55
in the upper photic layer of the ocean where they can actively photosynthesize.
Phytoplankton constitutes the primary source of food for higher level marine organisms so phytoplankton biomass, community composition, and productivity rates
constitute vital information for informed fishery management. Some phytoplankton
which produce highly toxic metabolites cause the harmful algal bloom (HABs)
known as red tides. These constitute a direct public health menace through respiration of aerosols and an indirect menace through consumption of contaminated shellfish. Shellfish fisheries are routinely closed under HAB threats. Animals may also
be endangered. Recently for example die offs of sea lions along the west coast of the
USA have been attributed to HAB poisoning. Public health officials consequently
require continued up-to-date information on the presence and abundance of such
organism in the plankton.
Since the principal photosynthetic pigment of plants, chlorophyll a (Chl a),
interacts strongly with visible light, it can be measured in the field using optical
techniques. Given this property and despite the variable content of Chl a relative to
other more suitable chemical proxies such as carbon, its concentration in the water
column is often used as a chemical proxy for estimating plant biomass expressed as
Chl a mass per unit volume (μg.l
−1
or its equivalent mg.m
−3
). In addition to Chl a,
commonly the principal component, the plant photosynthetic apparatus comprises
numerous accessory pigments including various other chlorophylls (b, c, c1, c2, c3)
plus xanthophylls and carotenes. These compounds are sparingly soluble in water if
at all and in nature are found packaged in hydrophobic environments within the
chloroplast or cell structure. Photosynthetic bacterioplankton (known colloquially
as blue-green algae) additionally contain the water-soluble photosynthetic protein
pigments phycocyanin and phycoerythrin containing phycobillin chromophores.
2.5.1 In Vitro/In Vivo Chlorophyll Fluorometry
Chlorophyll a concentration has been traditionally determined spectroscopically
following seawater filtration, sample grinding in acetone or other organic solvents
and extract clarification through centrifugation or filtration. During this procedure,
pigments are removed from their cell/chloroplast packaging and dissolved in an
organic matrix. Chlorophylls a, b, and c, having similar chemical structure, have
similar but clearly discernible absorption spectra with peaks in the blue and red
spectral bands and a prominent valley in the green, hence the green color of most
plants. Thus, judiciously chosen diagnostic measurements at the absorption peaks
of each of these pigments allowed the development of trichromatic equations that
served to solve for the three chlorophylls (and thus Chl a) from spectrophotometric
measurements of bulk pigment extracts (Strickland and Parsons 1972). Conversely
to the chlorophylls, xanthophylls and carotenes, accessory pigments which contribute to the bulk light absorption of the clarified extract, absorb in the green and blue
spectral bands and appear yellow, orange, or red to the eye. Pigment extracts can
further be separated individually in the laboratory by high performance liquid chromatography, optically scanned and individually identified from their unique optical
2.5 Sensors for Biological Compounds and Processes: Chlorophyll, Accessory…
in the upper photic layer of the ocean where they can actively photosynthesize.
Phytoplankton constitutes the primary source of food for higher level marine organisms so phytoplankton biomass, community composition, and productivity rates
constitute vital information for informed fishery management. Some phytoplankton
which produce highly toxic metabolites cause the harmful algal bloom (HABs)
known as red tides. These constitute a direct public health menace through respiration of aerosols and an indirect menace through consumption of contaminated shellfish. Shellfish fisheries are routinely closed under HAB threats. Animals may also
be endangered. Recently for example die offs of sea lions along the west coast of the
USA have been attributed to HAB poisoning. Public health officials consequently
require continued up-to-date information on the presence and abundance of such
organism in the plankton.
Since the principal photosynthetic pigment of plants, chlorophyll a (Chl a),
interacts strongly with visible light, it can be measured in the field using optical
techniques. Given this property and despite the variable content of Chl a relative to
other more suitable chemical proxies such as carbon, its concentration in the water
column is often used as a chemical proxy for estimating plant biomass expressed as
Chl a mass per unit volume (μg.l
−1
or its equivalent mg.m
−3
). In addition to Chl a,
commonly the principal component, the plant photosynthetic apparatus comprises
numerous accessory pigments including various other chlorophylls (b, c, c1, c2, c3)
plus xanthophylls and carotenes. These compounds are sparingly soluble in water if
at all and in nature are found packaged in hydrophobic environments within the
chloroplast or cell structure. Photosynthetic bacterioplankton (known colloquially
as blue-green algae) additionally contain the water-soluble photosynthetic protein
pigments phycocyanin and phycoerythrin containing phycobillin chromophores.
2.5.1 In Vitro/In Vivo Chlorophyll Fluorometry
Chlorophyll a concentration has been traditionally determined spectroscopically
following seawater filtration, sample grinding in acetone or other organic solvents
and extract clarification through centrifugation or filtration. During this procedure,
pigments are removed from their cell/chloroplast packaging and dissolved in an
organic matrix. Chlorophylls a, b, and c, having similar chemical structure, have
similar but clearly discernible absorption spectra with peaks in the blue and red
spectral bands and a prominent valley in the green, hence the green color of most
plants. Thus, judiciously chosen diagnostic measurements at the absorption peaks
of each of these pigments allowed the development of trichromatic equations that
served to solve for the three chlorophylls (and thus Chl a) from spectrophotometric
measurements of bulk pigment extracts (Strickland and Parsons 1972). Conversely
to the chlorophylls, xanthophylls and carotenes, accessory pigments which contribute to the bulk light absorption of the clarified extract, absorb in the green and blue
spectral bands and appear yellow, orange, or red to the eye. Pigment extracts can
further be separated individually in the laboratory by high performance liquid chromatography, optically scanned and individually identified from their unique optical
2.5 Sensors for Biological Compounds and Processes: Chlorophyll, Accessory…