Thompson Christine M.

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Thompson
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Christine M.
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  • Thesis
    Species-specific patterns in bivalve larval supply to a coastal embayment
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2011-02) Thompson, Christine M.
    Larval supply is an important process linking reproductive output to recruitment of benthic marine invertebrates. Few species-specific studies of bivalve larvae have been performed due to the lack of suitable methods for species identification. This thesis focused on applying a method to identify larvae from field samples from Waquoit Bay, MA using shell birefringence patterns. This method was then used to address variability in larval supply for three bivalve species on weekly, tidal, and hourly scales. Sampling weekly for six months during two years showed large variability in larval concentrations on this time scale. Abundances of most species were related to bay temperature, and species distributions among sampling sites were indicative of transport potential and population coherence. Greater growth of larvae in 2009 compared to 2007 was attributed to more wind-induced mixing and better food availability in 2009. Integrative samples over each tidal event for a 14-day period demonstrated that larvae were mostly constrained by water masses. During a period when there were sharp tidal signals in temperature and salinity, larval concentrations were higher in bay water compared to coastal waters on incoming tides. After a storm event, water mass properties were less distinct between tidal events and a semidiurnal signal in larval concentrations was no longer apparent. The timing of periods of high larval concentrations did not always coincide with periods of highest water mass flux reducing net export in some cases. On an hourly scale, the vertical distribution of larvae affected by water column stratification and strength of tidal flow. Strong currents and a fresh upper layer both prevented larvae from concentrating at the surface. There was little evidence of peaks in larval concentrations associated with a given tidal period. Species-specific data can provide new perspectives on larval transport. For the three species studied, Anomia simplex, Guekensia demissa, and Mercenaria mercenaria, different source areas, patterns for growth, and potential for export were observed. Applying species-specific identification methods to future studies of bivalve larval transport has the potential to relate larval abundance to settlement patterns, an important component of larval ecology and shellfish management.
  • Article
    Semi-automated image analysis for the identification of bivalve larvae from a Cape Cod estuary
    (Association for the Sciences of Limnology and Oceanography, 2012-07) Thompson, Christine M. ; Hare, Matthew P. ; Gallager, Scott M.
    Machine-learning methods for identifying planktonic organisms are becoming well-established. Although similar morphologies among species make traditional image identification methods difficult for larval bivalves, species-specific shell birefringence patterns under polarized light permit identification by color and texture-based features. This approach uses cross-polarized images of bivalve larvae, extracts Gabor and color angle features from each image, and classifies images using a Support Vector Machine. We adapted this method, which was established on hatchery-reared larvae, to identify bivalve larvae from a series of field samples from a Cape Cod estuary in 2009. This method had 98% identification accuracy for four hatchery-reared species. We used a multiplex polymerase chain reaction (PCR) method to confirm field identifications and to compare accuracies to the software classifications. Image classification of larvae collected in the field had lower accuracies than both the classification of hatchery species and PCR-based identification due to error in visually classifying unknown larvae and variability in larval images from the field. A six-species field training set had the best correspondence to our visual classifications with 75% overall agreement and individual species agreements from 63% to 88%. Larval abundance estimates for a time-series of field samples showed good correspondence with visual methods after correction. Overall, this approach represents a cost- and time-saving alternative to molecular-based identifications and can produce sufficient results to address long-term abundance and transport-based questions on a species-specific level, a rarity in studies of bivalve larvae.
  • Preprint
    Species-specific abundance of bivalve larvae in relation to biological and physical conditions in a Cape Cod estuary : Waquoit Bay, Massachusetts (USA)
    ( 2012-06) Thompson, Christine M. ; York, Richard H. ; Gallager, Scott M.
    Physical and biological conditions impact recruitment and adult population structure of 34 marine invertebrates by affecting early life history processes from spawning to post-settlement. We investigated how temperature, salinity and phytoplankton influenced larval abundance and larval size structure for three species of bivalves over two non-consecutive years in Waquoit Bay, MA. Abundance and size of Mercenaria mercenaria (quahog), Anomia simplex (jingle clam), and Geukensia demissa (ribbed mussel) larvae were compared between locations in the bay and with environmental conditions. Shell birefringence patterns using polarized light microscopy were used to distinguish species. Larval abundances for all three species were higher in 2009 than in 2007 and were positively correlated with temperature in both years. Differences in larval abundance and size structure between bay sites were attributed to salinity tolerances and potential source locations. Higher survival in 2009 than in 2007, as determined by number of pediveligers, was likely due to higher temperatures and greater food availability during the peak abundance months of July and August in 2009. Yearly differences in larval growth and survival can have a large impact on recruitment. Knowing the optimal periods and locations for larval abundance and survival can be useful for isolating species-specific patterns in larval dispersal and to aid resource managers in enhancing or restoring depleted populations.