Mussel Clumps Research Articles

Microhabitat variation in the hydrothermal vent mussel, Bathymodiolus thermophilus, at the Rose Garden vent on the Galapagos Rift

Clumps of Bathymodiolus thermophilus were collected from three discrete areas at the ‘Rose Garden’ site on the Galapagos Rift using the deep submersible Alvin. Two mussel collections were made from the central Riftia mass, an area associated with very active venting, and three other collections were of two different peripheral mussel clumps. Before collection the clumps were extensively photographed and the water at two of the ‘microhabitats’ was analysed in situ for oxygen silica, sulfide and temperature. Sulfide levels of up to 300 μM were recorded at the central collection site, while the highest sulfide level recorded at the peripheral site assayed was 35 μM. Levels of RuBP carboxylase activity in the gills were significantly higher in mussels collected from the central ‘Riftia site’ than in either peripheral site. ATP sulfurylase was significantly higher in the gills of mussels from the central clump than in one of the peripheral clump collections. The chemical composition (% water, protein, carbohydrate, lipid and ash) and stable carbon isotope ratios (δ13C) of the mussels showed the same trends, with highest lipid and carbohydrate and the lowest water content and δ13C in the central site mussels. Similarly, the mussels from the central site were significantly depleted in stable nitrogen (δ15N) when compared with the peripheral site mussels. Variations between sites and tissues of the same animal may be indicative of differential utilization of inorganic or dissolved molecular nitrogen sources. The condition index (CI = soft tissue dry mass / internal shell volume) was similar for all animals collected at Rose Garden. The presence of a commensal polychaete, Branchipolynoe symmytilida, in the mantle cavity of the mussels was also correlated with the collection site, with the highest incidence of occurrence in the central clump.

Rheotaxis and distribution of oysters and mussels, Georgia tidal creeks and salt marshes, U.S.A

Azimuth measurements on commissures of the oyster Crassostrea virginica and the mussel Geukensia demissa reveal preferred alignments by these animals to tidal current flow. In beds along tidal creeks, where ebb-current velocities exceed flood-current velocities most oysters orient parallel to channel trend and exhibit a slight preference for the ebb direction; in contrast, mussels nestling among these oysters tend to orient transverse to channel trend. Small clumps of oysters and mussels on the salt marsh surface also exhibit discernible orientations; most tend to be aligned with tidal flood, which is stronger than tidal ebb across the marsh. Locally, however, these trends may be difficult to relate to large-scale components of marsh hydrography, because of pronounced microtropography and its influences on current flow. Overall configuration of oyster biostromes evidently is controlled by a combination of slope, areal extent, and elevation of habitable substrates, and competition among individual oysters. Valve orientations per se seem to be governed primarily by hydraulic pressure gradients, including adaptations by the animals to both drag forces and passive disposition of waste materials. The latter also is considered to be the most important stimulus affecting the rheotaxis of salt marsh oysters and mussels.

Larval settlement behavior in competing species: Mytiluscalifornianus Conrad and M. edulis L.

Mytilus californianus Conrad and M. edulis L. are marine mussels that compete for attachment space in the mid and upper intertidal zones. Larval settlement behavior in these species was examined to determine which substrata were preferred or avoided. Monospecific adult mussel clumps were given special attention since they may be important settling sites if competition has played a role in the evolution of habitat selection behaviors. M. californianus larvae settled on many different substrata at Yoakam Point, Oregon: several species of algae, M. edulis beds, M. californianus beds, and bare rock with scattered barnacles. Filamentous algae had the highest densities of settlers while M. californianus beds and bare-barnacle surfaces had relatively low densities. Settler density in M. californianus beds was lowest during spring and early summer and highest in the fall. In laboratory choice experiments M. edulis larvae avoided adult patches of M. californianus, instead settling on M. edulis adults or the red alga, Rhodomela larix (Turn.) C. Ag. Mytilus californianus larvae selected M. edulis adult patches as settlement sites in choice experiments. Competition between these Mytilus species may have led to different settling behaviors: M. edulis larvae avoid adult clumps of M. californianus where competition is intense and survivorship is low. M. californianus larvae settle broadly, selecting patches of adult M. edulis if encountered. Since M. californianus is competitively superior over other sessile species in this community, there may be little evolutionary pressure for larvae to select specific substrata. The settling behaviors of M. edulis and M. californianus affect the rate and direction of succession in this intertidal zone.

Dahlella Caldariensis, New Genus, New Species: a Leptostracan (Crustacea, Malacostraca) from Deep-sea Hydrothermal Vents

ABSTRACT The leptostracan Dahlella caldariensis, new genus, new species, is common at hydrothermal vents on the Galapagos spreading center and the East Pacific Rise at 13°N and 21°N (2,450-2,620 m depth). It was found in the throat of vent openings and clumps of mussels and vestimentiferans. The genus is most strikingly recognized by its elongate, dentate eyestalk. Living leptostracans are realigned among two families, Nebaliopsidae, new family, and Nebaliidae, new combination, which are diagnosed herein.

Effect of dietary history on selection of prey, and foraging behaviour among patches of prey, by the dogwhelk, Nucella lapillus (L.)

Dogwhelks originating from a population without access to mussels but maintained on a mixed diet of barnacles and mussels subsequently showed a preference for barnacles, whilst those maintained for 60 days on mussels developed a strong preference for mussels. Those that had never experienced mussels largely ignored them when presented, but overwhelmingly preferred barnacles to which they were accustomed. Those maintained for 90 days on mussels and then for 60 days on barnacles regained a preference for barnacles but still consumed more mussels than dogwhelks maintained solely on barnacles. Effects of ingestive conditioning therefore persisted at least for 60 days during which they were modified by experience with the alternative prey. Preferences resulting from ingestive conditioning were never reversed by the relative profitabilities of barnacles and mussels or by their relative abundances in feeding trials. Nevertheless, except for those totally inexperienced with mussels, dogwhelks incorporated more of the currently less preferred species into their diet when it was relatively more abundant. They had an additional tendency to continue choosing the same species during a foraging bout, whether or not they had become ingestively conditioned to it, a tendency which would enhance the likelihood of ingestive conditioning in the field. The susceptibility of dogwhelks to develop a strong, but reversible, preference for mussels or barnacles through ingestive conditioning is conducive to switching which, if occurring naturally, would take at least several months to complete and the initially preferred prey would become depleted to low levels. Dogwhelks apparently perceived clumps of mussels, placed on Petri dishes 0.5 m apart, as discrete patches of prey. They foraged mainly in darkness, tending to rest in corners of the aquarium or at the edge of the water during the light. On encountering a patch, dogwhelks would crawl over it for ≈0.7 h if subsequently rejected and 6.0 h if accepted, contacting most of the component mussels. Patches were not chosen according to their initial profitability or to their initial biomass, but those already being exploited by dogwhelks were visited more frequently and rejected less frequently than unexploited ones. Dogwhelks stayed longer in the more profitable patches and depleted them more than the others because the larger mussels, comprising the more profitable patches, individually took longer to handle and accounted for a greater proportion of the total biomass. The aggregative feeding response and the preference for certain sizes of prey probably cause dogwhelks in the field to congregate and feed longer where the preferred prey are most plentiful. More profitable patches are expected to be exploited sooner than less profitable patches, as predicted by the Marginal Value Theorem, but contrary to the Theorem the chosen patches will probably continue to be exploited even when depleted to well below the average profitability of patches in the area.

Size‐Limited Predation: An Observational and Experimental Approach with the Mytilus‐Pisaster Interaction

In many space—limited systems, for instance forests, coral reefs, and mussel beds, the main biological component of the spatial matrix is provided by large—bodied species. At some point during their growth these matrix species surpass the ability of any single individual of a predator species to consume them, although they still may be overwhelmed by concentrated group attacks (i.e., by aphids, fungi, internal parasites). These species thus surpass through continued growth a size threshold limiting their consumers, and thereby attain a refuge in size. The implications of these refuges are discussed, with special reference to a predatory starfish, Pisaster ochraces, and its primary prey, the mussel, Mytilus californianus. The mean wet weight of Pisaster varies between localities from ° 150 g to 2,640g. Long—term (12—yr) observation indicates little annual variation and generally no trends within areas, yet consistent differences between areas. Five transplant experiments demonstrate that Pisaster is an indeterminate grower, andis capable of adjusting its body size through growth to local conditions. Limited recovery of individually marked starfish suggest that exchange between areas is restricted. Observations on the natural diet of Pisaster show a pronounced maximum body size limit to the mussels that can be consumed by intertidal starfish of a given size. This limit was explored experimentally in two ways. First, Pisaster was allowed to reinvade an area from which it had been manually excluded for 5 yr. In this interval those mussels comprising the matrix of the clump had attained shell lengths > 8—10 cm. and could not be consumed by Piaster weighing 203 g. Second, artificial clumps of known—size mussels were protected by plastic screening, allowed to attach, and then exposed to predation. Survival was significantly greater in those mussels expected to be too large to be eaten. The significance of size—limited predation is that prey and predator can coexist in very intimate proximity, that the surviving prey often attain large sizes and probably make a reproductive contribution greater than their abundance, and that these same prey diversify the spatial structure of the environment, usually by adding a vertical dimension not otherwise present.

Desiccation, higher temperatures and upper intertidal limits of three species of sea mussels (Mollusca: Bivalvia) in New Zealand

Distribution, abundance, and resistance adaptations to higher temperature and desiccation of three species of intertidal mussels (Mytilus edulis aoteanus, Perna canaliculus and Aulacomya maoriana) were studied in New Zealand. M. edulis aoteanus generally was more abundant upshore, with P. canaliculus dominating downshore. M. edulis aoteanus was more common than P. canaliculus on the outside of mixed-species clumps. Abundance of A. maoriana was variable, with individuals favouring damp habitats such as inside mussel clumps. In moving air at 75% relative humidity and at 20°C or 30°C, median lethal levels of water loss were similar for P. canaliculus and M. edulis aoteanus but lower for A. maoriana. Rates of desiccation varied inversely with size and were higher for P. canaliculus, due mainly to valve gaping with resultant loss of water from the mantle cavity. M. edulis aoteanus was more tolerant of higher water temperatures than were the other species. Success in colonizing upshore or more aerially exposed habitats seems to be related to ability of small mussels to tolerate desiccation, especially during hot, windy weather.