The shellfish ranching, its current exploitation status and its management are becoming a major interest in fisheries industry in Tunisia. In this respect, the coasts of the Gulf of Tunis were explored along 20 shore-perpendicular transects to evaluate the stock size of shellfish populations. 285 samples of malacological fauna were collected by a VanVeen grab. This sampling revealed the presence of six target bivalve species owing to their high commercial value. The determination of the weight–size relationships of each species pinpointed that five species have a negative allometric relationship (Tellina planata, Tellina nitida, Glycymeris violacescens, Donax semistriatus and Solen marginatus) whilst Mactra stultorum indicated an isometric growth. The stock size assessment of these target species revealed that abundance values ranged from 2 to 60 individuals m−2, and biomass values varied from 2 to 230 g m−2. The mapping of the spatial distribution of density and biomass showed that the majority of species colonized essentially shallow waters corresponding to sandy and muddy bottoms. These findings are consistent with ecological and physiological properties of species. Major physical parameters influencing spatial distribution patterns are discussed.

Wedge clam, Donax scortum occurrence was studied from February 2009 to January 2010 in Padukere sandy beach, Karnataka (India). The following biological parameters were measured in 2367 individuals of the wedge clam, Donax scortum: length, breadth, width, total weight, shell weight, wet meat weight, dry meat weight and number of clams. The calculated linear equation of length-breadth and length-width relationships were B = 3.5968 + 0.5421L and W = 0.8191 + 0.4345L respectively. The length-total weight, length-wet meat weight, length-dry meat weight and length-shell weight relationships were 0.0001414L3.0224, W = 0.0000037L3.5204, W = 0.0000011L3.4513 and 0.0000852L2.9912 respectively. The values of correlation coefficient for different shell dimensional relationships were very close to unity. It was clear from the study that the most ideal period for clam harvest was April, June and December, especially when condition index was maximum. Length showed a strong correlation with silt and clay. Dry meat weight was negatively correlated with air temperature. Shell weight showed positive correlation with length, breadth, width and dry meat weight, and abiotic parameters, silt and clay. Condition index was positively correlated with electrical conductivity, whereas it was negatively correlated with dissolved oxygen. It showed a strong positive correlation with salinity. Seasonal fluctuation of condition index in D. scortum was probably related to reproductive activity. The harvesting of wedge clam could be carried out considering the maximum sustainable yield without over-exploitation

The ‘Shinkai Seep Field’ is a serpentinite-hosted chemosynthetic ecosystem in the Southern Mariana Forearc. In June 2015 the site was revisited and a number of rissoiform gastropods were collected. Taxonomic investigations revealed that these specimens represent a hitherto undescribed species of Provanna (Gastropoda: Abyssochrysoidea), described herein as Provanna cingulata n. sp. This new species is characterized by numerous spiral keels, lack of significant axial sculpture, rounded and inflated whorls, and large size for the genus. With the shell height exceeding 16.5 mm (may reach 20 mm), it is the largest Provanna species known thus far. Phylogenetic analysis using 411 bp of the cytochrome oxidase c subunit I (COI) gene confirmed its systematic placement within the genus Provanna. This is the only gastropod from a family endemic to chemosynthetic ecosystems thus far known from the ‘Shinkai Seep Field’. Furthermore, with a collection depth of 5687 m, it represents the deepest known bathymetric range for the superfamily Abyssochrysoidea as a whole.

A method of estimating the maximum quantity of manganese available to plants in sea and fresh waters is described.

Samples of sea water collected off Plymouth in 1948 contained 0·7–1·0 mg. Mn/m.3 in solution plus any particles soluble at pH 4·6. After storage and sedimentation of particulate matter, the quantity decreased to 0·0–0·25 mg./m.3

Samples collected off the Isle of Man, an area with a rich summer population of flagellates, contained 2·0–2·6 mg./m.3

The river Yealm, south Devon, on leaving Dartmoor contained 1 mg., and after passing through agricultural land 10 mg.\m.3

Lakes and streams in the English Lake District contained 6–40 mg.\m.3 The least fertile waters contained the least soluble manganese.

Zooplankton biomass varies on temporal, horizontal and vertical scales. However, data sets which incorporate all these dimensions at high resolution are very rare. Two devices which measure all these aspects have recently been simultaneously deployed in the Celtic Sea, the continuous plankton recorder (CPR) and the Longhurst–Hardy plankton recorder (LHPR). This demonstrates that integrated biomass derived from the LHPR are not significantly different from those derived using the CPR. Values have, therefore, been combined for the first time to describe the vertical distribution of mesozooplankton biomass at the Celtic Sea shelf edge through an annual cycle. This suggests that the surface biomass peak is broader at the shelf break than in the open ocean and in the autumn the main biomass peak may be below the depth sampled by the CPR.

There are three British species of the wood-boring isopod Limnoria. The boreal L. lignorum is found around all coasts, but is least common on the south and west coasts, where the temperate L. quadripunctata is dominant. The latter also occurs in the Isle of Man, Ireland and the Channel Isles, but has not been found on the east coast. The warm-water L. tripunctata is found only on the central south coast and in South Wales. Each species can survive at levels equivalent to 60-65 % exposure, but in mixed populations L. tripunctata dominates the upper level of Limnoria attack, L. quadripunctata dominates the middle zone and L. lignorum is found at the base of exposed piling or sublittorally.

Life-history characteristics such as growth, mortality, and size at sexual maturity of the seahorse Hippocampus reidi were investigated in situ in north-eastern Brazil from August 2006 to July 2007. The von Bertalanffy growth constant K was estimated at 1.195 year−1 and L∞ was set as 20 cm according to Taylor's relationship, using a Lmax of 19 cm. The smallest male with a brood pouch and the smallest male with a fully mature pouch measured 9 and 9.5 cm (height), respectively, while the smallest mature female measured 8.8 cm. Appropriate reproductive individuals were recorded throughout the study, with peaks from May to November. The size of first effective reproduction (carrying embryos) was 12.4 cm for males, a value higher than previously reported. Estimated instantaneous rate of natural mortality ranged from 1.43 to 1.58 year−1. The estimated life span for the species was 30 months.

The following list includes all the Peridiniales identified in the plankton throughout the year from September, 1915, to September, 1916, from the water samples, details of which will be found in another paper in the same journal (p. 133). Also from the plankton in the tow nets in the same year and a portion of the summer 1915. As is shown in the abovementioned paper, the summer is the time for nearly all the Peridiniales, June being the maximum month. After October very few are seen in the water samples, although in the tow nettings the larger and stronger forms, such as Ceratium and Peridinium, are still present.

In the early summer of 1915 it was' noticed that many medusæ brought in with the tow-nettings contained larval Pycnogonids in the manubrium and at the junction of manubrium and stomach. The medusæ specially noticed to contain them were Obelia sp., Cosmetira pilosella, Turris pileata, Stomotoca dinema and Phialidium hemisphericum. By far the greater number were in Obelia, although many were in Phialidium hemisphericum and Cosmetira pilosella. They were extremely abundant in June, after that became scarcer, and finally disappeared by October. On examination they were seen to be larval stages of Anaphia petiolata (Kröyer), a Pycnogonid common in Plymouth Sound. The older larvæ sometimes were seen to cast their skins, so that the species could be easily recognised, although the fourth pair of walking legs were not fully developed. This is evidently the species described by Dogiel (1913) as Anoplodactylus pygmœus, the life history of which he traces from its first entry into the Obelia hydroid to the older stages when it is ready to leave its host. The form he refers to as Anoplodactylus petiolatus occurring in cysts in Coryne with Phoxichilidium femoratum must be some other species, as his figures prove clearly that it differs from A. pygmœus, and also the colour is totally different (a bright pink, while the present form is a pale yellow). Dogiel believes he has proved that Anoplodactylus petiolatus and A. pygmœus are different species from the difference in their life histories, and it is evident that he is dealing with two different species, but his A. petiolatus cannot be the same as our form, which is certainly identical with his A. pygmœus, and shows that Sars (1891) and Norman (1894) were right in regarding A. pygmœus as the young form of A. petiolatus (Kröyer).

Cyathura is a genus of Anthurid isopods represented by some fourteen estuarine species around the world (Miller & Burbanck, 1961). They are unusual amongst the isopods in that the majority of individuals in a population show protogynous hermaphroditism, adults breeding as females in their first year, then changing to males over the following winter (Legrand & Juchault, 1963; Burbanck & Burbanck, 1974). The adults are tubicolous, virtually incapable of swimming, and have limited mobility, resulting in disjunct, stable populations, some of which, in the case of C. polita (Stimpson), are known to have maintained the same locations and densities over a period of 20 years (Burbanck & Burbanck, 1975). The embryos develop within a marsupium or brood pouch on the thoracic somites of the female, and are released as interstitial juveniles 1 mm or more in length. With populations averaging 200 to 400 individuals per square metre, these animals are convenient for autecological studies. Indeed, Burbanck & Burbanck (1979) considered that as hardy, euryokous animals, consistent in their tolerance to fluctuating environmental conditions, and convenient for study, Cyathura species are ideal ‘indicator organisms’ in estuaries.

Morone labrax. Linn. Bass.

Towards the end of May a large female bass in one of the Aquarium tanks appeared to be approaching ripeness, and constantly swam round the tank followed by one or more of its companions, probably of the opposite sex. A fine-meshed net was accordingly placed over the overflow from the tank in question, and on the morning of the 29th May was found to contain a very large number of eggs, undoubtedly attributable to this species, the only other Teleostean inmates being turbot, congers, pollack, rocklings, and two species of wrasse.

All the eggs proved to be unfertilised, or, at most, showed only an approach to segmentation, which may have been due to the spermatozoa of a rockling. Circumstances seemed strongly to point to the fact that the eggs are not all shed at once, but owing to an unfortunate series of accidents with the net it is impossible to speak on this point with absolute certainty.

Although the bass is a common British fish, its ova find no place in the records of British naturalists, and are only known from the descriptions of Raffaele, who obtained them both from parents living in the tanks of the Naples Laboratory and from the neighbouring sea.

The eggs observed by us at Plymouth are spherical, and, while living but unfertilised, measure from 1·25 to 1·34 mm in diameter. Raffaele gives 1·155 to 1·2 mm as the diameter of Naples examples. The latter have an oil-globule of ·332 to ·366 mm.

Observations during four dives in the submersible ‘Alvin’ in June 1976 revealed that ctenophores were the most abundant large plankters between 400–700 m. From specimens collected with a slurp-gun device, Bathocyroe fosteri gen.nov., sp.nov., a species characterized by strong lobes, large auricles and red pigmentation of the gut, is described. Few ctenophores have been collected previously from deep water, but observations from submersibles indicate that several species occur throughout the mesopelagic zone.

Records are given on the abundance of the pelagic young of teleostean fishes off Plymouth as shown by half-hour oblique hauls with the 2-metre stramin ring-trawl.

In comparison with similar observations made since 1924 the year 1935 has been the poorest yet recorded.

A parallel between the quantity of phosphate in the water at the beginning of the year and the abundance of young fish is further confirmed. In January, 1935, the winter maximum phosphate value was the lowest yet recorded.

Light-adapted mysids as exemplified by Hemimysis lamornae display phototelotaxis which regularly alternates in sign from positive to negative and vice versa. This reaction may be disturbed by other activities such as feeding; it only takes place in horizontal illumination.

Dark-adapted mysids display negative geotaxis. When a light stimulus is given this geotaxis is reversed in sign irrespective of the direction of the incident light.

When the statocysts of the mysids are removed their responses are much more like those of planktonic creatures. In the light normal orientation is maintained by the “dorsal light reflex”, and in darkness by the “general position reflex”. In the darkness a feeble negative geotaxis is sometimes seen. In light, phototaxis is seen in both light-adapted and dark-adapted conditions; in the majority of cases it is negative but on occasion has been seen to be positive.

In spite of the large number of Chlamydomonas species which have been described, there is very little information on those occurring in marine or brackish environments. Many of the earlier descriptions may be disregarded as being not sufficiently complete for recognition (e.g. Schiller, 1913, 19255 West, 1916; Wille, 1903), whilst in recent years only a few marine species have been observed and studied in detail (Chadefaud, 1951; Dangeard, 1965; Ettl, 1967).

Between 8 May and 3 June 1987 horizontal distribution of Owenia fusiformis larvae (Annelida: Polychaeta) was studied in the eastern part of the Bay of Seine on two spatial scales to determine the role of larval dispersal by hydrodynamic factors on the population dynamics of a benthopelagic species. Larval dispersal occurred in two main directions, north-west and north-east, according to the residual tidal circulation. There was a substantial transport of larvae to a distance of 30–40 NM (48–65 km) from their emission point, resulting in a sizeable loss of larvae to the adult population. However, their densities were low in comparison with those observed in the eastern part of the bay, near the adult population. Larval densities remained highest near the adult population, principally under the influence of tidal processes. In contrast, there was a significant wind-induced larval movement at a time scale of a few days. The action of wind at a time scale of one month, the duration of larval life, appeared to be insignificant for dispersal in 1987 because of the frequent changes in wind direction. Climatological data collected between 1951 and 1980 showed that the wind effect observed in 1987 is probably typical of most years. The horizontal transport of Owenia fusiformis larvae, combined with the ontogenic vertical migration observed previously, causes a retention of these larvae in the eastern part of the Bay of Seine; this favours recruitment and may be one of the factors explaining the temporal stability of the adult population.

The belief for long was held by early investigators that among most if not among all Elasmobranch fishes the number of females in the stocks exceeded that of the males. As long ago as 1884 Day (4, p. 345) remarked concerning the Thornback Ray, Raia clavata, “It has been said that the number of females is in excess of that of the males.” Haacke (9, p. 246), writing in 1885, says of the Sharks and Rays which he had observed in South Australian waters, “Bei den südaustralischen Haien und Rochen, auf deren Fang ich zu wiederholten Malen ausgezogen bin und von denen mir auch nicht selten Exemplare für das Adelaider Museum zugeschickt wurden, habe ich die Wahrnehmung gemacht, dass Männchen verhältnismässig sehr selten gefangen werden. Ob diese Wahrnehmung auch anderswo gemacht worden ist, weiss ich nicht, jedoch ist es nicht unwahrscheinlich; in der mir zu Gebote stehenden Litteratur finde ich nichts darüber. Die seltenheit der geschlechtsreifen Männchen, soweit sie sich wenigstens durch die Fangresultate dokumentiert, gilt für sämtliche Species der ziemlich artenreichen südaustralischen Selachierfauna.”

Eupolymnia nebulosa (Montagu) is a tubicolous worm with its body divided into two regions: thorax with biramous segments and three pairs of gills; abdomen with numerous segments lacking notopodia. The head bears grooved foodgathering tentacles which are not retractile into the mouth. The worm, a typical deposit feeder, lives in mucous tubes encrusted with sand. Although the family Terebellidae is homogeneous in terms of body organization and feeding ecology, there is a remarkable heterogeneity of developmental pattern. In the genera Lanice and Loimia, the life-cycle involves two pelagic stages separated by a short benthic larval stage; in other genera the development is mixed or direct (Bhaud et al. 1987; Pechenik, 1979; Caswell, 1981). It is important to study the development of representatives of the family which may reveal the adaptive significance of the different modes of development or may yield information about evolutionary relationships within the family. In several previous papers larval development (Bhaud & Grémare, 1988 a, b) and reproductive biology (Bhaud et al. 1987) of E. nebulosa have been reported from the Mediterranean coast. The present article reports observations on juvenile growth and morphological organization in natural conditions. This is the first step to growth rate studies in terms of temperature and food supply (Bhaud, 1988).

Within the hepatopancreas of the shrimp Penaeus semisulcatus the functional develop ment and subsequent decay of M-‘midget’ cells is described and linked with the moult cycle. During the feeding stages the frequency of M-cells increases and they each form a large dense vacuole which contains proteinaceous material. Precursors for this material are probably derived from the haemolymph as the cells have no direct contact with the lumen of the gland. During the non-feeding stages before and after ecdysis the contents of the vacuole are progressively removed, probably to the haemolymph. Finally the cells die before the animals recommence feeding.

We compared the reproductive behaviours of two protandric simultaneous hermaphroditic species (Lysmata amboinensis and L. boggessi) that belong to two groups of Lysmata shrimp with different morphology, geographical distribution, and density. Lysmata amboinensis occurs in tropical waters at low population densities, and L. boggessi is found in aggregation in sub-tropical and temperate areas. Reproductive behaviour of L. boggessi under two densities and L. amboinensis in different habitats were compared. Results show that L. amboinensis was much less active during mating than L. boggessi. Male shrimp of L. amboinensis did not display obvious pre-copulation behaviour. They also took significantly longer to transfer spermatophores and lay eggs after mating than L. boggessi shrimp did. For L. boggessi, moulting time of female shrimp, copulation time and the interval between moulting and mating were significantly shorter when three male shrimp were present than when only one male shrimp was present. Our study suggests that the reproductive behavioural differences in the two shrimp species are possibly the results of density-dependent effect.