Preliminary experiments had suggested that the extent of the development of the bacterial flora which develops when sea water is confined in small vessels is an important factor in the laboratory culture of oyster larvae. In the experiments reported in this paper the growth and settlement of oyster larvae was compared in controls of normal sea water with those in which the bacterial flora was controlled with antibiotics.

A concentration of 50 i.u. of the sodium salt of penicillin G per ml. suppressed bacterial growth for at least 2 days and, in a series of experiments using fifteen different broods of larvae, significantly (P>0·001) more spat were obtained in those to which penicillin had been added than in the controls.

A mixture of 50 units of penicillin G and 0·05 mg streptomycin sulphate was tried in three series of experiments. This completely suppressed the development of bacteria for at least nine days. In all three series many more spat were obtained than in the controls, but in only one series was there more spat than in the comparable penicillin experiment. It is suggested that when the bacterial population is very vigorous, or perhaps when certain species are present, this mixture will be more useful than penicillin alone. Experiments with other concentrations of penicillin, and with streptomycin and chloromycetin alone were not successful.

1. In the Lamellibranchs, as typified by Pecten maximus, Mya arenaria and Ensis siliqua, the entire, gut has an acid reaction, the stomach being the most acid region and the pH rising along the mid-gut and rectum.

2. The origin of the acidity of the gut lies in the style. This has a low pH (5·4 in Pecten and Mytilus, 4·6 in Ensis and 4·45 in Mya), and, after it has been artificially extracted from Mya or induced to disappear, by keeping the animals under abnormal conditions, in Mytilus, Tapes and Pecten, the pH of the stomach invariably rises (by as much as 0·825 in Mya and 0·72 in Tapes), although the pH in the mantle cavity has fallen.

3. The style, which dissolves rapidly in alkaline or weakly acid media, is not dissolved in fluids below a certain pH—4·4 for Ensis, 4·2 for Mya, 3·6 for Pecten and Mytilus.

4. The style is never absent, even though animals are starved, so long as they are kept under otherwise healthy conditions. The disappearance of the style under abnormal conditions is probably due to a lowering of the vital activities, which include the secretion of the style substance, and the consequent dissolution of the style by the less acid contents of the stomach.

5. The style is only maintained as a result of a balance between the rate of its secretion and the rate of its dissolution.

6. There is a well-marked correlation between the tolerance of the presence of hydrogen ions possessed by the cilia from the various regions of the gut and the degree of acidity of the fluid with which they are normally surrounded.

7. The pH of the gut in five Gastropods has been investigated. The fore-gut and stomach have invariably the lowest pH.

8. This acidity may be caused by the salivary glands (Patella and Buccinum), the digestive gland (Doris and Aplysia), or the style (Crepidula).

9. The mid-gut and rectum have a high pH, except in Doris, where there is little secretion of mucus, the gut being free and muscular.

10. The style of Orepidula has similar properties to those of the Lamellibranchs. It has a pH of 5·8, and is not dissolved in fluid of pH 3·6 or lower.

11. The cilia from the gut of Buccinum and Doris can function in a pH of 5·0, but there is little difference in the toleration of the various cilia to the presence of hydrogen ions.

The patterns of habitat use by the franciscana dolphins (Pontoporia blainvillei) along its distribution are poorly known. This study investigates the patterns of habitat use with respect to depth for 181 individuals of different age, size, gender and reproductive condition off Rio Grande do Sul, southern Brazil. The results reveal that franciscanas are very homogeneously distributed according to depth. Individuals from all lengths utilize nearly the entire range of depths of the surveyed area. Larger or older animals do not use deeper waters than younger animals, indicating that body size and age are not limiting factors for franciscanas that occupy deeper or offshore waters. Gestation seems to not cause a change in the distribution of females. Although the sex-ratio of the overall data did not vary from 1:1 in different depth intervals, a small-scale comparison between the northern and southern coast demonstrated the existence of some kind of sexual segregation. Franciscana by-catch in Rio Grande do Sul is not sustainable and it is agreed that management procedures are needed. Nevertheless, the available data on species distribution do not allow the designing of a protected area in order to minimize the by-catches of a particular sex/reproductive class.

Evidence is presented to suggest that the salinity tolerance of the adult North Sea Asterias rubens is around 23‰, whereas that of the Baltic Sea animals is 8‰. This, together with other evidence outlined, is thought to be sufficient reason to justify the use of the term ‘physiological race’ where these two populations are concerned.

Adult A. rubens from the North Sea is incapable of any degree of weight regulation in diluted media within the ecological temperature range, size or state of the breeding cycle.

Similarly, it is incapable of any osmotic regulation and it is suggested that the two main coelomic cavities constitute an osmotic unity.

In many of the more general studies on marine zooplankton the part played by siphonophores is frequently ignored or only given a cursory mention. However, their ecological importance is far from insignificant. In this context we are indebted to the late Mr A. K. Totton whose publications have done much to draw attention to the siphonophores and the part which they play in the zooplankton community. His synopsis of the siphonophores (Totton, 1965) is a masterly work from which any student of this fascinating group can derive much benefit.

The position and structure of the North Atlantic Subtropical Front is studied using Lagrangian flow tracks and remote sensing (AVHRR imagery: TOPEX/POSEIDON altimetry: SeaWiFS) in a broad region (∼31° to ∼36°N) of marked gradient of dynamic height (Azores Current) that extends from the Mid-Atlantic Ridge (MAR), near ∼40°W, to the Eastern Boundary (∼10°W). Drogued Argos buoy and ALACE tracks are superposed on infrared satellite images in the Subtropical Front region. Cold (cyclonic) structures, called ‘Storms’, and warm (anticyclonic) structures of 100–300 km in size can be found on the south side of the Subtropical Front outcrop, which has a temperature contrast of about 1°C that can be followed for ∼2500 km near 35°N. Warmer water adjacent to the outcrop is flowing eastward (Azores Current) but some warm water is returned westward about 300 km to the south (southern Counterflow). Estimates of horizontal diffusion in a Storm (D=2.2×102 m2 s−1) and in the Subtropical Front region near 200 m depth (Dx=1.3×104 m2 s−1, Dy=2.6×103 m2 s−1) are made from the Lagrangian tracks. Altimeter and in situ measurements show that Storms track westwards. Storms are separated by about 510 km and move westward at 2.7 km d−1. Remote sensing reveals that some initial structures start evolving as far east as 23°W but are more organized near 29°W and therefore Storms are about 1 year old when they reach the MAR (having travelled a distance of 1000 km). Structure and seasonality in SeaWiFS data in the region is examined.

Gas-liquid and thin-layer chromatography have been used for the determination of 25 amino acids in the hydrolysates of 25 species of marine phytoplankton which had been grown in Erd-Schreiber medium. The general pattern of their distribution agrees with that found by earlier workers; the principal amino acids being glutamic acid, alanine, leucine and aspartic acids. Small amounts of 2-amino-n-butyric and 2-amino-iso-butyric acid together with compounds which have been tentatively identified as 4-amino-n-butyric acid and the 2-amino- and 2,5-diamino derivations of adipic acid were detected in many of the organisms. No differences were found which could be related to the taxonomy of the organisms.

The genus Gammarus, instituted by Fabricius in 1775, has come to include a large number of species—so many and so varied, in fact, that the necessity for a revision of the genus is well recognized. An extensive examination of the taxonomic literature has inevitably led to the conclusion that several more or less well-defined groups of species can be recognized among the total assemblage, and that some of these at least should be separated off as distinct genera.

This paper is the second of four dealing with the calanoid copepods taken with a modified Indian Ocean Standard Net (N113H) on the R.R.S. 'Discovery' SOND cruise of 1965. Details of the cruise are given by Currie, Boden & Kampa (1969), and the sampling methods used in the N113H series are described by Foxton (1969) and by Angel (1969).

The purpose of this paper is to assess the grazing capacity of Calanus finmar-chicus (Gunner.) in terms of the quantity of food eaten in the sea. The part played in the growth of the animal by the quantity eaten will only be briefly discussed. The parts played by nutrient lack, sinking and diffusion on the algal productive rates will also be discussed, leading to the conclusion that grazing mortality is the most effective controlling agent on algal production.

A subsidiary purpose of this paper is to relate changes in the weight of Calanus finmarchicus to changes in food consumed and to changes in water temperature. Measurements of C. finmarchicus have been made by a number of workers (Adler & Jespersen, 1920; Russell, 1928; Marshall, 1933; Stormer, 1929; Bogorov, 1934; Jespersen, 1939; Clarke & Zinn, 1937). It will be shown that in the North Sea, in spring, the greatest changes in weight are most readily related to changes in quantities of food consumed.

INTRODUCTION

The atomic ratio of oxygen-consumed to ammonia-nitrogen excreted by marine organisms (O:N ratio) is more conveniently and precisely determined with current analytical procedures than the respiratory quotient (R.Q.). When an organism is oxidizing protein exclusively the O: N ratio will be low, less than 7; it will be high when either fat or carbohydrate is oxidized.

The two new species, Gymnodinium vitiligo and G. veneficum, which are described below, are both small and highly motile, and in other respects very similar. The greatest difference between them is physiological, as G. vitiligo is harmless, whereas G. veneficum produces a very powerful toxin which is lethal to fish. There are also small morphological differences which are visible when the organisms are in culture, confirming the existence of two separate species.

Using a 25-year time series of monthly samples, it is shown that the fish community of Bridgwater Bay in the outer Severn estuary is rapidly responding to changes in seawater temperature, salinity and the North Atlantic Oscillation (NAO). The number of fish caught each year has followed an increasing trend, which could be related to increased temperature and decreased salinity. In contrast to this smooth change, there have been two discrete transitions in fish community structure around 1986 and 1993. The first of these step changes, which altered the relative abundance of the dominant species, was linked to a change in the NAO. The second, which was caused by a change in the set of occasional visitor species, was linked to an increase in average seawater temperature. A marked increase in population variability for many fish in recent years is linked to increased seawater temperature. Generally, the position of the southern geographical limit of a species is a good indicator of their individual responses to higher temperatures. The effects of future climate change are discussed. A 2°C increase in inshore seawater temperature is predicted to increase total species richness of fish in Bridgwater Bay by 10%, although most of this gain will be warm water tourists. Predicting future communities requires consideration of combined changes in temperature, the NAOI and salinity. While the system can change to a warmer water community, there is likely to be increased short-term community instability during periods with unfavourable combinations of the key environmental variables. Such a destabilization was observed in 2002 when the abundance of many species suddenly increased then declined. A different combination of NAO, high temperature and salinity may, in the future, produce a considerable less favourable combination resulting in recruitment collapse for many species.

Coralligenous bioconstructions are among the most important Mediterranean habitats for biodiversity maintenance. However some characteristic and sensitive organisms, such as the fan corals, are considered endangered in the international community; indeed, they may be severely damaged by fishing activities causing mechanical damage and increasing sedimentation rate. ROV (Remotely Operated Vehicle) investigations were carried out in order to characterize different morphological types of coralligenous habitat (rim, bank and shoal) located in the southern Bay of Naples (Italy), and to assess the presence of lost fishing gears and their impact on these benthic communities. A rapid classification of different fishing pressures and impacts was obtained through the development of new, representative and synthetic categories. Image analysis revealed the presence of rich and diversified communities, characterized by several fan coral colonies. However, fishing activity dramatically affects these coralligenous habitats, entangling and covering benthic assemblages and leading to necrosis and to parasitic epibionts growth especially on branched organisms. Monitoring programmes may provide a detailed assessment of coralligenous habitats characterization, distribution and health status. An accurate evaluation of fishing pressure and impact may be considered a useful tool to improve sustainable management of these valuable habitats.

Analyses of the cirratulid polychaete Tharyx marioni have shown that this species contains a high concentration of arsenic, its whole-body concentration usually exceeding 2000 μg/g dry weight, even when living under low ambient arsenic conditions. Similar levels of arsenic are present in both juvenile and adult worms. Other cirratulid species, such as Cirriformia tentaculata and Caulleriella caputesocis, from the same habitat contain low arsenic concentrations (< 100 μg/g dry weight).

Much of the arsenic in T. marioni (ca. 20 %) is contained in the palps which comprise about 4% of the body dry weight; in these organs, concentrations of 6000–13 000 μg/g dry weight have been measured. Some of the arsenic in the palps is bound with copper in granules but the bulk appears to be organically associated; extraction data indicate about 65% of the total arsenic is linked to the lipid pool with a further 25% being proteinbound arsenite (cysteine-extractable). The results of experiments using 74As suggest that most of the arsenic is derived from the sediments rather than the water but the mechanisms and functions of this arsenic accumulation by T. marioni remain to be investigated.

The Iceland scallop (Chlamys islandica) (O. F. Müller) has its main distribution within the subarctic transitional zone where it is found on gravel or sandy bottoms at depths ranging from 10–100 m and usually in places with strong currents (Ekman, 1953; Wiborg, 1962).

The following paper has been prepared in the hope that it will be of assistance to anyone desirous of carrying out experiments on Heredity with Gammarus chevreuxi. This Amphipod has been the subject of study at the Plymouth Laboratory since 1912, and the following notes are chiefly concerned with rearing and breeding it under Laboratory conditions.

Details of the work will be found in the papers mentioned in the bibliography on page 54.

The presence in the sea of vitamin B12, or of its analogues, has been found necessary for the growth of several species of unicellular plants (e.g. Provasoli & Pintner, 1953; Droop, 1954, 1955).

Bioassays of the quantities in inshore waters during winter have been made by Lewin (1954) and by Droop (1954). The present investigation, carried out in 1955, was designed to extend this study and compare different seasons of the year.

The endogenous activity rhythm of the estuarine amphipod Corophium volutator has been studied by direct observation and with the use of time lapse photography. The rhythm persists under constant conditions having a free running period of between 12 and 13 h, and with activity maxima occurring during the early ebb. Freshly collected animals show a rhythm which is modulated on a semi-lunar basis, the activity maxima being attenuated during the neap tide periods, and the rhythm has also been found to vary in definition throughout the year. The activity pattern is most clearly denned in early summer and autumn, the population becoming arrhythmic during the winter months. The rhythm is relatively unaffected by the ambient light intensity and temperature of the recording conditions, and is evident in all post-natal stages of development. The possibility of mutual entrainment is discussed.

The feeding rate of small specimens of Mytilus edulis (L.) has been determined in suspensions of colloidal graphite (‘Prodag’, grade ‘C’, and ‘Aquadag’, grade ‘S’), of flagellates, and of Nitzschia dosterium. The feeding rate was measured as the volume of water cleared from particles per unit time. In graphite suspensions, with particle size of about 4–5μ, as a rule only a small percentage of the particles was retained by the gills, whereas flagellates of about the same size were normally nearly all retained.