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A Comparison Between MD Phytoplankton Enumeration Techniques

A Comparison Between MD Phytoplankton Enumeration Techniques. Prepared by: Dr. Jon Anderson Ann Marie Hartsig Richard V. Lacouture Morgan State University Estuarine Research Center. Phytoplankton Enumeration Method Comparison. 500X Secondary Magnification Cells <10µm only

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A Comparison Between MD Phytoplankton Enumeration Techniques

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  1. A Comparison Between MD Phytoplankton Enumeration Techniques Prepared by: Dr. Jon Anderson Ann Marie Hartsig Richard V. Lacouture Morgan State University Estuarine Research Center

  2. Phytoplankton Enumeration Method Comparison 500X Secondary Magnification Cells <10µm only Minimum of 20 random fields No minimum organism count 312.5X Secondary Magnification Minimum of 20 random fields Count all cells not observed at 500X 125X Tertiary Magnification Scan of entire chamber All larger cells are counted that were not counted in other mags “New” Method 312.5X Primary Magnification Minimum of 10 random fields Minimum of 200 cells Count all cells ≥10µm Larger, rarer species not counted “Old” Method 500X Primary Magnification Minimum of 20 random fields Minimum of 200 cells

  3. METHODS • Sixty samples from July-October, 2005 and March-June, 2006 were enumerated with each technique. • Individual cells were counted or estimated for colonial, filamentous and chain-forming taxa. • A paired t-test was run on log transformed data in order to test the equality of mean densities by taxon and by phylum. • A paired variance ratio test was run to analyze for homogeneity of variances.

  4. Results of Paired t-test and Test of Variance Homogeneity by Phylum

  5. Results of Statistical Tests by Phylum (cont) • In general, total cell densities and variances were significantly higher using the old counting technique. • Silicoflagellates and microflagellates were the only phyla which were not characterized by significant mean differences between the enumeration techniques. • The variances for those two phyla as well as that for Cyanophytes were not significantly different between the two techniques. The variance for Cyanophytes was very high for each technique, especially the old technique. • With the exception of microflagellates, the new technique produced lower mean abundances by phyla.

  6. Means Variances Species Name Classification Difference p-value Difference p-value UNID. BLUE GREEN TRICHOME (CELL) SMALL DOMINANT 2.506E+06 1.710E-02 6.651E+13 1.90E-02 CRYPTOMONAS SP#1 LENGTH <10 MICRONS DOMINANT -1.151E+05 2.781E-04 4.350E+11 1.29E-09 CHAETOCEROS SUBTILIS DOMINANT 3.527E+05 4.264E-02 1.394E+12 5.87E-02 OSCILLATORIA CELLS #1 DIAM <5UM DOMINANT 8.667E+05 4.818E-03 1.705E+11 5.76E-02 CHAETOCEROS SP#1 DIAM <10 MICRONS DOMINANT 3.891E+05 1.944E-02 3.873E+11 7.19E-02 PROROCENTRUM MINIMUM DOMINANT 3.870E+04 4.326E-03 1.135E+11 1.08E-05 CYLINDROTHECA CLOSTERIUM DOMINANT -8.762E+04 2.144E-02 -3.386E+11 5.26E-04 GYMNODINIUM SP.#1 5-20UM W 10-20UM L DOMINANT 3.458E+04 8.632E-03 2.724E+09 1.02E-07 GYRODINIUM SP#1 5-20UM W 10-20UM L DOMINANT -7.069E+04 4.194E-02 -2.437E+10 3.58E-01 UNID. MICRO-PHYTOFLAG LENGTH >10 MICRONS DOMINANT -1.670E+05 6.377E-03 -1.319E+11 9.49E-02 AULACOSEIRA GRANULATA SUBDOMINANT 1.984E+05 4.169E-02 1.003E+11 1.38E-01 MELOSIRA SP#1 DIAM <20 MICRONS SUBDOMINANT 1.813E+05 2.910E-02 4.334E+10 4.55E-02 SCENEDESMUS QUADRICAUDA SUBDOMINANT 1.174E+05 5.458E-03 6.039E+09 2.92E-01 UNID. PENNATE DIATOM 10-30UM LENGTH SUBDOMINANT 5.789E+04 6.051E-03 9.017E+09 2.27E-02 SCRIPPSIELLA TROCHOIDEA SUBDOMINANT 1.457E+04 5.730E-03 -7.545E+08 3.10E-06 GYMNODINIUM SP.#2 21-40UM W 21-50UM L SUBDOMINANT 1.674E+04 7.197E-04 -2.700E+09 2.24E-05 HETEROCAPSA TRIQUETRA SUBDOMINANT 3.434E+04 9.050E-03 -1.022E+08 6.62E-03 UNID. CENTRIC DIATOM DIAM 31-60 MICRONS SUBDOMINANT 3.728E+04 1.866E-05 1.135E+09 1.34E-01 MONORAPHIDIUM SP. SUBDOMINANT 3.405E+04 7.074E-03 -6.629E+07 9.21E-02 AMPHIDINIUM SPHENOIDES SUBDOMINANT 4.538E+04 1.269E-02 -7.423E+07 1.46E-02 UNID. PENNATE DIATOM 31-60UM LENGTH SUBDOMINANT 2.035E+04 2.465E-02 2.344E+07 5.21E-02 Results of Statistical Tests by Taxa • 21 out of a total of 120 taxa exhibited significantly different mean densities between the two techniques • The old technique produces significantly higher estimates for 17 of the 21 taxa. • The taxa (6) with the highest mean differences between the two techniques were either filamentous or chain-forming cell types.

  7. CONCLUSIONS • The two techniques produce different means and variances at the phylum and taxon level of classification. • 4 of the 6 phyla and 21 taxa have been identified as having significantly different means. • The old technique generally produces higher means for taxa and phyla. • In order to compare historical MD phytoplankton data (old technique) with more recent and current data (new technique), conversion factors will have to be applied to individual taxa that are characterized by statistically significant differences in means between the two techniques.

  8. FURTHER WORK • Non-parametric statistical analyses should be run on these data. • There are many taxa which still need to be analyzed for mean comparisons between the two techniques. • A list of ‘relevant’ taxa could be generated by merging Jackie’s Top 100 lists. • Potential conversion factors for these taxa could be accomplished by using archived samples that have relatively high densities of the ‘relevant’ taxa. • Recommend evaluating effects of conversion factors and other MD/VA method changes on phytoplankton reference communities and PIBI thresholds.

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