The Orinoco River Delta, Venezuela
65
harrisonii and R. racemosa have also been reported for the mid-delta (Pannier 1979; MARNR 1991; Conde and Alarcon 1993). Rhizophora forests
tend to form a 100-m-wide belt along the margins of channels, with some
individuals growing up to 20m high (dbh 25 em). Mangroves are replaced
landward by tall stands of the herbaceous Montrichardia arborescens, followed by halophobic species, like the abundant Pterocarpus officinalis, Crinum erubescens and Tabebuia aff. aquatilis, which is endemic to swamp
forests of the Orinoco and Amazonian rivers ( Colonnello and Medina
1998).
In the areas where tidal flooding is reduced, mangroves give way to mixed
marsh forests, marsh palm groves (Morichales) and herbaceous marshes
(Rabanales). Extensive stands of tall mixed marsh forests, or mixed swamp
forest (Bacon 1990), often develop directly behind fringing mangroves in
the Lower Delta. The dominant trees include Symphonia globulifera,
Pterocarpus officinal is, Bombax aquaticum and the palms Euterpe oleracea
and Manicaira saccifera. On levees, Erythrina glauca forms an open mixed
forest with some palms (Euterpe, Mauritia) and heavy undergrowth (Bacon
1990). Marsh palm groves in the lower and mid-delta are represented by
dense stands of the palm Mauritia flexuosa. Associated palms are Euterpe
spp. and Manicaria spp. as well as dense herbaceous vegetation in waterlogged areas. Herbaceous marshes are dominated by the ra.bano (Montrichardia arborescens ), which occurs together with the giant fern Acrostichum
aureum, Paspalum fasciculatum and several aquatic species. Accreting
banks of tidal creeks are often invaded by sand dune vegetation (Paspalum
repens, Montrichardia arborescens, Avicennia germinans, Rhizophora
mangle), though on older banks which resist erosion, mangrove species are
replaced by mixed marsh forests (Pannier 1979).
4.3.3 Vertebrate Fauna
Although more than 450 species of fishes have been reported for the Orinoco River (Novoa 1990), in the delta extensive surveys are still lacking.
Nevertheless, 97 species have been cited for main channels and tributaries
and for other water bodies in marsh forests and palm groves of the lower
delta. Juveniles (e. g. Piaractus brachypomum, Hoplosternum littorale, Serrasalmus spp., Hoplias malabaricus) as well as a large number of small species are generally associated with the smaller water bodies and mats of
floating vegetation (Ponte 1995). The structure of fish assemblages is likely to be a direct influence of transparency, depth and size of water bodies
(Rodriguez and Lewis 1997). Some of the commercially important fish species in the delta are Colossoma macropomum, Piaractus brachypomum,
65
harrisonii and R. racemosa have also been reported for the mid-delta (Pannier 1979; MARNR 1991; Conde and Alarcon 1993). Rhizophora forests
tend to form a 100-m-wide belt along the margins of channels, with some
individuals growing up to 20m high (dbh 25 em). Mangroves are replaced
landward by tall stands of the herbaceous Montrichardia arborescens, followed by halophobic species, like the abundant Pterocarpus officinalis, Crinum erubescens and Tabebuia aff. aquatilis, which is endemic to swamp
forests of the Orinoco and Amazonian rivers ( Colonnello and Medina
1998).
In the areas where tidal flooding is reduced, mangroves give way to mixed
marsh forests, marsh palm groves (Morichales) and herbaceous marshes
(Rabanales). Extensive stands of tall mixed marsh forests, or mixed swamp
forest (Bacon 1990), often develop directly behind fringing mangroves in
the Lower Delta. The dominant trees include Symphonia globulifera,
Pterocarpus officinal is, Bombax aquaticum and the palms Euterpe oleracea
and Manicaira saccifera. On levees, Erythrina glauca forms an open mixed
forest with some palms (Euterpe, Mauritia) and heavy undergrowth (Bacon
1990). Marsh palm groves in the lower and mid-delta are represented by
dense stands of the palm Mauritia flexuosa. Associated palms are Euterpe
spp. and Manicaria spp. as well as dense herbaceous vegetation in waterlogged areas. Herbaceous marshes are dominated by the ra.bano (Montrichardia arborescens ), which occurs together with the giant fern Acrostichum
aureum, Paspalum fasciculatum and several aquatic species. Accreting
banks of tidal creeks are often invaded by sand dune vegetation (Paspalum
repens, Montrichardia arborescens, Avicennia germinans, Rhizophora
mangle), though on older banks which resist erosion, mangrove species are
replaced by mixed marsh forests (Pannier 1979).
4.3.3 Vertebrate Fauna
Although more than 450 species of fishes have been reported for the Orinoco River (Novoa 1990), in the delta extensive surveys are still lacking.
Nevertheless, 97 species have been cited for main channels and tributaries
and for other water bodies in marsh forests and palm groves of the lower
delta. Juveniles (e. g. Piaractus brachypomum, Hoplosternum littorale, Serrasalmus spp., Hoplias malabaricus) as well as a large number of small species are generally associated with the smaller water bodies and mats of
floating vegetation (Ponte 1995). The structure of fish assemblages is likely to be a direct influence of transparency, depth and size of water bodies
(Rodriguez and Lewis 1997). Some of the commercially important fish species in the delta are Colossoma macropomum, Piaractus brachypomum,