Physiological energetics of the horse mussel Modiolus modiolus in a cold ocean environment

Abstract

A population of Modiolus modjolus (horse mussel) inhabiting a sub-arctic environment in Logy Bay, Newfoundland, Canada, was studied for 2 yr. The main objective was to gain insight into the relationship between environmental factors (temperature and components of the seston) and the physiological response of this species. The highest values for energy acquisition (ingestion and absorption rates) by M. rnodiolus coincided with the spring phytoplankton bloom occurring during April-May in Logy Bay, whereas energy expenditure (oxygen uptake and ammonia excretion rate) was greatest during the summer (July and August). The result was a clear seasonal fluctuation in the 2 physiological integrations, scope for growth (SFG) and net growth efficiency (K,), for which lower values were associated with a high metabolic rate, high temperature and low quality of the food supply. Conversely, higher values of SFG and K2 were associated with a low metabolic rate, low temperature and a n energy-rich food supply provided by the phytoplankton bloom. M. modiolus appears to be a species which is able to compensate physiologically for the poor food conditions occurring in Logy Bay during a large part of the year. It does this by reducing feeding activity during fall and winter, when there is a poor food supply. Conversely, it increases clearance rate during spring and early summer, when the seston is mainly composed of phytoplankton. Furthermore, M modiolus has a high absorption efficiency, which may be an adaptation to the low seston concentration in Logy Bay Such physiological compensations minimise the periods dunng which SFG is negative, and enable the horse mussel to survive in a n environment characterised by an intermittent and often inadequate food supply.

Feeding physiology of infaunal (Mulinia edulis) and epifaunal (Mytilus chilensis) bivalves under a wide range of concentrations and qualities of seston

“…At the same time, flow rate (F ) was determined for each chamber, and a difference of 20 to 40% in particle numbers was maintained between the chambers containing bivalves and the control chambers as described by Navarro & Thompson (1996). Clearance rate (CR) was calculated from:…”

Absorption efficiency, ingestion rate, gut passage time and scope for growth in suspension- and deposit-feeding Yoldia hyperborea

“…65 and 74% when fed with 1500 and 5500 cells ml -1 , respectively, of the alga Tetraselmis suecica (Widdows & Bayne 1971). However, high AE can also be found under natural conditions, as demonstrated by Navarro & Thompson (1996) for Modiolus modiolus from Newfoundland, which exhibited a seasonal variation in AE between 50.3 and 93.3%. The authors suggested that these high values may have been the result of low particle loads.…”

“…) (Navarro & Thompson 1996), but higher than in Mytilus galloprovincialis (Labarta et al 1997) and Placopecten magellanicus (Cranford & Hargrave 1994) , respectively) (Table 4). However, our observed rates occurred at SPM concentrations ~50 times higher than those normally encountered by suspension-feeders, which indicates a low efficiency of suspended particle capture.…”

“…Navarro & Thompson 1996), suspension-feeding could become a beneficial strategy during the first bloom fallout, when sediment quality is at its lowest, but not once the sediment has been enriched. Although deposit-feeding is the main strategy followed by Yoldia hyperborea and related species (Bender & Davis 1984, Davenport 1988, Stead 2001, our data suggest that suspension-feeding can be advantageous under certain conditions, possibly as a response to water-borne chemical cues released by settling microalgae after a prolonged period of low food availability (Ward & Targett 1989).…”

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“…Suspension feeding bivalves are of considerable importance as primary consumers of plankton in many marine systems and they play a significant role in the energy transfer between trophic levels (Navarro and Thompson, 1996). The growth rate of suspension-feeding bivalves is dependent upon a number of endogenous and environmental factors (Bayne and Newell, 1983), especially the amount of food ingested, which depends upon the food availability, filtration activity and selection process (Page and Hubbard, 1987;Richoux and Thompson, 2001).…”