Post-glacial expansion and population genetic divergence of mangrove species Avicennia germinans (L.) Stearn and Rhizophora mangle L. along the Mexican coast.

Mangrove forests in the Gulf of California, Mexico represent the northernmost populations along the Pacific coast and thus they are likely to be source populations for colonization at higher latitudes as climate becomes more favorable. Today, these populations are relatively small and fragmented and prior research has indicated that they are poor in genetic diversity. Here we set out to investigate whether the low diversity in this region was a result of recent colonization, or fragmentation and genetic drift of once more extensive mangroves due to climatic changes in the recent past. By sampling the two major mangrove species, Rhizophora mangle and Avicennia germinans, along the Pacific and Atlantic coasts of Mexico, we set out to test whether concordant genetic signals could elucidate recent evolution of the ecosystem. Genetic diversity of both mangrove species showed a decreasing trend toward northern latitudes along the Pacific coast. The lowest levels of genetic diversity were found at the range limits around the Gulf of California and the outer Baja California peninsula. Lack of a strong spatial genetic structure in this area and recent northern gene flow in A. germinans suggest recent colonization by this species. On the other hand, lack of a signal of recent northern dispersal in R. mangle, despite the higher dispersal capability of this species, indicates a longer presence of populations, at least in the southern Gulf of California. We suggest that the longer history, together with higher genetic diversity of R. mangle at the range limits, likely provides a gene pool better able to colonize northwards under climate change than A. germinans.

[Microorganisms effect with probiotic potential in water quality and growth of the shrimp Litopenaeus vannamei (Decapoda: Penaeidae) in intensive culture]. / Efecto de microorganismos con potencial probiótico en la calidad del agua y el crecimiento de camarón Litopenaeus vannamei (Decapoda: Penaeidae) en cultivo intensivo.

The use of probiotics has gained acceptance in aquaculture, particularly in maintaining water quality and enhancing growth in organisms. This study analyzed the effect of the commercial (EM, Japan) natural product composed by (Rhodopseudomonas palustris, Lactobacillus plantarum, Lactobacillus casei and Saccharomyces cerevisiae) added to the water, in order to determine its effect in water quality, sediment and growth of L. vannamei under intensive culture. The evaluation included three treatments with a weekly addition of EM: i) tanks without probiotics (C), ii) tanks with a dose of 4 L/ha (EM1) and iii) tanks with a dose of 10 L/ha (EM2). The treatment C was carried out three times, while treatments EM1 and EM2 were carried out four times. A total of 4 350 shrimps were measured for total length and weight, to calculate total and porcentual weight gain, daily weight gain, specific growth rate (TCE), and food conversion factor (FCA); besides, the survival rate was estimated. The use of probiotics allowed a shorter harvest time in treatments EM1 (90 d) and EM2 (105 d) with relation to the treatment C (120d). Treatments EM1 and EM2 were within the recommended intervals for culture, with respect to treatment C. The use of probiotic bacteria significantly regulated pH (EM1, 8.03 +/- 0.33; EM2, 7.77 +/- 0.22; C, 9.08 +/- 0.35) and reduced nitrate concentration (EM1, 0.64 +/- 0.25 mg/L; EM2, 0.39 +/- 0.26 mg/L; C, 0.71 mg/L). Water pH mostly explained the variance with respect to the treatments. Treatment EM2 presented the greatest removal of organic matter (1.77 +/- 0.45%), whereas the contents of extractable phosphorus increased significantly in treatment EM1 with 21.6 +/- 7.99 mg/kg and in treatment EM2 with 21.6 +/- 8.45 mg/kg with control relation (14.3 +/- 5.47). The shrimp growth was influenced by dissolved oxygen, salinity and pH in the sediment, establishing that salinity was the most important variable in the weight with a negative association. Treatment EM1 recorded an improved TCE (2.69 +/- 0.35%/d) and FCA (1.46 +/- 0.20) with relation to the control treatment (TCE, 1.88 +/- 0.25%/d; FCA, 2.13 +/- 0.48). Survival was significantly greater in treatments containing probiotics with 61 +/- 8.76% and 60 +/- 10.5% for EM1 and EM2, respectively. This study indicated the positive effect obtained with the use of this commercial probiotic, to improve culture conditions and growth parameters in an intensive culture of L. vannamei.

Efecto de microorganismos con potencial probiótico en la calidad del agua y el crecimiento de camarón Litopenaeus vannamei (Decapoda: Penaeidae) en cultivo intensivo / Microorganisms effect with probiotic potential in water quality and growth of the shrimp Litopenaeus vannamei (Decapoda: Penaeidae) in intensive culture

The use of probiotics has gained acceptance in aquaculture, particularly in maintaining water quality and enhancing growth in organisms. This study analyzed the effect of the commercial (EM TM, Japan) natural product composed by (Rhodopseudomonas palustris, Lactobacillus plantarum, Lactobacillus casei and Saccharomyces cerevisiae) added to the water, in order to determine its effect in water quality, sediment and growth of L. vannamei under intensive culture. The evaluation included three treatments with a weekly addition of EM: i) tanks without probiotics (C), ii) tanks with a dose of 4L/ha (EM1) and iii) tanks with a dose of 10L/ha (EM2). The treatment C was carried out three times, while treatments EM1 and EM2 were carried out four times. A total of 4 350 shrimps were measured for total length and weight, to calculate total and porcentual weight gain, daily weight gain, specific growth rate (TCE), and food conversion factor (FCA); besides, the survival rate was estimated. The use of probiotics allowed a shorter harvest time in treatments EM1 (90d) and EM2 (105d) with relation to the treatment C (120d). Treatments EM1 and EM2 were within the recommended intervals for culture, with respect to treatment C. The use of probiotic bacteria significantly regulated pH (EM1, 8.03±0.33; EM2, 7.77±0.22; C, 9.08±0.35) and reduced nitrate concentration (EM1, 0.64±0.25mg/L; EM2, 0.39±0.26mg/L; C, 0.71mg/L). Water pH mostly explained the variance with respect to the treatments. Treatment EM2 presented the greatest removal of organic matter (1.77±0.45%), whereas the contents of extractable phosphorus increased significantly in treatment EM1 with 21.6±7.99mg/kg and in treatment EM2 with 21.6±8.45mg/kg with control relation (14.3±5.47). The shrimp growth was influenced by dissolved oxygen, salinity and pH in the sediment, establishing that salinity was the most important variable in the weight with a negative association. Treatment EM1 recorded an improved TCE (2.69±0.35%/d) and FCA (1.46±0.20) with relation to the control treatment (TCE, 1.88±0.25%/d; FCA, 2.13±0.48). Survival was significantly greater in treatments containing probiotics with 61±8.76% and 60±10.5% for EM1 and EM2, respectively. This study indicated the positive effect obtained with the use of this commercial probiotic, to improve culture conditions and growth parameters in an intensive culture of L. vannamei.

Los probióticos han ganado aceptación en la acuicultura para mantener la calidad del agua y aumentar el crecimiento de los organismos. En este estudio se analizó el efecto de una mezcla comercial de microorganismos eficientes (EM) (Rhodopseudomonas palustris, Lactobacillus plantarum, Lactobacillus casei y Saccharomyces cerevisiae) sobre la calidad del agua, sedimento y el crecimiento en un cultivo intensivo de camarón L. vannamei. La evaluación consistió en tres tratamientos: i) estanques sin EM (C), ii) estanques con dosis de 4L/ha (EM1) y iii) estanques con dosis de 10L/ha (EM2). Los resultados demostraron menor tiempo de cosecha en los tratamientos EM1 (90d) y EM2 (105d). Los tratamientos EM1 y EM2 mantuvieron significativamente regulados los valores del pH (EM1, 8.03±0.33; EM2, 7.77±0.22) y redujeron las concentraciones de nitrato (EM1, 0.64±0.25mg/L; EM2, 0.39±0.26mg/L). El tratamiento EM2 presentó la mayor remoción de materia orgánica (1.77±0.45%). El tratamiento EM1 mejoró la TCE (2.69±0.35%/d) y FCA (1.46±0.20). Los tratamientos EM1 y EM2 presentaron mayor supervivencia con 61±8.76% y 60±10.5%, respectivamente. Este estudio demostró el efecto benéfico del uso de la mezcla comercial en los parámetros ambientales y de crecimiento en un cultivo intensivo de L. vannamei.

Genetic diversity enhanced by ancient introgression and secondary contact in East Pacific black mangroves.

Regional distribution of genetic diversity in widespread species may be influenced by hybridization with locally restricted, closely related species. Previous studies have shown that Central American East Pacific populations of the wide-ranged Avicennia germinans, the black mangrove, harbour higher genetic diversity than the rest of its range. Genetic diversity in this region might be enhanced by introgression with the locally restricted Avicennia bicolor. We tested the hypotheses of ancient hybridization using phylogenetic analysis of the internal transcribed spacer region (ITS) of the nuclear ribosomal DNA and intergenic chloroplast DNA; we also tested for current hybridization by population level analysis of nuclear microsatellites. Our results unveiled ancient ITS introgression between a northern Pacific Central American A. germinans lineage and A. bicolor. However, microsatellite data revealed contemporary isolation between the two species. Polymorphic ITS sequences from Costa Rica and Panama are consistent with a zone of admixture between the introgressant ITS A. germinans lineage and a southern Central American lineage of A. germinans. Interspecific introgression influenced lineage diversity and divergence at the nuclear ribosomal DNA; intraspecific population differentiation and secondary contact are more likely to have enhanced regional genetic diversity in Pacific Central American populations of the widespread A. germinans.

Water quality and presence of pesticides in a tropical coastal wetland in southern Mexico.

The water quality of the Pozuelos-Murillo lagoon system in southern Mexico was evaluated during three periods between March and October 2002, with particular emphasis on the detection of organochlorine and organophosphorous pesticide residues in water and sediments. Physicochemical and microbiological parameters of water were also measured and integrated in a water quality index (WQI). Multivariate analysis was used to regionalise the lagoon system as a function of the behaviour of all measured parameters. Solid phase micro-extraction followed by gas chromatography (SPME-GC) was used for pesticide analysis. The concentration of phosphorous was found to be higher than that of nitrogenous compounds. This, besides a deficiency in dissolved oxygen and a high organic matter concentration (as COD), reflects eutrophication processes in some areas of the system. Measured levels of faecal coliforms and oils and greases were above the limits established by Mexican law and comparable to the concentrations reported for other highly polluted systems in Mexico. Residues of DDD (2.0 microg L(-1)) in water and DDE (247 ng g(-1)) and endosulfan I (814 ng g(-1)) sediments were detected by SPME-GC. The spatial distribution of these contaminants implies major potential risks because the most polluted sites were found to be those with the highest fishing activity. Although in general the WQI is on acceptable levels (65-80%), some contamination problems are evident.

Impact of logging on a mangrove swamp in south Mexico: cost/benefit analysis

Environmental changes caused by logging in a mangrove swamp were studied in Barra de Tecoanapa, Guerrero, Mexico. Original forest included Rhizophora mangle, Laguncularia racemosa, Avicennia germinans and halophytic vegetation, and produced wood (164.03 m3/ha) and organic matter (3.9 g/m2/day). A total of 3.5 tons of wood per year were harvested from this area. Later, an average of 2,555 kg of maize per planting cycle were obtained (market value of 88 USD). Succession when the area was abandoned included strictly facultative and glycophyte halophytes (16 families, Cyperaceae and Poaceae were the best represented). After logging, temperatures increased 13 degrees C in the soil and 11 degrees C in the air, whereas salinity reached 52 psu in the dry season. These modified soil color and sand content increased from 42.6 to 63.4. Logging was deleterious to species, habitat, biogeochemical and biological cycles, organic matter production, seeds, young plants, genetic exchange conservation of soil and its fertility, coastal protection, and aesthetic value; 3,000 m2 had eroded as the river advanced towards the deforested area (the cost/benefit analysis showed a ratio of 246:1). There was long-term economic loss for the community and only 30 of the site has recovered after five years.