In an earlier paper (Boney, 1973) the skeletal variations, and their quantitative significance, were described for autumn collections of Dictyocha speculum obtained with a 600 m.p.i. tow-net from surface waters in the Fairlie Channel, Firth of Clyde, in 1970. It was shown that skeletal abnormalities constituted a very small number (1·78%) of the 6025 skeletons examined. In these same samples numerous double skeletons were observed. These are regarded as pre-division stages (Gemeinhardt, 1930; Hovasse, 1932; Marshall, 1934), in which the replica of the first skeleton usually has thinner tubular skeletal rods (Marshall, 1934). A detailed examination of these double skeletons was undertaken to determine whether true mirror-imaging occurred, and the extent to which a ‘normal’ skeleton was joined to a partner of aberrant form. The methods used to obtain slide preparations in glycerine jelly were described in the previous paper (Boney, 1973) and the terminology of the components of the skeletal unit are also the same (Fig. 1A–C).

INTRODUCTION

Studies of established populations of Laminaria hyperborea (Gunn.) Fosl. have indicated that there is often less change of growth rate with depth than might be expected to result from the decrease in irradiance (Kain, 1967; Lüming, 1969; Jupp & Drew, 1974). This has been attributed to self-limitation by the canopy of Laminaria fronds (Lüning, 1969; Kain et al. 1976). The removal of this canopy can result in fast growth in shallow water (Kitching, 1941; Svendsen, 1972) and a marked differential in growth rate over a small depth range (Svendsen, personal communication). A series of rocky subtidal areas at two depths off the Isle of Man was cleared of vegetation at various times (Kain, 1975a). This provided an opportunity to make growth measurements on individuals of known age in the absence of a canopy formed by older plants.

INTRODUCTION

Little is known about the early growth history of solitary corals in relation to the substrates to which they are attached. An understanding of this relationship between coral and substrate, and of how it may change throughout the life of the coral, is particularly important in studies of the life history and ecology of solitary corals living in sand and other soft sediments. A knowledge of the variety of different substrates to which solitary corals are attached in the wide range of different environments in which they live is also of importance to the palaeontologist when attempting palaeoecological interpretation of transported coral debris.

INTRODUCTION

Between 4 May 1973 and 29 March 1975 we did not visit Duckpool. Indeed after the 1973 visit (Wilson, 1974, pp. 429–30) the intention had been to discontinue observations on colony formation and growth, for it seemed unlikely that much more data of value were obtainable, and that is still true. However, at Easter 1975 Monsieur Yves Gruet, who has done much excellent work on Sabellaria associations on the coast of France (references in Wilson, 1974), visited Plymouth with his family and wished to see Duckpool. We went there on 29 March and arising out of that visit my wife and I were again there the following October, with one main object in view as explained below, and this in turn led to a further visit in November. This paper records observations made during those visits.

INTRODUCTION

Work on pumping and filtration rates of bivalve molluscs was initially concerned with the physiological concept of pumping water through the mantle cavity. Comprehensive reviews are given by Winter (1970) and Ali (1971). The methods are of two kinds; direct, in which the flow of exhaled water itself is measured, and indirect, in which the rate of clearance of food particles is used to calculate water flow through the gills.

There is a disadvantage in the indirect method when used to calculate volumes of water pumped because it involves the assumption that a fixed percentage (often 100% with large particles) of the particulate matter passing through the gill system is retained. Pumping rate is thus estimated as a function of the particle collecting properties of the latero-frontal cirri, whereas the water current is produced by the lateral cilia. Although the structure of the latero-frontal cirri is now well documented (Moore, 1971), their efficiency in particle retention can alter under certain conditions (Dral, 1967). There is need, therefore, for direct measurement of the quantity of water pumped. Recent advances in the understanding of branchial innervation and the control of lateral ciliary activity also reinforce this point (Aiello, 1960, 1962, 1970; Paparo, 1972, 1973).

The constant level chamber for direct measurement of pumping rate was devised by Galtsoff (1926), to ensure that separation of the exhalant water current from the bivalve was not interfered with by pressure differences produced by the process of separation. The apparatus has been used in various forms by Galtsoff (1926, 1928, 1946), Nelson (1935, 1936), Collier & Ray (1948), Loosanoff & Engle (1947), Loosanoff & Nomejko (1946) and more recently by Drinnan (1964) and Davids (1964).

INTRODUCTION

The nauplius stages of many barnacle species have been described at the light microscope level (Bassindale, 1936; Knight-Jones & Waugh, 1949; Costlow & Bookhout, 1957; Karande, 1974), including those of the British barnacles Balanus balanoides (L.) andBalanus hameri (Ascanius) (Crisp, 1962a, b). Although these studies have included full descriptions of limb structure, it is not possible with the light microscope to resolve the topographical relationship of the limbs and other structures associated with feeding. Attempts to describe the feeding process of barnacle nauplii (Lochhead, 1936; Norris & Crisp, 1953; Gauld, 1959; Moyse & Knight-Jones, 1967) have necessarily been limited for this reason.

INTRODUCTION

The development of techniques to culture calanoid copepods over multiple generations in the laboratory has resulted in considerable advances in knowledge about a group of animals of major importance in the marine food web. A series of extensive studies have been made of two species of large calanoids, Calanus helgolandicus (Claus) (Mullin & Brooks, 1967, 1970a, 1970b; Paffenhöfer, 1970, 1971, 1976a, 1976b), and Rhincalanus nasutus Giesbrecht (Mullin & Brooks, 1967, 1970a, 1970b). Feeding, growth, and reproduction have been studied under controlled conditions, using different temperatures, food species, and food concentrations. Some of the information gained in these studies has been incorporated into a simulation model of the planktonic ecosystem of the North Sea (Steele, 1974). However, in the North Sea and in many other sea areas species of small copepod probably form an important component of the food web. Little information is available on the quantitative biology of these small copepods under controlled conditions.

INTRODUCTION

In an earlier study (Corner et al. 1974) the copepod Calanus helgolandicus (Claus) was found to feed actively on nauplii of the barnacle Elminius modestus Darwin, one adult female ingesting a maximum daily ration equivalent to 25% of the body nitrogen. The present work, in which Elminius nauplii have again been used as a diet, extends the earlier study by determining how efficiently Calanus digests an animal food. In addition, the methods used have provided information on other aspects of carnivorous feeding by Calanus, including the relationship between food concentration and size of ration ingested as well as gross growth efficiency, i.e. the proportion of ingested food invested in growth.

INTRODUCTION

Detailed studies of the vertical distribution and migration of the micronekton, plankton and sonic scattering layers in an oceanic environment off Fuertaventura in the Canary Islands were made from R.R.S. ‘Discovery’ during September to December 1965. A general account, including a statement of the objectives of the cruise, has been given by Currie, Boden & Kampa (1969). Foxton (1969) has described the biological sampling methods and techniques utilized. Results of sonic scattering investigations have been published by Blaxter & Currie (1967) and Boden & Kampa (1967). The present study deals only with the pelagic amphipods, and forms a contribution to a series (Angel, 1969; Clarke, 1969b; Baker, 1970; Foxton, 1970a, b; Badcock, 1970; Roe, 1972a, b, c, d; Pugh, 1974) dealing with the distribution and migration of the major taxa sampled during the investigation. An objective summary of the plankton data utilizing factor analysis and cluster analysis has been provided by Angel & Fasham (1973, 1974).

INTRODUCTION

This paper forms the second and last part of a study of the vertical distribution and migration of pelagic Amphipoda based on material collected off Fuertaventura, Canary Islands, during the SOND Cruise in 1965. The first part (Thurston, 1976b) dealt with the Gammaridea. The data presented herein deal with the Hyperiidea, to which is added a general discussion.

The background to the cruise has been given by Currie, Boden & Kampa (1969), and Foxton (1969) has described the gear and methods used. This analysis is based primarily on samples obtained from a series of 1 m2 ring-net (N 113) hauls, but has been supplemented by selected materials from modified 3 m Isaacs-Kidd Mid-water Trawl (IKMT), neuston net and 1 m2 Rectangular Mid-water Trawl (RMT 1) hauls. Thurston (1976b) has discussed the limitations of the sampling techniques as they affect the present results.

INTRODUCTION

The herring Clupea harengus L. and sprat Sprattus sprattus (L.) are physostomatous teleosts with narrow ducts connecting the swimbladder to both the gut and cloaca. With other clupeoids these two species were of great interest to the anatomists of previous generations because of the further tubular connexions between the swimbladder and air-filled otic bullae close to the labyrinth of the inner ear. Together with the Ostariophysi, which have a chain of Weberian ossicles between the swimbladder and the inner ear, the clupeoids were thought to have enhanced hearing compared with many other teleosts as a result of coupling the ear to the swimbladder.

Despite such interest in the system the earlier literature is very fragmented, with the descriptions ranging over at least a dozen clupeoid species, and much of the work was done on fairly advanced juvenile or on adult fish. Ridewood (1891) examined the swimbladder-inner ear relationship in adult herring, pilchard Clupea pilchardus, sprat, shad C. alosa, twaite C. finta and anchovy Engraulis encrasicholus; Tracy (1920) made a similar study of the American Atlantic clupeoids – the shad Alosa sapidissima, alewife Pomolobus pseudoharengus, summer herring P. aestivalis, fall herring P. mediocris and menhaden Brevoortia tyrannus and O'Connell (1955) of the Pacific sardine Sardinops caerulea and anchovy Engraulis mordax. Wohlfahrt (1936) considered the total swimbladder-inner ear-lateral line relationship in 100–120 mm pilchards, recognizing the much less obvious connexion between the perilymph and the lateral line through a membrane in the skull. The presence of such a connexion had been suggested earlier by Tracy (1920).

INTRODUCTION

The preceding paper (Allen, Blaxter & Denton, 1976) describes the development of the swimbladder-inner ear-lateral line system of the herring.

In the larval stage of herring the pro-otic bullae start to develop at a body length of about 18 mm. Between 18 and 30 mm the bullae become filled with gas. At 26 mm the lateral recess membrane starts to develop, becoming silvered at about 42 mm. The lateral line develops between 19 and 45 mm. The swimbladder silvers and contains gas from about 38 mm. The adult system is complete at 50–60 mm body length, some four months after hatching.

This paper concerns the system in its intermediate stages of development. It examines the problems of how the bullae are filled with gas and how the gas spaces are maintained. It gives evidence on the possible roles of the gas-filled spaces as hydrostatic pressure receptors and as aids to buoyancy and discusses the limitations of the system before it can gain or lose gas to a gas-filled swimbladder.

INTRODUCTION

Parasite-induced excess growth, or gigantism, has been reported in several mammals (reviewed by Cheng, 1971) and a fish (Summerfelt & Warner, 1970). Work on invertebrates has centred on size increase in gastropod molluscs associated with infections by larval trematodes (reviewed by Cheng, 1967, 1971). Among these the results have been variable, with some host species showing real gains in body size (soft tissue) (Rothschild & Rothschild, 1939), others initial gains with later stunting (Pan, 1965), and still others gains only in shell thickness (Cheng, 1967). Parasitic castration in other invertebrate groups, not necessarily accompanied by gigantism, has been reviewed by Kuris (1974).