RELATIONSHIP BETWEEN THE HYDRODYNAMICS AND THE COMMUNITY STRUCTURE
OF ZOOPLANKTON IN THE ALGERIAN COASTS
Hafferssas Aziz * and Seridji Rabea
Laboratoire d’Ecosystème Pélagique, Faculté des Sciences Biologiques, USTHB., B.P.64 El Alia, Bab Ezzouar, Alger, Algérie
Abstract
The spatial variation in zooplankton biomass, abundance and species composition in relation to hydrography and chlorophyll a(Chl a)
was studied in the upper 200 m of the water column. Both the biomass and the abundance of zooplankton were low in the two oligotrophic
systems and increased sharply toward the frontal zone. A total of 82 copepod species were identified, and three groups distributed along
well defined environmental gradients characterising the distribution of physical variables and Chl awere revealed.
Key words: Algerian coasts, copepods, biomass
Rapp. Comm. int. Mer Médit., 37,2004
370
Method and Materials
The total number of stations with physical, chemical and biological
measurements was 17 (1). At each station, vertical profiles of
temperature, salinity and Chl awere obtained using a Rosette sampler
SEABIRD, equipped with ?uometer. Various depth strata were then
sampled at 10 m intervals from the surface to the bottom. Zooplankton
samples were collected using a WP2 closing net Zooplankton is
sampled by vertical net hauls from 200 m to the surface. The dataset
was composed of three matrices representing the environmental data
collected at the 17 stations, the total abundance for the most 23 most
important copepods species at the various depth strata and the
biomass of the all zooplankton communities.
Results and Discussion
Temperature and salinity proprieties
The upper 150 m of the water column was characterised by a
in?uence of Modified Atlantic Water (MAW), as evidenced by the low
salinities (from 36.5 to 37.5).The vertical structure of the water
column demonstrated a strong halocline in the 20-60 m depth range
with a narrow thermocline at the bottom of this feature. From 150 to
300 m depth range the salinities values varied widely (37.5 – 38.30)
and the temperatures were around 14.25 °C (at 150 m), rising to 13.07
- 13.23 °C. (at 300 m). This lowest temperature is identified as the
relative minimum of potential temperature (
?
min
) mainly
characterised the Winter Intermediate Water (WIW). Above the WIW,
at 350-500 m depth range we found the Levantine Intermediate Water
(LIW). Our findings have also been reported by (3).
Chl aconcentrations
Surface Chl aconcentrations were generally low (<1 mg m
-3
). A
chlorophyll amaximum layer (> 0.30 mg Chl am
-3
) was observed
over the entire stations. The depth of DCM was rather stable around
40–99 m. At the Inshore MAW and Offshore SMW stations, depth-
integrated chlorophyll aranged between 11 and 50 mg m
-2
.
Chlorophyll aexceeded this range at stations located at the frontal
area. Here the values ranged from 65.49 (station 111) to 175.03 mg m
-2
(station 54). Same results were found in the Alboran sea (sites
1and5) (4)
Copepod species composition and abundance
A total of 81 taxa was recorded in the Algerian coast (1). In the
upper 200 m depth range total copepod abundance varied
considerably, ranging from 18.12 to 1330.66 ind. m
-3
(0–200 m).
Highest abundances were associated with the frontal zone and the
lowest with stations to the south and north of the front in oligotrophic
waters. Zooplankton abundance are much higher in the offshore rich
band corresponding to a frontal system. This has already been
observed by many authors (5, 6). PCA of log transformed abundance
data revealed three main groupings of populations along the Algerian
coasts. The first group included five species with abundance maxima
in the frontal region. The second group, included species with
numerical abundance maxima was recorded at the inshore MAW
stations. The third group included 13 species. This group had a broad
distribution; the species were recorded in upper 200 m layer of the
frontal, coastal and offshore waters
Zooplankton biomass and composition
Previous study in the Algerian coasts have described general
aspects of vertical and horizontal distribution of the zooplankton
biomass. As mentioned, the mean values recorded in the frontal
stations (21.89
±
1.32 mg.m
-3
) were 7 times higher than those
recorded in the MAW Inshore (3.41
±
0.70 mg.m
-3
) and SMW
offshore stations (3.35
±
0.55 mg.m
-3
). Elevation of zooplankton
standing stock in the upper water column (0-200 m), particularly in
the frontal system (52.56
±
2.95 mg.m
-3
), has been attributed to an
increase in the biomass of the smallest size fraction (100-300
µ
m)
(49.01
±
3.11 mg.m
-3
).
Relationships between parameters
The results of PCA showed that two components explained
42.75% of total variance. The first component, which explained
25.39% of the variance, was significantly correlated to the
temperatures values in and below the thermocline, surface salinity,
halocline, integrated Chl aconcentrations in the top 100 m and the
Chl amaximum values at the subsurface. In addition, the total
biomass and the biomass of small size fraction were inversely
correlated to the first axis. The second component, which explained
19.16 % of the variance, was significantly correlated to surface Chl a
concentrations and the biomass recorded in the 300-500
µ
m size
fraction. The projections of all variables in a bidimensional plane
defined by the first two components mirrored the link between the
species of the first group (maximum abundance of species
predominately herbivores), Chl amaximum values at subsurface, total
zooplankton biomass and the standing stocks in the smallest size
fraction (100-300
µ
m). The relationships between phytoplankton and
zooplankton biomass have been suggested earlier (7).
The significance of the second group of species (dominant coastal
copepods) is essentially linked to the Chl aconcentrations in the 0-
10m depth range. The coastal cluster was also associated with the
300-500
µ
m biomass size fraction.
The third group of species was associated with temperatures values
in and below the thermocline and with the salinities values recorded
at uppermost layer (0-10 m) and in the halocline. On the other hand,
species were significantly correlated to the standing stocks of the
largest zooplankters (> 500
µ
m).
Literatures cited
1-Seridji R. and Hafferssas A., 2000. Copepod diversity and community
structure in the Algerian basin. Crustaceana, 73 (1): 123.
2-Motoda M., 1953. New plankton samples. Bulletin of Faculty of
Fisheries, Hokkaido University, 5 (2): 149151.
3-Perkins H. and P. Pistek. 1990. Circulation in the Algerian basin during
June 1986. Journal of Geophysical Research, 95: 15771585.
4-Videau C., A. Sournia, L. Prieur and M. Fiala. 1994. Phytoplankton
and primary production characteristics at selected sites in the geostrophic
Almeria-Oran front system (SW Mediterranean Sea). Journal of Marine
System, 5:235-250.
5-Pingree R.D., Foster G.R. and P.G.K. Morrison. 1974. Turbulent
convergent tidal fronts. Journal of Marine Biological Association U. K.,
54: 469479.
6-Yamamoto T. and S. Nishizuwa. 1986. Small-Scale zooplankton
aggregations at the front of a Kuroshio warin core ring. Deep Sea
Research, 33: 17291740.
7-Paffenhôffer G.A., Atkinson L.P., Lee T.N., Verity P.G. and L.R.
Bulluck. 1995. Distribution and abundance of thaliaceans and copepods
off the southeastem U.S.A. during winter. Continental Shelf Research, 25
(2/3): 255280
