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biogeochemical cycles, etc. in an unperturbed environment. Phytoplankton in the area is dominated by diatoms, but red tide species are occasionally present Martinez-Lopez and
Garate-Lizarraga, 1994. For summer, Lechuga-Deveze 1994 reported bottom pigment
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concentrations of chlorophyll a Chl a between 7.1 and 45.5 mg l and chlorophyll b
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Chl b values between 10.4 and 99.1 mg l in more than a half of the area bay. These
values are high when compared with normal stations where Chl a and Chl b
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concentration maximum values, in general, are lower than 2 mg l . Although there are
several reports on the phytoplankton composition and abundance Kiefer and Laker, 1975; Gilmartin and Revelante, 1978; Martinez-Lopez and Garate-Lizarraga, 1994;
Lopez-Cortez, 1999; Lechuga-Deveze and Morquecho-Escamilla, 1999; Lechuga-De- veze et al., 2000, these high pigment concentrations are enigmatic because no one has
reported species or groups of species that can be related to such an increase of biomass. Recently, Lechuga-Deveze 1994 analyzed the spectra of acetone extracts and sug-
gested a population of prochlorophytes may be responsible for the high biomass. His reason is that highly pigmented samples have red-shift spectra when compared with
normally pigmented ones, similar to that existing between the Chl a and divinyl chlorophyll a DvChl a. Because of the difficulties of identifying and quantifying this
picoplanktonic group with traditional methods of microscopy, this hypothesis has not been tested.
We have used high-performance liquid chromatography HPLC to analyze the phytoplankton pigment and look for markers of phytoplankton groups in these samples.
Specifically, we tested for the existence of DvChl a, a marker of prochlorophytes Goericke and Repeta, 1993, or other phytoplankton group fingerprints that may be
responsible for this increase of biomass.
2. Material and methods
In August 1997, we sampled at several stations throughout the bay see Lechuga- Deveze, 1994 to detect the ‘anomalous’ highly pigmented area. Once the area was
located, one station was selected Fig. 1 as representative of the ‘anomalous’ area and a detailed profile at 0, 2, 4, 6, 8, 10, 12, 13, 15, 17, 19, 21, 22, 25, 26 and 27-m depth
was obtained for pigment, temperature, nitrates, oxygen and H S analysis. Additionally,
2
irradiance 400–700 nm striking an underwater quantum sensor LI-COR was measured using an integrating radiometer photometer LI-COR LI-188B. For pigments,
seawater 1 l was collected with Van Dorn bottles and transported on ice and in the dark to the laboratory where the water was filtered through GF F glass fiber filters and
immediately frozen at 2 208C. For pigment extraction, filters were put in 2 ml of acetone, grinding in glass tubes and then centrifuged. The extract 200 ml was mixed
with 100 ml of 0.5 N ammonium acetate and injected through a 100-ml loop into an HPLC system Hewlett Packard series 1100 with a diode-array detector. HPLC
conditions were as in Vidussi et al. 1996 and permit the separation of DvChl a. Briefly, a hypersil MOS 10-cm long by 4.6-mm I.D. C8 column was used with the following
solvent A MeOH: 0.5 N aqueous ammonium acetate, 70:30 v v and solvent B MeOH gradient min; percentage of solvent A, percentage of solvent B: 0; 75, 25,
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. Bustillos-Guzman et al. J. Exp. Mar. Biol. Ecol. 249 2000 77 –88 79
Fig. 1. Vertical variation of physical and chemical variables in Bahia Concepcion, Gulf of California: A temperature; B irradiance I as a percentage of incident irradiance I , and dissolved oxygen O ; C
2
nitrate and H S.
2
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J . Bustillos-Guzman et al. J. Exp. Mar. Biol. Ecol. 249 2000 77 –88
1; 50, 50, 15; 0, 100, 18.5; 0, 100 and 19; 75, 25. Pigments were detected with the diode-array absorbance signal set at 440 nm. Identification was made by comparing
retention time and spectral characteristics with those of commercial pigment standards
14
International Agency for C determinations, Denmark and a rich prochlorophyte
sample collected at the deep chlorophyll maximum from the Mexican Pacific Ocean 19852.2 N, 113811.99W during the USA METOX01 cruise for the DvChl a.
Quantification was done with the pigment response factor HPLC peak area pigment mass obtained with the commercial pigment standards according to Mantoura and
Repeta 1997. Nitrate and dissolved oxygen were measured according to Strickland and Parson 1972, sulfide by the iodometric method Clesceri et al., 1989, and temperature
and salinity with a Kahlsico salinometer model 140.
3. Results
