Luis A. Oseguera

Benthos of a prerennially-astatic, saline, soda lake in Mexico

The effects of multiple stressors on the benthic macroinvertebrate community were monitored in Tecuitlapa Norte, a shallow, perennially-astatic, warm, mesosaline, sodaalkaline lake in Mexico. Physico-chemical and biological variables were determined monthly for one year. Tecuitlapa Norte displayed a clear seasonal environmental pattern (dry and rainy seasons). The benthic macroinvertebrate community consisted of five species:Culicoides occidentalis sonorensis Jorgensen,Ephydra hians Say,Stratiomys sp.,Eristalis sp., andLimnophora sp. of which the first two were dominant and the rest scarce.C. occidentalis was the most important species numerically (76 percent of the total), whileE. hians dominated the biomass (73 percent of the total). Primarily salinity and secondarily pH appear to be the most important environmental factors controlling dominance of benthic organisms in Tecuitlapa Norte. Seasonal abundance dynamics of the dominant organisms was associated with phases in their reproductive cycles: environmentally-triggered (i.e., temperature rise, water-level descent) pupation and emergence periods. We concluded that whereas physical and chemical factors (i.e., salinity, pH) exerted the primary control on benthic macroinvertebrate community composition in Tecuitlapa Norte, another assembly of variables (e.g., water-level, temperature) influenced species distribution and abundance.

Phytoplankton Biomass and Water Chemistry in Two High-Mountain Tropical Lakes in Central Mexico

Abstract In this work we report the vertical phytoplankton biomass distribution (chlorophyll a depth-profiles) and the integrated phytoplankton biomass (chlorophyll a per unit area) of two high-mountain Mexican Lakes: El Sol and La Luna (19°06′N, 99°45′W, 4200 m a.s.l.). El Sol and La Luna are transparent, nonglacier-fed lakes. Both lakes are continuous warm polymictic with a uniform vertical distribution of phytoplankton biomass. Slight heterogeneities were observed in El Sol with a deep-water chlorophyll maximum above the sediments (maximum difference 0.71 μg L−1) associated to phytoplankton sunken cells and the presence of filamentous benthic algae. Phytoplankton biomass per unit area was low in both lakes (El Sol 1.91–8.36 and La Luna 1.13–4.80 mg Chla m−2), and similar to that of temperate high-mountain lakes. The temporal variations in the phytoplankton biomass were attributed mainly to a combined effect of nutrient input and zooplankton grazing pressure; the effect of low pH is also considered in La Luna.

Seston flux in a tropical saline lake

The dynamies of seston fluxes has been assoeiated with phytoplankton blooms in marine and freshwater systems (VINERMozziNI et al. 2003). The fate of these blooms is erucial to the understanding of earbon flow, nutrient eycling and eeosystem funetions. As a eonsequenee, it is important to unravel the meehanisms of particle sedimentation as well as the quantity and quality of settling particles. Eeosystem proeesses are important determinants o f the biogeoehemistry o f the oeean that ean be profoundly affeeted by ehanges in elimate (LE QuÉRÉ et al. 2005). The different routes that the particles take in the aquatie eeosystem (transfer in food-web, respiration, sedimentation, and burial) will define the availability of earbon to organisms and the time of return of earbon moleeules in the earbon eycle. The transfer in the food web and its proeesses are important eontrols of aquatie biogenie earbon flux and water-atmosphere earbon dioxide exehange (LEGENDRE 1999). Rapid inereases in phytoplankton biomass have a high potential for exporting partieulate organie matter from the euphotie layer, providing important information for the study of global fluxes of earbon in the inland water systems; however, if a larger fraetion of assimilated earbon is respired at low than at high latitudes, a smaller proportion o f produetion ean be exported in tropieal regions. The explieit inelusion of eeosystem proeesses in models will permit eeologieal ehanges to be taken into aeeount, allow us to understand how the uptake o f C02 in inland water systems is likely to ehange in the future, and improve our understanding o f the loeal and regional climate systems. The main losses forbloom biomasses are grazing, deeomposition in the mixing layer, and sedimentation to the bottom of lakes (ZoHARY et al. 1998). The dominant size fraetion o f phytoplankton defines the principal transfer path ofbiogenie earbon in the eeosystem. When the small fraetion (<2 f..Lm) dominates, the main route will be nutrient reeycling through the mierobialloop in the euphotie zone. In eontrast, when the large fraetion (>2 f..Lm) dominates, new produetion will either be exported to the bottom o f the lake or eonsumed by herbivores and eventually exported as feeal pellets (LEGENDRE 1999). The aim ofthis study was to evaluate the vertieal and temporai variation ofseston fluxes inLake Alchiehiea to betterunderstand the earbon dynamies of a tropieal, oligotrophie lake where the large size fraetion ofphytoplankton dominates.

The external micro-anatomy of the cephalon of the asellotan isopod Craseriella anops

The micro-anatomy of the cephalon is described in the troglobic asellotan isopod Craseriella anops from the Nohoch Nah Chich anchialine cave system in southeast Mexico. The cephalon is entirely covered by cuticular scales bordered by marginal spines. The anterior end of the cephalon is bordered by a carina that is wider medially. The isopod is eyeless. The distal seventh portion of the cephalon is characterized by the presence of two sutures and six setae. A suture is found on each side of the distal margin of the cephalon. Each suture is found on each side of the distal margin of the cephalon. Each suture is bordered by microtrichs. Two simple setae with a sensory hair, articulated on the base by a socket, are found one on each side of each of the sutures. Two additional setae, similar in shape and size, occur medially on the cephalon. A terminal pore is absent on the sensory hairs of al1 setae. These setae are suggested to be mechanoreceptors that provide directional sensitivity and enhance the sensibility of turbulent motion, viscosity and changes of hydrostatic pressure.

Anthropogenic impacts on tropical karst lakes: “Lagunas de Montebello,” Chiapas: Anthropogenic impacts on tropical karst lakes

Grupo de Investigación en Limnología Tropical, FES Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Mexico Unidad Académica de Ecología y Biodiversidad Acuática, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Ciudad de México, Mexico Departamento de Dinámica Terrestre Superficial, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad de México, México Correspondence Javier Alcocer, Grupo de Investigación en Limnología Tropical, FES Iztacala, Universidad Nacional Autónoma de México, Av. de los Barrios No. 1, Los Reyes Iztacala, Tlalnepantla 54090, Estado de México, Mexico. Email: jalcocer@unam.mx Funding information DGAPA‐PAPIIT, Grant/Award Number: IN219215; Fondo Sectorial de Investigación y Desarrollo Sobre el Agua CONAGUA/ CONACYT, Grant/Award Number: 167603

Seston dynamics in a saline Mexican lake

Organic and inorganic matter in aquatic ecosystems may occur in both dissolved and particulate form. Seston is the particulate matter present in the water column that is composed of 2 fractions: organic and inorganic matter (MARGALEF 1983, WETZEL 1983). Inorganic matter could be lithogenic (clay and silt), biogenic (silica), andlor originated by chemical precipitation (carbonates) (EFFLER et al. 2002, PENG & EFFLER 2005). The study of seston mass and composition is important to understanding the dynamics of the organic and mineral matter (PUNNING et al. 2003). Previous studies from a wide diversity of geographic regions covering temperate and tropical zones report organic matter as the most abundant fraction of seston, predominantly particulate organic carbon that exhibits seasonal dynamics similar to those of chlorophyll a (CALLIERI 1997, JÃRVINEN et al. 1999, BRZÁKOVÁ et al. 2003, PUNNING et al. 2003); however, the seston of some lakes, such as Lake Maggiore, could be dominated by the inorganic fraction during certain periods (CALLIERI 1997). Although previous studies on warm, monomictic Lake Alchichica relate to dynamic aspects such its hydrodynamics (ALcOCER et al. 2000), nutrient concentration (SÁNCHEZ SILVA 2006), and phytoplankton biomass (SÁNCHEZ REYES 2001), the dynamics ofthe seston concentration, distribution, and composition was unknown. The purpose of this investigation was to analyze the seasonal and vertical variation of seston in Lake Alchichica to better understand the organic and inorganic matter dynamics in tropical, saline lakes.