Physiological And Biochemical Aspects Of The Valve Snap And Valve Closure Responses In The Giant Scallop Placopecten-Magellanicus .1. Physiology

1. Catabolic processes of the phasic and catch parts of the adductor muscle ofPlacopecten magellanicus have been studied in relation to valve snap and valve closure responses. It is concluded that the snap response is powered by both parts of the adductor muscle and the valve closure response is powered exclusively by the catch part. 2. Both parts of the adductor muscle show a high glycolytic potential, reflected by high levels of glycolytic enzymes (Table 1) and high glycogen levels (Table 2). Lactate dehydrogenase could not be detected. In contrast, octopine dehydrogenase shows high activities in both parts of the adductor muscle. It is therefore concluded that a main anaerobic pathway in both tissues is the breakdown of glycogen to octopine. In the catch part, however, a considerable amount of the pyruvate formed from glycogen may also be converted into alanine (see below). The glycolytic flux in the catch part is much higher during the snap response than during valve closure. 3. The absence of phosphoenolpyruvate carboxykinase in the adductor muscle ofP. magellanicus and the observed changes in aspartate, alanine and succinate demonstrate that the energy metabolism in the catch part during valve closure shows great similarities to that which occurs only in the initial stage of anaerobiosis in the catch adductor muscle of the sea musselMytilus edulis L. 4. Arginine kinase activity and arginine phosphate content of the phasic part are much higher than those of the catch part (Tables 1 and 3). This may explain why in the phasic part during the snap response most ATP equivalents are derived from arginine phosphate, and in the catch part during both valve responses most are derived from glycolysis (Table 6). Despite the limited contribution of glycolysis in the phasic part during the snap response, the glycolytic flux increases by a factor of at least 75. 5. Evidence is obtained that octopine is neither transported from one part of the adductor muscle to the other, nor from the adductor muscle to other tissues.

Physiological And Biochemical Aspects Of The Valve Snap And Valve Closure Responses In The Giant Scallop Placopecten-Magellanicus .2. Biochemistry

1. Catabolic processes of the phasic and catch parts of the adductor muscle ofPlacopecten magellanicus have been studied in relation to valve snap and valve closure responses. It is concluded that the snap response is powered by both parts of the adductor muscle and the valve closure response is powered exclusively by the catch part. 2. Both parts of the adductor muscle show a high glycolytic potential, reflected by high levels of glycolytic enzymes (Table 1) and high glycogen levels (Table 2). Lactate dehydrogenase could not be detected. In contrast, octopine dehydrogenase shows high activities in both parts of the adductor muscle. It is therefore concluded that a main anaerobic pathway in both tissues is the breakdown of glycogen to octopine. In the catch part, however, a considerable amount of the pyruvate formed from glycogen may also be converted into alanine (see below). The glycolytic flux in the catch part is much higher during the snap response than during valve closure. 3. The absence of phosphoenolpyruvate carboxykinase in the adductor muscle ofP. magellanicus and the observed changes in aspartate, alanine and succinate demonstrate that the energy metabolism in the catch part during valve closure shows great similarities to that which occurs only in the initial stage of anaerobiosis in the catch adductor muscle of the sea musselMytilus edulis L. 4. Arginine kinase activity and arginine phosphate content of the phasic part are much higher than those of the catch part (Tables 1 and 3). This may explain why in the phasic part during the snap response most ATP equivalents are derived from arginine phosphate, and in the catch part during both valve responses most are derived from glycolysis (Table 6). Despite the limited contribution of glycolysis in the phasic part during the snap response, the glycolytic flux increases by a factor of at least 75. 5. Evidence is obtained that octopine is neither transported from one part of the adductor muscle to the other, nor from the adductor muscle to other tissues.

Rates Of Nitrogen-Excretion By Species Of Mytilus (Bivalvia - Mollusca)

The results of experiments recorded by Bayne & Scullard (1977) confirmed earlier studies (Bayne, 1973) in describing a decline in the rate of oxygen uptake (Vo2) by Mytilus edulis during starvation, eventually reaching a steady-state value, called the standard rate of oxygen consumption. Earlier experiments had also shown that if such starved mussels were fed, oxygen uptake increased rapidly to a high level called the active rate of oxygen consumption (Thompson & Bayne, 1972; Bayne, Thompson & Widdows, 1973). Some of this increase in metabolic rate is undoubtedly due to an increased filtration rate that is stimulated by the presence of food (the ‘mechanical cost of feeding’ discussed by Bayne et al. 1976), and part is due to the ‘physiological costs of feeding’, which includes energy utilized in digestion and assimilation of the food, and energy that is lost during deamination and other catabolic processes that accompany digestion (Warren & Davis, 1967). Increases in metabolic rate associated with feeding have been called the specific dynamic action (SDA) of the ration (see Harper, 1971, for a discussion) or the apparent SDA (Beamish, 1974)5 and they have been related to aspects of protein metabolism (Krebs, 1964). This paper describes the results of some experiments designed to examine the relationships between SDA and ammonia excretion in Mytilus edulis L.

Apparent Specific Dynamic Action In Mytilus-Edulis L

The results of experiments recorded by Bayne & Scullard (1977) confirmed earlier studies (Bayne, 1973) in describing a decline in the rate of oxygen uptake (Vo2) by Mytilus edulis during starvation, eventually reaching a steady-state value, called the standard rate of oxygen consumption. Earlier experiments had also shown that if such starved mussels were fed, oxygen uptake increased rapidly to a high level called the active rate of oxygen consumption (Thompson & Bayne, 1972; Bayne, Thompson & Widdows, 1973). Some of this increase in metabolic rate is undoubtedly due to an increased filtration rate that is stimulated by the presence of food (the ‘mechanical cost of feeding’ discussed by Bayne et al. 1976), and part is due to the ‘physiological costs of feeding’, which includes energy utilized in digestion and assimilation of the food, and energy that is lost during deamination and other catabolic processes that accompany digestion (Warren & Davis, 1967). Increases in metabolic rate associated with feeding have been called the specific dynamic action (SDA) of the ration (see Harper, 1971, for a discussion) or the apparent SDA (Beamish, 1974)5 and they have been related to aspects of protein metabolism (Krebs, 1964). This paper describes the results of some experiments designed to examine the relationships between SDA and ammonia excretion in Mytilus edulis L.

Long-term iceshelf-covered meiobenthic communities of the Antarctic continental shelf resemble those of the deep sea

Since strong regional warming has led to the disintegration of huge parts of the Larsen A and B ice shelves east of the Antarctic Peninsula in 1995 and 2002, meiofaunal communities covered by ice shelves for thousands of years could be investigated for the first time. Based on a dataset of more than 230,000 individuals, meiobenthic higher taxa diversity and composition of Larsen continental shelf stations were compared to those of deep-sea stations in the Western Weddell Sea to see whether the food-limiting conditions in the deep sea and the food-poor shelf regime at times of iceshelf coverage has resulted in similar meiobenthic communities, on the premises that food availability is the main driver of meiobenthic assemblages. We show here that this is indeed the case; in terms of meiobenthic communities, there is greater similarity between the deep sea and the inner Larsen embayments than there is similarity between the deep sea and the former Larsen B iceshelf edge and the open continental shelf. We also show that resemblance to Antarctic deep-sea meiofaunal communities was indeed significantly higher for communities of the innermost Larsen B area than for those from intermediate parts of Larsen A and B. Similarity between communities from intermediate parts and the deep sea was again higher than between those of the ice-edge and the open shelf. Meiofaunal densities were low at the inner parts of Larsen A and B, and comparable to deep-sea densities, again likely owing to the low food supply at both habitats. We suggest that meiobenthic communities have not yet recovered from the food-limiting conditions present at the time of iceshelf coverage. Meiofaunal diversity on the other hand seemed driven by sediment structure, being higher in coarser sediments.