Many studies have shown that the pnmary effect of shellfish culture on nearshore m a n n e systems is enhanced sedimentation T h~s study was d e s~g n e d to measure the effects of this enhanced sedimentation on the respiration and nutrlent fluxes of the benthic community and the coupling between the pelagic and b e n t h~c systems at a mussel culture s~t e (Mytllus edulls and M trossulus) In Upper South Cove, Nova Scotia, Canada There was a signif~cant association between chlorophyll In the water colun~n and sedimentation rate In Upper South Cove over the study year 1990, particularly under the mussel llnes, but the malority of the part~culate carbon and nitrogen whlch fell to the bottom was not Incorporated Into the sediments Suspended mussel culture had little Impact on sediment phosphorus dynamics The largest response of the sediment coinmunity to suspended mussel culture was ammonium release, whlch was higher under the mussel lines at all times of the year Over the year, the sedlments of the reference site were a net sink f o~ total dissolved nitrogen, whlle the sediments under the mussel line were a source

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IntroductionThis study investigated an incubation method which employed simultaneous measurement of CO 2 production and 02 consumption rates to calculate the RQ (respiratory quotient; CO 2 production rate: 0 2 consumption rate) of individual benthic marine invertebrates. Carbon dioxide production rates were calculated from changes in CO2 concentration determined using seawater pH. 02 consumption rates were calculated from changes in 02 concentration with a correction applied for 0 2 flux across the air/water interface due to gaseous exchange. Species examined were Triphyllozoon sp. cf. moniliferum (MacGillivray 1860), a bryozoan; Herdmania momus (Savigny), a solitary ascidian; Poneroplax albida (Blainville 1825), a chiton; and Haliotis roei (Gray 1826), an abalone. Six individuals of each were collected on 14 November 1985 from the limestone walls of a cave in a nearshore reef off Marmion, Western Australia. After acclimation for 6 h in experimental conditions, rates of CO2 production and 02 consumption were measured. A minimum period of 4 h was required to obtain consistent RQ values for each species. The standard error (SE) of the (calculated) RQ ratio was 14 to 33% of the mean in incubations of 4 h, and less than 14% in incubations of 4 to 12 h. The RQ is commonly used as an indicator of unknown catabolic substrates by comparing it with biochemically determined limits for known substrates. This study provides a strong argument against using the RQ of individual animals to draw any conclusions about catabolic substrates. Unexplained variation in the components of the RQ of an individual, measured over short time periods, and the potential involvement of stored reserves in catabolism, over longer time periods, obscure the relationship between the RQ of individual animals and the ratio's biochemically determined limits.The respiratory quotient (RQ) is a very important concept in metabolic physiology because it can give information about the fuel used in catabolism. Theoretically, this ratio varies from 0.7 when lipids are oxidized, to 1.0 when carbohydrates are oxidized (Schmidt-Nielsen 1975). RQ has not been used extensively by marine ecologists for two reasons. Firstly, measuring CO 2 in seawater has been presumed to be too difficult (Snow and Williams 1971). Common practice has been to measure 0 2 consumption rates of marine animals and assume an RQ of 1.0 in order to match metabolic rates to proposed catabolic substrates (Snow and Williams 1971, Ikeda 1977, Sasaki et al. 1986). Carbon dioxide is no longer considered difficult to measure in seawater, in the absence of sulphate reduction and surface wind stress (Skirrow 1975, Smith andKinsey 1978), and has been used in the measurement of CO 2 production by marine animals (Vink and Atkinson 1985). Secondly, unexplained variation in the RQ numerator and denominator, which can give values outside the theoretical limits, have been noted. Calculated metabolic ratios, such as RQ, are extremely variable which often causes problems in interpretation. One sourc...

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