Physiological-Responses Of Mytilus-Edulis L To Parasitic Infestation By Mytilicola-Intestinalis

Various levels of infestation by Mytilicola had no effect on the rates of oxygen consumption by Mytilus edulis in laboratory experiments. However, high levels of infestation (> 10 parasites per mussel) caused a depression in the feeding rate of the host at high temperatures (22° or 23° C) and low ration (maintenance or sub-maintenance). This depression of feeding resulted in a decline in the scope for growth, which would result in time in a decline in the “condition” of the host. It is concluded that similar effects may occur in the field when large numbers of small parasites are present at a time of high metabolic demand and low food availability.

Physiological Indexes Of Stress In Mytilus-Edulis

Multiple regression equations and response surfaces are used to describe the combined effects of body size, food concentration, acclimation temperature and season on physiological integrations such as the scope for growth, growth efficiency and O:N ratio. Maintenance and optimum ration levels are estimated for Mytilus edulis adapted to different factor combinations. Response surfaces illustrate the validity and sensitivity of the physiological integrations in quantifying the 'physiological condition' and the degree of stress experienced, under conditions ranging from near-optimal, through sub-lethal to lethal.

Physiological Ecology Of 2 Populations Of Mytilus-Edulis-L

Seasonal cycles in the rates of oxygen consumption, feeding, absorption efficiency and ammonia-nitrogen excretion in two populations of Mytilus edulis were measured in the field under ambient conditions and related to body size, the gametogenic cycle, the concentration of suspended particulate matter in the water and temperature. Relationships between the various physiological variables are also considered and protein and energy budgets estimated. Both the “scope for growth” and the “relative maintenance cost” were seasonally variable, demonstrating a minimum capacity for growth in the winter and a maximum capacity in the summer. In one population subjected to abnormally high temperatures in the winter the scope for growth was negative for four or five months between January and May. These population differences are discussed and the potential for using physiological integrations in intra-specific comparisons of fitness is identified.

Physiological Adaptation Of Mytilus-Edulis To Cyclic Temperatures

Mytilus edulis adapted to cyclic temperatures by reducing the amplitude of response of oxygen consumption and filtration rate over a period of approximately two weeks, and thereby increasing their independence of temperature within the range of the fluctuating regime. When acclimated to cyclic temperature regimes within the range from 6 to 20°C, the metabolic and feeding rates, measured at different temperatures in the cycle, were not significantly different from the adapted response to equivalent constant temperatures. Physiological adaptation ofMytilus edulis to different thermal environments was reflected in their metabolic and feeding rate-temperature curves. Animals subjected to marked diel fluctuations in environmental temperature showed an appropriate region of temperature-independence, whereas animals from a population not experiencing large diel temperature fluctuations showed no region of temperature-independence. In a fluctuating thermal environment which extended above the normal environmental maxima, respiratory adaptation occurred at higher temperatures than was possible in a constant thermal environment. The feeding rate was also maintained at higher temperatures in a cyclic regime than was possible under constant thermal conditions. This represented a shortterm extension of the zone of activity in a fluctuating thermal environment. The net result of these physiological responses to high cyclic and constant temperatures has been assessed in terms of ‘scope for growth’. Animals acclimated to cyclic temperatures between 21 and 29°C had a higher scope for growth at 29°C and were less severely stressed than those maintained at the constant temperature of 29°C.