Edlin Guerra-Castro

Patterns of Spatial Variation of Assemblages Associated with Intertidal Rocky Shores: A Global Perspective

Assemblages associated with intertidal rocky shores were examined for large scale distribution patterns with specific emphasis on identifying latitudinal trends of species richness and taxonomic distinctiveness. Seventy-two sites distributed around the globe were evaluated following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). There were no clear patterns of standardized estimators of species richness along latitudinal gradients or among Large Marine Ecosystems (LMEs); however, a strong latitudinal gradient in taxonomic composition (i.e., proportion of different taxonomic groups in a given sample) was observed. Environmental variables related to natural influences were strongly related to the distribution patterns of the assemblages on the LME scale, particularly photoperiod, sea surface temperature (SST) and rainfall. In contrast, no environmental variables directly associated with human influences (with the exception of the inorganic pollution index) were related to assemblage patterns among LMEs. Correlations of the natural assemblages with either latitudinal gradients or environmental variables were equally strong suggesting that neither neutral models nor models based solely on environmental variables sufficiently explain spatial variation of these assemblages at a global scale. Despite the data shortcomings in this study (e.g., unbalanced sample distribution), we show the importance of generating biological global databases for the use in large-scale diversity comparisons of rocky intertidal assemblages to stimulate continued sampling and analyses.

ACTIVITY PATTERNS AND ZONATION OF THE SWIMMING CRABS ARENAEUS CRIBRARIUS AND CALLINECTES ORNATUS

Abstract Home range, movements and zonation of Arenaeus cribrarius and Callinectes ornatus were analyzed in Ensenada de La Vela, in the Venezuelan Caribbean, using acoustic telemetry. Transmitters were attached to the carapace of 11 A. cribrarius and 11 C. ornatus, which were tracked during five campaigns between October 2002 and December 2003. The positions of each crab were registered every 12 hours, for periods of up to 10 days, and data were obtained on geographical localizations, distances traveled, speed, depth, perpendicular distance to the beachline, as well as type of bottom and physicochemical variables of the water. We found significant differences between the two species regarding home range size (sensu lato), movements, distance to the coastline, depth and the type of sediment where they appeared. Callinectes ornatus had a larger home range (x̄ = 72,475 m2) than A. cribrarius (x̄ = 16,625 m2) and presented one to three centers of activity, while individuals of A. cribrarius had only one center, with a few exceptions. Both species used intensively about half of their home range. Arenaeus cribrarius preferred the foreshore, while C. ornatus inhabited more distant waters; however, a certain degree of habitat interpenetration was observed. Callinectes ornatus was more active (x̄ = 74.6 m/12 hours, SE = 6.6) than A. cribrarius (x̄ = 56.6 m/12 hours, SE = 6.5), but a high variability in the movement rates existed even within an individual. Arenaeus cribrarius was associated with bottoms conformed by very fine mixed sands and low contents of organic matter, whereas C. ornatus appeared in silty bottoms with higher organic contents. New elements on the zonation of these swimming crabs are included in this study, complementing the patterns found in previous works.

Spatial variability and human disturbance of sponge assemblages associated with mangrove roots in the southern Caribbean

Assemblages growing on Caribbean red-mangrove roots are very diverse and characteristically dominated by sponges. The scales of spatial variation of this fauna in the Caribbean region have not been hierarchically quantified, although such information is necessary to understand the relative importance of ecological processes and possible responses to anthropogenic disturbances. We used a hierarchical nested design to identify patterns of spatial variability at different scales, namely among roots, sites, localities and regions within the southern Caribbean. Simultaneously, the sampling considered the relative distance from sources of human disturbance to test the null hypothesis of no difference in sponge diversity among localities as a result of anthropogenic stress. Significant spatial variability in species composition was detected at all spatial scales, especially at the among-root scale. However, there were no differences associated with distance from human disturbance. These results indicate high regional and local β diversity, and also suggest that results from small-scale experiments cannot be scaled up to the entire community. Further, spatial analysis of sponge assemblages is not enough to detect deleterious effects of human disturbances on mangrove areas.

Inventory of ascidians (Tunicata, Ascidiacea) from the National Park La Restinga, Isla Margarita, Venezuela

Although ascidians form a conspicuous part of sessile assemblages in the Caribbean, no specialized inventories have been developed in Venezuela, except for a list of 15 species reported from Margarita Island (1984). Here we present the results of a taxonomic workshop held in the Universidad de Oriente, Boca del Rio, Margarita Island during April 20-25 of 2009, sponsored by the NaGISA-Caribbean Sea program. La Restinga National park was surveyed and we found 29 species belonging to 19 genera and 10 families. The most abundant colonial species were Clavelina oblonga, Aplidium accarense, Polyclinum constellatum, Distaplia bermudensis, Symplegma rubra, S. brakenhielmi, Botrylloides nigrum and Ecteinascidia turbinata. Among the solitary ascidians Phallusia nigra, Ascidia curvata, Microcosmus exasperatus, Styela canopus, Styela sp.1 and Styela sp. 2 were the most abundant. The ascidian diversity in this lagoon is one of the highest for similar habitats in the Caribbean and seven species are new registers for Venezuela (Ascidia curvata, Ecteinascidia styeloides, Aplidium accarense, Distaplia stylifera, Trididemnum orbiculatum, Symplegma rubra, and S. brakenhielmi). One point of concern for the conservation of la Restinga National Park is the presence of possible introduced species, and some management procedures are suggested.

Biotelemetry of crustacean decapods: sampling design, statistical analysis, and interpretation of data

The implementation of ultrasonic telemetry as a technique to evaluate ecological traits of marine organisms has allowed biologists to obtain information that is hard or impossible to achieve by traditional sampling methods; which in turn improves the quantification, in their natural habitats, of activity patterns, movements, migrations, habitat utilization and zonation, among other biological and physiological variables. Despite its transcendence, this technique has been scantly applied in crustacean decapod studies, mainly due to the high costs involved (resources, time, and personnel) and the problem of how to analyze quantitatively telemetry data to test hypotheses. Thus, the aim of this article is to evaluate, discuss, and review the statistical methods employed in this discipline and make some recommendations concerning the sampling effort and efficiency, as well as to suggest appropriate ways to analyze data, specifically with frequentist statistics (parametric and nonparametric). Examples are given based on data previously published.

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

BackgroundThis 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, Archipiélago de Los Roques National Park, Laguna de La Restinga National Park, Isla de Cubagua, and Chichiriviche de la Costa.ResultsTwenty-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 Oceanológico Hermano Benigno Román, of Isla de Margarita, Venezuela, were examined and its taxonomic status updated.ConclusionsThe 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.