54
G. Rodriguez
and fishes in surface waters at the mouth of the bay roughly follows tidal
cycles; thus, neritic species form a front that sways back and forth with
tides. Only the post-larvae of Penaeus move continuously towards the bay
(except in July and September), which suggests the presence of an active
movement, possibly crawling on sediments, to prevent massive return to
the gulf (Rodriguez 1973).
The vertical displacement of zooplankton in the water column can be
attributed to turbulence (Rodriguez 1984). The zooplankton of the bay is
typically estuarine with copepods like Labidocera fluviatilis and Acartia
tonsa, which reaches high densities (up to 4,241 ind. m- 3 ). Total zooplankton biomass varies between 17 and 31 mg m- 3 • During the dry season, neritic species of coastal waters in the gulf (Lucifer faxoni, Centropages furcatus, Sagitta hispida, and medusae) are common. Although their tidal
dependence is less pronounced, both neritic and estuarine species follow
salinity cycles, with maximum density during inflowing seawater. In contrast, density changes of cirriped larvae tend to reflect their reproductive
period (Rodriguez 1973). The estuarine character of the zooplankton community decreases towards the strait and neritic organisms tend to disappear altogether (Rodriguez 1973). In the lake, zooplankton is dominated
by calanoid and cyclopoid copepods (i.e., Acartia tonsa, Metacyclops
distans, Mesocyclops ellipticus, Notodiaptomus maracaibensis; Escam
1991) with low biomass (7-10 mg m- 3 ). Several species of the Cladocera are
common (Diaphanosoma, Moinodaphnia, Ceriodaphnia, Bosmina) and
others are abundant (i.e., Alona davidi and Moina micrura, 191 ind.l- 1 ) .
Rotifers have high specific diversity (Brachionus, Keratella, Epiphanes,
Monostyla, Asplanchna, Hexarthra, Conochilus) but generally do not
represent more than 15% of the zooplankton community.
3.3.3 Vertebrates
The estuarine ichthyofauna of the Maracaibo System consists of three different species assemblages. Marine euryhaline species migrate between the
estuary and the sea or are permanently found in Tablazo Bay. A large group
of estuarine-resident species lives and reproduces only in mixohaline waters (i.e., the endemic species Cynoscion maracaiboensis).Alloxenic species
are usually found close to the margins of the lake and the Engraulidae Anchoa argenteus (gemminate of A. spinifer) and Anchovia nigra (gemminate
of A. clupeoides) are endemic to oligohaline waters of the lake. The sardine
Astyanax fasciatus, catfishes (Pimelodidae), Prochilodus reticulatus, Potamorhina laticeps, and Mylossoma acanthogaster migrate to the middle and
upper reaches of rivers between January and March, followed by Doradops
G. Rodriguez
and fishes in surface waters at the mouth of the bay roughly follows tidal
cycles; thus, neritic species form a front that sways back and forth with
tides. Only the post-larvae of Penaeus move continuously towards the bay
(except in July and September), which suggests the presence of an active
movement, possibly crawling on sediments, to prevent massive return to
the gulf (Rodriguez 1973).
The vertical displacement of zooplankton in the water column can be
attributed to turbulence (Rodriguez 1984). The zooplankton of the bay is
typically estuarine with copepods like Labidocera fluviatilis and Acartia
tonsa, which reaches high densities (up to 4,241 ind. m- 3 ). Total zooplankton biomass varies between 17 and 31 mg m- 3 • During the dry season, neritic species of coastal waters in the gulf (Lucifer faxoni, Centropages furcatus, Sagitta hispida, and medusae) are common. Although their tidal
dependence is less pronounced, both neritic and estuarine species follow
salinity cycles, with maximum density during inflowing seawater. In contrast, density changes of cirriped larvae tend to reflect their reproductive
period (Rodriguez 1973). The estuarine character of the zooplankton community decreases towards the strait and neritic organisms tend to disappear altogether (Rodriguez 1973). In the lake, zooplankton is dominated
by calanoid and cyclopoid copepods (i.e., Acartia tonsa, Metacyclops
distans, Mesocyclops ellipticus, Notodiaptomus maracaibensis; Escam
1991) with low biomass (7-10 mg m- 3 ). Several species of the Cladocera are
common (Diaphanosoma, Moinodaphnia, Ceriodaphnia, Bosmina) and
others are abundant (i.e., Alona davidi and Moina micrura, 191 ind.l- 1 ) .
Rotifers have high specific diversity (Brachionus, Keratella, Epiphanes,
Monostyla, Asplanchna, Hexarthra, Conochilus) but generally do not
represent more than 15% of the zooplankton community.
3.3.3 Vertebrates
The estuarine ichthyofauna of the Maracaibo System consists of three different species assemblages. Marine euryhaline species migrate between the
estuary and the sea or are permanently found in Tablazo Bay. A large group
of estuarine-resident species lives and reproduces only in mixohaline waters (i.e., the endemic species Cynoscion maracaiboensis).Alloxenic species
are usually found close to the margins of the lake and the Engraulidae Anchoa argenteus (gemminate of A. spinifer) and Anchovia nigra (gemminate
of A. clupeoides) are endemic to oligohaline waters of the lake. The sardine
Astyanax fasciatus, catfishes (Pimelodidae), Prochilodus reticulatus, Potamorhina laticeps, and Mylossoma acanthogaster migrate to the middle and
upper reaches of rivers between January and March, followed by Doradops