Comparison of phytoplankton distribution, biomass, photo-physiology and
estimated productivity among five marine ecosystems around Mauritius.
Poster
Paper Presenter: Dheeraj Dodhybul, University of Mauritius
Author: ranjeet bhagooli, university of mauritius
Abstract
Aquatic (marine/freshwater) microorganisms play a pivotal role as primary producers,
thus acting as the basis for population dynamics in ecosystems worldwide. The Mauritian
waters extend over some 1.9 million km2 inhabiting highly diverse ecosystems that
support our economic industries such as commercial fisheries, and both local and tourist
recreational activities. In addition, some of these micro-producers generally known as
phytoplankton (‘phyto” = plant like; “plankton’ = microscopic drifting organisms) have
some potential applications in identifying polluted areas, forensic investigations and
biofuel production while others can lead to seafood poisoning and even blooms that in
turn can cause massive fish kills, which are increasing in frequency and intensity
worldwide due to global climate change. However, very little is known about the local
micro-producers. In February 2008, the distribution, biomass and photosynthetic
activities of phytoplankton in water column and sediments were determined from five
different sites representing a range of marine ecosystems namely coral reef area, Blue
Bay; sandy beach area, Blue Bay; mangrove area, Point D’Esny; seagrass bed area,
Mahebourg and estuarine area, Le Goulet. Physical parameters at the time of sampling
were recorded at each site. Samples (3-5 per site) for cell count and chlorophyll a
analysis from water column were collected by concentrating 50 lt of seawater through
plankton net of mesh size of 5 µm and samples from sediments were collected using a
corer and filtering the sediments suspended in FSW (0.47µm) in the laboratory. Cell
counts were carried out using Sedgwich Rafter cells. Chlorophyll a content of
phytoplankton was carried by spectrometric method and photo-physiological responses to
varying environmental light intensities were determined by using Teaching-PulseAmplitude-Modulated (Teaching-PAM) fluorometer (Walz). The highest temperature of
34oC was recorded in the mangrove area and the lowest salinity of 24o/oo was recorded in
the water column of the estuary area (Fig. 1). The results for total cell counts showed that
the Estuary area of Le Goulet had the highest total density of phytoplankton, and the
Seagrass bed area at Mahebourg had lowest total density of cells (Fig. 2). The distribution
and abundance of phytoplankton in categories of diatoms, dinoflagellates and trichomes
were variable but diatoms and cyanobacterial trichomes peaked in the estuarine area (Fig.
3). The highest chlorophyll a content was found in the Estuary area of Le Goulet while
the lowest value was in the Coral reef area of Blue Bay (Fig. 4). The chlorophyll
fluorescence ratio (Fv/Fm) indicating the maximum potential quantum yield of
photosystem II (PSII) did not differ among samples collected from the five sites for both
the water column and sediment ones (Fig. 5). The highest mean relative electron transport
rate (rETRmax) was found in the Coral reef area of Blue Bay while the lowest value was at
Mangrove area of Pointe D’Esny (Figs. 6&7). The non-photochemical quenching (NPQ),
indicative of heat dissipation at PSII, showed that phytoplankton from the sediment
samples from the mangrove, seagrass bed and estuary areas were less capable of
dissipating absorbed light energy as heat (Fig. 8). Productivity estimates (Fig. 9), using
fluorescence parameters (Fig. 6) and chlorophyll data (Fig. 4), were high in the Estuary
area of Le Goulet since it had the highest chlorophyll a content even though its rETRmax
was average. These results taken together provided new insights into the comparison of
phytoplankton distribution, biomass, photo-physiology and estimated productivity among
Physical parameters
five marine ecosystems around Mauritius.
80
70
60
pH
50
Temperarture (°C)
40
Dissolved Oxygen
30
conductivity
20
Salinity
10
Seagrass Mangrove
bed Area
Area
Sediment
Water
Column
Coral
Reefs
Water
Column
Water
Column
Sandy
Area
Water
Column
Water
Column
0
Estuary Area
Marine ecosystems
cell counts (x103 L-1)
Fig. 1. Physical parameters (pH, temperature, dissolved oxygen, conductivity
and salinity) recorded at the five marine ecosystems studied.
16
14
12
10
8
6
Cell counts (x103 L-1)
12
10
8
Diatoms
Dinoflagellates
6
Trichomes
4
2
0
Coral Reef
Area
Sandy Beach
Area
Mangrove
Area
Seagrass Bed Estuary Area
area
Marine ecosystems
l chlorophyll (mg m-3)
Fig. 3. Cell counts, divided into three major categories of identified
phytoplankton, in the water column from the five studied marine ecosystems.
Data represent mean±SD (n=5).
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.6
0.5
Fv/Fm
0.4
0.3
0.2
0.1
Coral Reef
Area
Sandy Beach
Area
Mangrove
Area
Sed
Water
column
Sed
Water
column
Sed
Water
column
Sed
Water
column
Sed
Water
column
0
Seagrass Bed Estuary Area
Area
Marine ecosystems
Fig. 5. Chlorophyll fluorescence ratio (Fv/Fm) of phytoplankton samples from
the water column and sediments from the five studied marine ecosystems. Data
represent mean±SD (n=3-5).
ative maximum
on transport rate
(rETRm)
140
120
100
80
60
40
20
mated productivity
TRm*Chl mg m-2)
30
25
20
15
10
5