Subtidal Mussels Research Articles

Seston Dynamics and Food Availability on Mussel and Cockle Beds

To provide a better understanding of seston dynamics in relation to food supply to the benthos, a series of 13-h tidal cycle sampling programmes was executed in the Oosterschelde estuary (The Netherlands). Samples were taken near the surface and near the bottom on two subtidal mussel cultivation plots and on two intertidal cockle beds.Long-term annual variablity of seston concentrations was lower than coefficients of variance of the short-term tidal cycle seston data at the intertidal stations, and higher than at the subtidal stations. Near-bottom relative to surface concentrations were highest for suspended particulate matter (SPM), followed by particulate organic carbon (POC), and chlorophyll. There was no food depletion near the bottom but food quality was lower, presumably due to re-suspension of sediment, including low-quality biodeposits. Chlorophyll concentrations were lower in ebb than flood water at all stations, which was ascribed to feeding activity of the bivalves. At the subtidal stations, SPM and POC concentrations were also lower during low water, owing to sedimentation. There was a positive correlation at the intertidal stations of seston quantity with wind speed and wave action. At a wave length exceeding twice the water depth, re-suspension of low quality bottom material was observed and seston quality decreased.It was concluded that food availability for benthic suspension feeders was lower than suggested by routine monitoring data. At the intertidal stations, food quality was further reduced during periods of increased wind velocities and wave action. The low near-bottom food quality can partly be considered as an effect of the feeding activity of the benthic suspension feeders.

Natural Cd and Pb variations in Mytilus californianus during the upwelling season

The short term variability of Cd and Pb in Mytilus californianus in relation to upwelling events was studied. Sea water and mussel samples were taken daily for 4 weeks during the upwelling season (late summer) on the west coast of Vancouver Island. Upwelling indicators (PO 4, T and S) were measured and related to the variations in dissolved Cd and Pb in sea water. High variability in Cd and Pb mussel concentrations were detected, with significant differences found from one day to another. After normalizing, to account for the variability due to the condition of the mussel, significant differences among samples were still detected. The differences in mussel Cd were associated with the variations in dissolved Cd due to upwelling. Mussel Pb, however, was not related to variations in dissolved Pb. Principal component analysis was used to unravel patterns of variation among all variables measured. Parallel to the sampling of natural mussel beds, a transplant experiment was performed to compare the variability of intertidal vs. subtidal mussels. The transplanted mussels exhibited a less variable condition index and revealed more clearly the relation of dissolved Cd with the concentrations in the mussels. Lead in mussels, again, did not show a relationship with dissolved Pb. In addition, the mantle edge (from 3 days with highest and lowest Cd concentrations) was analyzed as an alternative indicator which could exhibit less variability. The Cd variability in the mantle edge was compared with that of the gills and the remainder. The mantle edge, even though it showed less variability than the gills and the remainder, still exhibited significant differences between days.

PCR-based nuclear markers identify alien blue mussel (Mytilusspp.) genotypes on the west coast of Canada

Two blue mussel sibling species, Mytilus edulis and Mytilus galloprovincialis, have been imported to Pacific northwest waters in separate attempts to circumvent early mortality experienced by the native species (Mytilus trossulus) when cultured. Here we describe two novel markers based on the polymerase chain reaction that discriminate the two non-native, or alien, mussel species from the native species. The two markers are inherited in a Mendelian fashion, show no evidence of close linkage, and are highly diagnostic. To screen British Columbian mussel populations for the presence of the alien species, we assayed genotypes at the two marker loci in 482 subtidal mussels collected at 12 sites. Animals with at least one alien allele were present at 9 of 12 sampling sites with an overall frequency of 6.2%. The distribution of alien alleles at the two marker loci differed among sampling sites, suggesting differential introgression. The widespread incidence of alien alleles, combined with evidence of extensive hybridization between the alien and native species, indicates that the introduced alleles will probably persist in British Columbia mussels for some time.

Effects of an oil spill on some organisms living on mangrove ( Rhizophora mangle L.) roots in low wave-energy habitats in Caribbean Panama

Following the discharge of more than 50000 barrels of crude oil into a tropical, mangrove-fringed estuary, we examined the effects of oiling on the epibiota of mangrove ( Rhizophora mangle) prop roots. Using data taken four years before the spill and for a year after the spill, we assessed the possible value of four bivalves and one barnacle as indicators of damage from oiling. Quarterly comparisons of abundances at matched oiled and unoiled sites showed strong indirect evidence of population reductions in six of seven comparisons. However, the shells of only two species persisted long enough on roots (3–6 months) to be useful direct indicators of recent mortality. Knowledge of conditions four years before oiling was important in establishing the extent of damage from this oil spill. Population reductions were most striking in brackish streams, where intertidal and subtidal mussels and barnacles were quickly devastated at oiled sites and showed no recovery during the year after the spill, and for an intertidal oyster in channels and lagoons. All other species showed at least some negative effects of oiling, but the strength of the evidence varied over time and among species.

Growth and population dynamics in mussels ( Mytilus edulis L.) cultured in the White Sea

Samples of mussels collected from net substrata suspended from production rafts in Chupa Inlet, the White Sea, were used to determine growth and population dynamics during 5 years. For comparison of growth, samples were also collected from tidal and subtidal mussel populations. Growth rate of cultured mussels was higher than that of benthic ones. Seasonal changes of growth rate were influenced mainly by sea-water temperature. By the first autumn after settlement, young mussels settled on the substrata could be divided into two main size groups. These groups could be distinguished until the 4th–5th year. The maximal mortality 1 in the cultured mussel population was observed during the 1st year after settlement and after the biomass reached more than 10 kg/m. Mussels of the main generation (settled in 1983) prevented spat settlement in the following years, until the 4th year when a considerable loss of large mussels occurred.

Effect of tidal exposure on utilization of dietary lignocellulose by the ribbed mussel Geukensia demissa (Dillwyn) (Mollusca: Bivalvia)

Utilization of 14C-labeled lignocellulose by the ribbed mussel Geukensia demissa (Dillwyn) was evaluated under simulated intertidal (50/50% exposure/submergence) and subtidal (100% submergence) conditions. Ingestion rates of mussels fed on [ 14C]lignocellulose did not differ significantly between mussels held in intertidal and subtidal conditions. The mean (± se) 14C absorption efficiency for intertidal mussels fed [ 14C]lignocellulose was 14.9 ± 0.5% in summer (June 1986) and 6.7 ± 0.5% in fall (October 1988). Mean (± se) summer (9.1 ± 0.6%) and fall (4.0 ± 0.2%) 14C absorption efficiencies of subtidal mussels fed 14C lignocellulose were significantly lower t test, p > 0.05 than those of intertidal mussels. It was estimated that the contribution of lignocellulose to the total summer energy requirements of intertidal and subtidal G. demissa was similar at 5.7 and 5.3%, respectively. Reduced metabolic expenditures and higher absorption efficiencies allow G. demissa to compensate for a limited period of feeding on lignocellulose in its intertidal habitat.

Subtidal Coexistence: Storms, Grazing, Mutualism, and the Zonation of Kelps and Mussels

At exposed sites in the Gulf of Maine, USA, subtidal mussels (Modiolus modiolus) dominated space on upper rock surfaces at intermediate depths (11—18 m), but not at shallow depths (4—8 m), where dominants were the kelps Laminaria digitata and L. saccharina. Observations and experiments were conducted to test the following hypotheses about factors limiting the vertical (depth) zonation of mussels and kelp: (1) that the upward distribution of Modiolus is limited by interference effects of kelp, or (2) that it is limited by the failure of larval recruitment to shallow depths, and (3) that sea urchin grazing controls the downward distribution of kelp. The recruitment failure hypothesis was rejected. Results indicated that storm—generated dislodgement of mussels overgrown by kelp was the mechanism reducing the ability of Modiolus to maintain and hold space in the shallow kelp zone. Dislodgement following kelp overgrowth was the most significant mortality source of large mussels. Removal of sea urchins, Strongylocentrotus droebachiensis, from the lower edge of the kelp zone resulted in the downward shift of kelp to a 12.5 m depth, demonstrating that the lower depth limit of kelp is set by urchin grazing. Storm disturbances varied in frequency and severity of damage to mussel populations, and were an important agent of patch creation in the subtidal zone. Small storms occurred on a monthly basis. Severe storms struck three times in 1982 and twice in 1983; an average of 11 658 mussels with attached kelp were dislodged and cast ashore on monitored beaches during such storms. Storm disturbances were synchronous between coastal and offshore sites. The mean density of patches cleared in mussel beds (2.5 patches/0.25 m2) was highest after fall storms. Mean patch size ranged from 91.0 cm2 (fall) to 122.0 cm2 (winter). With the exception of urchin fronts at 10.5—12.0 m, sea urchin densities were significantly higher inside Modiolus beds than outside. The hypothesis that urchins increase Modiolus survivorship by grazing kelp off mussels and decreasing the risk of mussel dislodgement was tested by an urchin—removal experiment. Removal of urchins from mussel beds led to rapid kelp recruitment, resulting in a 30—fold increase of mussel mortality (via kelp—induced dislodgement) compared to control beds with resident urchins. Significantly more force was required to pull large urchins out of mussel beds than to remove them from rock surfaces outside the beds, suggesting that urchins are less susceptible to predation and dislodgement—caused mortality while in Modiolus beds. The Modiolus—Strongylocentrotus interaction is identified as a facultative mutualism that appears to facilitate the coexistence of kelp and mussels at shallow depths. The ability of kelp and mussels to recover from dislodgement disturbance was examined by clearing patches in mussel beds and algal turf. Kelps recolonized and dominated all algal—turf patches and 47% of mussel patches within 7 mo. In contrast, Modiolus did not close patches by recruitment, or by a leaning response of mussels surrounding the patch, over a 3—yr period. This suggests that the ability of kelps to bounce back from dislodgement disturbance may enhance their competitive superiority. For Modiolus, the rate of storm—generated disturbance exceeded the rate of recovery.

ENERGY METABOLISM DURING AIR EXPOSURE AND RECOVERY IN THE HIGH INTERTIDAL BIVALVE MOLLUSC GEUKENSIA DEMISSA GRANOSISSIMA AND THE SUBTIDAL BIVALVE MOLLUSC MODIOLUS SQUAMOSUS

Metabolic responses to air exposure and recovery were investigated in the adductor muscles of the high intertidal mussel Geukensia demissa granosissima and the subtidal mussel Modiolus squamosus. Exposure to air for 12 h had no significant effect on the levels of high energy phosphates (arginine phosphate, ATP) in the adductor muscles of G. demissa granosissima, indicating minimal metabolic stress in this species. In contrast, there was a considerable decline in arginine phosphate and ATP during air exposure in the phasic and tonic adductor muscles of M. squamosus. In addition, there was a substantial accumulation of alanine and succinate under these conditions. Furthermore, D-lactate accumulated in the phasic muscle of M. squamosus during air exposure. During recovery, there were transient accumulations of alanopine/ strombine in both G. demissa granosissima and M. squamosus. The differences in metabolic responses between these two species reflect adaptations to specific micro-habitats. It appears that metabolism in the posterior adductor muscle of G. demissa granosissima is largely aerobic during air exposure. The subtidal species M. squamosus displays a much greater reliance on anaerobic pathways of energy production under these conditions.

Volume regulation and valve movements by marine mussels

1. 1. Patterns of valve movements and volume regulating responses of intertidal and subtidal mussels of the genus Modiolus exposed changing environmental salinity were examined. The generality of the data was tested by using populations of mussels from Florida and Massachusetts. 2. 2. The activity of both intertidal and subtidal species of Modiolus, as measured by valve movements, was reduced when the animals were exposed to either a high or a low salinity. 3. 3. The valve movements appear to return to normal after a period of time dependent on the magnitude of the salinity change. 4. 4. The volume of water in the tissues varies, over the salinity range of each species, but only by a very small amount, compared to the magnitude of change of the external salinity. 5. 5. These species of Modiolus regulate their cellular volume, in dilute sea water, by solute extrusion, but in concentrated salinities, they show no volume control; simply losing water to the medium.