Fernando A. González-Farias

Variation of antimicrobial activity of the sponge Aplysina fistularis (Pallas, 1766) and its relation to associated fauna

The sponge Aplysina fistularis (Pallas, 1766) was studied to determine if it produces different levels of antibiotic activity during an annual cycle, and to try to establish some ecological relations of this phenomenon. Monthly collections of sponges were made at Isla Espiritu Santo, Baja California Sur, Mexico from May 1989 to June 1990. Bioassays of antimicrobial susceptibility were carried out and densities of the associated organisms were recorded. Antibiotic activity levels of the sponge correlated with inquilism level. Because antimicrobial activity was always found, we believe that metabolites are produced continuously, although the sponge is probably able to change the substance production mechanism in the presence of a particular stimulus. The massive reproduction of the associated invertebrates and the arrival of large quantities of organisms over a short time could be important stress factors for the sponge and a stimulus that modifies the production of secondary metabolites.

Effect of mangrove humic-like substances on biodegradation rate of detritus

Abstract Laboratory measurements were made of the degradation rate of white mangrove Laguncularia racemosa Gaertn senesced leaves in the presence of various initial concentrations of humic-like substances obtained from the mangrove leaves. The control leaves presented an average degradation rate ( K = − 1.33 · yr −1 ) that was statistically different ( P K = −0.89 · yr −1 ). Chromatographic characterization of the humic-like substances was performed and the chromatograms were compared with those of the humic substances isolated from a tropical coastal lagoon and with tannins from mangrove leaves. The chromatogram of tannins showed two peaks, one of high molecular weight compounds (> 2000) and another of low molecular weight compounds (≈ 200) that are probably condensed and hydrolyzed tannins. The chromatogram of the lagoon humics showed a predominance of high molecular weight compounds, as compared with that of the humic-like substances which showed both peaks. This difference is probably due to the humification processes that take place in the lagoon. To evaluate the influence of these compounds on the biodegradation of mangrove detritus, we measured their inhibitory activity both as combined and selected Chromatographic fractions, using heterotrophic bacteria from the lagoon. The tannins, humic-like substances, and lagoon humics presented strong inhibitory activity. It is suggested that these compounds are responsible for a negative feedback between the input of detritus to the lagoon and its biodegradation.

Nutrient removal in a closed silvofishery system using three mangrove species (Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle)

The removal of ammonium (NH4(+)), nitrite (NO2(-)), nitrate (NO3(-)), and phosphate (PO4(-3)) in a closed silvofishery system was examined using three mangrove species (i.e., Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle). Specifically, six closed tanks were installed for this experiment with a population of 60 Dormitator latifrons fishes per tank. We planted 40 seedlings in each of three experimental tanks separated by species, while the remaining tanks were used as control. During 15 weeks, nutrient concentrations among the three mangrove systems presented no significant differences (P>0.05). However, nutrient removal variability was minimum during the last 2-5 weeks. Mangroves presented an average efficiency of 63% for the removal of NH4(+) and NO2(-). Contrary, the average removal potential of NO3(-) and PO4(-3) was 50%. Results from this study suggest that the three mangrove species could be used in a closed silvofishery systems for the biological removal of NH4(+), NO2(-), NO3(-), and PO4(-3).

Examining the Influence of Seasonality, Condition, and Species Composition on Mangrove Leaf Pigment Contents and Laboratory Based Spectroscopy Data

The purpose of this investigation was to determine the seasonal relationships (dry vs. rainy) between reflectance (400–1000 nm) and leaf pigment contents (chlorophyll-a (chl-a), chlorophyll-b (chl-b), total carotenoids (tcar), chlorophyll a/b ratio) in three mangrove species (Avicennia germinans (A. germinans), Laguncularia racemosa (L. racemosa), and Rhizophora mangle (R. mangle)) according to their condition (stressed vs. healthy). Based on a sample of 360 leaves taken from a semi-arid forest of the Mexican Pacific, it was determined that during the dry season, the stressed A. germinans and R. mangle show the highest maximum correlations at the green (550 nm) and red-edge (710 nm) wavelengths (r = 0.8 and 0.9, respectively) for both chl-a and chl-b and that much lower values (r = 0.7 and 0.8, respectively) were recorded during the rainy season. Moreover, it was found that the tcar correlation pattern across the electromagnetic spectrum was quite different from that of the chl-a, the chl-b, and chl a/b ratio but that their maximum correlations were also located at the same two wavelength ranges for both seasons. The stressed L. racemosa was the only sample to exhibit minimal correlation with chl-a and chl-b for either season. In addition, the healthy A. germinans and R. mangle depicted similar patterns of chl-a and chl-b, but the tcar varied depending on the species. The healthy L. racemosa recorded higher correlations with chl-b and tcar at the green and red-edge wavelengths during the dry season, and higher correlation with chl-a during the rainy season. Finally, the vegetation index Red Edge Inflection Point Index (REIP) was found to be the optimal index for chl-a estimation for both stressed and healthy classes. For chl-b, both the REIP and the Vogelmann Red Edge Index (Vog1) index were found to be best at prediction. Based on the results of this investigation, it is suggested that caution be taken as mangrove leaf pigment contents from spectroscopy data have been shown to be sensitive to seasonality, species, and condition. The authors suggest potential reasons for the observed variability in the reflectance and pigment contents relationships.

Accumulation and Regulation Effects from the Metal Mixture of Zn, Pb, and Cd in the Tropical Shrimp Penaeus vannamei

Environmental metal pollution is one of the major problems faced by humankind. This type of pollution affects aquatic systems (estuaries, coastal lagoons, etc.), which are very dynamic systems, therefore making the study of the effects on the organisms that inhabit them an essential issue. In this study, the capacity of metal regulation by decapod crustacean Penaeus vannamei juveniles was determined. The effects of zinc, lead, and cadmium were tested individually and as a metal mixture exposure to determine possible synergism. The results showed that juvenile shrimps were capable of regulating zinc and lead, whereas cadmium was accumulated without any excretion, at least within the concentrations studied. It was also proved that under the estuarine conditions tested here, P. vannamei juveniles showed capacity to act as a bioindicator for cadmium.

Water quality assessment of Aguamilpa Reservoir, Nayarit, Mexico.

An analysis of water quality data is presented for the Aguamilpa reservoir located in a tropical region of the state of Nayarit, Mexico. The analysis includes physicochemical and biological data including total chlorophyll and blue-green algae concentrations obtained at different depths during the period of June 2008 to April 2009. The observed measurements show that the reservoir is stratified during all the study period and has a relatively high primary productivity. The relatively high blue-green algae concentration on the surface waters indicates that eutrophication process occurs in this young reservoir which began operations in 1994. This eutrophication process may be explained by the nutrients enrichment in the system, relatively warm temperatures intrinsic to the tropical region where the reservoir is located, low turbulence in lower layers and stable circulation patterns due to the narrow morphology of the steep canyon walls where the reservoir is located.