Showing papers in "Ophelia in 1973"
TL;DR: The results of more than 30 years field observations and research work carried out from the Isefjord Laboratory, Vellerup Vig (Zealand, Denmark), which is owned and financed by the author, are represented.
Abstract: This paper represents the results of more than 30 years field observations and research work carried out from the Isefjord Laboratory, Vellerup Vig (Zealand, Denmark), which is owned and financed by the author. The Isefjord complex, 36 km long, including the main fjord and the Roskilde Fjord, and covering about 400 km2, is a shallow (7–10 m, max. 30 m) area dominated by substrata of fine sand to mud with a high content of organic matter. As a guidebook for future research the first part gives information about distribution, systematics, ecology, and breeding of the majority of the 477 animal species described. Nearly 400 species are invertebrates and of the chordates 68 species are true fishes. 63% of all animal species have not previously been recorded from the area, 27 species are new to Danish seas, and one (Polychaeta, Capitellidae) is new to science. The hydrography is treated mainly on the basis of literature. The fjord system may be classified as mixohaline: the Isefjord proper is polyhali...
695 citations
TL;DR: It was confirmed that bivalve larvae are able to make a choice of settling place in nature by comparing the number of settling specimens of the same species in the two localities, which suggested that the growth rate in the Oresund seems to be smaller than in most other temperate areas.
Abstract: The quantitative aspects of the settling of 11 bivalve species were registered in the Oresund, based on bottom samples from two localities. The time of spatfall and the numbers of settling specimens were related to existing data on occurrence of larvae in the plankton. The number per m2 of settling specimens, the decrease of this number and the growth of the bivalves during the first months after spatfall were calculated. The growth rate in the Oresund seems to be smaller than in most other temperate areas. The possible reasons for this discrepancy are discussed and it is suggested that some of the results previously recorded in the literature on growth of newly settled bivalves are inaccurate on account of inadequate sampling-sieving techniques. By comparing the number of settling specimens of the same species in the two localities it was confirmed that bivalve larvae are able to make a choice of settling place in nature. Causes of the heavy decrease in number of spat during the first months aft...
118 citations
TL;DR: The P/R ratio shows that the energy available for growth and reproduction decreases with increasing size as the absorption does not change significantly with size.
Abstract: Pumping rate (P), oxygen uptake (R), gill area (A), and absorption efficiency (Ab) in Mytilus edulis have been studied The parameters are expressed as functions of the dry weight of soft parts (W) by a power function Y = a·Wb where Y is the dependent variable It is found tha P = 390·W080 l/hr, R = 037·W075 ml O2/hr, A = 3434·W065 cm2, Ab = 7816·W−002‰ and P/R = 1047·W−016 l water pumped/ml O2 consumed The gill area increases significantly faster with size than the pumping rate The P/R ratio shows that the energy available for growth and reproduction decreases with increasing size as the absorption does not change significantly with size The effect of seasonal changes in P and R on the P/R ratio is discussed
109 citations
TL;DR: The growth of the species at Greenland is slow compared with its growth in most temperate areas and when the growth rate is related to day-degrees, growth at Greenland almost equals that found in similar habitats in temperate regions.
Abstract: The growth in length of Mytilus edulis L. from Disko and the Tliule district is estimated by means of the very distinct winter growth checks. The growth is highly sigmoid and can be described by a combination of the Gomperz equation (valid for the growth until about half the ultimate length is attained) and the von Bertalanffy equation (valid for the growth from about one third of the ultimate length) as neither of the two growth equations covers the whole size range of Mytilus. The growth of the species at Greenland is slow compared with its growth in most temperate areas. Doubtlessly low temperature is the cause of the slow growth. When the growth rate is related to day-degrees, growth at Greenland almost equals that found in similar habitats in temperate regions. An apparent size-dependent mortality occurs among the very small Mytilus living on Fucus. However, this phenomenon is probably caused by differential emigration among the small individuals. A conspicuous lack of young individuals in t...
98 citations
TL;DR: Electron microscopical investigations of nanoplankton from the Isefjord area have led to the enumeration of twenty different silicified choanoflagellates, three of which are new to science and nine of the remaining species have not previously been recorded from Denmark.
Abstract: Electron microscopical investigations of nanoplankton from the Isefjord area have led to the enumeration of twenty different silicified choanoflagellates. These include three species new to science, Acanthoecopsis unguiculata, Stephanoeca urnula and Pleurasiga sphyrelata. Nine of the remaining species have not previously been recorded from Denmark. An X-ray analysis, using a combined transmission-scanning electron microscope, has demonstrated that the costal strips of the lorica of Diaphanoeca grandis Ellis consist mainly of silicon.
61 citations
TL;DR: The newly hatched free-swimming larva of the endoparasitic turbellarian Kronborgia amphipodicola Christensen & Kanneworff, 1964 was studied by means of the scanning and transmission electron microscopes.
Abstract: The newly hatched free-swimming larva of the endoparasitic turbellarian Kronborgia amphipodicola Christensen & Kanneworff, 1964 (fam. Fecampidae) was studied by means of the scanning and transmission electron microscopes. The larva is covered by epidermal cells provided with cilia and microvilli. Processes, each ending in a clup-shaped modified cilium, penetrate the epidermis on the anterior end of the larva. These structures are supposed to be of chemoreceptive nature. Different types of gland cells open throughout the larval surface. Below the epidermis two or more thin muscle layers are found, and below these there occur neoblast-like cells and cells containing organelles similar to the organelles of the epidermal cells. These latter cells are suggested to be epidermal-replacement cells. The larva forms a cyst on the cuticula of the crustacean host with secretory products from two gland types opening throughout the larval surface. The penetration through the host cuticula is probably carried o...
41 citations
TL;DR: It is possible that the crystalline style functions by mechanically pressing nutritious particles against the absorptive epithelium of the style pouch and is a substitute for an almost total lack of muscular elements in the bivalve alimentary canal.
Abstract: The crystalline style disappears from Pacific oysters held out of water, but is completely reformed 1 hour after submergence. The style is secreted and dissolved along its entire length and does not move forward into the stomach. It is renewed every 8 hours in submerged oysters or follows the tidal cycle in tidal localities. The style carries a thin superficial coating of mucus and food particles which travel its length in 50 minutes at 17°C. It is possible that the crystalline style functions by mechanically pressing nutritious particles against the absorptive epithelium of the style pouch and is a substitute for an almost total lack of muscular elements in the bivalve alimentary canal.
35 citations
TL;DR: Tail-bearing and tailless intraredial cercariae of Neophasis lageniformis were studied in the transmission and stereoscan electron microscopes, and the adult stages were studied on the basis of spines, sensory structures, and cell types.
Abstract: Tail-bearing and tailless intraredial cercariae of Neophasis lageniformis were studied in the transmission and stereoscan electron microscopes, and the adult stages were studied in the stereoscan electron microscope. All developmental stages are provided with flattened, serrated spines which gradually diminish in size towards the posterior end. They also possess a few sensory structures, composed of an apical cilium and a bulbous base in connection with nerve tissue. Only one cell type, the tegumentary cells of previous authors, connects with the syncytial tegument. Vesicles synthetized in the tegumentary cells enter the tegument through the cytoplasmic connections. In the tegument the most apically located vesicles apparently release their contents into the surrounding medium. Several layers of muscle fibres rich in beta glycogen particles are found below the basal lamina of the tegument. In young tail-bearing cercariae processes of supposed parenchymal cells look nearly empty, whereas in taille...
35 citations
TL;DR: The physiological data found in these experiments fit in with the known ecological distribution of the three species and I. viridis was a significantly better osmoregulator than the two other species.
Abstract: The osmoregulation of Idotea baltica, I. viridis and I. granulosa from Denmark was investigated in an attempt to elucidate their ecological distribution. All were able to keep their haemolymph hyperosmotic relative to the medium in salinities below 30‰. Above this concentration they were isosmotic. The lower salinity limits tolerated varied, as it was 5, 7 and 9‰ for respectively I. viridis, I. baltica and I. granulosa. I. viridis was a significantly better osmoregulator than the two other species. When transferred from high to low salinity water the haemolymph concentration dropped rapidly in all species within the first three hours. After 24 hours an almost steady-state condition was reached. When exposed to a sudden raise in salinity all regulated to the new steady-state situation within three hours. The physiological data found in these experiments fit in with the known ecological distribution of the three species.
33 citations
TL;DR: Investigations on the ionic regulation of the haemolymph during the moult cycle of Crangon vulgaris (Fabr.) (Crustacea, Natantia) were made in a salinity of 10‰, and changes in ion concentrations can mostly be explained by an increased permeability and an increased water intake before the ecdysis and a swelling of the animal after Ecdysis before the new exoskeleton has hardened.
Abstract: Investigations on the ionic regulation of the haemolymph during the moult cycle of Crangon vulgaris (Fabr.) (Crustacea, Natantia) were made in a salinity of 10‰. Sodium showed a minimum immediately after ecdysis and a maximum in the intermoult stages, while potassium, which also is held at a level higher than the medium, showed a minimum in the intermoult stages and an increase prior to and after ecdysis. Calcium showed, contrary to species from fully marine areas, a minimum after ecdysis and then a rapid increase in calcium ion concentration and a slow decrease in the later intermoult phase and in the premoult stages. Magnesium, generally held at a very low concentration, showed an increase at ecdysis. Chloride varied in the same way as sodium. The changes in ion concentrations during the moult cycle can mostly be explained by an increased permeability and an increased water intake before the ecdysis and a swelling of the animal after ecdysis before the new exoskeleton has hardened.
27 citations
TL;DR: The activity patterns of both species showed great seasonal variations and under artificial light/dark conditions both species were nocturnal.
Abstract: The swimming activity of Idotea baltica and Idotea granulosa was investigated by means of photocells. The activity patterns of both species showed great seasonal variations. Both species showed no swimming activity in winter (Idotea baltica from November-March, and Idotea granulosa from September-March). The rest of the year both species had one activity peak between midnight and sunrise. Idotea baltica was nocturnal in early spring, in summer the activity was high all 24 hours, besides the nocturnal maximum an increased activity was evident in the afternoon till two hours after SS. At the end of September and the beginning of October I. baltica was nocturnal. The same variation in the activity pattern was found for I. granulosa. Under artificial light/dark conditions both species were nocturnal. When the light/dark change was right-angled this was the dominating Zeitgeber.
TL;DR: The hyper-hypoosmotic (isosmotic at 23‰) shrimp Crangon vulgaris was found to maintain Ca2+ and K+ more concentrated than the medium in 5-25‰, Na+ and Cl− more concentrated in the range 5–30(23)‰ and less concentrated in higher salinities.
Abstract: The hyper-hypoosmotic (isosmotic at 23‰) shrimp Crangon vulgaris was found to maintain Ca2+ and K+ more concentrated than the medium in 5-25‰, Na+ and Cl− more concentrated in the range 5–30(23)‰ and less concentrated in higher salinities. Mg2+ was held at a very low level throughout the saUnity range. The importance of various mechanisms (low permeability, active ion transport and hypo-osmotic urine) in assisting this efficient ion regulation is discussed.
TL;DR: The results of this study and observations in aquaria show that this sea-star is not solely a ciliary feeder as hitherto believed and among its prey are the octocoral Alcyonium digitatum, the brachiopod Crania anomala, and several species of ascidians.
Abstract: A study of the food uptake and feeding behaviour of 150 specimens of Porania pulvillus was performed in situ by SCUBA diving in waters off the Swedish Skagerrak coast. The results of this study and observations in aquaria show that this sea-star is not solely a ciliary feeder as hitherto believed. Among its prey are the octocoral Alcyonium digitatum, the brachiopod Crania anomala, and several species of ascidians.
TL;DR: The variations in the phytoplankton were measured during one year in the oligohaline Danish lake, Selso, and the primary production determined, as the maximum rate of gross production, of chlorophyll-a.
Abstract: The variations in the phytoplankton were measured during one year in the oligohaline Danish lake, Selso. Measurements were made of the variations in volume of total phytoplankton and in volumes of the different algal groups. The amount of chlorophyll-a was measured, and the primary production determined, as the maximum rate of gross production. Among the more important environmental factors measurements were made of temperature, transparency, conductivity, salinity, pH, alkalinity, oxygen content and the nutrients nitrate, phosphate and silicon. The relations between the variations in the phytoplankton volume and the variations in pH, alkalinity and the content of nutrients are discussed. A comparison is made with other, earlier investigated Danish inshore waters.