Guillermo Horta-Puga

Shifts in coral-assemblage composition do not ensure persistence of reef functionality

Coral communities are changing rapidly worldwide through loss of coral cover and shifts in species composition. Although many reef-building corals are likely to decline, some weedy opportunistic species might increase in abundance. Here we explore whether the reshuffling of species can maintain ecosystem integrity and functioning. Using four common Caribbean reef-building coral genera we modeled rates of reef construction and complexity. We show that shifting coral assemblages result in rapid losses in coral-community calcification and reef rugosity that are independent of changes in the total abundance of reef corals. These losses are considerably higher than those recently attributed to climate change. Dominance patterns of coral assemblages seem to be the most important driver of the functioning of coral reefs and thus, the future of these ecosystems might depend not only on reductions of local and global stressors, but also on the maintenance of keystone coral species.

The Ba/Ca record of corals from the Southern Gulf of Mexico: contributions from land-use changes, fluvial discharge and oil-drilling muds.

The Ba/Ca in the growth bands of Montastraea faveolata from the Veracruz Reef System was used to reconstruct the long-term environmental change associated to anthropogenic activity in the Southern Gulf of Mexico (SGM). The 168-yr coral record shows two periods of distinct Ba concentrations: a pre-industrial period (1835-1965: 7.54 micromol/mol) followed by an industrial one (1966-2000: 8.57 micromol/mol). As human population quadrupoled during the latter, sediment load in the fluvial discharge also increased due to changes in land-use, yielding a 14% increase in the Ba-levels. A remarkable finding is that the periods at which the coral Ba/Ca ratio losses its correlation with fluvial discharge coincide exactly with peak periods of high barite consumption (used for oil drilling) in the Northern Gulf of Mexico, and the onset of oil drilling in the SGM. This finding suggests that barite may be one of the dominant sources for dissolved-Ba in the SGM.

Cadmium, copper and lead in macroalgae from the Veracruz Reef System, Gulf of Mexico: Spatial distribution and rainy season variability

This study focused on the spatial distribution of trace metals in the Veracruz Reef System in the Southern Gulf of Mexico, and its variability in the early (July) and late (September) rainy season of 2008, by analyzing the concentration of Cd, Cu and Pb in benthic macroalgae. Mean concentrations are lower (Pb 295 ± 347 ng g(-1), Cd 17.9 ± 15.0 ng g(-1)), or similar (Cu 3.4 ± 4.5 μg g(-1)) to those reported from other coastal areas. Cd and Pb concentrations are influenced by the discharge of the Jamapa River, evidencing a fluvial control on coastal trace metal levels. Also, Cd and Cu concentrations were lower in the late rainy season, when there is a high load of suspended sediments derived from fluvial discharge, which probably adsorb dissolved metals decreasing their bioavailability. Pb concentrations have been decreasing in the last two decades in the SGM, after the banning of leaded-gasoline in the late 20th century.

Geochemical partitioning of lead in biogenic carbonate sediments in a coral reef depositional environment

The fate of trace elements in reef depositional environments has not been extensively investigated. The aim of this study was to determine the partitioning of Pb in sediments of the Veracruz Reef System, and its relation to local environmental sources. Lead was determined in four geochemical fractions: exchangeable (3.8±0.4μgg-1), carbonate (57.0±13.6μgg-1), organic matter (2.0±0.9μgg-1), and mineral (17.5±5.4μgg-1). For the mineral fraction, lead concentrations were higher in those reefs influenced by river discharge or by long-distance transport of terrigenous sediments. The bioavailable concentration of lead (range: 21.9-85.6μgg-1) indicates that the Veracruz Reef System is a moderately polluted area. As expected, the carbonate fraction contained the highest proportion of Pb (70%), and because the reef framework is largely made up of by biogenic carbonate sediments, hence, it is therefore the most important repository of Pb in coral reef depositional environments.

Metales pesados en macroalgas del Sistema Arrecifal Veracruzano, sur del Golfo de México

Se determinaron los niveles ambientales de los metales pesados Cd, Cu y Pb en macroalgasbentonicas durante el verano del 2007 en el Sistema Arrecifal Veracruzano, en el sur delGolfo de Mexico. Muestras de las algas Caulerpa, Dyctiota y Galaxaura fueron colectadasmanualmente a una profundidad de 8-10 m en el talud arrecifal de sotavento en seisarrecifes seleccionados: Galleguilla, Blanquilla, e Isla Verde del grupo norte, y La Blanca,Isla de Enmedio y Anegada de Afuera del grupo sur. La concentracion total promedio demetales pesados fue: Cu 2930±1867 ng/g, Pb 22.8±13.0 ng/g y Cd 13.7±9.5 ng/g, y seconsidero que estos varian en concordancia con su disponibilidad en columna de agua. Laconcentracion de metales pesados fue menor en los arrecifes del grupo sur que en los fdelgrupo norte, probablemente debido a la presencia de particulas sedimentarias quelantes. Lasbajas concentraciones de metales pesados en las macroalgas del Sistema ArrecifalVeracruzano aqui reportadas, sugieren que el area costera frente al puerto de Veracruz, nodebe ser considerada actualmente como un area contaminada.