Effects of hyposalinity in Thalassia testudinum (Hydrocharitaceae) from 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 rhi zome 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 +/- 0.35 g/m2/d and 2.15% leaf DW/d) were similar to the annual mean previously determined from Las Luisas (2.35 +/- 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 +/- 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.     

Benthic fauna associated to a Thalassia testudinum (Hydrocharitaceae) bed in Parque Nacional Morrocoy, Venezuela

The benthic fauna and diel variation in a shallow seagrass bed (Thalassia testudinum) were studied in Playa Mero, Venezuela. Samples of organisms and sediments were taken using PVC cylinders, 5cm in diameter, along a transect perpendicular to the coast. Seagrass cover, shoot density and biomass were estimated. The seagrass cover was homogeneous along the transect. The intermediate zone had the highest number of shoots and of above-ground and rhizome biomass. Composition and abundance of benthic organisms were related with seagrass and sediment characteristics. Sediment organic matter content and organism abundance were highest near the shore Molluscs, polychaetes, oligochaetes and nematodes were the most abundant groups. Species richness was higher in daytime (40 versus 28 at night). Gastropods were the most abundant organisms both at day and night while polychaetes and crustaceans increased during the day, and holoturids were more numerous at night.     

Environmental evaluation near a fuel vendor within Parque Nacional Morrocoy, Venezuela. II: Water quality, sediments and biota

This paper is the second part of a base line 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 close to the detection limit (0.8/ml). Vanadium was not 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.     

Zonation pattern of an isolated mangrove community at Playa Medina,Venezuela

This study focuses on a mangrove system which is completely isolated from the sea, lacking any connecting tidal channels or creeks and far enough from the coastline to prevent tidal flushing. The reason why it has become isolated remains unclear. But it is obvious that this situation may have introduced important changes in soil salinity and hydrological patterns, which might be reflected in the present composition and zonation patterns of the mangrove community. Main findings of this study suggest that: (1) Plant species distribution is affected mainly by water logging and mineral content of soils. (2) Ground water is the only permanent supply of water and salts to the isolated mangrove. (3) Soils are subjected to different degrees of leaching of salts. (4) The K: Na ratios support that mangrove community is not subjected to salinity stress. (5) Continuous leaching of salts favor the advance of terrestrial non-halophytes plants.     

Sponges (porifera) distribution along a depth gradient in a coral reef, Parque Nacional San Esteban, Carabobo, Venezuela

Sponges constitute one of the most diverse and abundant animal groups in the marine tropical benthos especially in coral reefs, though poorly studied to species level. The aim of this study is to characterize the sponge community along a depth gradient at Isla Larga (Parque Nacional San Esteban, Venezuela) fringe reef. Net and total sedimentation, roughness index, sponge species richness, density and proportion of the bottom covered by sponges, were evaluated at seven depths (1, 3, 6, 9, 12, 15, 18 m), 17 species were identified grouped in 10 demosponges families. The highest densities and coverage corresponded to 6 m of depth (6.03ind/m2; 11%), that coincides with the lowest net sedimentation and highest substrate heterogeneity. Most abundant species were Desmapsamma anchorata, Amphimedon erina and Scopalina rueztleri. Principal component analysis divided this community in three zones according to depth. The shallow zone of the reef (1 and 3 m), where wave force and high irradiance exert a constant stress sponges, shows the lowest density and coverage by sponges. In contrast, medium depth (6, 9 y 12 m) and deep zone (15 y 18 m) with lower light and sedimentation levels seem to enhance sponge growth and survival that are reflected on the higher densities and coverage of sponges.     

Syllinae (Syllidae: Polychaeta) of the Parque Nacional de Coiba, Panama]

Four expeditions were made to Coiba National Park between 1996 and 1998 to characterize this part of the poorly known Panamian Pacific polychaete fauna. The samples were collected by SCUBA diving, either by removing 4 kg blocks of dead coral (Pocillopora sp.) or scraping off 25 x 25 cm quadrats of Telesto multiflora or algae (Dyctiota cf. flavellata, Padina cf. durvillaei and another currently unidentified species). This paper deals with the Syllinae from hard substrates. Twenty-two species belonging to six genera of the subfamily Syllinae Grube, 1850 (Syllidae: Polychaeta) are reported. A new species, Syllis castroviejoi, is described. Four species are newly reported for the Eastern Pacific: Syllis beneliahuae (Campoy & Alquézar, 1982), S. botosaneanui (Hartmann-Schr?der, 1973), S. corallicola Verrill, 1900 and S. garciai (Campoy, 1982), and, likewise, two species are first reports for the Central American Pacific coast: Branchiosyllis pacifica Rioja, 1941 and Syllis truncata Haswell, 1920. Two species, Syllis magna (Westheide, 1974) and S. pigmentata (Chamberlin, 1919), are newly reported for Panama.     

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.     

Floral biology and pollinators of Trichocereus pasacana (Cactaceae) in Parque Nacional Los Cardones, Argentina]

Many columnar cacti are bat pollinated. It has been suggested that this kind of pollination would be more important in tropical than in temperate regions where flowers are open only one night. Thrichocereus pasacana produces big and resistant white flowers. We analyzed flower characteristics, floral cycle, stigmatic receptivity, nectar production, pollen presence and floral visitors in a T. pasacana population at National Park Los Cardones (Salta, Argentina) in November 1997. Flower features were constant between individuals of the population. Flowers start opening at evening and anthesis time is from 18 to 40 hs. The estigma was receptive throughout the floral cycle. Anther dehiscence occurs with flower opening. Nectar production was highest between 18 to 24 hs. Although T. pasacana are open during the night, floral visitors are diurnal. The most frequent was Xylocopa sp. In the study area, nectarivorous bats were not detected. The morphological features of T. pasacana flowers were similar but bigger compared to other columnar cacti. Anthesis time was also longer while nectar production was lower. T. pasacana pollination at National Park Los Cardones is done by bees.     

Great Barrier Reef butterflyfish community structure: the role of shelf position and benthic community type

The extent to which fish communities are structured by spatial variability in coral reef habitats versus stochastic processes (such as larval supply) is very important in predicting responses to sustained and ongoing habitat degradation. In this study, butterflyfish and benthic communities were surveyed annually over 15 years on 47 reefs (spanning 12° of latitude) of the Great Barrier Reef (GBR). Spatial autocorrelation in the structure of butterflyfish communities versus key differences in reef habitats was investigated to assess the extent to which the structure of these fish communities is influenced by habitat conditions. Benthic communities on each of the 47 reefs were broadly categorised as either: 1. Poritidae/Alcyoniidae, 2. mixed taxa, 3. soft coral or 4. Acropora-dominated habitats. These habitat types most reflected increases in water clarity and wave exposure, moving across the GBR shelf from coastal to outer-shelf environments. In turn, each habitat type also supported very distinct butterflyfish communities. Hard coral feeders were always the dominant butterflyfish species in each community type. However, the numerically dominant species changed according to habitat type, representing spatial replacement of species across the shelf. This study reveals clear and consistent differences in the structure of fish communities among reefs associated with marked differences in habitat structure.     

Geomorphology and community structure of Middle Reef, central Great Barrier Reef, Australia: an inner-shelf turbid zone reef subject to episodic mortality events

Middle Reef is an inshore turbid zone reef located 4 km offshore from Townsville, Queensland, Australia. The reef consists of four current-aligned, interconnected reef patches that have reached sea level and formed reef flats. It is regularly exposed to high turbidity (up to 50 mg l⁻¹) generated by wave-driven sediment resuspension or by episodic flood plumes. Middle Reef has a high mean hard coral cover (>39%), relatively low mean macro-algal cover (<15%) and a coral community comprising at least 81 hard coral species. Cluster analysis differentiated six benthic communities which were mapped onto the geomorphological structure of the reef to reveal a spatially patchy community mosaic that reflects hydrodynamic and sediment redistribution processes. Coral cover data collected annually from windward slope transects since 1993 show that coral cover has increased over the last ~15 years despite a history of episodic mortality events. Although episodic mortality may be interpreted as an indication of marginality, over decadal timescales, Middle Reef has recovered rapidly following mortality events and is clearly a resilient coral reef.     

Internal structure and Holocene evolution of One Tree Reef,southern Great Barrier Reef

Summary Analysis of core from six drill holes and ten vibrocores from One Tree Reef has delineated five major biosedimentological facies: algal pavement, coral head facies, branching coral facies, reef flat rubble facies and sand facies. Holocene growth began around 8,000 years B.P. with a high energy coral head facies on windward margins and a lower energy branching coral facies on patch reefs and on leeward margins. Vertical accumulation rates for these two principal facies are not greatly different; the coral head facies grew at 1.8–7.3 m/1,000 years and the branching coral facies at 0.6–8.3 m/1,000 years. Growth was initially much slower than the rate of sea level rise, a situation which changed only after sea level stabilized around 6,200 years B.P. A facies evolution model with rigidly imposed time constraints divides growth into three phases, i.e. vertical growth to sea level, transitional adjustment of biofacies at sea level, and leeward progradative phases.     

Mayan diver-fishers as citizen scientists: detection and monitoring of the invasive red lionfish in the Parque Nacional Arrecife Alacranes,southern Gulf of Mexico

Biological invasions research has increasingly incorporated the participation of citizen scientists to collect data for monitoring and management purposes. This study outlines collaborative efforts with Mayan lobster diver-fishers, who participated voluntarily as citizen scientists in surveys, to detect and monitor the invasive red lionfish, Pterois volitans, in a marine protected area off the northern Yucatan Peninsula, Mexico. We engaged these fishers by building local capacity and awareness of the threats of the lionfish invasion on the fishery resources of the area. During the lobster fishing season (July 2010–February 2011), 30 fishers collected 248 red lionfish (9–29 cm TL) and recorded ancillary data (day, month, depth, and approximate coordinates of capture site). This collaboration not only allowed the first lionfish detection in the Parque Nacional Arrecife Alacranes in 2010, but the volunteer-based monitoring effort revealed that the invasion reached levels from intermediate to advanced, with more than 200 specimens captured in less than a year. Our results support the notion that engaging citizen scientists can enhance research, reduce costs, and improve the possibility of a long term monitoring survey.     

Species richness and community structure of reef-building corals on the nearshore Great Barrier Reef

Species richness, cover and community structure of reef-building corals were assessed at 599 sites on 135 reefs along the Great Barrier Reef (GBR) between 1994 and 2001, with focus on the nearshore area. Communities were described hierarchically, with smaller regional communities forming part of higher level communities at increasing spatial scales. Site richness increased from the coast to the mid-continental shelf, declining on the outer shelf. Richness also increased with depth to 5 m, stabilizing thereafter. An anomaly was present in a 400 km section adjacent to the northern, ‘wet tropics’ coast, where site richness was 67 and 41% lower than the adjacent far northern and central GBR, respectively; this was probably due to the disturbance regime, with an apparent anthropogenic component. Site richness also declined in the Southern GBR, probably due to naturally marginal conditions. All indicator species had highest values in five small Far Northern and Central GBR communities. In the eight depauperate communities no indicator species had high values, indicating that these communities represent degraded, yet potentially transitional forms of the more diverse communities of the Far Northern and Central GBR. The study shows that on the GBR, disturbance results in the local removal of corals rather than a shift to suites of other coral species.     

Freshwater fishes of the Burdekin River, Australia: biogeography, history and spatial variation in community structure

Spatial variation in freshwater fish community structure in a large, structurally monotonous sub-tropical Australian river over 1989–1992 is described. The number of species collected (25) over the period of study, was low, given the large size of the river's catchment. The low diversity of fishes present in the river was suggested to be due to a combination of factors including the imposition of an ancient downstream barrier to fish movement (the Burdekin Falls), substantial volcanic activity during the late Tertiary, past climatic stress and little variation in habitat structure over the range of sites examined. Notwithstanding the low species richness, the Burdekin River's freshwater fish fauna is distinctive, containing elements of the fauna of both eastern and northern Australia, and this was suggested to reflect aspects of ancient landscape evolution. Spatial variation in fish community structure was most strongly influenced by the presence of the Burdekin Falls (the present site of a very large reservoir) and secondarily by minor differences in habitat structure of main channel and tributary streams.     

Sedimentary relationships and community structure of benthic crustacean assemblages of reef-associated sediments at Lizard Island,Great Barrier Reef

Samples were taken by diver-held corer at Lizard I., northern Great Barrier Reef, to investigate community organization and to relate community and sedimentary variables. Cluster analysis grouped the finest-sediment sites together and isolated a single mangrove site. Other site-groupings were more heterogeneous and supplementary analyses supported an individualistic continuum interpretation. Sites were also classified with respect to sediments. The finest-sediment site-group had significantly fewer species than coarser site-groups and a significant correlation existed between species richness and median phi. Species richness and evenness were positively related but the more variable sediments did not support more species. No relationship between number of individuals and sediments was apparent.     

Hemiuridae (Digenea) from marine fishes of the Great Barrier Reef,Queensland, Australia

The following species are described, figured and/or recorded from the Great Barrier Reef at Heron Island or Lizard Island, Queensland, with comparative material reported from other areas of the ocean around Australia or New Guinea: Dinurus longisinus (new synonym: D. hippuri) from Seriola lalandi, Heron Island and Coryphaena hippurus, Papua New Guinea; Ectenurus trachuri from Caranx sexfasciatus, Diploprion bifasciatus, Pterocaesio marri, Seriola lalandi and Atherinomorus capricorniensis, Heron Island; Erilepturus hamati (with 25 new synonyms) from Lutjanus carponotatus, Lizard Island, Platycephalus bassensis, Coff's Harbour, NSW, P. fuscus, Coff's Harbour, NSW and Moreton Bay, Queensland, P. endrachtensis, Sillago analis, S. maculata, S. ciliata, Pseudorhombus arsius and Polydactylus sp. from Moreton Bay, Queensland and Lates calcarifer, Darwin, Northern Territory; Tubulovesicula angusticauda from Echeneis naucrates and Lethrinus miniatus, Heron Island and Anguilla reinhardtii, Moreton Bay and Bribie Island, Queensland; Elytrophalloides humerus from Trachinotus botla and T. coppingeri, Heron Island; Lecithochirium kawakawa from Euthynnus affinis Heron Island and Lizard Island: Lecithochirium cirrhiti (new synonyms: L. sammarae, L. nohu) from Sargocentron rubrum, Heron Island; Lecithochirium caesionis from Pterocaesio marri, heron Island; Plerurus digitatus (new synonyms: P. cynoglossi, P. atulis, P. scomberomori) from Plectropomus leopardus, Heron Island, Lutjanus erythropterus, Variola louti, Scomberomorus semifasciatus, Grammatorcynus bicarinatus and Carangoides embureyi, C. gymnostethoides, Lizard Island, Scomberomorus commerson, Heron Island, Lizard Island, New Britain, Papua New Guinea, Point Lookout, Queensland and Moreton Bay, Queensland, Euthynnus affinis Heron Island, Lizard Island and New Britain, Papua New Guinea, Sphyraena barracuda, Heron Island and Lizard Island, Scomberomorus munroi, S. queenslandicus and Saurida undosquamis, Moreton Bay, Queensland and Chirocentrus dorab, Bundaberg, Queensland. The Lecithochirium species-group Cirrhiti is considered indistiguishable from the species-group Lotellae.     

Composition and seasonality of the zooplankton community of Lake Valencia, Venezuela

The composition and temporal abundance patterns of planktonicherbivores in Lake Valencia, Venezuela, were studied over a5-year period. The herbivore community was typically composedof only 9 or 10 species, of which four (Notodiapromus deeveyorus,Mesocyclops decipiens, Brachionus calyciflorus, Ceriodaphniacornuta) accounted for more than 90% of community biornass (67µg l^–1 mean dry mass). Annual average biomass variedby a factor of three over the 5-year study and this is comparableto interannual variation observed in lakes of the temperatezone. Lake Valencia has a pronounced seasonal cycle based onan annual mixing period and an annual stratification period.Herbivores were usually more abundant during the mixing seasonthan the stratification season. Proximate control of herbivoreabundance patterns could be ascribed largely to predation byChaoborus. Predation pressure was diminished during the circulationseason because the Chaoborus population was reduced by two mortalitymechanisms: catastrophic losses due to chemical changes at overturn,and increased predation by fish coincident with loss of thehypolimnetic refuge. Chaoborus fed on all herbivore speciesin Lake Valencia, but electivities for specific herbivores variedgreatly. The early developmental stages of both copepod speciesexperienced low predation pressure; Notodiaptomus nauphi escapedpredation entirely. Adult copepods, on the other hand, werehighly vulnerable to predation. A statistical analysis of temporalpatterns of abundance and production for the major herbivorespecies suggests that closely related species responded differentlyto growth control mechanisms; the two species with similar responses(M.decipiens and B.calyciflorus) also had coincident abundancepatterns. Despite statistical differences in responses to growthcontrol mechanisms, there was remarkable dietary similarityamong the species. There was no obvious dietary specializationand no statistical evidence of strong selectivity for or aversionto particular algal species. Zooplankton species compositionis very simple in Lake Valencia in contrast to the high speciesrichness of many other kinds of tropical communities. Herbivorecommunity abundance is highly seasonal in Lake Valencia; theamplitudes of abundance fluctuation exceed those of other largetropical lakes and are comparable to those in lakes of the temperatezone. Herbivore production in Lake Valencia, and in tropicallakes in general, is not necessarily higher than that in temperatelakes, but production per unit biomass probably is higher.     

Diet seasonality and food overlap among fishes of the upper Orituco stream, northern Venezuela.

The diets of four diurnal fish species (Creagrutus bolivari, Knodus deuterodonoides, Knodus sp. and Poecilia reticulata) were examined during a year in the Orituco stream at northern Venezuela. The fishes were sampled monthly from February 1991 to March 1992 (except October 1991 and February 1992) in the stream main channel with a beach seine and a cast net. Diet is reported as frequency of occurrence and numeric proportion because variation in prey sizes was small. Non-parametric statistical tests were applied. A total of 18 distinct prey items were found in stomachs. The diet of these fishes consisted of aquatic insects (Coleoptera, Diptera, Hemiptera, Odonata, Plecoptera and Trichoptera), allochthonous plant matter (fragments of leaves and seeds), microalgae (Chlorophyta and Bacillariophyceae) and terrestrial arthropods (Coleoptera, Diptera, Hymenoptera and Arachnida). The low percentage of empty guts and the high fullness percentage of guts suggest that food was always abundant. Aquatic insects were more important in the dry season (November-April) while plant matter and terrestrial arthropods increased in the wet season (May-October). The Proportional Similarity Measure (PS) was high between characid species and low between characids and P. reticulata in the dry season. PS decreased during the wet season because of a reduction in aquatic insect consumption. The seasonal diet shift indicated the greater importance of allochthonous food only in the wet season.