CHAPTER 22
Ultra plankton of the Gulf of Naples by Flow Cytometry
R. Casotti!, C. Brunet2, and A. Graziano l
ABSTRACT
Ultraplankton composition and distribution were investigated as a function of physical structures
and water masses of the Gulf of Naples in November 1995. Cyanobacteria were distributed all
over the Gulf, but mostly in the surface mixed layer. Prochlorophytes were more abundant offshore and at depth. Small eukaryotes were typical of the surface of coastal stations.
Prochlorophytes vertical distribution showed a peculiar profile, with two populations at depth.
where the Modified Atlantic Water (MAW) was present. A periodic sampling of a fixed station in
the Gulf of Naples started in June 1998 in order further to investigate environmental parameters
ruling this vertical distribution. Preliminary data interpretation is discussed. During the November
cruise, bacterial abundances were correlated to chlorophyll a concentrations, and, despite the
strong oligotrophy of the areal bacterial carbon never exceeded phytoplankton carbon.
Introduction
Phytoplankton represents the first step in the
trophic marine structure and it is the main producer of organic matter in the oceans, even in
coastal areas, where micro and macro benthonic
algae dominate (Charpy-Roubaud and Sournia
1990). Phytoplankton is generally studied using
chlorophyll a as biomass indicator. Values are
obtained by filtering variable amounts of seawater, in order to obtain significative measurements
even in oligotrophic regions. Although, such values represent a global phytoplankton community,
without considering the algal composition. the
trophic and physiological state of the algae, which
are the parameters driving primary production.
Therefore, valuable information is lost. Recently,
discriminant analyses have received increasing
attention, and among these. flow cytometry. Flow
cytometry allows a fast and precise analysis of
particles based on their scattering and fluorescence properties at a rate of thousands of cells per
second (Shapiro 1988). Commercially available
instruments, though, are limited by the maximum
sample volume (fraction of a ml),and by the maximum size of the particles to be analysed (50
1 Stazione Zoologica "A. Dohrn", Villa Comunale, Napoli, Italy
mm). For these reasons, flow cytometry of natural samples has been applied mainly to the study
of small-sized. very abundant plankton cells, the
ultraplankton sensu Li (1997), which includes
both heterotrophic bacteria and algae (ultraphytoplankton). Ultraphytoplankton (including picophytoplankton, < 2 J.LlD.) is composed of photoautotrophic organisms smaller than 5 J.LlD. ESD
(Equivalent Spherical Diameter) (Shapiro and
Guillard 1986), and includes prokaryotic and
eukaryotic cells. The prokaryotic component is
dominated by unicellular Cyanobacteria (around
1 Ilm ESD, Waterbury et al. 1986) and
Prochlorophytes (around 0.7 J.LlD. ESD, Chisholm
et al.198B). The eukaryotic component is mainly
represented by small flagellates (2-5 Ilm ESD,
Olson et al. 1989; Longhurst and Pauly 1987).
Algae of this size range are very abundant in the
oceans and can generate up to 80% of primary
production in oligotrophic areas (Li et al. 1983).
They represent, together with bacteria, a very
important component of microbial food webs,
and their discovery unveiled a whole new word
on the complex interactions between organisms
of different size (Pomeroy 1974). Small
autotrophs can use regenerated forms of nitrogen
2 Universit~ du Littoral.. Laboratoire Interdisciplinaire des Sciences de l'Environnement (LISE), Wimereull., France
F.M. Faranda, L Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springer-VerJag Italla 2001
Ultra plankton of the Gulf of Naples by Flow Cytometry
R. Casotti!, C. Brunet2, and A. Graziano l
ABSTRACT
Ultraplankton composition and distribution were investigated as a function of physical structures
and water masses of the Gulf of Naples in November 1995. Cyanobacteria were distributed all
over the Gulf, but mostly in the surface mixed layer. Prochlorophytes were more abundant offshore and at depth. Small eukaryotes were typical of the surface of coastal stations.
Prochlorophytes vertical distribution showed a peculiar profile, with two populations at depth.
where the Modified Atlantic Water (MAW) was present. A periodic sampling of a fixed station in
the Gulf of Naples started in June 1998 in order further to investigate environmental parameters
ruling this vertical distribution. Preliminary data interpretation is discussed. During the November
cruise, bacterial abundances were correlated to chlorophyll a concentrations, and, despite the
strong oligotrophy of the areal bacterial carbon never exceeded phytoplankton carbon.
Introduction
Phytoplankton represents the first step in the
trophic marine structure and it is the main producer of organic matter in the oceans, even in
coastal areas, where micro and macro benthonic
algae dominate (Charpy-Roubaud and Sournia
1990). Phytoplankton is generally studied using
chlorophyll a as biomass indicator. Values are
obtained by filtering variable amounts of seawater, in order to obtain significative measurements
even in oligotrophic regions. Although, such values represent a global phytoplankton community,
without considering the algal composition. the
trophic and physiological state of the algae, which
are the parameters driving primary production.
Therefore, valuable information is lost. Recently,
discriminant analyses have received increasing
attention, and among these. flow cytometry. Flow
cytometry allows a fast and precise analysis of
particles based on their scattering and fluorescence properties at a rate of thousands of cells per
second (Shapiro 1988). Commercially available
instruments, though, are limited by the maximum
sample volume (fraction of a ml),and by the maximum size of the particles to be analysed (50
1 Stazione Zoologica "A. Dohrn", Villa Comunale, Napoli, Italy
mm). For these reasons, flow cytometry of natural samples has been applied mainly to the study
of small-sized. very abundant plankton cells, the
ultraplankton sensu Li (1997), which includes
both heterotrophic bacteria and algae (ultraphytoplankton). Ultraphytoplankton (including picophytoplankton, < 2 J.LlD.) is composed of photoautotrophic organisms smaller than 5 J.LlD. ESD
(Equivalent Spherical Diameter) (Shapiro and
Guillard 1986), and includes prokaryotic and
eukaryotic cells. The prokaryotic component is
dominated by unicellular Cyanobacteria (around
1 Ilm ESD, Waterbury et al. 1986) and
Prochlorophytes (around 0.7 J.LlD. ESD, Chisholm
et al.198B). The eukaryotic component is mainly
represented by small flagellates (2-5 Ilm ESD,
Olson et al. 1989; Longhurst and Pauly 1987).
Algae of this size range are very abundant in the
oceans and can generate up to 80% of primary
production in oligotrophic areas (Li et al. 1983).
They represent, together with bacteria, a very
important component of microbial food webs,
and their discovery unveiled a whole new word
on the complex interactions between organisms
of different size (Pomeroy 1974). Small
autotrophs can use regenerated forms of nitrogen
2 Universit~ du Littoral.. Laboratoire Interdisciplinaire des Sciences de l'Environnement (LISE), Wimereull., France
F.M. Faranda, L Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springer-VerJag Italla 2001