Time-course of digestive-enzyme acclimation in the cockle Cerastoderma edule

We determined the temporal evolution of amylase, cellulase, laminarinase and protease in the digestive gland and crystalline style of cockles Cerastoderma edule held over 9 to 12 d in the presence and absence of food. Cockles were fed a constant diet of 1.5 mm³ l⁻¹ of Tetraselmis suecica for 9 to 12 d and were then starved for 6 to 8 d in late summer (September 1992) and in winter (January 1993). Feeding increased the dry weight and total cellulase, laminarinase and protease activities of the digestive gland irrespective of season, whereas amylase activity remained unchanged. In winter (i.e. when cockles are metabolically weak) the response was faster and stronger, especially for protease. An additional experiment in September starved cockles for 20 d before resuming feeding. In agreement with the seasonal differences, the presence of food after prolonged starvation induced a rapid and marked increase in protease in the digestive gland of the cockles. In winter, the possible effects of the biochemical composition of food on their enzymatic response were tested by feeding two groups of cockles with the same ration of T. suecica but harvested at different growth phases. A compensatory induction of cellulases occurred in cockles fed on T. suecica with a lower carbohydrate content. In the crystalline style, the protein level and carbohydrase fell during the first day of feeding and increased during the first day of subsequent starvation. These results indicate that the release of enzymes from the style prevails over the incorporation of enzymes during the early stages of feeding, whereas the opposite occurs during starvation. Received: 15 February 1998 / Accepted: 22 February 1999     

Physiological basis of extreme growth rate differences in the spat of oyster (Crassostrea gigas)

Juvenile oysters (Crassostrea gigas) (produced in November 2009) reared under uniform hatchery conditions for 4 months were selected for extreme growth rate differences by repeatedly taking larger and smaller individuals to achieve weight differences >30× between fast (F) and slow (S) growers. The physiological basis of differential growth was analyzed in experiments in June 2010, where components of energy gain (clearance and ingestion rates and absorption efficiency), energy loss (metabolic rates) and resulting scope for growth (J h^?1) were compared for groups of F and S oysters fed three different ration levels (≈0.5, 1.5 and 3.0 mg of total particulate matter L^?1). In both F and S oysters, a higher food ration promoted asymptotic increases in energy gain rates through regulatory adjustments to clearance rates, which maintained similar absorption efficiencies across the food concentrations. No significant differences were found between growth groups in mass-specific physiological rates (i.e., per unit of body mass). However, the scaling of these rates to a common size in both groups using allometric coefficients derived for C. gigas revealed higher energy gain rates coupled with lower metabolic costs of growth in fast growers. Thus, appropriate size-standardization is essential in accounting for observed differences in growth rate. Present results are in accordance with previous reports on other bivalve species on the physiological processes underlying endogenous growth differences, suggesting that the same interpretation can be applied to the extremes of these differences.     

Pyrolysis biochar systems for recovering biodegradable materials: A life cycle carbon assessment

A life cycle assessment (LCA) focused on biochar and bioenergy generation was performed for three thermal treatment configurations (slow pyrolysis, fast pyrolysis and gasification). Ten UK biodegradable wastes or residues were considered as feedstocks in this study. Carbon (equivalent) abatement (CA) and electricity production indicators were calculated. Slow pyrolysis systems offer the best performance in terms of CA, with net results varying from 0.07 to 1.25tonnes of CO(2)eq.t(-1) of feedstock treated. On the other hand, gasification achieves the best electricity generation outputs, with results varying around 0.9MWhet(-1) of feedstock. Moreover, selection of a common waste treatment practice as the reference scenario in an LCA has to be undertaken carefully as this will have a key influence upon the CA performance of pyrolysis or gasification biochar systems (P/GBS). Results suggest that P/GBS could produce important environmental benefits in terms of CA, but several potential pollution issues arising from contaminants in the biochar have to be addressed before biochar and bioenergy production from biodegradable waste can become common practice.