THE INTERTIDAL ESTUARINE COMMUNITIES
OF LAKE MARACAIBO, VENEZUELA
GlLBERTO RODRIGUEZ
Instituto Venezolano de Investigaciones Cientificas (IVIC), Caracas, Venezuela
ABSTRACT
The communities of rocky, sandy and muddy shores in the estuary are
analyzed and the dominant species are recorded. The observed salinity
ranges in mixohaline waters are combined with ranges observed in
euhaline waters to give the salinity tolerances for the invertebrates inhabiting the estuary. The action of the substratum is discussed. At the
end a summary of the physical conditions and a list of the plants and
invertebrates are given.
INTRODUCTION
In a previous paper (Rodriguez, 1959) I have analyzed the structure
of the intertidal communities of the tropical marine shores of Venezuela.
In the present contribution an attempt is made to extend this analysis to the
intertidal communities in mixohaline waters. For this purpose the estuary
of Lake Maracaibo has been chosen.
Lake Maracaibo lies in a geosynclinal basin of Miocene origin that
once was a part of the extensive sea that covered the central portion of
Venezuela. At present its area is 14,344 km2• Its maximal length, from
Santa Rosa Point to Palmas Point, is over 155 km, and its maximal width,
from El Guaco to Motatan del Lago, is 120 km. The greatest depth
recorded is 34 m.
This body of fresh water is in free communication with the marine
waters of the Golfo de Venezuela through a narrow strait 39 km long and
6 km wide in the narrowest part. It has two mouths, one very shallow
between the southern tip of Zapara Island and the east coast of the lake,
the other between the west coast of Zapara Island and the southern tip
of San Carlos Island. This mouth has been dredged to allow navigation
to Port Maracaibo. The dredged channel has a least depth of 10 m. It
is possible that the channel will allow a greater flux of sea water to enter
the estuary and consequently in time conditions of life will be altered.
The present survey was conducted at the time the channel was being
dredged (July, 1956).
Literature on the hydrography and biology of this estuary is very scanty,
although this is the oldest and most important center of oil production in
the country. In 1940, E. F. Robinson made a preliminary survey of the
hydrography in connection with a dredging project (Robinson, 1947). A
more detailed study was carried out by the Woods Hole Oceanographic
Institution in 1953 and 1954 (Redfield, Ketchum and Bumpus, 1955).
The Instituto N acional de Canalizaciones has published a report on
circulation and total discharge (Obadia, 1957).
198
Bulletin of Marine Science of the Gulf and Caribbean
[13(2)
Gessner has made studies on the hydrography and plankton of the
Lake (Gessner, 1953; Gessner and Vareschi, 1956), and Ten Broek
(195'0) has published a descriptive catalog of the molluscs. Crane (1943)
has reported on the fiddler crabs of the genus Uca.
ACKNOWLEDGMENTS
Several persons and institutions cooperated with the author during the
survey in 1956. The study was made while holding a postgraduate
scholarship from the Venezuelan Association for the Advancement of
Science. The lnstituto Nacional de Canalizaciones and especially lng.
Arturo Obadia, provided all the field facilities. Dr. Th. van Andel, from
the Compania Shell de Venezuela, made the granulometric analysis. Dr.
Ten Broek assisted in the identification of molluscs. Dr. A. C. Redfield
obtained permission from the Creole Petroleum Corporation to use the
salinity data contained in his report. Drs. Hilary B. Moore and Gilbert L.
Voss helped in many ways. To all these persons and institutions the author
expresses his deepest gratitude.
DEFINITION
OF TERMS
Description of communities.- The terminology used herein is as defined
in a previous paper (Rodriguez, 1959), as follows:
Zone: A band or region on the shore defined by physical conditions.
Association: A community dominated by more than one species that
creates special conditions for the secondary species different from the
bare physical factors.
Consocies: A community with one single dominant.
Formation: An extensive climax community that covers large portions
of a region.
The word community is used in its broadest sense as a group of organisms. Belt is interchangeable with zone, but is used specially for bands
of plants.
Classification of waters according to salinity.-The classification of marine
waters used here is in accord with the classification of salinity approved by
the Symposium on the Classification of Brackish Waters, Venice, 1958,
which is a modification of the Redeke- Valikangas system.
Euhaline
40-30 %0
Mixohaline
30-0.5%0
Polyhaline
30-18 %0
Mesohaline
18-5 %0
Oligohaline
5-0.5%0
Limnetic
< 0.5%0
1963]
Rodriguez: Intertidal Estuarine Communities
199
Tidal Levels.-Two
levels are considered as critical, Mean Low Water
(MLW) and Mean High Water (MHW). These determine three main
zones: Spray, from MHW up; Splash, from MHW down; and the Algal
Belt to MLW. Also used are the words littoral for the region between MLW
and MHW, supralittoral for the upper region and infralittoral for the lower
region.
STATIONS
In order to obtain a representative sample of the intertidal fauna and
flora of the estuary, eight conveniently spaced stations were established
(Fig. 1).
Capitan Chico Point (Station 1) is the southern limit of penetration for
several estuarine species, and has an almost limnetic biota. The channels
of San Carlos Island (Stations 2 and 3) are densely covered by mangrove
undisturbed by human activities. Calvert (Station 8) represented a
recently formed shore in process of colonization.
Vigia Point (Station 4), Piedras Point (Station 5), the north coast
of Zapara (Station 6, substation 4) and Toas Island were chosen as
representatives of rocky shores.
Zapara Island deserves special attention (Station 6). It is a narrow
strip of sand dunes that forms a barrier to the entrance of marine waters
into the estuary (Fig. 5). Its north coast is in contact with high salinity
water (23%0) while its southern coast is in contact with low salinity
water (6-8%0)' The island has been strongly altered by human action;
mangroves have partially disappeared and new shores have been formed
with sand from the dredgings. A breakwater has been laid on the north
coast to prevent deposition of sand in the channel by the clockwise
current in Golfo de Venezuela.
LIST
OF
STATIONS,
LAKE
MARACAIBO,
JULY,
1956
Station 1. Capitan Chico Point, 7.5 km north of Maracaibo.
Station 2. Juan Zenon Channel, San Carlos Island.
Station 3. Mouth of Juan Zenon Channel, San Carlos Island.
Station 4. Vigia Point, north of Palmas Point.
Station 5. Piedras Point, 5 km south of Altagracia Port.
Station 6. Zapara Island.
Substation 1. Entrance to the breakwater.
Substation 2. Small bay at the west of the island.
Substation 3. Shore on the southern coast of the island.
Substation 4. Shore on the northern coast of the island.
Station 7. Toas Island, shore on the west coast of the island, near the
quarry.
Station 8. Calvert, small peninsula, south of San Carlos Island.
Bulletin of Marine Science of the Gulf and Caribbean
200
o ,
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.(
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[13(2)
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DEPTH CONTOURS
2m.
''1
6m.
8·m.
MARACAIBO
1\1
FIGURE
1. Map of the northern portion of Lake Maracaibo, showing position
of stations.
1963]
Rodriguez: Intertidal Estuarine Communities
ECOLOGICAL
SURVEY
OF SANDY
AND ~UDDY
201
SHORES
Station 1 (Fig. 2) is a small peninsula 1 Ian long and 0.5 km wide.
The coastline is covered by Rhizophora, which is sometimes replaced by
a tall grass, Phragmitis communis, that fills the same ecological role as
does mangrove. The roots of Rhizophora and the stems of Phragmitis were
covered at ~HW by a zone of Balanus improvisus. This substratum was
sometimes shared by a red alga, Caloglossa leprieurii. The roots and stems
are often dotted with oil, which does not seem to affect the survival of
either the cirripede or the alga. Above the balanoid zone there was an
abundant community of an estuarine gastropod, Neritina reclivata. The
branches on the upper part were shared by three crabs, Rhithropanopeus
harrisii, Metasesarma rubripes and Aratus pisoni.
The supralittoral zone of the sandy beach had a crowded community
of Vca murificenta, with the entrance to the burrows surrounded by circular
walls. Below ~LW there was an extensive formation of Ruppia maritima.
In tropical estuaries this seagrass fills the same role as Thalassia in marine
bottoms. In places not covered by Ruppia there was a species of
pelecypod, Polymesoda arctata, buried in the sand and leaving only the
apex of the shell exposed to the water. This apex is used as a hard
substratum for attachment by filamentous green algae. Numerous specimens of the blue crab, Callinectes sapidus, were found swimming among
the Ruppia branches.
In a small bay south of Capitan Chico Point there was a dense consocies
of a fresh water submerged plant, Ceratophyllum demersum. Among its
branches there was a small species of fresh water gastropod, Potamopyrgus
sp. Floating in the water there were abundant specimens of Eichornia
crassipes, the water hyacinth. According to Villalobos (personal communication), the roots of this plant in ~exico are the habitat of small
atyid crustaceans, as well as other forms, but we were not able to
detect them.
The day we made our collections we obtained values of 1.32%0 for
the salinity at low tide. Grain size analysis for the substratum of Ruppia,
Uca murificenta and Ceratophyllum demersum respectively, are presented
in Table III.
The structure of the communities at this Station could be summarized
as follows:
A. Infralittoral, exposed places
1. Ruppia formation
2. Polymesoda consocies
B.
Infralittoral, protected places
Ceratophyllum consocies
C.
~angrove formation
1. Balanus-Caloglossa zone
202
Bulletin of Marine Science of the Gulf and Caribbean
[13(2)
zone
3. Supralittoral consocies of Uca murificenta
4. Aerial zone, Aratus-Rhithropanopeus-Metasesarma
aSSocIatIOn.
Station 2 (Fig. 2) is Juan Zenon Channel. This channel is 2 ill deep
and its muddy shores are densely covered by mangrove not influenced
by human action. The mangrove covers only the supralittoral zone, and
from there the slope of the channel is naked and very steep.
There was a very abundant community of Uca cumulanta from below
MLW to the supralittoral zone. We counted 330 burrows per square meter,
which gives a rough idea of the abundance of this crab. From above the
lower limit of Uca to the supralittoral zone there was another crab, Ucides
cordatus. We counted only 10 burrows per square meter for this species.
There were numerous specimens killed by a predator, possibly a racoon
(Procyon cancrivorus). Eight meters above high water mark there was an
abundant community of a gastropod, Melampus coJJeus, scattered over
the ground and with the shells covered by mud, thus concealing the animal.
We also collected an isolated specimen of Neritina reclivata.
The day we made our collections we obtained a value of 3.15~o for
the salinity at low tide. Grain size analysis for the substratum of UcaUcides-Melampus
is presented in Table 3.
Station 3 (Fig. 2) is a sandy shore with a gentle slope at the eastern
entrance of Juan Zenon Channel. The foreshore, from MLW up, was
devoid of vegetation. There were scattered specimens of Rhizophora
and a species of Cyperaceae, Fimbristylis spadicea.
Two species of crabs shared the substratum at this station: Uca
leptodactyla in uncovered dry places, from which we counted 85 and
113 burrows per square meter, and Uca rapax in places covered by
mangrove and sometimes inundated, from which 130 burrows per square
meter were counted. There seems to be a correlation between grain size
and the species of Uca present in a given substratum that we will discuss
later.
In the infra littoral zone there was a sparse community of Poly me soda
2. Neritina
arctata.
The day we made our collections we obtained a value of 2.57C!jro for
the salinity at low water. Grain size analysis for the substratum of Uca
leptodactyla and U. pugnax respectively are presented in Table 3.
The structure of the communities at these stations can be summarized
as follows:
A. Muddy shore (Station 2)
Mangrove formation
Uca-Ucides-Melampus
association
B. Sandy shore (Station 3)
Rhizophora-Fimbristylis
association
1963]
Rodriguez: Intertidal Estuarine Communities
STAT/ON
203
ARATUS
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SYMBOLS
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r
2. Zonation on muddy and sandy shores.
SILT
23m
I
-t
204
Bulletin of Marine Science of the Gulf and Caribbean
[13(2)
1. Uca leptodactyla consocies
2. Dca rapax consocies
3. Polymesoda infralittoral consocies
Station 4 at Vigia Point is a group of rocks interspaced by sandy shores.
In general the area was very poor in organisms and the sandy shores were
devoid of mangroves. We collected only a species of crab Sesarma miersii,
in the supralittoral zone.
The infralittoral zone was covered by Ruppia, with Polymesoda in
uncovered places. At this station we collected several specimens of
Callinectes bocourtii. Partially buried in the infralittoral sand there were
specimens of a sting ray, Potamotrygon magdalenae.
Station 6, substation 2 (Fig. 2), is a small bay on the west coast of
Zapara Island, with an extensive muddy shore. There were two species of
crabs sharing the substratum in the littoral zone, Uca cumulanta, of which
we counted 184 and 218 burrows per square meter, and Dca maracoani,
far less abundant.
Above MHW, in the few mangroves present there were two species of
gastropods, Littorina nebulosa and Thais haemastoma floridana. A crab,
Aratus pisoni, and a pagurid, Clibanarius cubensis, occasionally were
present in dry places.
Due to the absence of a hard substratum, sessile organisms were not
abundant. However, numerous specimens of the commercial oyster,
Crassostrea virginica, and another
pelecypod, Mytelia falcata, were
crowded together on the small amount of hard substratum that was
present. The shells of Crassostrea in turn were used as a substratum by
Balanus improvisus.
In the infralittoral zone there were scattered specimens of Polymesoda
arctata.
Zapara Island is covered by sand dunes sometimes colonized by low
vegetation. At substation 2 this vegetation was arranged as follows: near
MHW there was a tall grass, Paspalum distichum; above this band, where
the substratum changed from mud to cleaner sand, there were scattered
specimens of buttonwood, Conocarpus erectus, and two species of
Cyperaceae, Fimbristylis spadicea and F. glomerata, with a few specimens
of Dca leptodactyla on the substratum; next came a band of another grass,
Sporobolus virginicus. The tops of the sand dunes were covered by
Ipomoea pescaprae.
The. days we made our collections we recorded salinities of 7.25,
9.90 and 10.42%n. Grain size analysis for the substratum of the Sporobolus
consocies is presented in Table 3.
The structure of the communities at this substation can be summarized
as follows:
A. Infralittoral consocies of Polymesoda
1963]
Rodriguez: Intertidal Estuarine Communities
205
B. Muddy shore, littoral zone
Uca cumulanta-U.
maracoani association
C. Mangrove formation, very altered
Littorina-Thais zone
D. Supralittoral vegetation
1. Paspalum consocies
2. Fymbristylis glomerata-F. spadicea association
3. Sporobolus consocies
Station 6, substation 3, is a muddy shore on the south coast of Zapara
Island. The mangroves have been partially felled and only a community
of Uca cumulanta was present. We collected numerous adult specimens
of the commercial shrimp Penaeus schmitti at depths of 2-3 feet below
MLW.
The day we made our collections we obtained a value of 7.02%0 for
the salinity at low tide. Grain size analysis for the substratum of Uca
cumulanta is presented in Table 3.
Station 8 (Fig. 2) is a small, sandy peninsula south of San Carlos,
recently formed by deposition of sand from dredgings.
In most places the littoral zone was devoid of organisms. Above MHW
there was a community of Ocypode quadrata of which we counted two
burrows in 25 square meters. In other places, the ample littoral zone had
a community of Uca leptodactyla of which we counted 3, 4, 4, and 5
burrows respectively per square meter. The same species was present in the
supralittoral zone and we counted from 56 to 70 burrows per square meter.
In some places, the supralittoral zone was covered by low vegetation
distributed as follows: near MHW there was a band of Fimbristylis
spadicea partially intermingled with Sesuvium portulacastrum. Ocypode
quadrata was present on the substratum, and we counted 2 burrows per
square meter. Above this band there were successive bands consisting of
Ipomoea pescaprae, Sporobolus virginicus and Sesuvium, and Fimbristylis
spadicea.
The day we made our collections we obtained a value of 3.31%0 for
the salinity at low tide. Grain size analysis for the substratum of Uca
leptodactyla and Sesuvium-Fimbristylis association respectively are presented in Table 3.
The structure of the communities at this station can be summarized
as follows:
A. Littoral and supralittoral zone
1. Ocypode consocies
2. Uca leptodactyla consocies
B. Supralittoral vegetation
1. Fimbristylis-Sesuvium association
2. Ipomoea-Sporobolus association
206
Bulletin of Marine Science of the Gulf and Caribbean
ECOLOGICAL
SURVEY
OF ROCKY
[13(2)
SHORES
Station 5 is a group of rocks 5 km south of Port Altagracia, on the east
bank of the estuary. This area is very polluted and poor in organisms.
At low water mark there was a green colony of the fresh water sponge,
Spongilla aspinosa, covering the cavities of the rocks. Above high water
mark there were some specimens of Neritina reclivata and the mangrove
crab, Metasesarma rubripes.
The structure of the communities at this station can be summarized
as follows:
A. Littoral zone
Spongilla consocies
B. Supralittoral zone
Neritina-Metasesarma association
Station 6, substation 1, is a group of rocks near the entrance to the
breakwater on the north coast of Zapara Island. The breakwater was
constructed, two years before our survey, with rocks extracted from the
quarry on Toas Island. In the littoral zone there was a band of filamentous
green algae. Above MHW there was a zone of Littorina nebulosa and a
few Thais haemastoma {loridana. An unidentified terrestrial isopod was
very common in the crevices of the rocks in this zone.
The structure of the communities at this station can be summarized as
follows:
A. Zone of filamentous green algae between ML Wand MHW
B. Littorina-Thais zone, above MHW
Station 6, substation 4, on the NE coast of Zapara Island, is a shore
with a sandy supralittoral zone and hard substratum in the littoral and
infralittoral zone. There was community of Ocypode quadrata in the
supralittoral zone, of which we counted 8 burrows in 25 square meters
in the upper portion, and 25 per square meter in the lower portion.
In the spray zone, on the rock and sandstone substratum, there was
a dense community of Thais haemastoma {loridana. In the fissures of the
rocks we counted 70 and 120 specimens respectively in one square foot.
We also collected the egg capsules of this species. Another gastropod,
Neritina meleagris, also was present, although in smaller quantities, and
an occasional specimen of Neritina reclivata was collected.
Among the rocks there was a crab, Panopeus occidentalis, and on the
loose fragments of a small, unidentified sea anemone and a hydrozoan,
Bougainvillea superciliaris. Growing on this there was another hydrozoan,
Obelia oxydentata.
In the splash zone, on the sandstone substratum, there was a crowded
community of Balanus amphitrite niveus and Mytella taicata. This association covered an extensive platform of several square meters.
1963]
Rodriguez: Intertidal Estuarine Communities
207
In the infra littoral zone we collected a few Callinectes bocourti.
The day we made our collections, we obtained a value of 23.78%0
for the salinity.
The structure of the communities at this station can be summarized
as follows:
A. Supralittoral zone, sand
Ocypode consocies
B. Spray zone, rock
Thais-Neritina association
C. Splash zone, sandstone
Balanus-Mytella association
Station 7 is a rocky shore near the quarry on Toas Island. In the
supralittoral zone there were three species of crabs, Panopeus rugosus
Metasesarma rubripes and Sesarma miersi. In the crevices of the rocks
there were two species of isopods, Ligia baudiniana and an other
unidentified species.
In the spray zone there was a community of Neritina reclivata and in
the splash zone a few specimens of Mytella falcata.
The day we made our collections at this station we obtained a value of
2.21 % c for the salinity at low water.
The structure of the communities at this station can be summarized as
follows:
A. Splash zone
Mytella falcata consocies
B. Spray zone
Neritina reclivata consocies
C. Supralittoral zone
Panopeus-Sesarma~Metasesarma consocies
GENERAL
REMARKS
Biotic structure of the communities.-Mangroves
constitute a climax
formation in the tropics in euhaline and mixohaline waters. This formation
is in turn the conditioning agent for several subordinate communities.
Alteration of the mangroves by human action or lack of a suitable substratum determines the replacement of these subordinate communities by
others.
In shores newly formed by deposition of sand from dredgings (e.g.,
Station 8) an interesting situation arises. On the supralittoral zone appears
a pioneer community of Gramineae and Cyperaceae arranged in bands.
It is possible that this community in time will lead to the establishment of
the mangroves as a climax formation.
A striking fact in the mangroves of mesonaline and oligohaline waters
208
Bulletin of Marine Science of the Gulf and Caribbean
[13(2)
is the absence of the rich community that appears as a ring on the roots
in euhaline waters (ct. Rodriguez, 1959). The mud around the roots has
also a poorer fauna, Uca, Ucides and Melampus being almost the only
organisms present.
The zonation on rocks and other hard substrata (Fig. 3) in mixohaline
waters is also simpler as compared with that in euhaline waters. The splash
and spray zones stilI could be distinguished, although the wave action is
very restricted in most cases. The splash zone is a balanoid zone as in
euhaline waters, and the spray zone is occupied by species of gastropods
similar to those found in euhaline waters, although quite different in their
salinity tolerances. In the estuary, this band is made up of Littorina
nebulosa, Neritina meleagris and Neritina redivata, whereas in seashores
STATION
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1963]
Rodriguez: Intertidal Estuarine Communities
209
it consists almost exclusively of Littorina ziczac. Thais ranges in this same
zone from mesohaline to euhaline water. The algal belt is not so well
defined as in the sea rocks, and only Caloglossa (Station 1) and the
filamentous green algae give some indication of the presence of this zone.
A. Soft bottom, mangrove formation
1. Littoral and supralittoral
Mangrove roots and other hard substratum
Balanoid zone
Neritina or Littorina zone
Fine sand or silt
Vca - Vcides-Melampus, associated in several ways
Aereal fauna
Aratus - Metasesarma - Rhithropanopeus association
2. Infralittoral
Ruppia formation
Polymesoda consocies
Ceratophyllum consocies
B. Soft bottom, mangroves absent
1. Supralittoral
Ocypode consocies
Bands of vegetation
2. Littoral
Vca, associated in several ways
3. Infralittoral
Ruppia formation
Polymesoda consocies
Salinity tolerances.-The salinity ranges observed for various invertebrates
that inhabit the estuary are presented in Figure 4. The solid lines indicate
the range in Lake Maracaibo. The broken lines indicate the range observed
in Margarita Island (Rodriguez, 1959) and in other localities in the
Venezuelan coast. The dotted lines indicate the range from data taken from
other sources in the Caribbean, especially those from Tabb and Manning
(1961).
The majority of species are marine euryhalines. In this category could
be grouped the majority of Crustacea, and Thais haemastoma floridana,
Melampus coffeus and Crassostrea virginica among the molluscs. The
lower limit of tolerance is different for several species and in each case
determines the degree of penetration into the estuary.
A small group is limnetic, with some tolerance for salinity. We recorded
only two species in this category, Spongilla aspinosa and Potamopyrgus sp.
A third group is restricted to mixohaline waters. Four molluscs, Nerilina
reclivata, N. meleagris, Littorina nebulosa and Polymesoda arctata, and
210
Bulletin of Marine Science of the Gulf and Caribbean
3PONGILLA ASPINOSA
BALANUS IMPROVISUS
BALANUS AMPHITRITE NIVEUS
LIGIA BAUDINIANA
CALLINECTES SAPIDUS
CALLINECTES ORNATUS
CALLINECTES BOCOURTI
PANOPEUS OCCIDENTALIS
PANOPEUS RUGOSUS
RHITHROPANOPEUS HARRISII
METASESARMA RUBRIPES
SESARMA MIERSII
ARATUS PISONI
UCIDES CORDATUS
OCYPODE ~UADRATA
UCA MARACOANI
UCA HAPAX
UCA MURIFICENTA
UCA CUMULANTA
UCA LEPTODACTYLA
MELAMPUS COFFEUS
NERITINA RECLIVATA
NERITINA MELEAGRIS
LITTORINA NEBULOSA
PO'l'AMOPYRGU.s
.sP.
THAIS HAEMASTOMA FLORIDANA
POLYMESODA ARCTATA
MYTELLA FALCATA
CRAS30STRBA VIRGINICA
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10
S ALINITY
FIGURE
[13(2)
••
•••••••
20
30
~o
4. Salinity ranges of the invertebrates found in the estuary.
1963]
Rodriguez: Intertidal Estuarine Communities
211
the crabs Rhithropanopeus harrisii, Metasesarma rubripes, Sesarma miersii
and Ucides cordatus belong here.
The range recorded for Uca, especially U. murificenta is doubtful.
Polymesoda arctata is an estuarine mussel restricted to the Maracaibo
estuary, although other species of this genus are found elsewhere in the
Caribbean.
Substratum preferences.- The availability of a suitable hard substratum
is an important factor for the presence of some communities. The structure
of the splash zone shows variations depending on the nature of the hard
substratum. Balanus is a dominant element on rock, sandstone and mangrove roots. Mytella is present on rock or sandstone, but not on mangrove
roots, although the salinity ranges are comparable.
In the majority of cases the soft substratum is fine sand with variable
amounts of medium sand and silt (Table 3). There seems to be some
correlation between the species of Uca and the grain size of the sediments.
The substratum for U. cumulanta has equal amounts of silt, 51.5, 40.1 %,
and fine sand, 46.9, 40.5%. For U. leptodactyla the proportion of silt is
smaller, 10.2, 30.3, 17.6% silt, and 76.9, 67.6, 82.2% fine sand. For
U. rapax and U. murificenta the proportion seems to be even smaller,
3.0% silt, 74.2% fine sand for the first, 5.0% and 94.4% for the second. The amount of medium sand is very variable for any species.
PHYSICAL
CONDITIONS
IN MARACAIBO
ESTUARY,
JULY,
1956
1. Temperature.-The
temperature of the water varies very little from one
place to another with time, ranging from 26 to 31 C, and consequently
was not taken into account in the present survey. Extreme air temperatures
could be slightly greater.
0
0
2. Tides.-In the region of the estuary the tide is semidiumal. Its amplitude
decreases from one foot at Zapara to less than half foot in Capitan Chico.
3. Salinity.-The surface salinity of the Lake is less than 2%0' and increases
slightly with depth. During the rainy season there is a marked decrease in
salinity (Gessner, 1953).
Figure 5 shows the distribution of salinity at the mouth of the estuary.
There is a sharp increase toward the north coast of Zapara Island, while
a large body of mesohaline water that advances through the center of the
channel is deflected to the west of the Golfo de Venezuela. All the pertinent
data are compiled in Table I.
Figure 6 shows the salinity at the mouth of the estuary in a transect from
Calvert to Zapara Island. There is a vertical stratification of salinities,
increasing in values from the center to the margins of the channel. The
data taken from four stations, at three different levels in 24 hours are
shown in Table 2.
Bulletin of Marine Science of the Gulf and Caribbean
212
[13(2)
.~
.'
~
<0
i
"\::::.:::::~:,:'
I(,)
W
l/l
Z
ct
Q:
I-
l/l
W
..J
0..
:::E
ct
l/l
't
>-
I-
~
CO)
r•
...J
ct
l/l
en
0
v
~
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ill
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l\.
•..•..
0
I.)
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fuQ
FIGURE
5. Distribution of surface salinities (%0) at the mouth of the estuary,
July 1956, and position of transect Calvert - Zapara.
1963]
Rodriguez: Intertidal Estuarine Communities
213
4. Sediments.-Samples
of the substrata were analyzed for grain size in
order to ascertain the nature of the sediments in each Station and for
several communities. The results are presented in Table 3, reported according to the ASTM (1961) standards.
TAXONOMIC
TREATMENT
OF THE FAUNA
MARACAIBO
AND FLORA
OF
ESTUARY
INVERTEBRATES
The only published records of the bottom-dwelling invertebrates of
Maracaibo Estuary are those of Ten Broek (1950) for the Mollusca, and
Crane (1943) for the genus Uca. To Ten Broek's list we have added
Thais haemastoma {ioridana, Potamopyrgus sp., Crassostrea virginica and
Mytella talcata. He found only a few empty shells of Melampus cofJeus,
while we found it to be abundant. Crane's paper was based partially on
an extensive collection from Maracaibo. From 526 specimens collected,
15 were Uca murificenta and the remainder U. rapax. We have found five
species living in the estuary.
The planktonic invertebrates reported by Gessner and Vareschi (1954)
LOW WATER
10
5
5
10152015
"
11 m
HIGH
WATER 1520'.5
o
12m
FIGURE
I
115
10
5
5
10 15
10
•
I
6. Transect Calvert - Zapara. Upper, stratification of salinities at low
water. Lower, stratification of salinities at high water.
214
Bulletin of Marine Science of the Gulf and Caribbean
[13(2)
from the estuary (from Capitan Chico Point to Zapara Island) include two
copepods, Metacyclops distans Kiefer, an endemic, and Acartia tonsa
(Dana), a cosmopolitan, and ten rotatorians, Brachyonus calyciflorus
Pallas, B. calyciflorus vaT. amphiceros (Ehrenberg), B. caudatus f. provectus Ahlstr., B. havanaensis var. thrahea (Murray), B. plicatilis Muller,
Filinia longiseta (Ehrenberg) F, longiseta var. acaudata Hauer, Keratella
americana Carlin, Lecane bulla (Gosse) and Pedalia fenica (Levander).
PORIFERA
Spongilla aspinosa Potts. Station 5.
CNIDARIA
HYDROZOA
Bougainvillia superciliaris Agassiz. Station 6, subst. 4
Obelia oxydentata Stechow. Station 6, subst. 4.
ARTHROPODA
CRUSTACEA
Cirripedia
Balanus improvisus Darwin. Station 1; Station 6, subst. 2.
Balanus amphitrite niveu.r Darwin. Station 6, subst. 4.
Isopoda
Ligia baudiniana Milne Edwards. Station 7.
Malacostraca: Decapoda
Penaeus schmitti Burkenroad. Station 6, subst. 3.
Clibanarius cubensis (Saussure). Station 6, subst. 2; Station 8.
Callinectes sapidus Rathbun. Station 1.
Callinectes ornatus Ordway. Station 6, subst. 1.
Callinectes bocourti Milne Edwards. Station 4; Station 6, subst. 4.
Panopeus occidentalis Saussure. Station 6, subst. 4.
Panopeus rugosus Milne Edwards. Station 7.
Rhithropanopeus harrisii Gould. Station 1.
Metasesarma rubripes (Rathbun). Stations 1,5,7.
Sesarma miersii Rathbun. Stations 4, 7.
Aratus pisoni (Milne Edwards). Station 1; Station 6, subst. 2.
Ucides cordatus (Linnaeus) Station 2.
Ocypode quadrata (Fabricius). Station 6, subst. 1, 3, 4.
Uca maracoani (Latreille). Station 6, subst. 4.
Uca rapax (Smith). Stations 2, 3.
Uca murificenta Crane (= Uca vocator Herbst, fide Holthuis, 1959).
Station 1.
Uca cumulanta Crane. Station 2; Station 6, subst. 2, 3.
Uca leptodactyla Rathbun. Station 3; Station ,6, subst. 2;,Station 8.
1963]
Rodriguez: Intertidal Estuarine Communities
215
MOLLUSCA
GASTROPODA
Neritina reclivata (Say). Stations 1,2,5,7.
Neritina meleagris Lamarck. Station 6, subst. 2, 4.
Littorina nebulosa (Lamarck). Station 6, subst. 1, 2, 4.
Thais haemastoma floridana Conrad. Station 6, subst. 1, 2, 4.
Melampus cofJeus (Linneus). Station 2.
Potamopyrgus sp. Station 1.
PELECYPODA
Crassostrea virginica (Gmelin). Station 6, subst. 2.
Mytella falcata (Orbigny). Station 6, substs. 2, 4; Station 7.
Polymesoda arctata (Deshayes). Stations 1, 2, 4; Station 6, subst. 2.
EsTUARINE
PLANTS
The planktonic diatoms of the Maracaibo estuary have been reported
by Huestedt in Gessner and Vareschi (1956).
We collected many littoral filamentous green algae, but they were not
identified.
ALGAE
Caloglossa leprieurii (Montagne). J. Agardh. Station 1.
Polysiphonia sp. Station 1.
EMBRYOPHYT
A
MONOCOTYLEDONEAE
Ruppia maritima Linnaeus. Stations 1, 4.
Phragmites communis Trio. Station 1.
Sporobolus virginicus (Linnaeus) Kunth. Station 6, subst. 2. Station 8.
Paspalum distichum Linnaeus. Station 6, subst. 2.
Fimbristylis spadicea (Linnaeus) Yah!. Station 3; Station 6, subst. 2;
Station 8.
Fimbristylis glomerata (Retz) Urban. Station 6, subst. 2.
DICOTYLEDONEAE
Eichornia crassipes (Martius) Solm. Station 1.
Sesuvium portulacastrum Linnaeus. Station 8.
Ceratophyllum demersum Linnaeus. Station 1.
Rhizophora mangle Linnaeus. Stations 1, 2, 3; Station 6, substs. 2, 3.
Ipomoea pes-caprae (Linnaeus) Roth. Station 6, subst. 2; Station 8.
Conocarpus erectus Linnaeus. Station 6, subst. 2.
216
Bulletin of Marine Science of the Gulf and Caribbean
[13(2)
TABLE 1
SURFACESALINITIESIN MARACAIBO
ESTUARY,JULY 1956
Locality
Station 1
Station 1
Station 2
Station 3
Station 6, sst. 2
Station 6, sst. 2
Station 6, sst. 2
Station 6, sst. 3
Station 6, sst. 4
Station 7
Station 8
South coast Zapara
%0
Date
Time
Time LW
2.08
1.32
3.15
2.57
7.25
9.90
10.42
7.02
23.78
2.21
3.31
7.12
20
20
25
4
25
23
26
26
26
24
4
23
9.00
10.00
10.00
15.00
8.35
14.45
8.12
8.30
8.35
11.00
15.40
15.30
9.24
9.24
12.20
18.38
12.20
11.12
12.58
12.58
12.5&
11.44
18.38
11.12
TABLE 2
SALINITIESIN A TRANSECTACROSSTHE MOUTH OF THE ESTUARYFROM
CALVERTTOZAPARA,JULY 1956
Position
lOo59'5"N
}
Date
Time
Depth (m)
23
23.15
23.20
23.25
05.05
05.15
05.25
18.40
18.42
18.43
23.20
23.22
23.25
19.11
19.12
19.13
01.15
01.16
01.17
19.45
19.46
01.00
01.01
01.02
0
2.9
5.8
0
2.9
5.8
0
5.0
9.9
0
5.0
9.9
0
6.0
9.8
0
6.0
9.8
0
4.6
0
4.6
9.3
71°36'4"W
24
o
lO 59'9"N
}
24
71°35'52''W
24
o
lO 59'15"N}
25
7] °35'50"W
26
lO 59'22"N}
26
71°35'42''W
27
O
;.00
9.38
14.78
21.65
20.60
21.92
21.41
5.80
5.39
12.79
4.09
4.43
5.08
4.01
6.02
7.12
4.25
7.64
11.04
24.46
12.79
25.01
25.51
25.82
Tide
Low
High
High
Low
High
Low
High
Low
1963]
Rodriguez: Intertidal Estuarine Communities
217
TABLE 3
GRAIN SIZE ANALYSISOF THE SUBSTRATAFOR SEVERALCOMMUNITIES
ASTM SPECIFICATIONS
Station
Community
1
1
1
1
1
6, sst. 2
6, sst. 2
2
3
3
8
8
Ceratophyllum
Ruppia
Polymesoda
Phragmites
U. mwrificenta
U. leptodactyla
U. leptodactyla
U. cumulanta
U. 'rapax
U. cumulanta
Sporobolus
U. leptodactyla
Medium
Sand, %
Fine
Sand, %
(Peat completely organic)
1.0
18.0
0.2
27.0
10.2
27.0
0.6
94.4
12.9
76.9
0.2
82.2
1.6
46.9
11.8
74.2
2.5
84.1
18.5
76.6
2.1
67.6
Silt %
81.0
72.8
63.0
5.0
10.2
17.6
51.5
3.0
13.4
4.9
30.3
SUMARIO
LAS COMUNIDADES
DE ESTUARIOS
DE LA ZoNA
MARACAIBO,
DE LAS MARE AS DEL LAGO
VENEZUELA
Son analizadas las comunidades de orillas rocosas, arenosas y fangosas
en el estuario y se reportan las especies dominantes. Los cambios de salinidad observados en aguas de amplia variaci6n de salinidad son combinados
con los cambios observados en aguas de salinidad normal, para dar la
tolerancia de salinidad para los invertebrados que habitan el estuario. Se
discute la acci6n del substratum. Al final, se da un sumario de las condiciones flsicas y una lista de las plantas e invertebrados.
LITERATURE
CITED
AMERICANSOCIETYFORTESTINGMATERIALS
1961. Book of ASTM Standards, Part 4. Baltimore.
GESSNER,F.
1953. Investigaciones hidrograficas en el Lago de Maracaibo. Acta Cient.
Venez.,4 (5): 173-177.
GESSNER,F. ANDV. VARESCHI
1956. Ergebnisse der Deutsche Limnologischen Venezuela-Expedition 1952.
Band 1. Berlin.
OBADlA,A.
1958. Informe sobre aforos en el canal exterior de la Barra de Maracaibo.
Instituto Nacional de Canalizaciones. Caracas.
REDFIELD,A. C., B. H. KETCHUMANDD. F. BUMPUS
1955. Report to Creole Petroleum Corporation on the Hydrography of
Lake Maracaibo, Venezuela. Unpublished manuscript. Woods Hole
Oceanographic Institution.
218
Bulletin of Marine Science of the Gulf and Caribbean
[13(2)
E. F.
.
1947. A project for deepening and improving the entrance to Lake Maracaibo, Venezuela. Washington.
ROBINSON,
RODRIGUEZ, G.
.1959. The marine communities of Margarita Island, Venezuela. Bull. Mar.
Sci. Gulf and Carib., 9 (3): 237-280.
D. C. AND R. B. MANNING
1961. A checklist of the flora and fauna of northern Florida Bay and adjacent brackish waters. Bull. Mar. Sci. Gulf and Carib., 11 (4): 552649.
TABB,
A. N. CH.
1950. On some brackish water mollusca
Zool. Meded. 31 (8): 79-87.
TEN BROEK,
from the Lake of Maracaibo.