Dry Flesh Weight Research Articles

The production of Macoma balthica (L.) in the Ythan Estuary

Macoma balthica (L.) is an important food species for many vertebrate predators on the Ythan Estuary. It occurs throughout much of the estuary and in the intensive study area had a maximum density of about 6000/m 2 after spat settlement. The animals have a marked stratification in their depth distribution. Small animals live chiefly near the surface and larger animals deeper down. Some individuals live for about 6 years but before spat settlement, the population was made up chiefly of 1 + animals (from 87–93% of the total) and after spat settlement was dominated by 0 + animals (from 85–91% of the total). In (1972), growth took place mainly in the spring and early summer but continued until October for the 0 + year group. There was a large seasonal variation in the condition of M. balthica, the dry flesh weight of animals of a given size being two to three times greater in summer than in winter. The spawning season lasted from late February to early April. The biomass of the population was greatest in June even though the density was then lower than in winter. The average production of M. balthica in the intensive study area was 10·07 g dry wt m −2 year −1 (42·8 kcal m −2) and the annual P B ratio 2·07. The mean annual biomass of M. balthica over the whole estuary in (1973) was 2·77 g dry wt m −2 and production therefore equal to 5·73 g dry wt m −2 year −1.

Seasonal changes in flesh weight and biochemical composition of mussels ( Mytilus edulis L.) in the Conwy Estuary, North Wales

Sublittoral Mytilus edulis L. from natural mussel beds of the Conwy Estuary fishery exhibited an annual cycle of dry flesh weight, biochemical composition, and caloric value during 1971–1974. Mean percentage values of the main components of dry flesh, with seasonal extremes in parentheses, were: protein 58.7 (46.4–73.1), carbohydrates 22.5 (4.1–36.7), lipids 7.0 (3.9–9.6), and ash 11.8 (8.8–17.2). The mean caloric values of dry flesh were 5.57 kcal/g ash-free and 4.92 kcal/g ashinclusive. Individual dry flesh weight was highest in summer and autumn, when protein and carbohydrate were maximal, and decreased through the winter to a post-spawning minimum in spring. Weight loss in winter resulted from rapid utilization of carbohydrate (glycogen) reserves and a depletion of both protein and lipid content. It is considered likely that mussels were then stressed by food shortage at the time when metabolic demands, due to gametogenesis, were highest. During the six main fishing months, October to March, the average weight of dry flesh fell by 30–50 % and caloric content by 35–45 %. The likelihood of similar losses in cultivated mussel stocks is indicated and the need for comparable information in fishery management is emphasized. The extent to which predators compensate for these seasonal changes in prey quality also requires examination.

Biochemical composition and energy reserves in the larvae and adults of the four british periwinkles Littorina littorea, L. littoralis, L. saxatilis and L. neritoides

The biochemical composition of the adult body tissue is similar in Littorina littorea, L. littoralis, L. saxatilis and L. neritoides. In the newly crawling metamorphosed young of L. littoralis and L. saxatilis, the biochemical composition is similar to that of the mature adults. The newly released planktonic veliger larvae of L. littorea and L. neritoides, which represent and earlier stage of development than the newly crawling young, have a neutral lipid level (mean, 16.5% of ash-free dry flesh weight) approximately three times the level (5.4%) in the newly crawling young of L. littoralis and L. saxatilis. Otherwise the biochemical composition of free-swimming larvae is similar to that of newly crawling young and adults. Neutral lipid is apparently utilised by L. littoralis and L. saxatilis larvae during larval development and metamorphosis. It is suggested that neutral lipid is the major energy reserve of Littorina veliger larvae whereas in the adults, as exemplified by L. littorea, both lipid and carbohydrate are important as energy reserves.

Experimental studies on the effects of copper on a marine food chain

Effects of copper sulphate on a marine food chain were investigated in large tanks at Loch Ewe on the west coast of Scotland. The food chain consisted of phytoplankton, the bivalve Tellina tenuis da Costa, and O-group plaice (Pleuronectes platessa L). During initial months after settlement, T. tenuis siphons are an important food for juvenile plaice, which feed by grazing the siphon tips; these subsequently regenerate. Copper dose rates of 10, 30 and 100 μg Cu/1 were investigated; the distribution of added copper was monitored and its metabolic effects were determined. Copper levels in water, sand, in algae on tank walls, in T. tenuis shell and flesh, and in plaice muscle and viscera were measured by atomic absorption spectrophotometry. Copper accumulated in sand, T. tenuis flesh and shell, and plaice viscera. Accumulations were dose-dependent and in no case was a plateau concentration reached. Most of the added dose was taken up by the sand; accumulations in T. tenuis shell were small — less than twice background in all cases. High levels were found in T. tenuis flesh, where concentrations after 100 days were 270, 470 and 1100 μg Cu/g dry flesh for dose concentrations of 10, 30 and 100 μg Cu/1, respectively. The mean control concentration was less than 50 μg Cu/g dry flesh. There was no accumulation of copper in plaice muscle. Visceral accumulations after 100 days were 71, 147 and 567 μg Cu/g dry flesh for dose concentrations of 10, 30 and 100 μg Cu/1, respectively. The mean control level was 30 μg Cu/g dry flesh. The effect of copper on phytoplankton metabolism was investigated by measuring plant pigment levels and rates of primary photosynthetic fixation of C14-labelled bicarbonate. All dose concentrations reduced both the standing crop and the rate of photosynthesis per unit of chlorophyll a. The effects of copper on growth and condition of T. tenuis and P. platessa were investigated. All dose concentrations adversely affected T. tenuis condition (dry flesh weight for standard individual). The effect was most marked during deposition of winter reserves. In the absence of plaice predation, there was a decrease in the mean siphon weight for T. tenuis exposed to 30 and 100 μg Cu/1. For plaice, all dose concentrations of copper resulted in reduced growth, but there was no significant change in condition or biochemical composition. The ash weight of fish exposed to copper was significantly higher than for controls.

Productivity and Production: Biomass Ratios of Bivalve and Gastropod Populations in an Eastern Canadian Estuary

In a narrow, shallow estuary on the east coast of Canada, the dominant intertidal invertebrates were bivalve and gastropod molluscs. On a sand flat Mya arenaria produced 11.6 g∙m−2∙yr−1 flesh dry weight with a production:biomass ratio of 2.54, whereas Macoma balthica produced 1.93 g∙m−2∙yr−1 with a P:B ratio of 1.53. On a Spartina marsh, Littorina saxatilis produced 3.25 g∙m−2∙yr−1 with a P:B ratio of 4.11. Approximate P:B ratios were applied to biomass figures for four other species to give the following estimates of productivity: Mytilus edulis on Zostera beds 19.7 g∙m−2∙yr−1 flesh dry weight; M. edulis on Spartina beds 3.5 g∙m−2∙yr−1; Nassarius obsoletus 1.15 g∙m−2∙yr−1; Melampus lineatus 1.1 g∙m−2∙yr−1; Lacuna vincta 0.06 g∙m−2∙yr−1. A total production of the molluscs in the estuary is estimated at 4.7% of the production of Spartina and Zostera (all measured in kcal). It is postulated that molluscs are the chief primary consumers in the inlet.

Production ecology of two Caribbean marine ecosystems: I. Physical environment and fauna

A quantitative study was made of the invertebrate macrofauna and fish fauna of two shallow water ecosystems. One was in an inlet on a clean sand bottom (1) while the other was on a muddy bottom (2) near a discharge point for domestic effluent. The largest average biomass of littoral infauna of 2·894 g/m 2 dry flesh weight was found at (2) while the largest average biomass of sublittoral infauna of 5·839 g/m 2 was found at (1). Fish biomass was 5·048 g/m 2 at (1) and 1·200 g/m 2 at (2) suggesting an avoidance reaction to the contaminated water at the latter locality. Diets of demersal fish were predominantly benthic infauna at (1) and epifauna at (2), the latter being related to the presence of a prolific weed fauna in the sublittoral.

Studies on Tellina tenuis Da Costa. III. Aspects of general biology and energy flow

During a four-year study of food chains in Loch Ewe on the west of Scotland, the bivalve Tellina tenuis da Costa has been studied in some detail. Data have been collected for two populations in Loch Ewe, one in Firemore Bay, which has been studied in more detail, and one in Inverasdale. For comparison another population outside Loch Ewe, in nearby Gruinard Bay, has also been sampled. Tellina tenuis occurs from mid-tide level down to a few metres below low water. It lies in the sand at a depth of a few centimetres, generally on its left side. The inhalant siphon extends more or less vertically into the water column while faeces and water are expelled through the exhalant siphon which is usually extended into the sand more or less horizontally below the surface. Food, consisting of plankton and organic detritus, is probably obtained mainly from the sand-water interface, and the siphons do not normally extend far above the surface. Experimentally, low oxygen content, extremes of temperature, and lack of food may stimulate the inhalant siphons to extend further out into the water. At low tide it is thought that Tellina takes in interstitial water, and with it some sand grains. Filtration rates, measured as the clearance of a Phaeodactylum suspension were 20–60 ml/h for animals of 15–20 mg dry weight, giving ingestion of at least 250 μg of particulate organic matter per day if active filtration occurs during 50 % of the time. Oxygen uptake was measured over the natural temperature range throughout the year and a value of 6 mg O 2/g/day has been suggested as a mean value for the year. The inhalant siphons are preyed upon by 0-group plaice. The extent of predation varied during the years studied. Changes are partly due to changes in the relative density of predator and prey, and also in the abundance of other prey species such as polychaetes. Siphon regeneration occurs at the rate of about 0.3 mg/week. The ‘condition’ (dry flesh weight of a standard animal) of Tellina from the three beaches shows a similar seasonal pattern with low values in the winter, a rise in the spring, one or two peaks in the summer and a fall in the autumn to the low winter values. The peaks are largely due to gonad proliferation, with a sudden decrease on spawning, The ‘condition’ of Tellina at the three localities has improved from 1967 to 1968, and in Firemore has improved steadily since 1965. Relevant climatic data have been examined. The seasonal pattern of growth follows closely the changes in temperature, which may have a direct effect on growth and an indirect effect via the food supply. Northerly winds may have an adverse effect on the condition of Tellina in Loch Ewe since they give rise to a swell and so to sand disturbance, which in turn may prevent the animals from feeding normally. In 1968 there was more bright sunshine and less rain than in the three previous years and this may partly explain the good growth and condition of Tellina in that year. Similarly, high rainfall and low values for hours of sunshine may have had an adverse effect on Tellina in 1967. Heavy mortalities and very small recruitment to the population of Tellina in Firemore Bay have resulted in a decrease in population numbers. A table of production data has been drawn up to show the proportion of energy channelled into growth, reproduction, siphon regeneration, and respiration. Factors which may affect the changes in production of the Tellina population in Firemore Bay are discussed, and the growth efficiency is compared with published data for some other invertebrates.