Mussel Mortality Research Articles

Effect of an allozyme polymorphism on regulation of cell volume.

Biochemical differences have been described among allozymes1–4, but the physiological consequences (that is, physiological phenotypes) of such differences have only rarely been demonstrated5–7. Such a relationship is necessary both to the argument that natural selection maintains allozymic diversity in natural populations and for understanding biochemical mechanisms of adaptation8. We report here a genotype-dependent difference in the rate of cellular free amino acid accumulation during adjustment to hyperosmotic conditions in the mussel Mytilus edulis. The product of the Lap locus in M. edulis is the lysosomal enzyme aminopeptidase-I (AM-I; E.C.3.4.11.-) which hydrolyses oligopeptides to their constituent amino acids9. Total AM-I activity is positively correlated with salinity; a 120% increase in salinity increases AM-I activity twofold10–13. Adjustment to hyperosmotic stress in osmoconforming marine bivalves, including M. edulis, involves rapid accumulation of cellular free amino acids14,15. The biochemical properties of AM-I, and its activation by salinity changes, suggest that it is important for providing cellular free amino acid pools during adjustment to hyperosmotic stress11. We show that individuals carrying the allele for high catalytic efficiency (kcat) accumulated cellular amino acids more rapidly than other genotypes. The difference in accumulation rate was also demonstrated by an interruption of hyperosmotic adjustment, which resulted in genotype-dependent rates of amino acid excretion. These results demonstrate the role of AM-I in the physiological processes that regulate cell volume. Thus, differing catalytic properties of allozymes are manifested as phenotypic differences at the physiological level and provide a mechanism for the known selective mortality of mussels in natural populations7.

A nitrogen budget of the ribbed mussel, Geukensia demissa, and its significance in nitrogen flow in a New England salt marsh1

The annual nitrogen budget of a mussel (Geukensia demissa = Modiolus demissus) population in a salt marsh was determined and compared to the nitrogen budget of the marsh. During each tidal cycle in summer, the mussels filter a volume of water in excess of the tidal volume of the marsh. Yearly, the mussels filter 1.8 times the particulate nitrogen exported from the marsh by tidal flushing. Half the nitrogen filtered is absorbed by the mussels and half deposited as feces and pseudofeces (biodeposition). Of the nitrogen absorbed, 55% is excreted as ammonia. As a result, the mussel population releases more ammonia into the marsh water than does any other population in the marsh. Four percent of the nitrogen absorbed by the mussels is secreted in byssal threads, 20% invested in growth, and 21% released in gametes. Gametes are the largest component of mussel production to enter the food web, because mortality of adult mussels is very low.

Production and energy flow in relation to age and shore level in the bivalve Choromytilus meridionalis (Kr.)

Annual production ( P ) in terms of growth ( P 2 ) and reproduction ( P r ) was calculated for individual Choromytilus meridionalis of various shell lengths. Peak growth production occurred at approximately 60 mm ( P 2 =5·6 kJ individual −1 year −1 ). Reproductive output increased with increasing size once sexual maturity was attained and rose from 5·2 kJ year −1 in a 20-mm mussel to 51·4 kJ year −1 in a 100-mm individual, representing 61–97% of total production. Population production was calculated for each of three successive years (Y 0 -Y 2 ) at four shore levels (sublittoral, LWS, Midshore and Topshore) following spat settlement in the lower shore areas. Production was greatest in the sublittoral and at LWS and declined with increasing shore height. Maximum production took place in Y 1 , when the mussels were fully mature and P r represented 80% of production. Production in Y 2 decreased as a result of slowing growth rates, particularly at higher shore levels, and a decline in density throughout the population. Maximum population production was 100×10 3 kJ m −2 year −1 (sublittoral in Y 1 ), when the mussels grew from 26 to 38 mm and the P: ratio was 5·1 Population respiration at the various shore levels was calculated taking into account aerial respiration during exposure at low tide. Respiration averaged 66% of assimilation, where A=P g +P r +R . Population energy flow was highest in the lower sampling stations, the maximum assimilation at LWS being 211×10 3 kJ m −2 year −1 . Energy budgets were calculated for mussels in the sublittoral and Topshore areas. Approximately 90% of the energy filtered from seawater per annum was released to other consumers in the form of gamete output, faeces and pseudofaeces production and through mortality of mussels.

Mussel mortality in the Gulf of La Spezia, Italy

High mortality of mussels on culture-ropes observed during dredging operations in the Gulf of La Spezia, Italy, was due primarily to reduced levels of dissolved oxygen. Mud particles blocking the mantle cavity produced suffocation, and their presence on the valves and in the vicinity of the mussels produced a high BOD which markedly reduced the oxygen concentration in the water. The effect of soluble and insoluble phases of copper released from the perturbed mud and re-suspended in the water column is difficult to ascertain, but under certain conditions it may have introduced additional mechanical and physiological stress.

EXPERIMENTAL CULTURE OF Mytilis edulis (L.) IN A NORTHERN ESTUARINE GRADIENT: GROWTH, SURVIVAL, AND RECRUITMENT

AbstractMussels (Mytilus edulis L.) were experimentally cultured at 12 sites (1.5 km intervals) in an estuarine gradient on the Damariscotta River, Maine. Growth, survival, and recruitment of mussels were monitored and hydrographic data were collected. Peak growth of mussels occurred in May and June. The 4 upper‐estuarine sites were characterized by (1) earlier timing of peak growth, (2) suppressed growth in June and July relative to lower estuary mussels, and (3) marked mortality in September. Mussels grew rapidly in the lower 10 km of the estuary, exhibiting different temporal patterns of growth, but achieving comparable seasonal growth and survival. Seed mussels used for the growth experiments had settled on collectors during the previous summer and, accordingly, grew to 50 mm length in approximately 12 months: 15 months of growth yielded 57–71 mm mussels. Recruitment varied considerably, but was consistently high throughout the middle estuary, where settlement densities of 5–8 seed mussels per cm2 were observed. A 5‐year record of spatfall at one site in the middle estuary indicated that recruitment there was relatively consistent from year to year. The high mortality of mussels in the upper estuary of the Damariscotta River was associated with temperatures of 20°C and above, but may be related to factors other than temperature stress per s***a. Reduced ration during periods of warm temperature and increased metabolism may be responsible for these mortalities. Dense populations of newly‐settled mussels survived at some locations where temperatures exceeded 20°C and adult mortalities were high, indicating that high settlement densities and the existence of extensive populations of very young mussels do not, by themselves, provide enough information to adequately assess the potential of a site for mussel aquaculture. This potential may be meaningfully assessed by the use of a small experimental mussel raft and the collection of temperature and salinity data. Our results indicate that extensive areas of estuaries similar to the Damariscotta may be utilized for the culture of mussels.

東京湾の潮間帯におけるムラサキイガイの付着,生長および死亡について

Mussel (Mytilus edulis galloprovincialis LAMARCK) is the most important animal in the inter-tidal sessile fauna of Tokyo Bay. The settlement of young mussel to the mussel beds occurred during the period from March to September with the peak May to July in Tokyo and Yokohama Harbors, and occurred throughout the year with the peak May to August in Yokosuka Harbor. The growth and mortality were studied on the mussel population found on a horizontal plane (D. L.+1m) in the intertidal zone of Yokohama Harbor. The linear growth of shell length was found during the warm season (April to December), but the growth was almost absent during the winter. The annual variations in growth were illustrated for two different year mussels, i.e. the mean shell sizes of one yearage mussels settled in 1973 and 1974 were 33mm and 28mm, respectively. The life span of mussels after settlement was about two years. The monthly mortality rates of juvenile mussels (less than 20mm in shell length) settled in 1974 and 1975 were 25% and 55%. respectively. Increases of mussel biomass during the spring to summer and the fall were caused by growth in 0 and one year-age mussels of same year settlement, and decreases of the biomass occurred in August and January when the maximum solar radiation and colder weather seemed to contribute to mass mortality of mussels during the exposure to the air.

EXPERIMENTAL CULTURE OF BLUE MUSSELS Mytilus edulis L. IN HEATED EFFLUENT WATERS OF A NUCLEAR POWER PLANT1

ABSTRACTGrowth, mortality, and recruitment of blue mussels (Mytilus edulis L.) at varying distances from the heated effluent waters of a nuclear power plant were monitored using experimental rafting techniques Data were obtained at monthly intervals from April through November over a 3‐year period (1973 to 1975). Highest growth rates during April (surface water temperatures less than 25 C) were observed in the immediate vicinity of the effluent. Nortality during April was negligible and growth rates at other stations were negatively correlated with linear distance from the discharge. During May of both 1973 and 1974, with surface water temperatures rising above 25 C, growth rates in the effluent waters declined sharply and by the end of June, mortality ranged from 89% to 100%. Growth rates and survival at other stations from May through November were positively correlated with linear distance from the effluent. With the discontinuation of heated discharge from the plant in May 1975, mortality by November at the “effluent” station was 17% (only slightly greater than control sites). The number of Mytilus edulis spat attached to experimental collector ropes in, and adjacent to, the effluent waters was several orders of magnitude less than that found at control sites during each of the 3 years. Results suggest that, for optimum growth of this species, cultivation operations should probably be restricted to environments in which the upper limit of annual temperature ranges does not exceed 20 c.

High intertidal community organization on a rocky headland in Maine, USA

A mosaic patchwork of the barnacle Balanus balanoides L., the mussel Mytilus edulis L., and the alga Fucus vesiculosus L. was found in the transitional region between the mid and high intertidal zones on a rocky headland on Mount Desert Island, Maine, USA. The development of the mosaic was observed by following recruitment and survival of B. balanoides in denuded patches located at the same tidal level along a 60 m stretch of shore. Barnacle recruitment was least under canopies of F. vesiculosus and greatest in open areas kept moist at low tide by surf. Barnacle survival after settlement was least under the F. vesiculosus canopy due to the whiplash effect of the algal fronds in the surf and greatest in open areas free from competition from mussels. In open areas, early mortality was correlated with settlement density. In areas of dense settlement (60 spat cm-2) up to 90% mortality resulted within 5 months from crowding associated with growth. In older individuals crowding produced hummocks of elongated, weakly attached barnacles which were more prone to removal by surf than uncrowded barnacles. Mussels exerted competitive dominance over barnacles for space and the presence of mussel beds prevented further barnacle recruitment. Mussels suffered extensive mortality during winter storms when surf removed dense mats of weakly attached mussels. The patchy distribution of mussels and barnacles results from irregular rock substrata producing numerous environmental patches with respect to wave exposure and drainage at low tide, and from densitydependent mortality of both mussels and barnacles which creates patches of new colonizable space within each environmental patch.

Effects of leached mirex on experimental communities of estuarine animals.

Experimental communities of various estuarine animals in outdoor tanks were exposed to a continuous flow of water containing mirex for 10 weeks. The mirex was leached from fire ant bait (0.3% active ingredient) by fresh water which was then mixed with salt water to yield exposure concentrations averaging 0.038 mug/L. The experiment simulated runoff from treated land into estuarine areas. Mortality of grass shrimp (Palaemonetes vulgaris), pin, shrimp (Penaeus duorarum), common mud crabs (Panopeus herbstii), and striped hermit crabs (Clibanarius vittatus) was significantly high in tanks containing the toxicant. Mortality of ribbed mussels (Modiolus demissus) and American oysters (Crassostrea virginica) was significantly lower in treated tanks, probably because numbers of both species of crabs, which ate the bivalves, were reduced. Sheepshead minnows (Cyprinodon variegatus) were least affected by mirex. Almost all deaths occurred after 10 or more days of exposure. All exposed animals accumulated mirex, with maximum concentrations ranging from 5,500X (pink shrimp) to 73,700X (soft tissues of oysters) above the concentration in the water. Sand substratum contained mirex up to 1,500X that in the water. The study demonstrated that mirex can be leached from bait by fresh water and concentrated by and affect survival of members in an experimental estuarine community.

Experiments on the survival, growth and yield of relaid seed mussels (Mytilus edulis L.) in the Menai Straits, North Wales

The survival, growth and yield of young mussels relaid on small plots, at densities of 8·75 and 13·25 kg/m2 live weight, were studied at low-water mark of spring tides in the Menai Straits, North Wales. Populations grew from mean lengths of 27 mm to minimum market size (50 mm) in 15–20 months, and to 55–58 mm in two years, but good growth was offset by high mortality so that no significant gains in live crop weight resulted. Heavy predation by shore-crabs (Carcinus maenas (L.)) upon mussels smaller than 45 mm shell length was the major factor restricting crop growth. During the first year, mortality of unprotected mussels was very high (70–85%), whereas losses within crab-proof cages were significantly less (17–41%). Second-year mortality on open plots fell significantly to 22–57%, most losses then being caused by storms and bird predators, but that in cages rose to 27–54% due to overcrowding and smothering in biodeposits (‘mussel-mud’). Dry-flesh biomass (ash-inclusive) of unprotected mussels amounted to 4–6% of live crop weight (shell inclusive) and fluctuated seasonally, attaining peak values in late summer and early autumn. Standing crops were usually between 0·4 kg/m2 and 0·8 kg/m2, with a maximum of 1·2 kg/m2. Total production of dry-flesh over the two year growing period was 0·75–1·43 kg/m2, most production (about 69%) occurring in spring and summer of the first year. For optimum utilisation of mussel stocks and cultivation grounds the relaid mussels should be harvested at peak biomass, in late summer and autumn, and at a smaller size (45–50 mm) than at present.

A Note on Trophic Complexity and Community Stability

A Note on Trophic Complexity and Community Stability

On the Ecology and Distribution of the Parasitic Copepod Mytilicola Intestinalis Steuer

Critical appraisal of the literature data on Mytilicola intestinalis, combined with personal experience in this field, led to formulation of answers on a series of questions re the ecology and distribution of the parasitic copepod Mytilicola intestinalis Steuer. It is confirmed that Mytilicola has been the causative agent in extensive mussel mortalities. The explosion of Mytilicola in several places on the coastlines of North Sea and Atlantic Ocean should be explained in terms of Mytilicola, being a new intruder in these waters. There is no ground for the view that a special set of ecological conditions saw to the explosive development of the autochthonous species Mytilicola intestinalis, normally existing in small numbers only. Mytilicola intestinalis has a wide ecological range in all phases of its life cycle. The number of hosts living in a given volume of water, together with the amount of flushing of that water, is the main factor governing the number of parasites per host. Since two individuals of opposite sex have to meet in the intestinal tract of one and the same host, some scattered pelagic larvae cannot easily lead to establishment of a new focus of infection. Stretches of coast devoid of mussels form an almost unsurmountable barrier against the natural spreading of this parasite. It is usually man, through his multiple activities, who should be held responsible for the invasion of mussel areas previously devoid of Mytilicola intestinalis.

STRUCTURE AND ENERGY FLOW OF A MUSSEL POPULATION IN A GEORGIA SALT MARSH1

Modiolus demissus Dillwyn was studied near Sapelo Island, Georgia. The size distribution of the mussels was bimodal with maximum numbers in the dry weight (body) classes 0–24 mg and 400–599 mg. The total weight of mussels smaller than 200 mg was less than 2% of the total population weight. Random samples gave an estimated population density of 7.8/m2 for the entire inhabited marsh; the estimated organic biomass was 11.5 gm/m2, one third of which was body and two thirds was shell conchiolin. The population was most dense near the heads of small creeks, averaging 32 mussels/m2. The mussels, however, were not only more abundant in some types of marsh than in others, they were also clumped within areas of uniform marsh. Shell growth occurred throughout the year, especially in small and medium‐sized individuals, but it was more rapid during the warm months. The height‐to‐weight ratio changed with the seasons, the mussels being heaviest prior to spawning. Growth and mortality of mussels in flower pots in the marsh indicated a net annual population growth of 445 mg/m2 (dry body weight) and a net annual mortality loss of 1200 mg/m2. Allowance for bias would place the steady state growth‐mortality rate necessary to just maintain the population somewhere between these two estimates. Population growth and gamete production accounted for an energy flux of about 13.9 and 2.8 kg‐cal/m2/yr, respectively. Respiration by the population accounted for approximately 39 kg‐cal/m2/yr, over two thirds of which took place in air during ebb tide. Total assimilation amounted to 56 kg‐cal/m2/yr.