In recent years the external morphology of marine choanoflagellates has been the subject of close scrutiny. This is a result of the attention given to marine nanoplankton, of which choanoflagellates are a part, and the relative ease with which choanoflagellates with loricae of costal construction can be observed in shadowcast whole mounts with an electron microscope. However, detailed ultrastructural studies of choanoflagellate protoplasts have been limited to one freshwater species Codosiga botrytis (Ehr.) Saville-Kent (Petersen & Hansen, 1954; Fjerdingstad, 1961; Hibberd, 1975) and four marine species Salpingoeca pelagica Laval (Laval, 1971), Stephanoeca diplocostata Ellis (Leadbeater & Manton, 1974), Savillea micropora (Norris) Leadbeater (Leadbeater, 1974) and Codosiga gracilis James-Clark (Leadbeater & Morton, 1974b). Of these only the recent studies by Hibberd (1975), Laval (1971), Leadbeater & Manton (1974), Leadbeater (1974) and Leadbeater & Morton (1974b) contain micrographs of material processed by modern methods.

As two pigmented taxa attributed to the class Chrysophyceae had been discovered (Lackey, 1939; Scagel & Stein, 1961) with apparently similar organization to the Choanoflagellida this group of protista was included in the Revised Check-list of British Marine Algae (Parke & Dixon, 1964) following Bourrelly (1957). The group was placed in the class Craspedophyceae erected by Chadefaud (1960) and a first revision of the genus and species list was included in the Check-list of British Marine Algae - Second Revision (Parke & Dixon, 1968).

Three species of Gracilaria, G. foliifera (Forsk.) Børg., G. verrucosa (Huds.) Papenf., and G. bursa-pastoris (S. M. Gmel.) Silva are recognized from the British flora (Parke & Dixon, 1976). In Britain G. verrucosa is widely distributed, although not common, whereas the other two species are rare and their distribution restricted (Newton, 1931). G. foliifera was described from the Red Sea as Fucus foliifer Forsk. (Børgesen, 1932). Plants referable to this species are now reported from various parts of the world, including both the eastern and western coasts of the north Atlantic (South & Cardinal, 1970; Taylor, 1957, 1960). However, considerable variation exists within species of Gracilaria (e.g. May, 1948), thus delimitation of species is often extremely difficult. Gracilaria foliifera from Britain (Fig. 1 A) is similar morphologically to the original material of Fucus foliifer as illustrated by Børgesen (1932, fig. 1), and therefore, we have limited our consideration to G. foliifera as it occurs in Britain (also see Harvey, 1846, pl. 15). However, little information is available on G. foliifera from the British Isles, and in the present instance we have investigated the life history of this alga in culture together with preliminary results on growth in small-scale tanks with running sea water.

Recent studies on the osmotic responses of marine invertebrates to dilution of the external medium have tended to emphasize the osmotic and ionic regulation at the intracellular level rather than at blood/body fluid level. Even in those invertebrates, principally euryhaline crustaceans, possessing osmoregulatory mechanisms which enable them to maintain concentrations of the blood above those of dilute media, the regulation is not perfect, and there is some lowering of the blood concentration below the level exhibited in full-strength sea water (Lockwood, 1962). This requires the establishment of a new osmotic equilibrium between the intracellular solutes and those of the blood. The nature of the intracellular osmotic constituents is, however, strikingly different from those of the blood, even in those invertebrates which are stenohaline and purely marine in their distribution (Robertson, 1961). The osmotic pressure of the blood is due almost entirely to the same inorganic electrolytes as are present in sea water, although the percentage contribution of the various ions may differ. On the other hand these inorganic ions account for only about one third to one half of the intracellular osmotic pressure. The remainder is accounted for by organic solutes, most particularly free amino acids.

Some understanding of the mechanisms involved in the development and maintenance of forests of Laminaria hyperborea (Gunn.) Fosl. can be gained from the analysis of populations under different conditions. The main variable is depth and unfortunately the available depth range of suitable substrata in the Isle of Man is limited. For this reason two visits were made to western Scotland and the Outer Hebrides, in 1970 and 1976. This paper, which is intended as the last in this series, reports on results obtained rom there and from certain sites in the Isle of Man.

The order Isochrysidales was erected by Pascher in 1910 to accommodate chrysomonads with two equal flagella. It was based on the family Hymenomonadaceae (Senn, 1900) and included such genera as Synura Ehrenberg (later shown to be heterokont and therefore incorrectly placed here; Hovasse, 1949; Manton, 1955), Wyssotzkia Lemmermann and Hymenomonas Stein. Papenfuss (1955) used the name in a similar sense but encompassing also the coccolithophorids, while those genera with two equal flagella and a ‘short third flagellum’ ((Prymnesium Massart, Platychrysis N. Carter, Chrysochromulina Lackey) were placed in the order Prymnesiales. Subsequently it was demonstrated that members of the Isochrysidales and Prymnesiales differ from other chrysomonads in that the two true flag-ella are smooth with no coarse hairs (‘mastigonemes’) and that the third appendage found in genera of the latter order is a unique structure, termed the ‘haptonema’ by Parke, Manton & Clarke (1955). On the basis of these observations, Christensen (1962) erected a new class, the Haptophyceae (now referred to by the typified name Prymnesiophyceae; Hibberd, 1976 a), to contain the two orders although Bourrelly (1968) preferred to retain them within the Chrysophyceae whilst recognizing their unique status by the erection of a sub-class, the Isochrysophycidae.

Nutritionally, there are three basic types of Dinophyceae: (1) free-living photosynthetic autotrophs; (2) parasitic heterotrophs living on or in other organanisms and (3) free-living phagocytic or chemosynthetic heterotrophs. Representatives of the first type, the free-living photosynthetic autotrophic species, have been extensively investigated at the fine-structural level (for a review see Dodge, 1971). There are fewer species of the second type, the parasitic Dinophyceae, but many of these have been investigated in the electron microscope (Cachon & Cachon, 1966, 1970, 1971a, b; Cachon et al. 1968; Soyer, 1969 c; Manier, Fize & Grizel, 1971; Siebert & West, 1974). The third type, the free-living heterotrophic Dinophyceae, probably comprises the greatest number of species in the class; as Kofoid & Swezy (1921) state ‘One cannot work with the marine unarmored Dinoflagellata for even a short time without being struck by the fact that the majority of the individuals observed show evidence of holozoic nutrition and that the number actually containing chromatophores is relatively small throughout the entire Dinoflagella’. While the free-living heterotrophic Dinophyceae comprise the largest proportion of the class they have been, by far, the most poorly studied at the fine structural level. Investigations on these organisms have been limited to a comprehensive study of Oxyrrhis marina (Dodge & Crawford, 1971a, b, 1974) plus studies on specific parts of Cryptothecodinium cohnii (Kubai & Ris, 1969; Pokorny & Gold, 1973) and Noctiluca miliaris (Afzelius, 1963; Soyer, 1968, 1969a, b; Zingmark, 1970).

Arenicola marina (L.) is one of the most common members of the outer estuarine sandy and muddy shores. A moderately euryhaline osmoconformer, this polychaete cannot survive in water of less than about 10‰ constant salinity and then only in the Baltic; however, in the outer portions of estuaries, it is not uncommon for the overlying water to be practically fresh at some stages of the tide. Wells (1949b) postulated that parts of the complex burrowing behaviour of the animal prevents irrigation of the burrow with noxious water, but the advantages to the lugworm of its periodic inactivity have never been fully investigated.

Off the coast of Cornwall from the Lizard Head to Padstow there has been, for many years, a small but locally important fishery for crawfish Palinurus elephas (Fabr.).

The fishermen had used pots and tangle nets up to the outbreak of the Second World War in 1939. From 1945 tangle nets had been little used and the fishery was pursued mainly by pot fishermen until the early 1960s when divers using self-contained under-water breathing apparatus began to collect crawfish. Tangle nets were re-introduced widely in the late 1960s.

Tube-dwelling diatoms are found in a variety of habitats, from marine to fresh water on different types of substrata; rock, wood, plant and animal. I have described species as tube-dwelling (Cox, 1975 b) if they produce mucilage which is consolidated into a tubular structure around the cells, yet within the mucilage tube individual cells move and divide. The tube is usually attached to the substratum at its base and is extended apically by the secretion of more mucilage by the enclosed diatoms. Tube volume thus increases to accommodate the increased endotubular diatom population. The presence of tube-dwelling diatoms on rocky shores has been recorded by some workers (Aleem, 1949, 1950; Castenholz, 1963, 1967; Hopkins, 1964), while Castenholz (1963, 1967) correlated seasonal and distribution patterns of some littoral species with their response to light intensity and day-length. Carter (1932,1933) described the algal flora, including several tube-dwelling species, of two salt marshes but little work has been done on tube-dwelling diatoms occurring in estuaries. During the course of a study on the biology of these diatoms (Cox, 1975 ft) variation in their distribution at two Severn Estuary sites prompted an investigation into their distribution in the estuary as a whole. Diatom distribution was recorded with reference to the geographical location in the estuary and to the position on the shore at two sites lower down the estuary (Clevedon and Weston-Super-Mare).

Southward & Butler (1972) discussed changes in sea and air temperature in the Plymouth area this century, and showed that there was an increase from about 1900 to 1945 followed by a decrease. In the present analysis the data, updated to 1974, have been subjected to a more rigorous statistical treatment, made possible by the availability of a computer; inshore and offshore sea temperatures have been compared in greater detail, and sea-bed temperatures included. The results are described and discussed in relation to the biological changes that have been observed in the western English Channel during the same period. Data on rainfall and westerly weather have also been examined, and correlated with the temperature values.

In the Galway Bay area the carragheen species, Chondrus crispus Stackh. and Gigartina stellata (Stackh.) Batt., are still collected using traditional methods. The weeds are picked by hand, spread out on any convenient area of grass, allowed to dry and, in the case of Chondrus, bleach in the open air. Most collecting is done during the autumnal equinoctial spring tides and is virtually restricted to the intertidal zone.

The Irish seaweed industry has declined since 1960, when according to Chapman (1970) production reached its peak. When describing the industry in 1974, Cahill & Sweeney made the following comments. ‘A small number of firms are engaged in harvesting and primary processing. Between 1000 and 1250 people are seasonally employed. Almost 40000 tons of wet weed are harvested annually with a landed value of approximately £200000. Harvesting techniques are largely manual and there is a possibility that the industry may decline in the medium term as alternative and more lucrative employment opportunities become available.’

Parathemisto gaudichaudi (Guerin) (= P. gracilipes, Sheader & Evans, 1974) is a species of planktonic hyperiid amphipod which occurs in temperate and subpolar regions in both hemispheres (Dunbar, 1964; Kane, 1966; McHardy, 1970, Ph.D. thesis, Edinburgh University).

Our previous studies have dealt with the taxonomy (Sheader & Evans, 1974), feeding and gut structure (Sheader & Evans, 1975), and morphological variation (Sheader, 1975) of P. gaudichaudi. These studies involved the routine maintenance of the species in laboratory conditions, allowing behavioural and developmental data to be gathered. The present paper deals with fertilization of the eggs and subsequent development up to the time of release from the marsupium. Animals were collected at a station 5 miles east of Blyth, Northumberland (55° 07′ N, 1° 22′ W). Laboratory culture is described in previous papers (Sheader & Evans, 1974, 1975).

The amplitude and phase of tidal characteristics in the English Channel have been described both using numerical models (Grijalva, 1962; Hyacinthe & Kravtchenko, 1967) and a hydraulic model on a rotating table (Chabert d'Hières & le Provost, 1970). The aim behind the development of the numerical model described here is first to derive an accurate representation of the principal lunar semi-diurnal (M2) tide in the English Channel and then to use the currents generated by the tidal input to determine the tidal circulation patterns and residual flow through the English Channel. A test of the model must be its ability to reproduce the known clockwise eddy in Lyme Bay and the south-ward flow either side of Portland Bill. If these known tidal residuals can be reproduced then the model may help to elucidate residuals in other regions where the flow is unknown. In addition to deriving the mean tidal velocities, horizontal distributions for the mean squared and cubed values are calculated and the importance of these distributions in determining the nature of the bottom and the degree of stratification of the water column in summer is demonstrated.

In his search for evidence illustrating the botanical/zoological affinities of the sponges (Porifera), James-Clark (1867) studied a number of colourless flagellates. The genus Salpingoeca (Craspedophyceae, Christensen, 1962; cf. Chadefaud, 1960) was thus erected to comprise certain solitary, lorica-dwelling organisms, characterized by a single anterior flagellum encircled by a ‘filmy, membranous, colourless collar’ (James-Clark, 1867).

About fifty species (approximately twenty marine) are at present allocated to this genus, provided it is defined as e.g. by Norris (1965) and Bourrelly (1968) (i.e. including Lagenoeca Kent and Pachysoeca Ellis).

On 11 August 1976 an observant yachtsman noted an unfamiliar alga between Misery Point and Warren Point at the mouth of the River Yealm. Suspecting that it might be ‘Japweed’ he collected a piece and took it to Mr B. W. P. Sparrow of the International Marine Coatings Laboratory who contacted the Marine Biological Association, where Dr Boalch confirmed that it was a part of a fertile plant of Sargassum muticum, the first to be recorded from the Plymouth area (see Fig. 1).

Earlier studies on the problems of the Adriatic Sea and the knowledge of its hydromedusae are restricted to the northern part. Will (1844) mentioned six species of hydromedusae found in the Bay of Trieste. Several studies ensued from the northern part of this sea, until Neppi (1912, 1915, 1922), Pell (1911, 1938), Kramp (1924), Babnik (1948) and Benović (1971 a) included other areas. Some specimens from the middle and southern Adriatic are mentioned in the planktonic works of Gamulin (1948, 1976), Hure (1955, 1961), Buljan, Hure & Pucher-Petković (1973) and Vučetić (1957, 1961, 1966).

In spite of the controversy surrounding the accidental introduction of the Japanese seaweed Sargassutn muticum (Yendo) Fensholt onto two continents, the startling south-ward expansion of its range on the Pacific coast of North America (Norton, 1977 a), and the failure of an eradication campaign on the south coast of England, surprisingly little is known about the ecology of this species. Work has recently begun in both southern California and Britain (Nicholson et al. 1977; Lewey & Farnham, 1977). Unfortunately the ecological studies in Britain have been hampered by the conflicting aims of trying to study the plant and at the same time trying to eradicate it.

Although the nitrogenous excretory products of a number of marine bivalve molluscs have been identified (Hammen, Miller & Geer, 1966; Hammen, 1968; Emerson, 1969; Allen & Garrett, 1971; Bayne, 1973 a) and average values for rates of nitrogen excretion recorded for some species (Lum & Hammen, 1964; Hammen et al. 1966; Bayne, 1973a), there is little information available on the ways in which environmental factors may affect either the balance between the various nitrogenous end-products, or their rates of excretion. The most thorough investigations have dealt with the effects of reduced salinity, which causes an increase in the rates of excretion of ammonia by Macoma inconspicua (Emerson, 1969), Mya arenaria (Allen & Garrett, 1971) and Mytilus edulis (Bayne, 1975). Dilution of the medium is also known to accelerate the loss of amino acids from the body, as part of the mechanism of volume regulation (Pierce & Greenberg, 1972, 1973). There is some evidence of altered rates of excretion during starvation (Hammen, 1968; Emerson, 1969; Bayne, 1973 a, b) and differences in excretion rate due to differences in animal size have been documented for Donax vittatus by Ansell & Sivadas (1973) and for Mytilus californianus by Bayne, Bayne, Carefoot & Thompson (1976 a, b).

Ampelisca tenuicornis Lilljeborg, 1855, is a member of a widely distributed genus of benthic tube-dwelling amphipods. Population studies of A. macrocephala Lilljeborg in the Øresund show it to have a generation length of 2 years (Kanneworff, 1965), and A. vadorum Mills off Massachusetts, U.S.A., produces two generations per year (Mills, 1967). A. brevicornis (Costa) in the Mediterranean breeds throughout the year with a generation time of 5–7 months (Kaim-Malka, 1969), but has only one generation per year in Helgoland Bight (Klein, Rachor & Gerlach, 1975).