Soft-Bottom Fauna of a Tropical and a Temperate Intertidal Area
269
et al. 1982; Wolff et al. 1993a) would increase the species number of the Banc
d' Arguin considerably and the complete spectrum is probably still far from
being assessed. A high species richness appears to be a general characteristic
of tropical tidal flat areas, as confirmed by studies from Vargas (1987,1988),
Reise (1991), Dittmann (1995) and Baron et al. (1993). On the other hand, the
modest richness of the Juist area is a general characteristic of the Wadden Sea
confirmed in numerous surveys with many thousands of sampling stations
(see Michaelis 1987; Essink et al. 1998; Beukema 1989; Reise 1991 and literature cited therein). Next to differences between tropical and temperate areas
in general, an important additional explanation could be salinity conditions.
Along the coast of the southern North Sea these are rather variable and
considerably low compared with the open sea. Stenohaline marine species
could be either completely excluded from the coastal waters or displaced into
the sublittoral waters with higher salinities.
Because of differences in body size, the usefulness of the parameter total
abundance of individuals is limited without additional information on biomass. Total abundance in tropical and subtropical localities appears to
depend considerably on habitat type, season, and other conditions (Alongi
1990). Examples of highly different figures are available which may, however,
be only cautiously compared because of different methods of sampling and
calculation of mean values. Total abundances of < 1000 individuals m- 2 were
found in intertidal seagrass stands of New Caledonia (Baron et al. 1993),
numbers of 1000-2000 individuals m- 2 in sandy and muddy flats of the
Andaman Sea (Reise 1991) and in estuarine flats of the NE Australian coast
(Dittmann 1995); high numbers from 10,000-20,000 individuals m- 2 are
reported from Costa Rica (Vargas 1987, 1988), and a very high total abundance of 45,000 individuals m- 2 (annual average) is given by Puttick (1977) for
a locality in Langebaan Lagoon, South Africa. Against this background, the
total abundance figures for the Banc d' Arguin may be considered as rather
modest. The survey of February-April 1986 (Wolff et al. 1993a; Wijnsma et al.
1999) yielded a mean total abundance of about 1400 individuals m- 2 ; in
September 1988 (present study) the average of all stations (sebkha excluded)
amounted to roughly 2000 individuals m- 2 (Table 12.2). In the temperate Juist
area (where samples were sieved with 1 mm mesh size!), the mean total abundance varies from 1000 (light sandy flats) to 18,000 individuals m- 2 (microbial
mats). The means of both the largest habitat (dark sandy flats) and of all habitats (excluding high sands) lie close to each other around 4000 individuals m- 2
(Table 12.3). From these figures no major difference between the total abundances at low and high geographical latitudes can be derived, a fact also confirmed by the "comprehensive, but not exhaustive" compilations of Alongi
(1990).
In the previous studies the interest was focused on the biomass of the
intertidal macrozoobenthos of the Banc d' Arguin, and its role as a food
269
et al. 1982; Wolff et al. 1993a) would increase the species number of the Banc
d' Arguin considerably and the complete spectrum is probably still far from
being assessed. A high species richness appears to be a general characteristic
of tropical tidal flat areas, as confirmed by studies from Vargas (1987,1988),
Reise (1991), Dittmann (1995) and Baron et al. (1993). On the other hand, the
modest richness of the Juist area is a general characteristic of the Wadden Sea
confirmed in numerous surveys with many thousands of sampling stations
(see Michaelis 1987; Essink et al. 1998; Beukema 1989; Reise 1991 and literature cited therein). Next to differences between tropical and temperate areas
in general, an important additional explanation could be salinity conditions.
Along the coast of the southern North Sea these are rather variable and
considerably low compared with the open sea. Stenohaline marine species
could be either completely excluded from the coastal waters or displaced into
the sublittoral waters with higher salinities.
Because of differences in body size, the usefulness of the parameter total
abundance of individuals is limited without additional information on biomass. Total abundance in tropical and subtropical localities appears to
depend considerably on habitat type, season, and other conditions (Alongi
1990). Examples of highly different figures are available which may, however,
be only cautiously compared because of different methods of sampling and
calculation of mean values. Total abundances of < 1000 individuals m- 2 were
found in intertidal seagrass stands of New Caledonia (Baron et al. 1993),
numbers of 1000-2000 individuals m- 2 in sandy and muddy flats of the
Andaman Sea (Reise 1991) and in estuarine flats of the NE Australian coast
(Dittmann 1995); high numbers from 10,000-20,000 individuals m- 2 are
reported from Costa Rica (Vargas 1987, 1988), and a very high total abundance of 45,000 individuals m- 2 (annual average) is given by Puttick (1977) for
a locality in Langebaan Lagoon, South Africa. Against this background, the
total abundance figures for the Banc d' Arguin may be considered as rather
modest. The survey of February-April 1986 (Wolff et al. 1993a; Wijnsma et al.
1999) yielded a mean total abundance of about 1400 individuals m- 2 ; in
September 1988 (present study) the average of all stations (sebkha excluded)
amounted to roughly 2000 individuals m- 2 (Table 12.2). In the temperate Juist
area (where samples were sieved with 1 mm mesh size!), the mean total abundance varies from 1000 (light sandy flats) to 18,000 individuals m- 2 (microbial
mats). The means of both the largest habitat (dark sandy flats) and of all habitats (excluding high sands) lie close to each other around 4000 individuals m- 2
(Table 12.3). From these figures no major difference between the total abundances at low and high geographical latitudes can be derived, a fact also confirmed by the "comprehensive, but not exhaustive" compilations of Alongi
(1990).
In the previous studies the interest was focused on the biomass of the
intertidal macrozoobenthos of the Banc d' Arguin, and its role as a food