RESUMO
Introduction: The taphonomic attributes of a faunal assemblage provide information about which agents affect the distribution and preservation of ancient or newly formed biogenic materials during depositional and post-depositional processes. Actuotaphonomy thus is a valuable tool for reconstructing fossil communities because it establishes analogies between observable processes in the present and those that happened in the past. Objective: The taphonomic attributes of a marginal marine environment were analyzed to assess the origin of fragmentation, bioerosion, and encrustation processes and the role of these characteristics in the deterioration of current sediment accumulations of mollusks (gastropods and bivalves). Methods: The material studied was collected from a shell-remain accumulation called "El Conchal" in the Laguna de Mandinga, Veracruz, a lagoonal complex located in the Gulf of México. Taphonomic analysis included fragmentation, bioerosion, and encrustation features on recent gastropods and bivalve's shells. The categories of each attribute were classified in three degrees: poor, regular and good. The analysis was performed only in complete shells. Results: A bulk sample of 1 697.9 g was processed, recovering 1 165 complete specimens, of which 5 genera of bivalves and 4 genera of gastropods were identified. The fragmentation and bioerosion were classified as regular (grade 1), this may be the results of the water energy in the environment, that permits a constant rework, and exhumation of the remains at the lagoon's water-sediment interface; meanwhile, three eroders were identified to ichnogenus level: Entobia, Oichnus, and Caulostrepsis, being Caulostrepsis the least abundant. The encrustation was classified as poor (grade 2); the result can be interpreted based on the ecosystem intrinsic conditions that do not allow many encrusting organisms to develop properly. The encrusters are represented by calcareous organisms including bryozoans, serpulids tubes, and barnacles. The results yielded an actuotaphonomic model that could be applicable to analogous ecosystems in Laguna de Mandinga (Mandinga Lagoon), in Veracruz, Mexico. Conclusions: In marine marginal environments as in lagoon areas the encrustation does not have an important role in the preservation or destruction of shelly assemblages, being taphonomically more important than fragmentation and bioerosion as potentially destructive agents that can be a source of loss of fidelity in the fossil record.
Introducción: Los atributos tafonómicos de los conchales proveen información acerca de cuáles agentes afectan la distribución y preservación de la acumulación de materiales biogénicos recientes o fósiles, especialmente durante las etapas deposiconales y postdeposicionales. La actuotafonomía es una herramienta valiosa para la reconstrucción de las comunidades fósiles, para establecer analogías entre los procesos observables en el presente con los que ocurrieron en el pasado. Objetivos: Evaluar el impacto de los rasgos tafonómicos y su papel en la formación de los conchales en ambientes de lagunas costeras. Métodos: El material estudiado fue recolectado en una acumulación de restos de conchas llamado "El Conchal" en la Laguna de Mandinga, Veracruz, un complejo lagunar ubicado en el Golfo de México. El análisis tafonómico incluye las características tafonómicas de fragmentación, bioerosión e incrustación en conchas de gasterópodos y bivalvos recientes. Las categorías de cada atributo se clasificaron en tres grados: pobre, medio y alto. El análisis fue realizado solo en conchas completas. Resultados: Se procesaron 1 697.9 g de sedimentos, recuperando 1 165 ejemplares completos, de los cuales se identificaron 5 géneros de bivalvos y 4 géneros de gasterópodos. La fragmentación y bioerosión se clasificaron como un "grado regular", esto puede ser el resultado de la energía del agua en el ambiente, que permite el constante retrabajo y la exhumación de los restos en la interfase agua-sedimento en la laguna; en tanto que, se identificaron tres erosionadores a nivel de género, estos corresponden a los icnogéneros: Entobia, Oichnus y Caulostrepsis, siendo Caulostrepsis el menos abundante. La incrustación mostró un "grado pobre"; el resultado puede interpretarse basado en las condiciones intrínsecas del ecosistema que no permiten que muchos incrustantes se desarrollen de la manera adecuada. Los incrustantes están representados por organismos calcáreos incluyendo briozoarios, tubos de serpúlidos y balanos. Se analizaron los atributos tafonómicos para generar un modelo actuotafonómico que pueda ser aplicable a ecosistemas análogos en el registro fósil. Conclusiones: En ambientes marino marginales como son las áreas lagunares la incrustación no tiene un papel importante en la preservación o destrucción de los conchales, siendo tafonómicamente más importante la fragmentación y bioerosión como agentes potencialmente destructivos que pueden ser un recurso de pérdida de la fidelidad en el registro fósil.
Assuntos
Exoesqueleto/crescimento & desenvolvimento , Fósseis/anatomia & histologia , Moluscos/anatomia & histologia , MéxicoRESUMO
The development of the Grijalva-Usumacinta river basin exerts modifications on its discharge area. A sediment core was studied to reconstruct environmental changes and trace element contamination status during the past 45 years. 210Pb-derived mass accumulation rates indicate higher sediment input to the area since 1995, related to increased precipitation and floodings in the catchment area. Sediments show finer particles from the late 1970s on, likely related to dams construction upriver and/or land use changes. Heavy metal enrichment factors (EF < 2) suggest minimum contamination. Benthic foraminifera and redox-sensitive - elements (As, Ba, Co, Cr, Cu, Ni, Pb, V and Zn) indicate the sediments before 2000 were deposited under oxygenated conditions. Afterwards, environmental conditions changed and benthic foraminifera and dinocysts assemblages changed suggesting eutrophication and lower oxygen conditions during the last 20 years. Monitoring should be continued to assess eutrophication/hypoxic/pollution trends that could become deleterious to the marine biota.
Assuntos
Metais Pesados/análise , Poluentes Químicos da Água/análise , Monitoramento Ambiental , Sedimentos Geológicos , Golfo do México , RiosRESUMO
A Western blot assay for identification of 26 kDa and/or 8 kDa antigens in a crude saline extract (CSE) of Taenia solium metacestodes, previously developed for human cysticercosis, was evaluated for use with pigs. The test population used for assay standardisation consisted of 45 cysticercotic pigs (5 pigs positive by necropsy and 40 selected by tongue palpation and LL-Gp immunoblot but not confirmed by necropsy), 48 pigs with heterologous infections and 40 negative controls from endemic and non-endemic areas. The test detected 93% of the cysticercotic group and was 100% specific. In a field study this antigen preparation was compared by immunoblot with antibody recognition for Gp13-50 antigens in a lentil-lectin semi-purified glycoprotein extract of T. solium (LL-Gp). The seroprevalence to CSE antigen was slightly lower (26/75) when compared to LL-Gp (29/75) and this represented a non-significant difference. The CSE Western blot assay was used to assess seroprevalence of T. solium cysticercosis in pig populations in the state of Yucatan, Mexico. A total of 1099 pigs sampled at random from 25 villages revealed a seroprevalence of 23% (253/1099). Seroprevalence in intensively reared, farmed pigs was 2% (7/228). In comparison with farmed pigs, the seroprevalence was 33% (172/513) in free-roaming backyard pigs (OR=13.86, CI=4.0747.22, p<10(-6)) and 25% (74/98) in semi-confined backyard pigs (OR=14.03, CI=5.60-35.16, p<10(-6)). There was no significant difference in seroprevalence by sex (p=0.23). Seroprevalence decreased with age (chi(2)-test for linear trend=7.803, p<0.006). Results of this study demonstrate that the CSE Western blot can be applied for reliable immunodiagnosis of T. solium cysticercosis in pigs. Furthermore, variation in pig husbandry in Yucatan indicated significantly higher exposure to cysticercosis in free-roaming backyard pigs compared to intensively reared animals from the same area.