Martín E. Jara-Marini

Trace metals accumulation patterns in a mangrove lagoon ecosystem, Mazatlan Harbor, southeast Gulf of California.

Water, surface sediments, the mussel Mytella strigata, the mangrove oyster Crassostrea corteziensis, and the green macroalgae Caulerpa sertularioides from four locations in Mazatlán Harbor on the southeast coast of the Gulf of California, were analyzed to determine concentrations and distribution patterns of cadmium, copper, mercury, lead, and zinc. Total metal concentrations in water in the present study exceed the background levels in open sea and coastal waters. Total metal concentrations in sediments were ordered as follows: Zn > Pb > Cu > Cd > Hg, but for the bioavailable fraction were ordered as Zn > Cu > Pb > Cd > Hg. The concentrations in bioavailable levels fall between the Threshold Effects Level (TEL), and Probable Effects Level (PEL), criteria for sediment quality. Distribution patterns for metals in organisms were ordered Zn > Cu > Pb > Cd > Hg with seasonal variations for Pb and Zn. Correlations between Cd, Cu, Pb and Zn were indicative of similar assimilation and storage mechanisms and common sources of contamination. These correlations also indicated that bioavailability was not simultaneous for Cd and Pb. Bioconcentration factors (BCF) show different patterns in different organisms. For the oyster the metals were ordered Zn > > Cu > Cd ≈ Hg > Pb, for the mussel Hg > Cu ≈ Zn ≈ Cd > Pb and for the macroalgae Zn > > Cu > Pb > Cd > Hg. Based on BCF results in the lagoon system, the oyster C cortezienzes can be used as a biomonitor of Zn and Cu exposure, the mussel M. strigata of Hg exposure and the green macroalgae C. serticularioides of exposure to all five metals studied.

Mercury transfer in a subtropical coastal lagoon food web (SE Gulf of California) under two contrasting climatic conditions

Mercury (Hg) transference through an established and defined food web from an urbanized subtropical coastal lagoon (SE Gulf of California) was examined by using carbon and nitrogen stable isotope and Hg analyses. Concentrations of Hg in seawater (0.045–0.078 μg L−1), predominantly incorporated to the particulate fraction (60% of total), were lower than those found in highly contaminated coastal areas around the world (0.18–16 μg L−1). Although levels of Hg available for the biota (e.g., associated to the reactive and pyrite fractions; 0.11–0.15 μg g−1) were within of effects range‐low (ER‐L, 0.15–0.71 μg g−1) these concentrations represented from 46.6 to 67.0% of the total Hg pool that may be transferred through food web. The sequence of bio‐accumulation of Hg in studied species was according with their functional guild: tertiary consumer (0.85–1.15 μg g−1) > secondary consumers (0.084–0.168 μg g−1) > primary consumers (0.014–0.160 μg g−1) > primary producers (0.016–0.056 μg g−1). Hg concentrations increased for each successive trophic position estimate through δ15N isotopic values, although these relationships showed differences between dry and rainy seasons (R2 = 0.37 and R2 = 0.39 between δ15N vs. Hg in organisms, respectively). We concluded that Hg is being positively transferred (biomagnification factor >1) through the studied food web probably enhanced by the favorable environmental conditions for Hg‐methylation (e.g., fine sediments rich in organic matter, and environmental conditions changes of the redox, pH, and temperature) found in this urbanized coastal water, however, the study of processes methlylation and biomagnifcation of Hg need further investigations.

BIOLOGICAL RESPONSES OF A SIMULATED MARINE FOOD CHAIN TO LEAD ADDITION

This investigation sought to assess the biological responses to Pb along a simplified four-level food chain, from the primary producer, the microalgae Tetraselmis suecica, grown in a control medium with < 1 µg/L of Pb and exposed to a sublethal dose (20 µg/L of Pb) and used as the base of a simulated food chain, through the primary-, secondary-, and tertiary-level consumers, namely, the brine shrimp, Artemia franciscana; the white-leg shrimp, Litopenaeus vannamei; and the grunt fish, Haemulon scudderi, respectively. Growth of Pb-exposed T. suecica was 40% lower than that of the control cultures, and survival of A. franciscana fed this diet was 25 to 30% lower than the control. No differences in the growth rates of Pb-exposed and control shrimp and fish and no gross morphological changes were evident in the exposed specimens. However, the exposed shrimp and fish had 20 and 15% higher mortalities than their controls, respectively. In addition, behavioral alterations were observed in exposed shrimp and fish, including reduction in food consumption or cessation of feeding, breathing air out of the water, reduction of motility, and erratic swimming. The negative correlation between Pb concentration in whole body of shrimp and fish and Fultons condition factor suggested also that the exposed organisms were stressed because of Pb accumulation.

Distribution and accumulation of Cd, Cu, Hg, Pb and Zn in the surface sediments of El Tobari Lagoon, central-East Gulf of California: An ecosystem associated with agriculture and aquaculture activities.

The purpose of this research is to provide a comprehensive assessment of the concentration levels and spatial variability of cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb) and zinc (Zn) in El Tobari Lagoon in surface sediments during two seasons for several geochemical variables that could explain the observed heavy metal variability. Seventy-two surface sediments samples were collected in 12 different sites of the El Tobari Lagoon. Sediment samples were dried and subjected to acid extraction using a microwave system and five metals (Cd, Cu, Hg, Pb and Zn) were measured using atomic adsorption spectrometry. A certificate sediment material and blanks were used as quality control purposes. The enrichment factor (EF) and the index of geoaccumulation (Igeo) were calculated as index of metals contamination for the sediments, using aluminum as the conservative element. The five metals examined in sediments from El Tobari Lagoon exhibited a linear correlation with Al as result of the large specific surface areas of these sediment components and the chemical affinities between them. The metals contents in sites of the El Tobari Lagoon were variable, and Cd, Cu and Hg presented a seasonal behavior. The enrichment factor and index of geoaccumulation analysis indicated that Cd and Hg exhibited a certain extent (EF for Cd ranged from 4.10 to 10.29; EF for Hg ranged from 2.77 to 12.89) of anthropogenic pollution, while Cu showed sporadic (EF ranged from 0.43 to 2.54) anthropogenic contamination. The highest concentrations of Cd, Cu and Hg were found in the sites that regularly received discharge effluents from agriculture and aquaculture.

Trophic Relationships within a Subtropical Estuarine Food Web from the Southeast Gulf of California through Analysis of Stable Isotopes of Carbon and Nitrogen

We identified the sources of carbon supporting an estuarine food web in the Southeast Gulf of California. The trophic food web in the Estero de Urias Lagoon (EUL) was studied through the carbon and nitrogen isotopes in the potential food sources (plankton, macroalgae, plants) and organisms including filter-feeding mollusks, crustaceans, fishes and seabirds. The isotopic composition of sediment suspended organic matter (SSOM) and suspended particulate organic matter (SPOM) showed that there are diverse organic matter sources in EUL. The greater inputs of mangrove to detritus were reflected in their similar δ13C values with respect to SSOM and SPOM. The δ13C data suggest a direct transfer of C from SSOM and zooplankton to filter-feeders organisms and to a lesser degree from SPOM and phytoplankton. The isotopic composition of the different groups of organisms showed the complexity of the food web. However, there was a continuous gradient of 15N-enrichment from SSOM and SPOM to seabird with intermediate values for filter-feeders and crustaceans. The δ15N values in the EUL food web were consistent with 5 trophic levels. Fishes were strongly dependent on macrobenthos and pelagic derived nutrition. Cormorants occupied the highest trophic level and its major diet contributors were fishes. The studied food web was not segregated by time because isotopic trends were similar between dry and wet seasons.