Hill Richard W.

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Hill
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Richard W.
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  • Article
    Metabolism of dimethylsulfoniopropionate (DMSP) by juvenile Atlantic menhaden Brevoortia tyrannus
    (Inter-Research, 2006-09-30) Hill, Richard W. ; Dacey, John W. H.
    Dimethylsulfoniopropionate (DMSP) synthesized by marine phytoplankton is the principal source of dimethylsulfide (DMS), an important climate-affecting gas. Prior research has demonstrated that grazing by invertebrate phytoplanktivores often affects the dynamics of DMS production from algal DMSP, but the effects of grazing by phytoplanktivorous fish have not previously been investigated. We studied the fate of algal DMSP following grazing by juvenile Atlantic menhaden Brevoortia tyrannus (13 cm fork length), which are generally viewed as the most specialized for phytoplanktivory of all postlarval fish. The menhaden were fed the dinoflagellate Prorocentrum micans, containing 1 to 2 pmol DMSP cell–1. During the first 24 h following ingestion of algal DMSP, almost none of the DMSP (ca. 1%) appeared as DMS. About 21% of ingested DMSP appeared in the water column as dissolved DMSP, peaking in concentration 9 to 11 h after feeding; in natural settings, this fraction would be poised for microbial metabolism, including potential conversion to DMS in surface waters from which outgassing to the atmosphere could occur. About 10% of ingested DMSP appeared in fecal pellets that tended to sink rapidly toward the bottom of the tanks. About 33% of ingested DMSP was deposited in the tissues of the menhaden, in particular in the red and white swimming muscles, in which we observed concentrations exceeding 0.7 µmol g–1. This final fraction could ultimately be metabolized to DMS, or it could be passed up food chains and possibly act as a taste factor in commercially important piscivores such as striped bass and bluefish. In total, our research demonstrated that at least two-thirds of the ingested DMSP ends up in tissues or feces or in solution in the ambient water in the first 24 h after feeding, and virtually none is converted to ambient DMS during that time period.
  • Article
    Dimethylsulfoniopropionate in six species of giant clams and the evolution of dimethylsulfide after death
    (National Research Council Canada, 2004-06-23) Hill, Richard W. ; Dacey, John W. H. ; Hill, Susan D. ; Edward, Ahser ; Hicks, Wayne A.
    Substantial accumulation of dimethylsulfoniopropionate (DMSP) is documented in tissues of all six of the common species of giant clams (Tridacnidae). Results include measures of DMSP concentrations in siphonal mantle, byssal mantle, adductor muscle, and gill tissues obtained by gas chromatography of alkalized extracts plus evidence of DMSP from mass spectrometry. Formation of dimethylsulfide (DMS) by tissues after death is documented. The tridacnid clams maintain symbiotic associations with populations of dinoflagellates, which live within the enlarged siphonal mantle. We postulated that because of their association with dinoflagellates, the clams would chronically accumulate DMSP to high concentrations. Our results show that DMSP occurs at over 30 mmol·kg–1 in many tissues of tridacnid clams (sometimes 50–60 mmol·kg–1), meaning that these clams accumulate DMSP to the highest documented tissue concentrations in the animal kingdom. DMSP at such concentrations could affect multiple properties and functions. Our particular interest for this research was to assess whether postmortem breakdown of DMSP is responsible for the rapid development of potent off-odors and off-tastes that have blocked the commercial success of giant clam aquaculture. High concentrations of DMS produced in the day after death probably account for the peculiar perishability of giant clam tissues.
  • Article
    Processing of ingested dimethylsulfoniopropionate by mussels Mytilus edulis and scallops Argopecten irradians
    (Inter-Research, 2007-08-07) Hill, Richard W. ; Dacey, John W. H.
    Dimethylsulfoniopropionate (DMSP) synthesized by marine phytoplankton is the principal source of dimethylsulfide (DMS), an important climate-affecting gas. Grazing by small zooplankton on phytoplankton often accelerates DMS production from algal DMSP. The effects of grazing by benthic suspension feeders, such as bivalve molluscs, however, have not been studied, even though their populations sometimes process a sizable fraction of local phytoplankton production. We fed Tetraselmis sp. Strain UW474 (27 to 42 fmol DMSP cell–1) to adult mussels Mytilus edulis and scallops Argopecten irradians and studied the fate of the algal DMSP during the 24 h following ingestion. Almost none of the ingested DMSP reappeared in the environment as DMS or DMSP; the amount that appeared in the ambient water as DMS was <1% of that ingested, and the sum total that appeared either as fecal DMSP (which microbes might convert to DMS) or in the water as DMS or DMSP was ≤3 to 4% of that ingested. In the short term, therefore, thriving bivalve populations probably strongly reduce the rate of DMS formation (direct or indirect) from local algal DMSP, in contrast to zooplankton populations. Ingested DMSP is likely accumulated in the bodies of mussels and scallops. However, although we have weak evidence of partial accumulation in scallop gastrointestinal tissue, we were unable to document accumulation in mussels because of high variability and statistical nonnormality in their naturally occurring DMSP content. In total, we showed that in the 24 h following feeding, mussels and scallops do not facilitate ambient DMS formation from algal DMSP and evidently sequester most of the algal DMSP they ingest.
  • Preprint
    Exceptional accumulation and retention of dimethylsulfoniopropionate by molluscs
    ( 2015-05) Hill, Richard W. ; Dacey, John W. H.
    Molluscs often play major roles in processing phytoplankton-synthesized dimethylsulfoniopropionate (DMSP) in local ecosystems. We find that some mollusc species retain tissue DMSP exceptionally tightly and exhibit unusually great and statistically nonnormal interindividual variation in DMSP accumulation and retention. Individual mussels (Mytilus, Geukensia) living within a single clump, for example, range 6- to 11-fold in tissue [DMSP] and are often nonnormal in statistical distribution. These properties cannot be explained by the elevation of the substrate on which the mussels are living or by mussel position in a clump. When mussels (M. edulis) are deprived of DMSP for up to 5 weeks in depuration experiments, some individuals retain high tissue [DMSP], whereas others exhibit reduced [DMSP]. Such interindividual divergence helps explain nonnormal distributions of tissue [DMSP] after depuration. We re-analyze published data from which the half-time for tissue DMSP loss during depuration can be calculated. In the only mollusc so studied (Haliotis), the half-time is 13-25 times longer than in similar-size fish. Besides posing a challenge for DMSP mass balance studies, retention and interindividual variation may point to as yet unknown properties of molluscs: Tight retention suggests functional roles for DMSP, and nonnormal statistical distributions suggest discontinuities among individuals in DMSP metabolism.