Ruth D Turner

Wood-Boring Bivalves, Opportunistic Species in the Deep Sea

Wood exposed for 104 days at a depth of 1830 meters at the permanent station of the research submersible D.S.R.V. Alvin was completely riddled by two species of bivalve wood borers (subfamily Xylophagainae, family Pholadidae). Their high reproductive rate, high population density, rapid growth, early maturity, and utilization of a transient habitat classify them as opportunistic species, the first recorded from the deep sea. Xylophaga is shown to be the most important species involved in decomposing woody plant material in the deep sea.

A cellulolytic nitrogen-fixing bacterium cultured from the gland of deshayes in shipworms (bivalvia: teredinidae).

A novel bacterium has been isolated in pure culture from the gland of Deshayes in six species of teredinid bivalves. It is the first bacterium known to both digest cellulose and fix nitrogen, and it is a participant in a unique symbiotic relation with shipworms that may explain how teredinids are able to use wood as their principal food source.

Larval dispersal of a deep-sea hydrothermal vent bivalve from the Galápagos Rift

The prodissoconch morphology of an unclassified mytilid from a hydrothermal vent on the Galápagos Rift indicates the presence of a planktotrophic larval stage with longrange dispersal capabilities. Recorded abyssal currents are probably sufficient to transport such larvae hundreds of kilometers. It is suggested that one or more aspects of the unusual biological or physico-chemical conditions (such as high microbial densities, elevated water temperatures, and hydrogen sulfide concentrations) encountered at vents, provide a stimulus to larval settlement. Such a behavioral response, perhaps coupled with a “gregarious settling” response, would provide a means of concentrating relatively sedentary organisms in and around these restricted, geographically isolated regions.

Larval Development and Dispersal at Deep-Sea Hydrothermal Vents

Deep-sea hydrothermal vent communities exhibit an array of reproductive strategies. Although a few vent species undergo planktotrophic, high-dispersal modes of development, most exhibit relatively low dispersal, but probably free-swimming nonplanktotrophic development. This predominance of nonplanktotrophy may be largely a reflection of phylogenetic constraints on the vent colonizing taxa; intervent dispersal among these forms may be facilitated by reduced developmental rates in the cold abyssal waters away from the vents. It is proposed that for those vent species with nonplanktotrophic development, larval dispersal is a stepwise process with oceanic ridge axes serving as discrete dispersal corridors.

Recruitment of marine invertebrates to hard substrates at deep-sea hydrothermal vents on the East Pacific Rise and Galapagos spreading center

Abstract Recruitment panels were placed at and near hydrothermal vent communities at three sites on the Galapagos spreading center and one site on the East Pacific Rise at 21°N. Deployment periods ranged from 26 days (Clam Acres, 21°N) to 260–320 days (Rose Garden, Garden of Eden, Mussel Bed, GSC) to 1216 days (Clam Acres). Recruitment of gastropod post-larvae and juveniles was observed on arrays deployed at Clam Acres for 26 days. Regardless of length of deployment, populations of polychaetes, mollusks, and barnacles colonizing the panels were predominantly post-larval, juvenile, or sub-adult stages. We suggest that some combination of competition, migration, and predation maintains these populations in immature stages. Size distributions of individuals within a taxon on panels deployed for 1216 days are broad, suggesting intermittent or continuous recruitment in many of the vent-associated species rather than a single episodic recruitment event. Folliculinid and foraminiferan protozoans were the most abundant eucaryotic organisms colonizing long-term deployments at Clam Acres. On the Galapagos spreading center, level of recruitment differed among the vent sites, with Rose Garden > Garden of Eden ⪢ Mussel Bed. Recruitment of vent-associated species was greater on panels placed within vent communities compared to panels placed adjacent to these communities. This observation is consistent with the maintenance of vent communities in discrete regions of hydrothermal flux.

Development, metamorphosis, and natural history of the nudibranch Doridella obscura Verrill (Corambidae: Opisthobranchia)

Abstract The doridacean nudibranch Doridella obscura Verrill was raised through one complete generation in laboratory culture, and spawning behavior monitored for a year at monthly intervals in Barnegat Bay, New Jersey. The nudibranch deposited egg masses throughout the year in Barnegat Bay, and the larvae remained viable at temperatures ranging from 1.5 to 28 °C. At 25 °C the eggs hatch 4 days after oviposition, and the planktotrophic veliger larvae swim and feed for 9 days before they metamorphose. Settlement occurs specifically on the bryozoan Electro crustulenta (Pallas). The spirally coiled larval shell grows rapidly until the dorsal mantle fold is retracted from the aperture 5–6 days after hatching. Although starved larvae grow only slightly and do not metamorphose, they resume normal development on introduction of suitable food. Newly metamorphosed juveniles consume algae and debris on the surface of the bryozoan until they grow large enough to attack the living zooids of E. crustulenta . The life cycle of Doridella obscura is short (26 days at 25 °C), allowing the nudibranchs to take advantage of short-lived Electra crustulenta colonies in unstable habitats in bays and estuaries.

Physiological aspects of wood consumption, growth, and reproduction in the shipworm Lyrodus pedicellatus Quatrefages (Bivalvia:Teredinidae)

Single specimens of the shipworm Lyrodus pedicellatus Quatrefages (Mollusca, Bivalvia) were grown for 4 months in individual wooden dowels in either phytoplankton free sea water or sea water enriched with the flagellate Isochrysis galbana Parke. Increases in burrow length, tissue dry weight, percent carbon and nitrogen, total wood consumption, larval production, biodeposition, respiration and ammonia excretion were monitored routinely throughout the experiment. No significant differences in measured parameters were observed between the two experimental conditions. Although previous studies showed significant algal 14C incorporation into Lyrodus pedicellatus tissue, a phytoplankton supplement is not required to satisfy dietary needs; however, ingestion of wood alone is not sufficient to account for the carbon and nitrogen levels present in shipworm tissue, larvae and faecal material. No significant quantities of ammonia-N excretion were detected. Shipworms appear to be extremely nitrogen-conservative and may be capable of recycling proteinaceous catabolic end products, via bacterial associations, to augment their dietary input.

Characterization and site description of Solemya borealis (Bivalvia; Solemyidae), another bivalve-bacteria symbiosis

Solemya borealis Totten was collected from anoxic sediments in Buzzards Bay, Massachusetts in April and July 1989 and examined for the presence of symbiotic, chemoautotrophic bacteria. In addition, sediment cores collected at the same site were analyzed throughout the year, to provide a detailed description of the S. borealis habitat. Here we present structural, enzymatic, biochemical, and stable isotope data which suggests that S. borealis, like the related species Solemya velum Say and Solemya reidi Bernard, contains high concentrations of symbiotic chemoautotrophic bacteria in gill bacteriocytes which play a significant role in nutrition. Transmission electron microscopy revealed the presence of rod-shaped cells, which resemble Gram-negative bacteria, within gill epithelial cells. Ribulose-1,5-bisphosphate carboxylase activity in cell-free extracts of S. borealis gill tissue was comparable with that found in other invertebrate-chemoautotroph symbioses. Very negative δ34S ratios (-32.6 to-15.7‰) suggest the utilization of porewater sulfides as both an energy and a sulfur source for the symbionts. Carbon and nitrogen stable isotope ratios were extremely negative (δ13C=-32 to-34.6‰, δ15N=-9.7 to-8.6‰), similar to those of other bivalve-chemoautotroph symbioses. High concentrations of cis-vaccenic acid, a fatty acid previously found in other invertebrate-chemoautotroph symbioses, were found in all the major lipid classes of the gills of S. borealis. The stable isotope ratios and lipid composition of S. borealis suggest that most of this bivalves nutritional requirements are supplied by bacterial endosymbionts. High levels of taurine in the free amino acid pool of S. borealis suggest the existence of unusual amino acid metabolic pathways which may be the result of endosymbiont activity. The S. borealis specimens were found in relatively shallow water sediments dominated by silts and clays. The sediments contain high concentrations of organic carbon and nitrogen, exhibit limited oxygen penetration, and have high rates of ammonium and sulfide input from the anaerobic microbial community. Sediment C and N stable isotope ratios reflect the input of algal-derived nutrients to the sediments (δ13C=-20.7 to-20.9‰, δ15N=+7.7 to +20.8‰). Sediment δ34S ratios ranged from-18.7 to-25.1‰ demonstrating the presence of sulfur produced by bacterial dissimilatory sulfate reduction processes.

Larval development of the deep-water wood boring bivalve, Xylophaga atlantica richards (Mollusca, bivalvia, pholadidae)

Abstract Adult Xylophaga atlantica obtained from lobster pots set at a depth of 100m released gametes in the laboratory when the water temperature was raised from 4 to 9 °C. Sperm were rarely observed but spawned eggs invariably developed, suggesting internal fertilization. Mean egg diameter was 45μm; eggs were round, yellow to light brown. Larvae reared at 9 and 14°C and 31 % salinity were free swimming in 30-40 hours and 20–24 hours respectively. Swimming larvae held in tall culture vessels congregated in a horizontal band where the temperature was 11–13 °C. Straight-hinge veligers developed in 4 days and averaged 62 μm in length. The umbo veligers ranged from 150 to 255 μmin length and had a very large characteristic velum. Pediveligers appeared 50days after fertilization and averaged 280 x 268 μm in length and height, respectively. They were smooth, inequivalved, and had a well developed hinge. The foot had a tuft of long cilia at the tip. The first signs of metamorphosis were observed on the 57th day...

Dwarf males in the Teredinidae (Bivalvia, Pholadacea)

Extreme sexual dimorphism in the Bivalvia is rare. The occurrence of dwarf males in Zachsia appears to be the first case in the Teredinidae and the first outside the Leptonacea. Female Zachsia release straight-hinge larvae that develop in the plankton and settle on living rhizomes of Phyllospadix. Larvae entering mantle pouches of females become males. Evolution of this life history pattern is tied to problems of living in a fragile, patchy habitat—that is, the rhizomes of Phyllospadix.