Morrocoy National Park Research Articles

Describing the dynamics of recruits and juvenile scleractinian corals using 3d models: a case study from Cayo Mero reef, Morrocoy National Park, Venezuela

Understanding the dynamics of coral recruitment and post-settlement is fundamental to a better comprehension of coral reef dynamics and recovery. We studied the abundance and survivorship of coral recruits and juveniles together with benthic dynamics at a scale of months and centimeters in Playa Mero reef, a disturbed reef in Morrocoy National Park. For this, we used photogrammetry to monitor eight permanent 50x50 cm quadrats haphazardly deployed every 3–4 months over 18 months. Juveniles and recruits of Agaricia spp. were at least four times more abundant than reef builders such as Orbicella spp. A distance-based linear model showed that rugosity, macroalgae, coral cover, and sand were the most important benthic variables and predicted up to 46% of the spatial and temporal variation of recruit and juvenile corals. The mortality of juvenile corals was higher than net recruitment rates, and only a limited number of genera such as Agariciids, Colpophyllia, Porites, and Scolymia were observed as recruits. Using a logit model, we also found a positive relationship between the mean growth rate and survivorship of juvenile corals (Nagelkerke R2= 0.67). We concluded the lack of recruitment of large reef builders, and the rapid mortality of a limited number of juvenile species, might be a sign of a coral community's failure to increase coral cover.

Sorption and desorption of phenanthrene and fluorene in mangrove forest soils of the Morrocoy National Park, Venezuelan Caribbean

Sorption and desorption of phenanthrene and fluorene in mangrove forest soils of the Morrocoy National Park, Venezuelan Caribbean

ANALYSIS OF POLYCYCLIC AROMATIC HYDROCARBONS (PAH) IN SOIL OF MANGROVE FOREST OF THE VENEZUELAN CARIBBEAN COAST

In order to identify the levels of contamination of mangrove soils by polycyclic aromatic hydrocarbons (PAH), their concentration was determined by gas chromatography coupled to mass spectrometry in the fraction of aromatic hydrocarbons obtained from soluble organic matter (SOM). Soils are located in Cuare Inlet and Morrocoy National Park from Venezuela, and samples were collected in Punta La Matica (PLM) and Tucacas Bay (ETU) respectively. Naphthalene, acenaphthene, acenaphthalene, benzo(ghi)perylene, dibenzo(ah)anthracene and indene have concentrations lower than the detection threshold for the technique employed (≤ 20 ng/g). Fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo(k)fluoranthene, benzo(b)fluoranthene and benzo(a)pyrene present concentrations ranging from 24 to 967 ng/g, and in some cases were not detected (≤ 20 ng/g). The PAHs concentration are classified in a pollution level from moderate to high in ETU and low in PLM. These results indicate a major anthropogenic pollution level of soils from ETU in relation to PLM soils. Based on the fact that the PAHs detected are not substituted and dominate the 3- and 4-rings, three diagnostic ratios to identify the contamination source were calculated: [anthracene/(anthracene+phenanthrene), fluoranthene/(fluoranthene+pyrene); and benzo(a)anthracene/(benzo(a)anthracene+chrysene)]; these ratios suggest a source from combustion of organic matter. Additionally, the normalization of total PAHs related to total organic carbon (TOC) or SOM represents a linear relationship between total PAHs with PAH/TOC and PAH/SOM, and suggests that the PAHs detected are from the same source, that is, the combustion of organic matter from anthropogenic activity or natural fires.

Estructura de la comunidad de peces arrecifales de Playa Mero, Parque Nacional Morrocoy, Venezuela

The coral reef fish community was studied in Playa Mero, Morrocoy National Park, after the mass mortality of January, 1996 with a systematic sampling design. Transects and quadrates were used for corals, and a visual census for fishes. The coral community is highly disturbed with extensive areas of dead coral covered by algae, and low coverage and richness of coral species, gorgonians, sponges and briozooans. These factors have generated a relatively homogenius environment with respect to the fish community, which was dominated by Scaridae and Pomacentridae that represented 75% of fish. Dominant fishes were mainly herbivorous all fish) apparently because of the disturbance that caused the settling of algae.

Evaluación del ambiente aledaño a un expendio de com­bustible dentro del Parque Nacional Morrocoy, Venezuela. II: Calidad de aguas, sedimentos y biota

This paper is the second part of a baseline study carried out in the coastal region near a marine ser­vice station located in Morrocoy National Park, Venezuela. Results from a physical and chemical characteriza­tion of the water and sediments of four sites located around the service station are presented. The physical and chemical factors measured in water included: temperature, salinity, specific conductance, dissolved oxygen, sat­uration percentage of dissolved oxygen, pH, total suspended solids, transparency, oil and grease, total residual petroleum hydrocarbon, vanadium and lead, total coliform bacteria, and the presence of coliform bacteria. The factors measured in sediments include: granulometry, organic material, total carbonates, vanadium, lead, oil and grease, and total hydrocarbons. In addition, the amount of vanadium and lead in sample tissue from three species which are abundant and widely distributed in each site was measured in order to evaluate the potential of these species as bio-indicators. The water in the area where this study was conducted is shallow, warm, and thermally homogeneous, with high salinity and normal pH and dissolved oxygen, and supersaturated with oxygen in cer­tain hours in sites adjacent to abundant underwater vegetation. The water is moderately turbid with a tendency towards less dissolved oxygen with increased depth. The estimated values of NMP/100 ml of the coliform fecal organisms is within legal limits even though the total number of water coliforms measured in Site 2 was ten times higher than in Site 1. This increase is associated with the proximity of Site 2 to an outflow of pre-treated sewage. The values of TRPH in the water collected from each site were low and very dose to the detection limit (O.5/ml). Vanadium was no! found, while lead was detected in 11 of the 12 samples. Compared to the values measured for Site 1, which was the local reference, only one sample had a concentration of three times the maximum baseline. The amount of lead found in all analyzed samples was acceptable, according to the standards set by the State of Washington (maximum value: 292 mg/kg), while the concentration of lead in the sediments around the supply dock were 1.5 to 3.4 times greater than the Dutch norm. It can be concluded that there is no evidence of an accu­mulation of Va or Pb in the species selected as bioindicators. An observation program is proposed in which vari­ables similar to those measured for this characterization will be studied with some modifications. A more intense sampling of some variables is recommended (lead in water and sediments, total coliform and fecal matter in con­secutive samples and in days following a high concentration of visitors) as is the elimination or minimization of other variables.

Efectos de la hiposalinidad en Thalassia testudinum (Hydrocharitaceae) del Parque Nacional Morrocoy, Venezuela

The year 1996 had a high pluviosity in Morrocoy National Park (western coastal zone, Venezuela) and low salinity in December 1996 affected the seagrass beds, dominated by Thalassia testudinum. Patches without T. testudinum were observed in localities of the park that used to have very dense populations of this plant. Sampling was done at Las Luisas to determine leaf productivity, turnover rate, short shoot density and relative biomass of plant sections, in order to compare with data obtained in September 1996, previous to the event. Green leaves, roots and rhizomes were the most affected parts. Mean green leaf biomass decreased in January and February 1997 to 5% of the plant's total biomass; mean root biomass decreased in March to 40% and mean rhizome biomass decreased in February to 30%. The density of the active short shoots decreased to a minimum in February, but in April it reached a value similar to that of September 1996. The density of the inactive short shoots decreased to a minimum in March, and they dissappeared in April, matching the increasing density of the active short shoots between these two months. In February 1997, 56% of the inactive short shoots showed evidence of leaf initiation. In January 1997 the leaf productivity and turnover rate values (2.72 it 0.35 g/m2/d and 2.15% leaf DW/d) were similar to the annual mean previously determined from Las Luisas (2.35 it 0.72 g/m2/d and 1.96% leaf DW/d). Nevertheless, the values of productivity and turnover rate detected at Las Luisas in April 1997 (4.88 it 2.14 g/m2/d and 4.66% leaf DW/d) were higher than those values previously reported for this location. In response to the mortality episode, the leaf productivity and turnover rate of T testudinum increased and the leaf initiation was activated in the inactive short shoots.

Elaboración de un Plan de Gestión Ambiental para el Parque Nacional Morrocoy, Venezuela

Ante la dificultad para prevenir los impactos ambientales sobre ecosistemas costeros se propone un método que centra los esfuerzos de evaluación y gestión en sus causas. Las causas de los impactos, llamadas aspectos ambientales (efluentes líquidos, residuos sólidos, emisiones atmosféricas), pueden predecirse, medirse y evaluarse con precisión y con un enfoque preventivo. Se desarrolló un procedimiento que consiste en identificar los Aspectos Ambientales y contrastarlos con una serie de criterios independientes (límites legales, sensibilidad del medio, riesgos). Se aplicó el método en ecosistemas costeros del Parque Nacional Morrocoy, con énfasis en el arrecife, para evaluar los impactos (degradación del arrecife) y sus causas (aspectos ambientales) proponiendo un Plan de Gestión Ambiental que minimice dichos aspectos ambientales y consecuentemente mitigue los impactos continuos sobre el arrecife. Por lo que se concluye que la gestión de los aspectos ambientales en las zonas costeras es una forma eficaz de prevenir los impactos ambientales, y en particular la degradación del arrecife, independientemente de los efectos ambientales globales, sobre los que los actores locales no tienen control.

Soil organic carbon of mangrove forests (Rhizophora and Avicennia) of the Venezuelan Caribbean coast

In order to understand the processes that control organic matter preservation in tropical wetlands, we have evaluated the mineralogy, total organic carbon (TOC wt%), soluble organic matter (SOM wt%), bulk density (g/cm3), and carbon stock (Mg/ha), and used FTIR to identify functional groups in SOM of soil in mangrove forest dominated by Rhizophora or Avicennia with different conditions (live, deteriorated and dead). Six locations along the Cuare Inlet and Morrocoy National Park were studied. Mineralogical analysis showed the presence of minerals, such as pyrite and rhodochrosite, from anoxic environments. Rhizophora mangrove soils have higher TOC compared with Avicennia, but we did not find significant differences in SOM. TOC/SOM ratios were lower for Avicennia soils. The carbon content ranged from 11.30 to 59.84Mg/ha for the first 10cm of soil. Regardless of stand condition, the TOC/SOM ratio was lower at a depth of 20–40cm. The results of the TOC/SOM ratio are attributable to: (a) the association of TOC with clays and non crystalline minerals; (b) the leaching processes of soluble compounds of the OM; (c) a higher proportion of recalcitrant compounds; (d) a lower decomposition rate for recalcitrant or non-recalcitrant compounds; and (e) physicochemical conditions that limit biological activity, such as high salinity, soil anoxia and hypoxia. The soils can be divided into three groups according to the presence and intensity of functional groups detected by FTIR. The functional groups identified could not be related to the sampling sites, to species composition or conditions. These differences may be due to other sources of organic matter, as well as to degree of preservation. Information of soil organic matter properties and their relationship with mangrove composition and conditions is important to understand carbon sequestration and storage potential in Venezuelan Caribbean mangrove systems.

Sea anemones (Cnidaria: Actiniaria, Corallimorpharia, Ceriantharia, Zoanthidea) from marine shallow-water environments in Venezuela: new records and an updated inventory

This study compiles the diversity of sea anemones in different shallow habitats (i.e. rocky shores, coral reefs, mangroves and sandy bottoms) in several locations of Venezuela, including the most important marine reserves of Venezuela: Morrocoy National Park, Mochima National Park, Archipielago de Los Roques National Park, Laguna de La Restinga National Park, Isla de Cubagua, and Chichiriviche de la Costa. Twenty-six species of sea anemones sensu lato were documented, from which only two actiniarian species are newly recorded in Venezuela. In addition, specimens of the scientific collection of the Museo Oceanologico Hermano Benigno Roman, of Isla de Margarita, Venezuela, were examined and its taxonomic status updated. The diversity of sea anemones in Venezuela is updated to 44 species. An illustrated guide of living specimens and short descriptions of the external anatomy of the specimens is included to facilitate sea anemone species identification in the field and to provide a base line for ecological studies that require accurate identification to species level.

Influencia del nitrógeno y Halimeda opuntia (Cholorophyta) en la abundancia de Potamilla sp. (Polychaeta: Sabellidae) en campos de Thalassia testudinum

Nitrogen, as a nutrient, is considered a rate-limiting factor. Additionally to the pool nutrients, abundance of particular species can be delennined by biomass of seagrass and plant architecture. including algae associated to Thalassia meadows. To test this, mree sampling stations of T. testudinum beds were studied al Morrocoy National Park Venezuela (lOO52'N-6go16W). Al each, a 20 X 20 meter plot was markedpennanently and, alleast, ten random quadrats were sampled moothly during 13 months. Nitrogen colltents in sediments and biomass of H. opunlia influence positively me abundance of Potamilla sp. (A= 21.49; B= 6.0; C= 1.05). Both parameters showed the following gradient: A>B>C (r= 0.6549; p<0.0l). The influence of me algae was noled particulary on me Morisita dispersion index (Ig).

What can two years of monitoring tell us about Venezuelan coral reefs? The Southern Tropical America node of the Global Coral Reef Monitoring Network (STA-GCRMN)

In spite of their economic importance, coral reef communities of the world are rapidly decreasing, and an adequate management planification is needed. The benthic and fish communities of Dos Mosquises Sur and Madrizqui at Los Roques National Park, and Caiman and Cayo Norte at Morrocoy National Park, in Venezuela were monitored during 2003 and 2004. The CARICOMP method was used to describe the benthic community, and the AGRRA protocol was applied to the fish community assessment. The benthic cover of five broad living categories (i.e. corals, algae, sponge and octocorals) differed across the sites (Nested ANOVA, p < 0.05), but there were no statistical differences between parks. Despite being on different parks, the benthic cover in Dos Mosquises Sur and Cayo Norte was similar (76% based on Bray-Curtis), whereas Caiman differed greatly (57- 68%) from all other sites. The cover of hard coral, algae, sponges and octocorals was similar between 2003 and 2004 in all four sites. Similarly, the fish community structure of both parks did not change over time, and was dominated by herbivores (Pomacentridac, Scaridae and Acanthuridae). However, commercially important carnivores (e.g. Lutjanids and Serranids) were more abundant in Los Roques than in Morrocoy. Although it was expected that the benthic cover and fish community would reflect greater differences between Los Roques and Morrocoy, only the fish community appeared healthier in Los Roques, whereas Cayo Norte (Morrocoy), had a coral cover similar or higher than both sites of Los Roques. Thus, our results suggest that in Venezuela, oceanic reef sites are not necessarily 'healthier' (i.e. higher coral cover) than land-influenced coral communities. The addition of three new sites and the reincorporation of Caiman has improved and expanded the monitoring capabilities in Venezuela and it represents the first step towards the consolidation of a coral reef monitoring program for the country.

Arbuscular mycorrhizal fungi communities in a coral cay system (Morrocoy, Venezuela) and their relationships with environmental variables

Knowledge of the natural diversity of arbuscular mycorrhizal fungi (AMF) and understanding of their biogeographical patterns and what drive them might help to the maintenance and preservation of ecosystems under a changing environment. The objective of this study was to evaluate the contribution of different environmental factors to the determination of the composition of AMF assemblages in representative sites within the Morrocoy National Park (Venezuela). The community structure of the AMF under the canopy of Coccoloba uvifera was investigated in four cays (Borracho, Muerto, Peraza, and Paiclás) and one mainland location (Las Luisas). Based on partial sequences of the nuclear small subunit ribosomal DNA gene, the AM fungi in soil samples were divided into 31 operational taxonomic units, grouped in eight families. The canonical correspondence analysis showed that environmental factors related to insularity (the mean annual rainfall, the distance to the mainland coast, and the cay land area) and a soil property related to biological activity (the total carbohydrate content) were significantly related to the distribution of the AMF communities.

Estructura de la comunidad de esponjas (Porifera) en tres arrecifes del Parque Nacional Morrocoy, Venezuela y su relación con algunas variables ambientales

Sponges have an important ecological role in coral reef ecosystems. However, when compared to other benthic Phyla, it has been little researched. This research was focused in the variability of the community structure of sponges in three locations at Morrocoy National Park (Cayo Sombrero, Playa Mero and Punta Brava) exposed to different environmental conditions (transparency and currents intensity) and affected in different degree of severity by a mass mortality event in 1996. A total of 15 transects (10 m long and 1 m wide) were evaluated in three strata (between 3 and 15 m depth) in each site, where all the individuals were counted by species. Relative abundance by species, diversity and evenness were calculated. Locations showed differences respect turbidity, wave and current intensity. 27 species were found in Morrocoy; Cayo Sombrero (23), Playa Mero (18) and Punta Brava (15). Agelas sceptrum, Amphimedon erina and Niphates erecta were the most common in first location; Niphates erecta and Dysidea etheria in Playa Mero and Dysidea etheria, Niphates erecta and Amphimedon erina in Punta Brava. The species composition showed statistical differences between all three locations; Cayo Sombrero resulted the most diverse and even, followed by Playa Mero and Punta Brava. According to Sorensen Similarity Index results, Cayo Sombrero and Playa Mero were more similar, while Punta Brava resulted the most different. The variability in environmental conditions and the differential mass mortality effects of 1996 in all three reefs, were probably the main causes of the differences between their sponge communities. Nevertheless, we cannot conclude about the weight of these factors.

Nuevas especies de la familia Marginellidae (Mollusca: Neogastropoda: Muricoidea) de Venezuela

To date, 10 species of the genus Volvarina and one species of the genus Hyalina have been cited in Venezuela, but only 2 of them are certain. In this paper 4 new species of mollusks of the family Marginellidae are described, based on specimens collected from 3 different locations: La Tortuga Island, Morrocoy National Park and Aves Island. Additionally, the records in Venezuela of all the species of both genus and the validity of Caribeginella flormarina, synonymized with Hyalina pallida, are discussed. Illustrations of the living animals for all the species are included, so as new photos of the shell of the Neotype of H. pallida, housed in the Natural History Museum in London. The new species are characterized by: Volvarina morrocoyensis Caballer, Espinosa & Ortea new species; 5 brownish bands in the shell, paired parallel plications, white body with red spots, mantle with black spots grouped in bands. Volvarina monchoi Caballer, Espinosa & Ortea new species; white shell with a brown band, uneven plications, white body without spots. Volvarina avesensis Caballer, Espinosa & Ortea new species; 3 orange bands in the shell, parallel plications, orange body, lacking spots, mantle with dull spots. Hyalina nelsyae new species; 3 dull bands in the shell, posterior plications divergent, anterior plications quasi-parallel, body with reddish spots forming a diamond in the tail, mantle with reddish spots forming 3 bands.

Reproducción y dinámica poblacional de Cheirodon interruptus (Ostariophysi: Characidae) en el arroyo El Portugués, alta cuenca del río Samborombón, Argentina

The coral reefs of Morrocoy National Park are currently deteriorated. After the massive mortality of 1996, Acropora palmata has shown some signs of recovery, a process that could be hampered by Coralliophila. We observed only three colonies of A. palmata in an entire reef in Cayo Sombrero. In July 2005, these colonies registered Coralliophila abbreviata densities of 4, 0, and 2 ind/col and Coralliophila caribaea densities of 22, 14, and 0 ind/col; in January 2006, said densities were 8, 0, and 4 ind/col (C. abbreviate) and 22, 14, and 0 ind/col (C. caribaea). Four sites of damage (two per predator) were observed in the three colonies. In one colony, C. abbreviata caused a loss of tissue of 66.14 to 162.85 cm2, indicating a predation rate of 0.52 cm2 day-1. In the other colony, the damage ranged from 37.41 to 72.50 cm2, with a predation rate of 0.19 cm2 day-1. The areas damaged by C. caribaea did not show any change. The high density and predation rate of Coralliophila likely affected the recovery of the scant specimens of A. palmata in Morrocoy National Park.

Nota sobre la densidad y tasa de depredación de Coralliophila abbreviata y Coralliophila caribaea sobre colonias jóvenes de Acropora palmata en un arrecife deteriorado de Cayo Sombrero, Parque Nacional Morrocoy, Venezuela

The coral reefs of Morrocoy National Park are currently deteriorated. After the massive mortality of 1996, Acropora palmata has shown some signs of recovery, a process that could be hampered by Coralliophila. We observed only three colonies of A. palmata in an entire reef in Cayo Sombrero. In July 2005, these colonies registered Coralliophila abbreviata densities of 4, 0, and 2 ind/col and Coralliophila caribaea densities of 22, 14, and 0 ind/col; in January 2006, said densities were 8, 0, and 4 ind/col (C. abbreviate) and 22, 14, and 0 ind/col (C. caribaea). Four sites of damage (two per predator) were observed in the three colonies. In one colony, C. abbreviata caused a loss of tissue of 66.14 to 162.85 cm 2

Ichthyofauna associated to a shallow reef in Morrocoy National Park, Venezuela

Ichthyofauna associated to a shallow reef in Morrocoy National Park, Venezuela. Morrocoy National Park is one of the most studied coastal marine environments in Venezuela; however, efforts have been concentrated in south zone. In this study we select a shallow reef located in the north zone, characterized the benthic community and the structure of the fish community was studied using visual censuses. The benthic community was dominated by dead coral covered by algae (31%) and the live coral coverage was 12%. A total of 65 fish species belonging to 24 families were recorded, being Pomacentridae (43%), Scaridae (19%) and Haemulidae (15%) the most abundant families. Significant differences in the fish species abundances were found along the depth gradient, which could be related to the habitat characteristics, nevertheless herbivorous species dominance was evident at all depth strata. There seems to be a trend towards greater richness and density in the south zone reefs, and these differences may be related to the presence of extensive seagrass meadows and mangrove forests in that area or to differences in the recruitment patterns.

Metals in Waters and Sediments of the Morrocoy National Park, Venezuela: Increased Contamination Levels of Cadmium over Time

Concentrations of heavy metals in the western coast of Venezuela are partly driven by anthropogenic influences. To detect metal changes over time, the waters and sediments from 19 sites, across various marine ecosystems, were sampled seven times between 2000 and 2001 and compared with previous studies. The water samples had mean concentrations of Cd, Cu, Pb, and Zn above the guideline values proposed by NOAA as capable of producing chronic effects in the marine biota. In sediments, the mean Cd concentration also exceeded NOAA’s Effects Range–Low values for all habitat types, and in sheltered sites, it exceeded NOAA’s Effects Range–Median values. The meta-analysis indicated that metal concentrations in water were higher in 2000–2001 than in 1995–1997, with the exception of Pb. In sediments, however, only the concentrations of Cd, Cu, and Pb increased in this period. This increase was particularly noticeable for Cd which, by 2000–2001, showed Igeo values indicating that Morrocoy National Park could be considered strongly to extremely polluted. This increment in the metal concentrations could be associated with: (1) an anomalous precipitation event that occurred at the end of 1999 and which caused a disturbance in the sediment chemistry of most metals and/or (2) an increase in the anthropogenic and natural input of Cd probably associated with the production of fertilizers in the region during the period analyzed. Special attention should be paid to Cd levels in this area as it represents a high toxicological risk for the biota in different habitats.

Selectividad de presas de Coralliophila abbreviata y C. caribaea en arrecifes coralinos del Parque Nacional Morrocoy, Venezuela: una aproximacion experimental

Coralliophila abbreviata and C. caribaea are tropical gastropods of the Caribbean Sea. These gastropods have shown to be important corallivores. The objective of this work was to evaluate in situ the prey selectivity of C. abbreviata and C. caribaea in some coral reefs of Morrocoy National Park by means of experimental and descriptive methods. We used quadrats of 1 m 2 to estimate coral abundance and richness, number of Coralliophila specimens, and coral species preyed on by Coralliophila sp. in three sites at each locality. For the experiment, we enclosed in cages five coral colonies of different species together with 10 individuals of C. abbreviata located in the center of the cages and equidistant to all colonies. A total of 8 exclusion cages of 1 m 3 were evaluated. We observed in situ a higher relation predator-prey between C. abbreviata and the hexacoral species M. annularis, representing 56.8% of the total interactions at all localities, followed by D. strigosa (19.3%), A. agaricites (12.2%), C. natans (4.6%) and A. tenuifolia (3.1%). C. caribaea presented a higher relation predator-prey with the octocoral species E. caribaeorum (42.6%), followed by those with the hexacoral species C. natans (24.1%) , M. faveolata (11.1%) , P. porites (7.4%) and D. strigosa (11.1%). The experiment showed a major relation between C. abbreviata and M. annularis , with 53.3% of total interactions, followed by those of C. natans (17.8%), A. tenuifolia and D. strigosa (11.1%) and A. agaricites (6.7%). According to the outcomes C. abbreviata is thought to generate a larger impact than C. caribaea on Morrocoy National Park because its more common preys are mainly coral reef building species while C. caribaea predate mainly on E. caribaeorum , which is a competitive species of hexacorals.

Gametogenic cycle of the tropical vermetids Eualetes tulipa and Dendropoma corrodens (Mollusca: Caenogastropoda: Vermetidae)

The population density, annual gametogenic cycle, and size at sexual maturity of two vermetid species, Eualetes tulipa (invasive) and Dendropoma corrodens was studied in the southern Caribbean at the Planta Centro power plant intake channel and at Punta Mayorquina, Morrocoy National Park, respectively. Minimal size of mature females of E. tulipa and D. corrodens was 5.0 and 0.7 cm in body length respectively. The gonad represented between 44 to 47% of total body length, while it represented between 15 to 18% of total body volume (for both males and females). Gonad volume was significantly related to total body volume. A significant quadratic relationship between the number of capsules and female body volume was obtained for E. tulipa, indicating that females measuring 6–10 cm in body length are those that have the highest number of egg capsules. Females larger than 11 cm have a lower fecundity in terms of brooded capsules. Gonad sections of males and females of both species showed that several gametogenesis stages are simultaneous within the same individual. In the female, germ cells, oogoniums and primary oocytes with yolk granules were observed simultaneously. In the male, the spermatogonium, primary and secondary spermatocytes, spermatids and sperm cells were also observed within one gonad. The same pattern was observed throughout the year, showing no maturation/resting period or annual cycle. The area covered by D. corrodens was about 700 m2 with a mean density of 13,000 ind/m2. The area covered by the invasive E. tulipa was at least about 1000 m2, with a density of 27,000 to 29,000 ind/m2 in the first 3 m of depth. A follow up of the E. tulipa population showed that its density is increasing in time and has doubled in 20 years. This population increment could be related to an increase in organic suspended matter as evidenced in the region.