The Intertidal Estuarine Communities of Lake Maracaibo, Venezuela

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 in- habiting 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 Nacional 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. 200 Bulletin of Marine Science of the Gulf and Caribbean [13(2)

o , 2 3 .( 5 I

DEPTH CONTOURS

2m. 6m. ''1 8·m. MARACAIBO 1\1

FIGURE 1. Map of the northern portion of Lake Maracaibo, showing position of stations. 1963] Rodriguez: Intertidal Estuarine Communities 201

ECOLOGICAL SURVEY OF SANDY AND ~UDDY 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) 2. Neritina 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 Uca- Ucides-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 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 203

ARATUS STAT/ON 1 M£TASESARMA RHITHROPANOP£US N£RITINA HWM 8ALANUS-CALOfJ. . •••.~ AL------RtJPPIA II. MURIFICENTA ., • -. POLYM£SOOA

STAT/ON 3 STATION 2

~--U.LEPTOOAC TYLA ---.-._._ U.RAPAX -

STAT/ON 6, SST 2 IPOMOEA SPOROBOLVS FIM8RISTYLIS PASPALUM

~l!UlllllU.~~ { ti,#~JlHhJH t;~~~~-;:iHAIS HWM U.LEPTOOACTYLA / •.•J}~TTfY

. 1.J...i.l1..tl..!.LU.U~~Uh~t~Hl(l~b\

U. L£PTODACrYLA

SYMBOLS USED FINE ,... POL YMESODA SAND jk.. RUPPIA P MANGROVE •• I OMOEA I • SILT m.. t SESUVI0MfSPOROBOLUS \UCA 23m iFIMBRISTYL/S t PASPALUM ~. OC YPODE r I -t

FIGURE 2. Zonation on muddy and sandy shores. 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 [13(2)

ECOLOGICAL SURVEY OF ROCKY 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 MLWand 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 infralittoral 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 STATION sr 6 ST6 STATION

1 5 SUBSr 1 SUBST4 7

« « « V'l ).. lu ~ « ~ ~ V'l V'l ~ « ~ « ~ j:: 0 C) i:: ~ ;q i:: <: ~ Q::: lt~C)- h 0.. V) I\i - ct :t It 0 lu lu o 0.. - .... V'l <: ~ t: ~ 0 lu ~ -....• V'l- <= <: -

SPONGILLA ::r: lu V'l V'l « « (J) ...• ....• q: ~ ;:) ;:) ....• ....• C) <= <= GJ lu I\i .... 0.. « V'l « )...... J ....• ).. V'l ;:) « I.U « t t en ~ ~ « en V'l ~ 0 ....• ..J ~ ~ t « C) ....•« ..J ..J q: .... L4:: ..J « I::l U ..J lu « en

FIGURE 3. General scheme of zonation on hard substratum. 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 [13(2)

3PONGILLA ASPINOSA !If BALANUS IMPROVISUS ...... , •••• BALANUS AMPHITRITE NIVEUS •••••••• ••••••• •• LIGIA BAUDINIANA 1- •••• •••••• •••••• •••• CALLINECTES SAPIDUS ••••••• •••••• •••••• .., CALLINECTES ORNATUS •••• ------CALLINECTES BOCOURTI . ...., •••• __ I PANOPEUS OCCIDENTALIS ~--- PANOPEUS RUGOSUS •••••• ••••••• •••••• • •• RHITHROPANOPEUS HARRISII •••••• ••••••• METASESARMA RUBRIPES •••• SESARMA MIERSII ••• ____ I __ I ARATUS PISONI •...-- UCIDES CORDATUS ---- ••• __ I OCYPODE ~UADRATA UCA MARACOANI t--~ -- UCA HAPAX ------. -. UCA MURIFICENTA ~---t- UCA CUMULANTA ---.-- --. -_I UCA LEPTODACTYLA MELAMPUS COFFEUS ...------, .------NERITINA RECLIVATA I-- NERITINA MELEAGRIS LITTORINA NEBULOSA PO'l'AMOPYRGU.s.sP. •• THAIS HAEMASTOMA FLORIDANA . - -. _I POLYMESODA ARCTATA MYTELLA FALCATA • CRAS30STRBA VIRGINICA t- •••••• ••••••• ••

0 10 20 30

S ALINITY ~o

FIGURE 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 sec- ond. 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 260 to 310 C, and consequently was not taken into account in the present survey. Extreme air temperatures could be slightly greater. 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. 212 Bulletin of Marine Science of the Gulf and Caribbean [13(2)

.~.'

~ <0

i "\::::.:::::~:,:'

l/l I- W (,) ..J W 0.. l/l :::E Z ct ct l/l Q: 't I- >- I- ~ CO) ...J ct en l/l :::E l\o r • :It:

0 ~ E E E E 0 v •... CO) ill l\. •.. !.. ~ •.. l"- I.) ~ fu Q

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 AND FLORA OF MARACAIBO 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 10 5 5 10 15 10

• o 115 12m I I FIGURE 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. pro- vectus 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 MARACAIBOESTUARY,JULY 1956 Locality %0 Date Time Time LW Station 1 2.08 20 9.00 9.24 Station 1 1.32 20 10.00 9.24 Station 2 3.15 25 10.00 12.20 Station 3 2.57 4 15.00 18.38 Station 6, sst. 2 7.25 25 8.35 12.20 Station 6, sst. 2 9.90 23 14.45 11.12 Station 6, sst. 2 10.42 26 8.12 12.58 Station 6, sst. 3 7.02 26 8.30 12.58 Station 6, sst. 4 23.78 26 8.35 12.5& Station 7 2.21 24 11.00 11.44 Station 8 3.31 4 15.40 18.38 South coast Zapara 7.12 23 15.30 11.12

TABLE 2 SALINITIESIN A TRANSECTACROSSTHE MOUTH OF THE ESTUARYFROM CALVERTTOZAPARA,JULY 1956

Position Date Time Depth (m) ;.00 Tide

lOo59'5"N } 23 23.15 0 9.38 Low 23.20 2.9 14.78 71°36'4"W 23.25 5.8 21.65 24 05.05 0 20.60 High 05.15 2.9 21.92 05.25 5.8 21.41 o lO 59'9"N } 24 18.40 0 5.80 High 18.42 5.0 5.39 71°35'52''W 18.43 9.9 12.79 24 23.20 0 4.09 Low 23.22 5.0 4.43 23.25 9.9 5.08 o lO 59'15"N} 25 19.11 0 4.01 High 19.12 6.0 6.02 7] °35'50"W 19.13 9.8 7.12 26 01.15 0 4.25 Low 01.16 6.0 7.64 01.17 9.8 11.04 lOO59'22"N} 26 19.45 0 24.46 High 19.46 4.6 12.79 71°35'42''W 27 01.00 0 25.01 Low 01.01 4.6 25.51 01.02 9.3 25.82 1963] Rodriguez: Intertidal Estuarine Communities 217 TABLE 3 GRAIN SIZE ANALYSISOF THE SUBSTRATAFOR SEVERALCOMMUNITIES ASTM SPECIFICATIONS Medium Fine Station Community Sand, % Sand, % Silt % 1 Ceratophyllum (Peat completely organic) 1 Ruppia 1.0 18.0 81.0 1 Polymesoda 0.2 27.0 72.8 1 Phragmites 10.2 27.0 63.0 1 U. mwrificenta 0.6 94.4 5.0 6, sst. 2 U. leptodactyla 12.9 76.9 10.2 6, sst. 2 U. leptodactyla 0.2 82.2 17.6 2 U. cumulanta 1.6 46.9 51.5 3 U. 'rapax 11.8 74.2 3.0 3 U. cumulanta 2.5 84.1 13.4 8 Sporobolus 18.5 76.6 4.9 8 U. leptodactyla 2.1 67.6 30.3

SUMARIO LAS COMUNIDADES DE ESTUARIOS DE LA ZoNA DE LAS MARE AS DEL LAGO MARACAIBO, 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 condi- ciones 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)

ROBINSON, E. F. . 1947. A project for deepening and improving the entrance to Lake Mara- caibo, Venezuela. Washington.

RODRIGUEZ, G. .1959. The marine communities of Margarita Island, Venezuela. Bull. Mar. Sci. Gulf and Carib., 9 (3): 237-280.

TABB, D. C. AND R. B. MANNING 1961. A checklist of the flora and fauna of northern Florida Bay and adja- cent brackish waters. Bull. Mar. Sci. Gulf and Carib., 11 (4): 552- 649.

TEN BROEK, A. N. CH. 1950. On some brackish water mollusca from the Lake of Maracaibo. Zool. Meded. 31 (8): 79-87.