Revista de Biología Tropical

Introduction: Cyanobacterial blooms in tropical water bodies are increasingly common, because of eutrophication and rising temperatures. Consequently, many freshwater systems are affected, by reducing water quality, biodiversity, and ecosystem services. With the increased frequency of harmful algal blooms, the development of biological tools to improve water quality is an urgent issue. Objective: To evaluate the effects of a submerged macrophyte and a cladoceran on the microcystin-producing cyanobacteria Microcystis aeruginosa (NPLJ-4) and the chlorophyte Raphidocelis subcapitata (BMIUFRPE-02) in mixed cultures. Methods: Two parallel experiments were carried out for ten days to evaluate the effects of the submerged macrophyte Ceratophyllum demersum and the cladoceran Moina micrura on microalgal interactions. Microalgal strains were cultivated in the ASM1 culture medium, under controlled laboratory conditions. The first experiment presented four treatments: M (C. demersum), Z (M. micrura), MZ (C. demersum and M. micrura), and C (control). Meanwhile, the second experiment consisted of five treatments, in which the microalgae were cultivated together at different Microcystis:Raphidocelis ratios: 1:0, 3:1, 1:1, 1:3, and 0:1. Biomass and growth rates of the strains were evaluated every two days, which were statistically treated with three-way or two-way repeated-measures ANOVA. Results: In the first experiment, M. aeruginosa was significantly inhibited in M and MZ treatments from the second day, and Z from the fourth, while R. subcapitata showed no reduction in its biomass in any treatment. On the other hand, R. subcapitata was stimulated from the eighth and tenth days in M treatment and only on the eighth day in Z treatment. In the second experiment, M. aeruginosa was significantly inhibited when cultivated with R. subcapitata in low ratios (Microcystis:Raphidocelis ratio of 1:3) throughout the experiment, while the chlorophyte was stimulated in that treatment. Conclusions: The coexistence of a cyanobacterium with a green alga did not alter the main negative response of M. aeruginosa to the submerged macrophyte and zooplankton but stimulated the green alga. Accordingly, the introduction of submerged macrophytes and cladocerans already adapted to eutrophic conditions, both isolated and combined, proved to be a good method to control cyanobacterial blooms without negatively affecting other coexisting phytoplankton species.

Population structure of Avicennia germinans trees (Acanthaceae) in a disturbed mangrove in the Gulf of Mexico. Introduction: Globally, mangroves are declining; characterizing their structure and regeneration at different disturbance levels can help understand their responses to stressful situations. Objective: The study's primary goal was to analyze the mangrove community structure and to estimate the populations' trajectories of Avicenia germinans at different mangrove sites that present three levels of disturbance. Methods: Eight transects of approximately 500 m in length and laid perpendicular to the Tamapamchoco lagoon, Veracruz, intersected three levels of disturbance currently present on the mangrove forest. On each transect, 10 x 10 m, 5 x 5 m, and 1 x 1 m quadrants served to account for all mangrove trees by species and stage of maturity in 2017 and 2018. Results: The most abundant species was: A. germinans followed by Rhizophora mangle and Laguncularia racemosa. Based on their abundance, we found significant differences for the three levels of disturbance (ANOSIM R = 0.6, P < 0.001) presented in a non-metric ordination (nMDS). A life table for A. germinans allowed a population analysis that showed an intrinsic rate of population increase (r) that was negative at the disturbed sites (-0.0027 and -0.0774) and positive (0.0289) at the apparently undisturbed site. Seedling to juvenile stage survival ranged from 50 % at the undisturbed site to 5 and 4 % at the disturbed sites. Conclusions: Measures to increase the survival of seedlings are necessary to reverse the decreasing population trajectories at the disturbed sites; otherwise, the mangrove will have reduced viability in the medium term.

Introduction: Forests and agroforestry systems (AFS) provide ecosystem goods and services for society, such as climate change mitigation. Objective: The potential for emission reductions and carbon sequestration in forests and cocoa agroforestry systems in the Munguidó river sub-basin in Colombia was estimated. Methods: Three land use systems were selected (primary forest, secondary forest and AFS with cocoa). Eighteen temporary sampling plots were established, six per system, to measure trees (diameter at breast height -dbh ≥ 10 cm) and cocoa shrubs. Aboveground biomass was quantified with allometric equations and a carbon fraction of 0.5. Carbon fixation in secondary forest and AFS with cocoa was estimated as the ratio of carbon stored to its age. Carbon loss from primary forest was estimated based on deforestation for Chocó and that sub-basin (0.6 and 0.3 %/year, respectively). An analysis of variance and LSD Fisher mean comparison was performed to determine differences in carbon storage and carbon sequestration between uses. Results: Primary Forest stored more carbon than secondary forest and AFS with cocoa (190.1, 22.3 and 5.3 Mg/ha, respectively). The carbon fixation of secondary forest and AFS with cocoa did not differ (2.23 vs. 1.33 Mg/ha/year). In 20 years, the primary forest would present an emission reduction of 1.4-2.6 Tg CO2; and the secondary forest and the PFS with cocoa would present a sequestration of 100.8 and 30.7 Gg CO2, respectively. Conclusion: In the Munguidó river sub-basin, it is possible to establish projects for the reduction of emissions in primary forest and carbon sequestration in secondary forests and AFS with cocoa, which could emit 1.4-2.6 million tons of CO2.

Introduction: The presence of microplastics (MPs, particles smaller than 5 mm) and the increase in temperature in the oceans, have been generating disturbances in marine life, which can be related to alterations in the metabolism of filter-feeders, such as Mythilids. Objective: The effect of different temperatures and concentrations of MPs on the filtration rate (TF) of Semimytilus algosus is evaluated. Methods: A sample of organisms (N = 72) was exposed to four temperatures (17, 20, 23 and 26 °C), and a control without microplastics (MPs0) and two concentrations of MPs (< 125 µm) of 0.125 mg/l (MPs1) and 0.250 mg/l (MPs2), all in combination with Isochrysis galbana microalgae (1x106 cells/ml/day) for 21 days. Results: As the concentration of MPs increased, the TF of S. algosus decreased. Regarding temperature, during day 7 a higher TF was observed at 23 °C in all treatments, and during days 14 and 21 the lowest TF values were obtained at 23 and 26 °C. The joint action of the increase in temperature and MPs, negatively affected the TF of S. algosus, where both factors caused the decrease in TF for all evaluation times. No mortality was recorded at 17 °C for any treatment, and in the case of mytylids exposed to MPs1 at 20 °C and 26 °C, the highest mortality (67 %) occurred. Conclusions: The study demonstrates the adverse effect of the increase in temperature and MPs on the TF of S. algosus.

Summary. Introduction: To increase the number of sea turtle hatchlings, it is necessary to improve conservation strategies, such as nest incubation in hatchery conditions that counteract the effects of extreme weather conditions. Objective: To compare five reproductive success parameters (hatching success, undeveloped eggs, dead hatchlings, embryonic mortality, and incubation period) of the sea turtle Lepidochelys olivacea. Methods: The incubation of nests was evaluated under two periods of nest relocation (P1 and P2) under hatchery condition, in 2018 in Guerrero, Mexico. Results: Significant differences were found in hatching success and embryonic mortality between nest relocation periods (P <0.001). In P1, lower values ​​of hatching success (77.0% P1 vs 88.6% P2) and higher values ​​of embryonic mortality (13.7% P1 vs 3.3% P2) were observed compared to those of P2. No differences were found between periods regarding the parameters undeveloped eggs, dead hatchlings and incubation period. Conclusions: The differences between the most extreme or hot environmental conditions during the first period of nest relocation seem to affect the hatching success and embryonic mortality of L. olivacea. Therefore, it is important to take action on this during this incubation stage.