion of the tidal cycle during which current speeds are not too high to prevent settlement seems likely to be important.

Provided that other conditions are favourable B. balanoides settles readily on surfaces continuously immersed and individuals which settle under these conditions grow more rapidly, at least for the first few months after settlement, than their contemporaries on the shore.

The larvae of B. crenatus appear in the plankton rather earlier than those of B. balanoides, but the time taken to complete the larval sequence from the 1st stage nauplius to the cyprid is roughly the same as that for the latter species, namely 1 month. In B. crenatus, however, hatching is not limited to a short period during March but continues at intervals through the summer. There are indications that the successful completion of the larval sequence of this species is less affected by an abundance of phytoplankton than is that of B. balanoides.

Settlement of B. crenatus is periodic and individuals which settle early in the spring can attain practically their full size (28–30 mm. basal length) during the same season. Growth during the summer takes place at average rates which vary from 0·1 to 0·2 mm. increase in basal length per day. Growth is negligible during the winter months.

Specimens of B. crenatus which settle early in April contain developing ova by the beginning of July, so that spring-settled forms can produce larvae which themselves may settle before the end of the summer.

Observations on Verruca stroemia have been limited to the occurrence of the larvae in the plankton. Like those of Balanus crenatus, the larvae of Verruca stroemia are present at intervals through the summer. Early-stage nauplii of this species may dominate the plankton early in the year, but no correspondingly heavy hauls of later-stage nauplii have been recorded. Possible explanations of this discrepancy are discussed. The cyprid never occurs in any numbers in surface hauls.

Incidental observations on the planktonic occurrence of the nauplii of Sacculina (probably S. carcini) and of Peltogaster paguri are given.

Details are given of the abundance of all Cirripede larvae in the plankton for the years 1944–47 which emphasize the extent of variation that can occur from year to year.

The population of Scoloplos armiger O. F. Müller at Whitstable was investigated from January 1964 to April 1965. Initially the population density was high, being over 600/m2, but the numbers sharply declined during the summer of 1964 and by the following winter the density had dropped to under 100/m.2 In addition to this decline, the population structure changed, and the overall effect was a marked reduction in the fecundity of the population. The cause of the high mortality in the summer of 1964 is unknown.

A study of the respiration and of the function of hæmoglobin in Planorbis corneus and Arenicola marina has been undertaken.

The oxygen consumption of Planorbis is of the order of 0·026 c.c. per gm. per hour, measured at 15° C.

The blood volume is approximately 0·581 c.c. per gm.

The combined oxygen of the blood is 0·013 c.c. per c.c. of blood, the total oxygen being 0·014 c.c. per c.c. The total oxygen capacity of the blood per gm. of snail is estimated to be 0·0081 c.c.

The oxygen supplied by the blood is calculated to last 18 minutes and is found by experiment to last 25 minutes.

The snail does not immediately oxidise its hæmoglobin after subjection to anaerobiosis. Oxidation begins after 10 minutes and is complete within 20 minutes.

Preliminary culture assays were made using marine algae to elucidate the ‘quality’ of sea waters from the North Sea and North Atlantic Ocean for phytoplankton growth. Assays with (a) bacteria-free Skeletonema costatum, (b) unialgal Skeletonema and Peridinium trochoideum and (c) mixed phytoplankton organisms indicated change of quality according to location, depth and season. Assay results correlated best with zooplankton indicator quality and to a lesser extent with phytoplankton abundance. Assay results were also compared with the distributions of temperature, salinity, oxygen, phosphate, U.V. fluorescence, phytoplankton dominants, zooplankton dominants and abundance. Assessment of sea-water quality was biased for the assay organism used. Factors which altered sea-water quality were added thiamine and B12 (40% improved), IAA (25% improved) and EDTA (almost invariable manyfold improvement). Destructive chemical treatments removed almost completely any good qualities for growth of Skeletonema but seldom for that of Peridinium.

Mar Chiquita, an irregularly shaped brackish-water coastal lagoon, is located in the Buenos Aires province of Argentina and considered since 1996 by the Coordination Council of the Man and Biosphere Program of UNESCO as a World Reserve of Biosphere. The present paper aims to study both the spatial and temporal variation of fish composition in this coastal lagoon and the influence of some environmental variables on the relative abundance of the main fish species. Monthly sampling surveys over a two-year period in three different areas were conducted, using a beach-seine net and three monofilament-gill nets with different mesh size. Twenty-eight species belonging to four bio-ecological categories were identified, five of them are new records for Mar Chiquita fish community. The correspondence analysis showed strong relationships between high salinity range and the abundance of Brevoortia aurea, Cynoscion guatucupa and Pomatomus saltatrix. Conversely, low salinity range corresponded to high abundance of Mugil platanus and Odontesthes argentinensis. High temperatures were corresponded with abundance of Micropogonias furnieri and Brevoortia aurea. In contrast, high abundance of both Odontesthes argentinensis and Oligosarcus jenynsii were corresponded to low temperatures. Brevoortia aurea, Mugil platanus and Odontesthes argentinensis were the most abundant species, representing more than 80% of the total capture. The group of estuarine-nondependent-marine fish presented the highest species richness. Estuarine-dependent-marine species presented for both juveniles and adults specimens the highest abundance values.

The herring is a physostome with no gas secretion mechanism in the swimbladder. The swimbladder volume was measured in fish from about 3–33 cm in length. It was rarely large enough to give the fish neutral buoyancy at the sea surface. Swimbladder volumes were also measured after periods of up to 1 week at pressures from 1·9 to 5·5 ATA (0·9–4·5atm above atmospheric pressure) in a laboratory pressure vessel and in a sub-surface cage in the sea. The swimbladder gas was lost within a few hours in the larval herring and in a few days in smaller juvenile fish; no change was found in older fish under experimental conditions. The findings were in accord with measurements of the guanine content of the swimbladder wall which was low in those fish which lost gas quickly. This supports the view that gas diffusion is limited by guanine crystals. While it seems likely that larger fish can exist for several weeks without the need to replenish the swimbladder gas some large spawning herring were caught at sea with empty swimbladders, suggesting a long stay near the sea bed. Analysis of swimbladder gas showed that oxygen tended to diffuse out more quickly than nitrogen. Behaviour experiments showed that fish with artificially emptied swimbladders could refill them by swallowing air at the surface, in some cases very quickly and efficiently. Fish with empty swimbladders and no access to the surface suffered a high mortality. The ecological implications of these results and their relevance to the interpretation of sonar ‘target strength’ measurements are discussed.

INTRODUCTION

Much of the rocky coast of Norway is known to form a favourable habitat for Laminaria hyperborea (Gunn.) Foslie. In June and July 1965 observations of this species and its competitors were made both in an area near Espegrend (60° 16.23′ N, 5° 13.42′ E), 15 km south of Bergen, and near Tromso (69° 39.2′ N, 18° 57.6′ E) for comparison with populations round the Isle of Man.

The problem of how a fish can make itself invisible in the natural light-conditions in an aquatic environment is discussed with particular reference to the silvery surfaces of fish.

In fish which we have examined, the silvery surfaces are of two types: (1) an argenteum which consists of long thin crystals of guanine whose reflecting surfaces are approximately parallel with the surface of the fish; (2) layers of guanine crystals lying either on the inner surfaces of the scales or in the subdermis—these crystals are not, in general, orientated with their reflecting surfaces parallel with the surfaces of the fish, and are much broader than those of the argenteum.

Methods are described by which the orientation of the crystal planes with respect to the planes of the scales on which they lie can be determined.

The orientation of the crystals of type 2 in different parts of the body is described for the horse mackerel, Trachurus trachurus (L.), and for the bleak, Alburnus alburnus (L.).

For the bleak it is shown that although the planes of the crystals are often very much inclined with respect to the planes of the scales, the long axes of the crystals are always approximately parallel with the planes of scales. The inclination of the crystals, therefore, is away from the scales across their short axes.

Measurements of the light transmitted by silvery scales of the bleak show that they reflect light strongly when this falls obliquely on the crystals which they contain and that they are most transparent to light which strikes the scales in a direction perpendicular to the reflecting planes of the crystals.

1. Attempts to obtain good cultures of Thalassiosira gravida in a purely artificial medium, made by dissolving in doubly distilled water Kahlbaum's pure chemicals in the proportions in which the salts occur in sea-water, adding nitrates, phosphates and iron according to Miquel's method and sterilizing the medium, have not succeeded.

If, however, a small percentage of natural sea-water (less than 1 per cent will produce a result) be added to the artificial medium and the whole sterilized excellent cultures are obtained, which are often better than any which have been got when natural sea-water forms the foundation of the culture medium.

The result appears to be due to some specific substance present in minute quantity in the natural sea-water which is essential to the vigorous growth of the diatoms. The nature of this substance it has not been possible to determine, but some evidence seems to suggest that it is a somewhat stable organic compound.

Provided the 1 per cent of natural sea-water is added, the various constituents of the artificial sea-water forming the basis of the culture medium can be varied in amount within wide limits. The salinity of the medium can also be considerably altered without serious detriment to the cultures.

The experiments recorded are of interest as furnishing another instance of the importance in food substances of minute traces of particular chemical compounds. They may also eventually throw light upon the nature of the conditions in the sea which are specially favourable to the production of plant life and therefore also of the animal life which that plant life sustains.

Specimens of Pagurus bernhardus (with and without shells) were exposed to both gradual (sinusoidal) and abrupt (square-wave) salinity fluctuations and changes in haemolymph osmolality, tissue water content and oxygen consumption monitored. Oxygen consumption was also monitored under steady-state conditions; under these conditions there was no significant difference between the rate of oxygen consumption by animals with shells and animals without shells. Oxygen consumption was found to vary with body weight according to the equation O2 consumption = 0·292 W0·668. During exposure to fluctuating salinities the crabs with shells were seen to increase loco-motory activity when the external medium declined to approximately 75% sea water. Haemolymph osmolality values followed the same pattern of change as the external medium; the haemolymph of crabs without shells became significantly more dilute during exposure to low salinity than did that of crabs with shells. P. bernhardus showed significant increases and decreases in hydration level as salinities fell and rose respectively. Crabs with shells showed a marked temporary increase in oxygen consumption when the external medium declined to approximately 75% sea water; crabs without shells showed no such response. The importance of the shell as a means of protection against dilute media is discussed.

Aspects of the reproductive biology of two exploited deep water sharks, Centroscymnus coelolepis and Centrophorus squamosus were investigated, based on trawl and longline surveys of the continental slopes and commercial samples from fishing vessels. Gravid Centrophorus squamosus were totally absent from this area, but analysis of uterine width data showed that small numbers of post-natal females were present. Mature males and pre-ovulatory females predominated in the middle of the bathymetric range for both species, indicating that mating occurs at these depths. Gravid Centroscymnus coelolpeis occurred only in waters shallower than 1200 m, though peak abundance of the species was between 1300 and 1400 m. There was no obvious bathymetric segregation of male Centrophorus squamosus, contrary to Centroscymnus coelolepis, where immature males occurred deeper than 1100 m, and the proportion of mature males increased up-slope. Centroscymnus coelolepis apportions twice the resources to gonadal tissue as Centrophorus squamosus. Hepatosomatic index declined during vitellogenesis in Centroscymnus coelolepis. Both species have low reproductive outputs and commercial exploitation should proceed with caution.

The distribution of shore crabs, Carcinus maenas (L.), within the intertidal and shallow subtidal zones of a rocky shore in the Menai Strait, North Wales, was recorded regularly by diving throughout the tidal cycle. Samples were also obtained by searching the shore during low tide and by collecting crabs in baited pots. It was found that the smaller individuals (<35 mm carapace width) in the population tend to remain within the intertidal throughout the tidal cycle whilst others, mainly the red-coloured adults, appear to remain permanently below low-water mark. The remainder of the population, predominantly green males larger than 35 mm carapace width, migrate upshore with the flood tide and downshore again with the ebb. The behaviour of C. maenas on the shore appears to be affected, at least in part, by a tidally rhythmic pattern of responsiveness to directional light which is seen in freshly collected crabs in the laboratory.

As part of an investigation into the impact of commercial trawling on the benthos of Strangford Lough a map of the distribution of the benthic communities in the Lough was required. To provide this an acoustic bottom classification survey of the Lough was carried out using a commercially available system, RoxAnn. RoxAnn processes the information from a conventional echo-sounder to determine the nature of different substrata. Underwater cameras were used to obtain ground truth data to compare with the RoxAnn data. Used in conjunction, the two surveys provided valuable information on the different bottom substrata and associated epibenthic communities present in the Lough.

The distribution and activities of animals and plants upon the sandy beach are largely influenced by the special physical factors operating in that environment. The paper is a contribution to the knowledge of these factors.

The tidal ebb and flow, and the resulting alternations of exposure, are the outstanding factors. The extent to which other factors may be operative upon the beach, during the period of ebb-tide, depends upon the vertical distance of the point in question above or below mean sea-level.