Enrique Ávila

A preliminary assessment of the invasiveness of the Indo-Pacific sponge Chalinula nematifera on coral communities from the tropical Eastern Pacific

This is the first report of a sponge that overgrows live corals in the tropical Eastern Pacific ocean. Chalinulanematifera, native from the Indo-Pacific region, is an invasive sponge recorded for the first time in 2003 on coral communities from the Isla Isabel National Park (Mexican Pacific Ocean). Later, in 2006, it was found also on coral reefs from the Cabo Pulmo National Park; 217 nautical miles far away. It has been suggested that C. nematifera was introduced as fouling on ship hulls that have arrived at Isla Isabel from the Indo-Pacific. In this paper we examined the habitat specificity and the distribution and abundance through time of C. nematifera. While there were no significant variations in abundance through time, this species showed a very high specificity for living on live corals of the genus Pocillopora (94% vs. 6% on rocks). One of the environmental parameters that may explain this specificity for ramified corals is the low light intensity inside the coral colony, which was 96% lower than outside it. Coral reefs are currently struggling with a multitude of impacts that have weakened their resilience and pushed them away from equilibrium. As a result, more attention on ecology of corals is necessary. Although the abundance of C. nematifera seems to be stable, long-term monitoring programs (including studies of growth rates and recruitment) are needed to determine if this species could represent a threat to the Mexican coral ecosystem in the future.

PHENOTYPIC PLASTICITY INDUCED IN TRANSPLANT EXPERIMENTS IN A MUTUALISTIC ASSOCIATION BETWEEN THE RED ALGA JANIA ADHAERENS (RHODOPHYTA, CORALLINALES) AND THE SPONGE HALICLONA CAERULEA (PORIFERA: HAPLOSCLERIDA): MORPHOLOGICAL RESPONSES OF THE ALGA1

The association between the red macroalga Jania adhaerens J. V. Lamour. and the sponge Haliclona caerulea is the most successful life‐form between 2 and 4 m depth in Mazatlán Bay (Mexican Pacific). J. adhaerens colonizes the rocky intertidal area and penetrates into deeper areas only when it lives in association with H. caerulea. The aposymbiotic form of the sponge has not been reported in the bay. To understand the ecological success of this association, we examined the capacity of J. adhaerens to acclimate in Mazatlán Bay using transplant experiments. The transplanted aposymbiotic J. adhaerens did not survive the first 2 weeks; however, J. adhaerens when living in association with H. caerulea, acclimated easily to depth, showing no sign of mortality during the 103 d of the experiment. We conclude that the ability of J. adhaerens to colonize in deeper areas in this hydrodynamic environment may in part rely on the protection provided by the sponge to the algal canopy. Both species contribute to the shape of the associated form. Nevertheless, the morphological variation in the association appears to be dominated by the variation in J. adhaerens canopy to regulate pigment self‐shading under light‐limited conditions and/or tissue resistance under high hydrodynamics. Consequently, our results are consistent with light as the abiotic controlling factor, which regulates the lower depth distribution of the association in Mazatlán Bay, through limiting the growth rate of J. adhaerens. Hydrodynamics may determine the upper limit of the association by imposing high mass losses.

A preliminary evaluation of shallow-water rhodolith beds in Bahia Magdalena, Mexico

The aim of the present study was to describe the structure of shallow-water rhodolith beds from Bahia Magdalena, one of the most productive estuarine systems of the Mexican Pacific coasts. From September 2008 to May 2009 four rhodolith beds were found (between 1 and 3 m depth) and population descriptors such as rhodolith density, size classes, branch density, volume and weight were determined. The dominant rhodolith forming species was Lithophyllum margaritae. The size of beds ranged from 7,600 to 17,800 m2 approximately with densities from 42.2 to 215.9 ind.m-2. In these beds, L. margaritae shows fruticose and foliose growth forms, from which spherical forms were predominant (81-99%). Branch density (from 3.0 to 13.3 branches.cm-2) varied significantly (p < 0.05) among beds. The average volume (from 2.0 to 400 mL) and wet weight (from 32.4 to 84.8 g) was not significantly different among sites, but a significant positive correlation (r = 0.95, p < 0.05) was found between these parameters. The size of plants ranged from 2.0 to 11.5 cm with predominant size classes of 40.1-60 mm. Differences in rhodolith density, branch density and sphericity were attributed to possible differences in hydrodynamic conditions among sites. These beds were also a suitable habitat for high diversity of associated sponges. A non-metric multidimensional scaling (MDS) analysis using sponge species data revealed variability in the distribution of sponge assemblages among sites, which is likely the result of differences in environmental conditions. Although these rhodolith beds are not as extensive as those of other regions, our preliminary surveys revealed that they are a common habitat in Bahia Magdalena and likely have an important role in the productivity of this estuarine system.

Integrative taxonomy reveals the first record and a new species for the previously monotypic genus Tethytimea (Tethyida: Tethyidae) in the Gulf of Mexico

The first record of the previous monotypic genus Tethytimea and the description of a new species from cryptic habitats of Gulf of Mexico are presented. Tethytimea carmelita sp. nov., is a red orange cushion shaped sponge (about 5 mm thick) with a tuberculate to granular surface. The spicular complement is formed by tylostyles (200-1120 µm length), smooth spheres (12.5-55 µm in diameter); megasters-spheroxyasters (12.5-90 µm in diameter); and micrasters in two categories: oxy-strongylasters (12.5-27.5 µm in diameter) and spherotylasters (2.5-25 µm in diameter). The new species differs from the only species known T. tylota (Hentschel, 1912) mainly by differences in the size and shape of spicules. T. tylota possesses tylostyles in two size categories; megasters include giant oxyspherasters up 250 µm and micrasters in a single category. Additionally, to the morphological characteristics, we integrated partial sequences of a large sub-unit ribosomal 28S rDNA gene region (D1-D2 domains), in order to establish the molecular taxonomic position of our new species (and genus). Tree topologies (Maximum Likelihood and Bayesian Inference) were congruent in phylogenetic hypothesis, retrieving the Order Tethyida as monophyletic. In this clade, the family Timeidae was separated from the other families Tethyidae + Hemiastrellidae. Inside this latter group and according to the taxonomic hypothesis based on morphology, Tethytimea carmelita sp. nov. was included in Tethyidae clade, together with a sequence of Tethya sp. (AY626300), forming a sister group with representatives of genera Xenospongia and Thectitethya. Our new species constitutes the second valid known species for the genus Tethytimea and the first record of genus for the Atlantic Ocean.

Alien barnacle Amphibalanus amphitrite epizoic on two native oyster species in the southern Gulf of Mexico: spatio-temporal variability and current status of its epibiosis

ABSTRACT The study examines the current invasive status of the barnacle Amphibalanus amphitrite on natural populations of two native oyster species (the eastern oyster Crassostrea virginica and the mangrove oyster C. rhizophorae) in a estuary of the southern Gulf of Mexico. The spatio-temporal variability of the frequency of occurrence, density and coverage of A. amphitrite on shells of each oyster species was examined and compared with those of other native congeners (A. eburneus, A. venustus and A. improvisus) with which it coexists. These three variables were significantly higher in C. rhizophorae than in C. virginica and were within the range recorded for its congeners. The density of this invasive barnacle varied significantly at spatial and temporal scales. Its highest overall mean density occurred in February (at temperatures 26–27°C and salinities 29–32). Multivariate analyses showed a separation of Amphibalanus assemblages into three main groups according to variations in their composition and abundance among sampling sites and dates. It was also determined that salinity and sedimentation rate were the variables that best explain the distribution of the Amphibalanus species within the estuary. The limited presence of A. amphitrite on C. virginica reefs is likely due to (amongst other factors) the relatively higher sedimentation loads (370–5709 g m−2 d−1) and lower salinities (9–23) recorded in these sites. This study can act as a reference point for the subsequent monitoring of this invasive species, since possible increases in its population density and competitive ability could threaten the integrity of oyster populations and other organisms in the southern Gulf of Mexico.

A Reciprocal Inter-habitat Transplant Reveals Changes in the Assemblage Structure of Macroinvertebrates Associated with the Sponge Halichondria melanadocia

Sponges harbor great diversity and an abundance of organisms. Although this community can vary temporally, and between and within sponge species, it is not known how an induced change in habitat-specific environmental conditions might affect the structure of macroinvertebrate assemblages associated with sponges. Here, a reciprocal transplant experiment of individuals of the estuarine sponge Halichondria melanadocia was conducted between two neighboring habitats (seagrass and mangrove prop root habitats) in the Southern Gulf of Mexico. Transplanted sponges experienced different hydrodynamic and light conditions. Multivariate analyses showed differences in community structure of associated assemblages among treatments, which were mainly driven by changes in the abundance of common species. Sponges moved from seagrass to mangrove habitat experienced a significant increase in abundance and taxonomic richness of 88 and 35%, respectively. Given that changes in the volume and aquiferous system (oscula diameter and density) of the hosts and in salinity were also recorded during the study period, it is concluded that the structure of the H. melanadocia-associated assemblages was not only influenced by the habitat change but also by other factors such as host morphology and short-term variations in the population abundance of associated organisms.