Effect of environmental factors on byssal thread formation

The effects of various factors on byssal thread formation have been examined in the laboratory using Modiolus demissus and Mytilus edulis. With M. demissus thread formation (threads/mussel/h0 and proportion of mussels forming threads decreased with increasing size; prior exposure to air enhanced subsequent thread formation; mechanical agitation reduced thread formation. In addition, low salinity acclimated mussels adapted more rapidly to 32 ppt than high salinity acclimated mussels did to 16 ppt; threads were not formed in the absence of calcium and/or magnesium; and there was no reduction in thread formation at temperatures as high as 27° to 28°C. M. edulis died and thread formation approached zero at temperatures exceeding 26°C.     

The significance of temperature,salinity and zinc as lethal factors for the mussel Mytilus edulis in a polluted estuary

Mussels, Mytilus edulis L., were subjected to high temperatures, low salinities and dissolved zinc in order to investigate possible environmental hazards of a discharge of heated effluent near Newport on the Yarra River estuary, Victoria, Australia. Exposure to zinc at 0.8 mg l^-1 for 14 d in otherwise favourable conditions significantly increased mortality resulting from subsequent exposure to temperatures between 29° to 31°C for 24 h without added zinc. Mussels collected from water of temporarily lowered salinity (8–16 S) showed significantly lower thermal resistance than controls collected from marine salinities (35 S). Mussels taken from a marine environment and exposed to 10 S died at a rate which increased with temperature. Mussels acclimated for 14 d to combinations of 10°, 16° and 22°C and 22 and 35 S, and subsequently exposed to increased zinc concentrations accumulated zinc to levels which were independent of temperature and salinity. The zinc was lethal more quickly at 22°C and 35 S than at the lower temperatures and salinities. The modes of toxic action of the salinity, zinc and temperature factors are discussed and it is argued that zinc which has been found accumulated in mussels near Newport could be reducing their resistance to raised temperatures and perhaps other stresses, probably as a result of effects on lysosomal functioning. The evidence suggests that the heated effluent will accelerate any toxic effects of zinc or low salinities which occur near Newport and so poses a hazard in winter as well as in summer.     

Effects of oil pollution on the freezing tolerance and solute concentration of the blue mussel Mytilus edulis

Exposure of blue mussels (Mytilus edulis L.) to oil-polluted sea water for 7 d in the laboratory did not affect their body fluid concentrations of inorganic ions and free amino acids. Mussels exposed to-4°C for 12 h did not freeze, whereas freezing occurred invariably in mussels exposed to-7°C or lower temperatures for the same period. Following freezing at-10°C, oil polluted mussels resumed normal activity considerably more slowly than unpolluted ones, but oil-polluted as well as unpolluted mussels showed normal activity 3 h after thawing. Freezing at-15°C was invariably lethal to individuals of both groups. One possible explanation of the delayed recovery of oil-polluted mussels frozen at-10°C may be that oil components had become concentrated to toxic levels as the amount of solvent water diminished during freezing.     

Growth and size structure in a baltic Mytilus edulis population

Since Mytilus edulis L. has very few predators and competitors for space, it has become a biomass dominant in the Baltic proper covering hard substrates from the water surface to more than 30 m depth. In order to investigate the factors controlling size and production in a Baltic M. edulis population, growth was studied by the analysis of annual growth rings, measurements of caged individuals and the analysis of size classes in the population, and on settlement ropes. The total number of mussels in a representative mussel bed at 4 m depth varied between 36 000 and 158 000 ind · m^-2 during the year, mainly due to variations in very small mussels (<2 mm), whereas the abundance of mussels 2mm was rather constant between about 17 000 and 28 000 ind · m^-2. Maximum numbes of mussels < 2 mm, amounting to 132 000 ind · m^-2, were found after settlement in summer, but still half a year later in spring, 65 000 ind · m^-2 < 2 mm were registered, due to very strong intraspecific competition for food and space leading to the competitive suppression of small individuals and large variations in growth rates. Due to the special size-structure of the population only the analysis of annual growth rings could be used to estimate natural shell growth. From being very low in the smallest mussels, growth was linear between about 2–10 yr of age, corresponding to about 3–20 mm length, after which it decreased with a L=32 mm. Over the linear interval, growth in the populations from 3–6 m and 10–15m depth was 3.1 and 2.2 mm · yr^-1, respectively. Meat growth showed strong annual variations mainly due to gonad production. Starving mussels could, however, while utilizing energy reserves, survive losses of up to 78% of their meat biomass. This ability of M. edulis to respire away its own biomass and its apparent tolerance of weight loss has important implication. It will drastically reduce the energy flow to destruents from mussels dying naturally, which is of special significance in the Baltic, where predators and scavengers are scarce. It enables the mussels to endure bad food conditions and buffer strong seasonal variations in food abundance, maintaining the strongly food-and space-limited Baltic M. edulis population at the carrying capacity of the area.     

The combined effects of salinity and temperature on larvae of the mussel Mytilus edulis

The combined effects of salinity and temperature on survival and growth of larvae of the mussel Mytilus edulis (L.) were studied. The effects of salinity and temperature are significantly related only as the limits of tolerance of either factor are approached. Survival of larvae at salinities from 15 to 40 is uniformly good (70% or better) at temperatures from 5° to 20°C, but is reduced drastically at 25 °C, particularly at high (40) and low (20) salinities. Larval growth is rapid at a temperature of 15 °C in salinities from 25 to 35, at 20 °C in salinities from 20 to 35. Optimum growth occurs at 20 °C in salinities from 25 to 30. Growth decreases both at 25° and 10 °C; the decline is most drastic at high (40) and low (20) salinities.Part of a study completed at the Bureau of Commercial Fisheries, Biological Laboratory, Milford, Connecticut, USA, while on a UNESCO Fellowship.     

Isolation of DNA and RNA from ascidians

Combined effects of temperature, salinity and nutrition on larval survival and growth of the European oyster Ostrea edulis L. were studied over a period of seven days in the laboratory. Larvae were obtained in August 1985 from oysters reared under field conditions on the Mediterranean coast. Four temperatures (15°, 20°, 25°, 30°C), four salinities (20, 25, 30, 35 S) and two levels of nutrition (fed or unfed) were used in the experimental design; the fed larvae received a mixed algal diet of Isochrysis galbana and Chaetoceros calcitrans forma pumilum at a concentration of 100 cells per microlitre. Larvae survived over a wide range of temperature and salinity; statistical analysis indicated that nutrition had the greatest effect on the development of O. edulis larvae, explaining 85 to 88% of the variance in growth. Compared with temperature, the effect of salinity was very slight, usually statistically insignificant. The combined effects of temperature and nutrition produced the only significant interaction. Growth of starved larvae seems to be independent of both temperature and salinity within the range of levels tested.     

Temporal patterns of shell-gape in Mytilus edulis

Hitherto published evidence of the presence or absence of endogenous activity rhythms in bivalve molluscs is equivocal. Mytilus edulis L. were collected from a North Wales (UK) estuary in 1985, and shell-gaping was investigated in individual mussels under constant conditions in the laboratory. Results suggest that there is no endogenous circatidal rhythm of shell-gaping in this species, This is consistent with the view that, unlike mobile species, sessile intertidal species are much more likely to exhibit exogenous rather than endogenous responses to tidal fluctuations. There is some evidence of weak circadian rhythmicity of shell-gaping in M. edulis, with greater duration of shell-closure during hours of expected daylight. Such behaviour could represent an adaptational defence against visually-feeding predators.     

Influence of high temperature and residual chlorine on marine phytoplankton

Marine phytoplankton forms are frequently exposed to sudden biological changes such as rapid rise in water temperature and chlorine content of their environment, resulting from the use of sea water for cooling purposes by electric generators. The direct influence of these effluents, i.e. inhibitory effects of high temperature and residual chlorine on growth and photosynthesis of Chlamydomonas sp. and Skeletonema costatum, were investigated experimentally. Chlamydomonas sp. and S. costatum exposed to high temperatures were affected in their growth from 43° and 35°C, respectively, by immersion of the respective cultures in a warm bath for 10 min. Treatment at high temperatures of 40 °C and 30° 35°C for 10 min, influenced their photosynthetic activities, which were completely inhibited immediately after 10 min exposure at 42° and 37 °C, respectively. S. costatum was killed by chlorine at a concentration of 1.5 2.3 ppm when exposed for exactly 5 or 10 min, while Chlamydomonas sp. was not irreversibly damaged even at 20 ppm chlorine or more with the same exposure period. These results lead to the conclusion that the high temperature of, and residual chlorine in, effuents from a power plant discharging into the open sea, should not cause great damage to marine phytoplankton in that area.     

Some aspects of the thermal tolerance of Trichomya hirsuta (Mollusca: Bivalvia) of Eastern Australia

The upper temperature tolerance range for Trichomya hirsuta L. is described for acclimation temperatures of 10° to 32°C at 30% S. Changes in thermal resistance with time are described along with the incipient lethal temperatures. The eurythermicity for the species is 240.7 C°-squared. The ultimate upper incipient lethal temperature is 35.1°C. Definition of the incipient sublethal temperature is given, and is equal to 32°C. Diet effects are shown not to be significant in short-term lethal experiments, but indicate that unfed mussels reduce their resistance after prolonged exposure to high temperatures. Size was also shown to have no effect on resistance and tolerance. A comparison of the tolerance triangle of T. hirsuta with those of the temperate species Mytilus edulis and Mya arenaria revealed that the 24-h LT₅₀ minus 2.2 C° approximates the incipient lethal temperature. The eurythermicities of the temperate species are Mytilus edulis, 363 C°-squared; and Mya arenaria, 415 C°-squared.     

Microprofiles of oxygen in epiphyte communities on submerged macrophytes

Mussels (Mytilus edulis) transferred in net bags from clean to chronically mercury polluted water readily accumulated mercury during an exposure period of three months. Growth of the transplanted mussels had a diluting effect on the mercury concentration, but the absolute weight of mercury uptake increased throughout the entire period, though there was a tendency for decreased efficiency of the removal of mercury per liter of water filtered by the mussels. Mussels were also translocated from polluted to clean (laboratory) water to depurate mercury. The biological half-lives of mercury was 293 d for M. edulis from the chronically polluted area in contrast to only 53 d for mussels from a temporary massive mercury polluted area near a chemical deposit. In both cases about 75% of the total mercury in the mussels was inorganic, and it is suggested that both inorganic and organic mercury species were immobilized in mussels from the long-term mercury polluted area, whereas the immobilization capacity was exceeded in the short-term mercury exposed mussels near the chemical deposit. Very slow elimination of mercury was observed in the deposit-feeding bivalve Macoma balthica from the chronically polluted area, and about 6% of the total mercury was methyl-+phenyl-mercury. This is more than three times lower than found in M. edulis from the same collecting site. A pronounced difference in the mercury speciation (i.e., total mercury, total organic mercury, methyl-mercury and phenyl-mercury) in M. edulis from the two mercury polluted areas is thought to reflect the different character of the mercury pollution in the two areas.     

Hydrocarbon uptake and loss by the mussel Mytilus edulis

The dynamics of accumulation and elimination of hydrocarbons by the blue mussel Mytilus edulis were studied in a continuous-flow system. Mussels were exposed for as long as 41 days to 200 – 400 g/l of diesel fuel adsorbed on kaolin particles. Hydrocarbons were accumulated in the tissues in excess of 1000 times the exposure levels. Upon termination of dosing, the mussels exhibited a rather rapid loss of hydrocarbons for the first 15 to 20 days (biological half-life=2.7 to 3.5 days). Subsequently, however, elimination was reduced to a minimum and a considerable fraction of the hydrocarbons could be recovered from the tissues after as long as 32 days of depuration. The mussels exhibited definite signs of physiological stress due to chronic exposure to diesel fuel, although recovery was rapid upon termination of dosing. It is concluded that mussels could be utilized as a test organism for monitoring long-term hydrocarbon pollution in marine waters. The implications for the mussel culture industry are discussed.     

Seasonal,geographical and size-induced variability in mercury content of Mytilus edulis in an estuarine environment: a re-assessment of mercury pollution level in the Estuary and Gulf of St. Lawrence

Seasonal variability of mercury content of Mytilus edulis (L.) was studied at monthly intervals for 18 mo (June 1978–December 1979) in a natural population from a typical estuarine environment (St. Lawrence Estuary). Body-size-induced variability was observed in the same population in spring 1980. The regression coefficients of log-log relationships between mercury content and body size of the mussels varied with time. However, the regression coefficients were never higher than 1; this indicates, therefore, no net accumulation of mercury with age of the bivalve. A normalization method, taking into account shell length and soft-tissue dry weight, is proposed to minimize the metal variations due to size differences of the mussels. The normalized mercury contents vary seasonally by a factor of two. Minimum values were observed during summer. This factor (2) is taken as the minimal difference which can be accepted as indicating a significant geographical trend in a mussel watch-type study in estuarine environments. In the St. Lawrence Estuary and Gulf, size-normalized concentrations range from 69 to 378 ng Hg g^-1 (dry weight); highest levels were observed in areas where freshwater influence is maximum, while lower contents were encountered in regions of highest Atlantic influence. In the Gulf, mercury in mussel soft tissue is 3x10⁴ times that of the seawater. There is some indication of a decrease in the previous measured levels near the mouth of the Saguenay fjord in the Lower St. Lawrence estuary.     

External synchronizers of tidal activity rhythms in the prawns Penaeus indicus and P. monodon

Phasing of persistent circatidal rhythmicity to an artificial tidal cycle was assessed in the prawns Penaeus indicus Milne Edwards and P. monodon (Fabricius) collected from the Vellar estuary, South India, in the period between June and December 1984. Simulated 6 h cycles of 20 and 30 S, and 6 h cycles of 20° and 30°C induced a persistent tidal rhythmicity after 20 cycles. The imposed 6 h cycles of 25 and 30 S, and 25° and 30°C induced tidal rhythms after 30 cycles. In both cases, re-established tidal activity rhythms were evident for at least 48 h — higher activity occurring during the higher salinity and lower temperature phases of the simulated tidal cycles. Artificial tidal cycles of still water and running water synchronized the tidal rhythm after 20 cycles. Combined 30 S, 20°C, for 6 h and 20 S and 30°C for 6 h established a persistent tidal rhythm after 10 cycles, whereas wave action had no influence on tidal synchronization. The influence of possible interactions of tidal rhythms and in situ tidal variables on circatidal activity is discussed.     

Effect of temperature and food on the heart beat,ventilation rate and oxygen uptake of Mytilus edulis

The heart beat, ventilation rate and oxygen uptake of Mytilus edulis L. were measured simultaneously, in response to changes in temperature and food level. There was no thermal acclimation of heart-beat frequency or amplitude to temperatures from 5° to 25°C. Oxygen consumption and ventilation rate acclimated to 10°, 15° and 20°C, but not to 25°C. Starvation reduced the rate of oxygen uptake and heart-beat frequency to a standard level and, in response to food, the ventilation rate and oxygen consumption immediately increased to an active level. Feeding was maintained after the initiation of active metabolism, and during the following 10 days the heart-beat frequency gradually increased to the level characteristic of fed individuals. There was no direct correlation between the rate of oxygen consumption and heart rate, and an apparent absence of a close nervous coupling between ventilation rate and heart rate in M. edulis.     

Genetic variation among life-history stages of mussels in a<Emphasis Type="Italic"> Mytilus edulis–M</Emphasis>.<Emphasis Type="Italic"> trossulus</Emphasis> hybrid zone

The mussel species Mytilus edulis L. and M. trossulus Gould coexist and hybridize throughout a large area that includes the north coast of Maine and Atlantic Canada. Previous studies provided genetic evidence for limited hybridization between the two species for mussels >15 mm. The present study used two genetic markers (ITS, Glu-5) to examine the genetic composition of early life-history stages by sampling veliger and pediveliger larvae, juveniles (<2.0 to 15.0 mm shell length) and adults (>15 mm shell length) in Trinity Bay, Newfoundland, during three consecutive years (1995–1997) to determine if differential mortality limits the relative abundance of hybrids. The relative frequency of the two species and the different hybrid genotypes was similar among the larvae, juveniles and small adult mussels. The double hybrid genotype (F₁-like) was the rarest genotype observed. There was no evidence for differential mortality during the early life-history stages, and factors limiting production of hybrids appear to operate before the late larval stage. The observed frequency of hybrids is probably due to a combination of pre- and postzygotic reproductive isolating mechanisms operating early in the mussels life history. M. trossulus dominated the early life-history stages, possibly due to a higher population density and a greater reproductive output than M. edulis. Differential mortality may explain the observed decrease in frequency of M. trossulus and increase in frequency of M. edulis with increasing shell length. A similar frequency of hybrid mussels from larvae to the size class of 55 mm shell length may indicate a rate of mortality intermediate between the two parental species. The M. edulis–M. trossulus hybrid zone appears to be maintained by reproductive isolating mechanisms limiting the production of hybrids and life-history differences that allow the two species to coexist.Communicated by J.P. Grassle, New Brunswick     

Responses of Asterias rubens to bivalve prey in a Y-maze

Experiments carried out in a Y-maze apparatus using a constant number of mussels, Mytilus edulis L., as prey showed the presence of a food-seeking period in the predatory starfish Asterias rubens L. collected in the Menai Strait, Anglesey, North Wales. The starfish orientated towards the mussels in the experiment conducted from Novemeber-December to May. The food-seeking activity was not significantly different from random expectation between June and October. It is suggested that this seasonal change in the behaviour of A. rubens can be due either to a lowering of chemo-sensitivity and failure to respond by A. rubens, or to a seasonal change in production of attractant(s) by the prey, or to a combination of the above. A. rubens does not move towards a bait of oyster spat (Ostrea edulis L.) in the Y-maze unless it has been previously conditioned to eat the oysters for about a month. In the Menai Strait, oysters would rarely be encountered by A. rubens and, therefore, the experiments confirmed the concept of ingestive conditioning (Wood, 1968).     

Laboratory study of effects of temperature and salinity on survival and larval development of a population of Rhithropanopeus harrisii from the Mondego River estuary,Portugal

Rhithropanopeus harrisii (Gould) is an introduced species in the estuary of the Mondego River (Portugal): it was first recorded from the Iberian Peninsula in 1989. The larval development of this population was studied under laboratory conditions at different temperatures and salinities, and showed a larval development pattern very similar to that reported for American estuarine populations of this species. Larval development was negatively correlated with temperature. Time to megalopa varied between 7 and 35 d; the first crab (C₁) was reached after a maximum of 11 to 43 d. Larval development was optimum at 25°C and 15S. Larval survival was maximum at 10, 15 and 20S at all three temperatures studied (20, 25 and 30°C). The percentage of abnormal megalopae increased with increasing salinity to a maximum (100%) at 30S; incidence of abnormality was not affected by temperature.     

Composition chimique élémentaire (C,H, N) et équivalent énergie d'Acartia clausi (Crustacea: Copepoda), espèce importante dans la bioénergétique des écosystèmes côtiers de Méditerranée nord-occidentale

Fixed-point sampling of a shallow tidal estuary was performed hourly for 14 d in summer of 1982 and again in winter of 1983. This sampling regime was of statistically appropriate duration to allow characterization of the variability between periods of 2 to 96 h by spectral analysis of the time-series. The project (PULSE) took place in the Newport River Estuary, located behind the Outer Banks of North Carolina, USA. In all, twentyeight parameters were monitored, encompassing the meteorology, hydrology, water chemistry and phytoplankton-production physiology. Although the annual cycle was monitored, only the winter and summer seasons are compared here, i.e., the lowest water temperatures with the highest water temperatures. The physics, chemistry and biology of the estuary at the hourly scale were highly variable and non-random. The estuary is riverine in winter; growth-limiting nitrogen is supplied as nitrate (NO ₃ ^- ) and ammonium (NH ₄ ⁺ ) by runoff from the drainage basin. In summer, the estuary is lagoonal; nitrogen is supplied as NH ₄ ⁺ by biological regeneration. Chlorophyll a biomass varies primarily at the 4 d period in winter and at the diel period in summer. Although finely tuned to environmental variability, phytoplankton abundances were at equilibrium insofar as daily chlorophyll production was balanced by losses, i.e., grazing, export and deposition. Most important, high-frequency processes, here periods at the scale of cell-division times, can be very important in phytoplankton ecology.     

Effects of constant and cyclic temperatures on the salinity tolerance of the estuarine sandhopper Orchestia chiliensis

The survival of Orchestia chiliensis (Milne Edwards, 1840) was investigated at salinities between 0.3 and 68 and constant or 10 C° cyclic temperatures between 5° and 25° C. Mortality increased with age, temperature and at salinity extremes. Small individuals show little seasonal acclimatisation apart from increased thermal tolerance at the highest exposure temperature. Larger individuals show a lateral shift in the mortality curve to the right in summer, giving increased survival at most salinities. Salinity had less effect on amphipods in cyclic regimes and survival was similar in 5° to 15° C and 10° to 20° C cycles. Mortality of larger individuals was higher in the 15° to 25° C cycle, but seasonal acclimatisation gave increased resistance at all fluctuating temperatures during the summer. Mortality in cyclic temperatures was higher than at similar constant temperatures. O. chiliensis does not actively evade immersion and diel temperature changes of 10 C° represent an important stress factor. This would affect all life stages and influence field populations both in the winter and the summer.     

Synergistic effects of cadmium and salinity combined with constant and cycling temperatures on the larval development of two estuarine crab species

The developmental stages from megalopa to third crab of the blue crab Callinectes sapidus Rathbun were tested in 12 combinations of cadmium (0, 50, and 150 ppb) and salinity (10, 20, 30, and 40) at 25°C. A reduction in survival and a significant delay in development from megalopa to third crab occurred within each salinity regime in 50 ppb compared with the control. Comparison of the delay in development within each salinity regime revealed that the sublethal effect of cadmium was most pronounced in the salinities normally preferred by C. sapidus. A similar comparison within each cadmium concentration, however, showed that the developmental time from megalopa to third crab was approximately the same irrespective of salinity. The developmental stages from hatch to first crab of the mud-crab Rhithropanopeus harrisii (Gould) were examined in 63 combinations of cadmium (0, 50, and 150 ppb), salinity (10, 20, and 30), constant temperature (20°, 25°, 30°, and 35°C) and cycling temperature (20° to 25°C, 25° to 30°C, and 30° to 35°C). The results indicated that cycling temperatures may have a stimulating effect on survival of the larvae compared to constant temperatures, both in the presence and in the absence of cadmium. Effects of cadmium and salinity and their interaction on the survival of the larvae from zoeae to megalopa were documented at most of the temperatures by analyses of variance. The zoeal larvae were more susceptible to cadmium than the megalopa. Effects of different combinations of cadmium and salinity on the duration of larval development were assessed by a t-test.