The changing form of Antarctic biodiversity

Antarctic biodiversity is much more extensive, ecologically diverse and biogeographically structured than previously thought. Understanding of how this diversity is distributed in marine and terrestrial systems, the mechanisms underlying its spatial variation, and the significance of the microbiota is growing rapidly. Broadly recognizable drivers of diversity variation include energy availability and historical refugia. The impacts of local human activities and global environmental change nonetheless pose challenges to the current and future understanding of Antarctic biodiversity. Life in the Antarctic and the Southern Ocean is surprisingly rich, and as much at risk from environmental change as it is elsewher

Calibration of Sr/Ca and Mg/Ca paleothermometers in coral Porites sp. from San Benedicto Island, Revillagigedo Archipelago, Mexico

A better understanding of the global climate system depends on our ability to expand the limited instrumental records of sea surface temperature (SST) of tropical regions. The Sr/Ca and Mg/Ca ratios contained in the growth bands of corals have proved to be an accurate tool to reconstruct SST variability. In this study we show the calibration obtained from the seasonal geochemical measurement of the Sr/Ca and Mg/Ca molar ratios in the skeleton of coral of the genus Porites from San Benedicto Island, in the Revillagigedo Archipelago, and SST. The geochemical ratios measured (precision ±0.2%, 2σ) showed a high seasonal covariation closely related to the region's SST. The calibration equation calculated for the Sr/Ca–SST relation (n = 52) was Sr/Ca (mmol mol–1) = 10.467 (±0.067) – 0.0524 (±0.003) × SST (r2 = 0.894), and for the Mg/Ca?SST relation it was Mg/Ca (mmol mol–1) = 1.550 (±0.095) + 0.0956 (±0.0043) × STT (r2 = 0.906). When comparing the SST time series reconstructed from the Sr/Ca and Mg/Ca ratios with the mean SST of a spatial grid of 2º × 2º (longitude × latitude) that comprises San Benedicto Island, we found a high concordance between both temperatures, showing the robustness of the procedure. A drawback of this method is that no unique calibration exists for the Sr/Ca–SST and Mg/Ca–SST relations, and the different calibrations published generate discrepancies of up to 8ºC in the calculated temperature, regardless of whether the thermal sensitivity (i.e., the slope of the paleotemperature equation) of corals is similar. We therefore concluded that the Sr/Ca and Mg/Ca paleothermometers are highly reliable in this region of the Pacific Ocean, provided that a specific equation exists for the area under study

Organotin compounds in marine water and sediments from the port of Ensenada, Baja California, Mexico

 During September and October 1995, samples of surface sediments and water were collected to develop an analytical set-up to determine the concentrations of the organic compounds known as tributyltins (TBTs), including tributyl-, dibutyl- and monobutyltin. The method was then used to measure the levels of these contaminants in the port of Ensenada, Baja California. The method is based on hydride generation with atomic absorption detection. The concentrations determined were found to be relatively high (33 to 1021 ng g–1 of Sn in sediments and 66 to 469 ng L–1 in water samples), when compared to those obtained in similar works at San Diego Bay in California, USA. Comparisons are also made with other geographical locations. These results suggest that the port of Ensenada is an area that is receiving substantial amounts of these chemicals and might already be affecting the health of local biota. Two sources of these chemicals were identified: the activities associated with painting and cleaning of both commercial and sport boats, and the presence, at the time of the sampling, of an old platform near the entrance to the port facilities. The presence of the three compounds suggests that there is a permanent entry of these pollutants; furthermore, the presence of decreasing concentrations, starting with the more butylated compounds, suggests a recent introduction. Thc higher concentrations found in the sediment samples indicates the existence of an eflicient method of removal from the water column to the sediments of these compounds. The removal mechanism is associated with the presente of organic matter in the port area. In the sediments, the distribution of TBTs was partially dictated by the organic content, as a significant correlation (α = 0.05) between TBT concentration and organic content was found

Bioaccumulation of metals in mussels from four sites of the coastal region of Baja California

This study analyzes the concentrations and variations of Cu, Mn, Zn, Al, Cd, Ag, As and Se among different size classes of Modiolus capax, from Punta Estrella, Bahía de los Ángeles and Santa Rosalía in the Gulf of California, and of Modiolus modiolus and Mytilus californianus, from Bahía Tortugas in the Pacific. During November 1988, mussels of these species were collected and 45 organisms were selected (three replicates of 15 organisms each). Their biometric variables were measured: large size (88–98 mm), medium size (70–87 mm) and small size (56–66 mm). The reference standards and procedural blanks were analyzed for each group of 15 samples. The results indicate that the geographic distribution and accumulation of metals in the different sizes are mainly influenced by the sources of input, bioavailability in each place and the biological condition of the organisms. The mussels presented Cu levels independent of size in the region, except at Santa Rosalía. Zn, Cd and Se showed strong regional variability, but no clear trend with respect to the size of the organisms. Al showed high regional variability and a tendency to accumulate in small organisms. As and Se presented higher concentrations in the large to medium mussels, regardless of the sampling site. Mn tended to accumulate in large and medium mussels and was dependent on the sampling site. In Bahía Tortugas, M. californianus accumulates Cu, Mn and Cd at a rate three times lower than M. modiolus at the same level of exposure. Within the Gulf of California, the geographic distribution of Mn, Al and Zn was similar, with higher concentrations in the northern part. This is probably because the mussels are exposed to these metals through the sedimentary material resuspended in the Colorado River Delta. Cd presented levels of 70 and 27 µg g–1 at Bahía Tortugas and Bahía de los Angeles, respectively; both sites are exposed to coastal upwelling. Cu presented relatively low levels (<35 µg g–1), except at Santa Rosalía (89 µg g–1), where Cu is mined. As, Se and Ag presented low variability in the study area, with low levels that reflect natural levels at the sites studied

Persistent organic pollutants in sediment cores from the southern region of the Bight of the Californias

 In January 1998, four sediment cores were collected to reconstruct the history of contamination by persistent organic compounds in the southern region of the Bight of the Californias. Two groups of compounds were determined using chromatographic methods: petroleum hydrocarbons (aliphatic hydrocarbons, AHs, and polynuclear aromatic hydrocarbons, PAHs) and chlorinated hydrocarbons (pesticides and polychlorinated biphenyls, PCBs). The AHs had low concentrations, from 0.30 to 3.38 µg g–1, and presented a biogenic allocthonous origin. The PAH concentrations ranged from 0.99 to 673 ng g–1. The distribution of the alkyl homologues and the compound indices showed a clear predominance of PAHs of petrogenic origin. The chlorinated hydrocarbons presented a surface maximum, decreasing with depth to non-detectable levels. The PCB concentrations ranged from 0.18 to 7.15 ng g–1 and pesticides from 0.09 to 19.71 ng g–1. The pesticides that occurred most frequently were p,p'-DDT and its metabolites (p,p'-DDE and p,p'-DDD). Other pesticides detected were γ-chlordane and BHC isomers (α and γ). The statigraphy of the cores was carried out with molecular markers (chlorinated hydrocarbons), which were used to calculate a rate of sedimentation of 0.17 to 0.55 cm yr–1

Pesticides in coastal waters of the Gulf of California: Mussel watch program 1987-1988

A monitoring program was carried out in 1987 and 1988 using the mussel Modiolus capax as bioindicator to establish the contamination by organochlorine and organophosphate insecticides along the western coast of the Gulf of California. The results show that p,p′-DDE (5.78-105.3 ng g–1 dry weight) is the most bioavailable organochlorine toxic substance found in waters of the Gulf of California. The highest levels of this metabolite of the DDT insecticide were detected at the sites of Bahia de los Ángeles, San Rafael and San Francisquito, located in the central Gulf. The geographical distribution of p,p′-DDE was similar in 1987 and 1988. The results do not show a definite trend with regard to the temporal pattern of the contamination by pesticides. Heptachlorepoxide was detected in 18% and endrin in 8% of all the samples collected. Dieldrin, cis-chlordane, dacthal and endosulfan I were detected in less than 5% of the samples. The higher concentrations recorded in the central Gulf may originate in the agricultural valleys of Sonora and Sinaloa. The concentrations of pesticides detected in M. capax during the two years of the study were below the international limits established for the protection of aquatic biota

Heavy metals in coastal sediments of the Baja California (Mexico)-California (USA) border zone

Metal pollution and distribution in marine surface (0-5 cm) sediments of the Baja California border region were characterized during 1989. The total organic carbon, clay, silt and sand contents in the sediments and their correlation with the metals examined were also analysed. The results show higher concentrations (µg g–1 dry weight) of Al (7493), Mn (78.8) Cr (24.2) Zn (16.5) Cu (6.2) Cd (0.29) and Ag (0.30) in sediments of the 60-m isobath, with a gradient in their concentrations toward the shoreline. Analyses of simple correlation, principal components and similarity indicate that this behaviour is explained by the association of the elements with grain size and with silicoaluminate and organic matter contents. The possible influence of pollution and productivity phenomena as other processes that may control the distribution and origin of the metals in the study area, particularly Cd and Ag, is also noted. The results obtained show a decrease in Zn (15%), Cu (16%) Ag (20%) and Cd (22%) with respect to the values measured in coastal sediments of San Diego, California, in 1979