286
s. Dittmann and J.A. Vargas
mudflat at Punta Morales (Vargas 1987; Dittmann 1995,2000). Snails, grazing
on the microphytobenthos at the sediment surface, dominated in the tidal
flats in the Hinchinbrook Channel (Fig. 13.5). Suspension-feeders were scarce
at most studied sites. However, suspension-feeding bivalves and brachiopods
were abundant in the Hinchinbrook Channel (Fig. 13.5) and Cocorocas, and
bivalves accounted for most of the biomass in tropical tidal flats on the west
coast of Australia (Wells 1983; Pepping et al. 1999).
The dominance of deposit-feeders appears to be a general characteristic of
tropical tidal flats in Australia and Central America. Deposit-feeders also
dominated in tidal flats of the Banc d' Arguin in west Africa (Wolff et al.
1993b) and in temperate tidal flats (Sanders et al.1962; Whitlatch 1977); therefore, no latitudinal variation could be detected for the composition of trophic
types (Dittmann 2000). The abundance of deposit-feeders in the tropical tidal
flats of Australia and Central America is probably sustained by detritus
derived from mangrove litter and the microphytobenthic layer.
13.4.3 Species Interactions
To assess whether related or unrelated species take similar ecological roles
within tropical tidal flats, we followed the conceptual hierarchy on ecological
processes of Reise (1985) and looked at the respective species in the tropical
tidal flats of Australia and Central America (Table 13.4). This table shows that
on either side of the Pacific many related species (genus or family level) occur
with similar ecological roles, while not many unrelated species with similar
roles were listed. Tropical tidal flats provide similar niches and, following a
diversification on either side of the Pacific, macrobenthic species take comparable ecological roles. In a few cases, no counterpart for a specific role has
been found, indicating some singularities of ecological functions in specific
areas. The structural and functional similarity seen between tropical tidal
flats is therefore to a large extent a result of related species occupying similar
niches and only to a smaller degree due to unrelated species taking analogous
ecological roles (Vargas 1987; Reise 1991).
13.4.3.1 Promotive Interactions
A prominent example of promotive interactions in tidal flats is the provision
of microhabitats in the burrows of larger macrofauna (Reise 1985). An
example for this type of accommodation on associated infauna was reported
by Dittmann (1996) for burrows of callianassid shrimps in tidal flats of
northeast Australia. These shrimps are abundant in the muddy sandflat of the
mid-intertidal and their promotive effect is a major process structuring the
s. Dittmann and J.A. Vargas
mudflat at Punta Morales (Vargas 1987; Dittmann 1995,2000). Snails, grazing
on the microphytobenthos at the sediment surface, dominated in the tidal
flats in the Hinchinbrook Channel (Fig. 13.5). Suspension-feeders were scarce
at most studied sites. However, suspension-feeding bivalves and brachiopods
were abundant in the Hinchinbrook Channel (Fig. 13.5) and Cocorocas, and
bivalves accounted for most of the biomass in tropical tidal flats on the west
coast of Australia (Wells 1983; Pepping et al. 1999).
The dominance of deposit-feeders appears to be a general characteristic of
tropical tidal flats in Australia and Central America. Deposit-feeders also
dominated in tidal flats of the Banc d' Arguin in west Africa (Wolff et al.
1993b) and in temperate tidal flats (Sanders et al.1962; Whitlatch 1977); therefore, no latitudinal variation could be detected for the composition of trophic
types (Dittmann 2000). The abundance of deposit-feeders in the tropical tidal
flats of Australia and Central America is probably sustained by detritus
derived from mangrove litter and the microphytobenthic layer.
13.4.3 Species Interactions
To assess whether related or unrelated species take similar ecological roles
within tropical tidal flats, we followed the conceptual hierarchy on ecological
processes of Reise (1985) and looked at the respective species in the tropical
tidal flats of Australia and Central America (Table 13.4). This table shows that
on either side of the Pacific many related species (genus or family level) occur
with similar ecological roles, while not many unrelated species with similar
roles were listed. Tropical tidal flats provide similar niches and, following a
diversification on either side of the Pacific, macrobenthic species take comparable ecological roles. In a few cases, no counterpart for a specific role has
been found, indicating some singularities of ecological functions in specific
areas. The structural and functional similarity seen between tropical tidal
flats is therefore to a large extent a result of related species occupying similar
niches and only to a smaller degree due to unrelated species taking analogous
ecological roles (Vargas 1987; Reise 1991).
13.4.3.1 Promotive Interactions
A prominent example of promotive interactions in tidal flats is the provision
of microhabitats in the burrows of larger macrofauna (Reise 1985). An
example for this type of accommodation on associated infauna was reported
by Dittmann (1996) for burrows of callianassid shrimps in tidal flats of
northeast Australia. These shrimps are abundant in the muddy sandflat of the
mid-intertidal and their promotive effect is a major process structuring the