Species composition and abundance of the phytoplankton community in Acapulco Bay, Mexico, were studied from May to December 2009. Samples were collected at 5 stations (4 coastal and 1 oceanic) at 3 depths (1, 5 and 10 m). Eighty-seven species were identified: 54 dinoflagellates, 32 diatoms and 1 silicoflagellate. The community was structured mainly by adiaphoric species, that is, species adapted to both neritic and oceanic environments. Species abundance and composition varied significantly during the sampling period due to increased nutrient concentrations in the rainy season. Dinoflagellate species were more abundant during the dry season, and diatom species dominated numerically during the rainy season.

Resumen. Entre abril de 2000 y noviembre de 2002 se examinó la composición de la comunidad de parásitos metazoarios de la charra, Cichlasoma trimaculatum a partir de muestras temporales. Fueron recuperadas 12 especies de parásitos (40 969 individuos) de 231 hospederos examinados; 10 helmintos: Ascocotyle (Phagicola) longa, Austrodiplostomum compactum, Cladocystis trifolium, Clinostomum complanatum, Crassicutis cichlasomae, Posthodiplostomum minimum, Pseudoacanthostomum panamense, Neoechinorhynchus golvani, Southwellina hispida y Contracaecum sp., y 2 crustáceos: Argulus sp. y Ergasilus sp. La comunidad se caracterizó por un número mayor de parásitos generalistas y pocos especialistas de cíclidos, además por ser pobre en especies. De las 5 especies comunes dentro de la comunidad, 4 presentaron variación temporal en su dinámica de infección a lo largo del tiempo, la cual fue asociada con cambios ambientales generados durante las temporadas de secas y lluvias. La variación en la dinámica de infección de las especies comunes fue capaz de generar cambios en la estructura, tanto en el nivel de componente como en el de infracomunidad; sin embargo, no se observó un patrón claro, lo que indica que la comunidad puede ser poco predecible, como se sugiere para otras comunidades de parásitos de peces dulceacuícolas.

Abstract.-Chitons are marine mollusks morphologically composed of a large muscular foot which allows them to conform to irregular surfaces. Few species as Chiton articulatus are used for human consumption. During April, July and December of 2009and 2011, an evaluation was conducted on C. articulatus at Acapulco, Mexico. Number, size and weight of individuals caught in fishing were recorded. Simultaneously, during October and December 2009, February and April 2010, field work was carried at 4 locations to record the amount, size and weight of individuals caught for biometric analysis of the total length versus foot length and foot weight. Two models were obtained to estimate the total length. There were 4,007 C. articulatus feet acquired; the linear model estimated lengths from 39.75 to 48.27 mm; and the potential model calculated lengths from 43.09 to 54.97 mm. On a time scale, both estimates showed a trend of decreasing the annual arithmetic mean captured. The caught of C. articulatus in Acapulco can be considered as coastal artisanal fisheries. Furthermore, the variations in amount and sizes of the specimens were related to capture and weather season. Unregulated fishing effort may impact the population dynamics affecting the community structure and dynamics on the rocky shore. Key words: Chiton articulatus, Polyplacophora, Acapulco, fisheryResumen.-Los quitones son moluscos marinos con un gran pie muscular que les permite amoldarse a superficies irregulares. Algunas especies como Chiton articulatus, se utilizan para el consumo humano. Durante abril, julio y diciembre de 2009, 2010 y 2011, se realizó un diagnóstico de su pesca en Acapulco, México. Se registró la abundancia total de captura, tallas y pesos de ejemplares capturados en pesca artesanal. En octubre y diciembre 2009 así como febrero y abril 2010, se realizaron muestreos biológicos de la especie para analizar relaciones biométricas de la longitud total con la longitud y peso del pie. Se obtuvieron dos modelos para estimar la longitud total. Se registraron 4.007 pies de la especie. Con el modelo lineal se estimaron longitudes del organismo entre 39,75 y 48,27 mm; con el modelo potencial se encontraron entre 43,09 y 54,97 mm. En una escala de tiempo, ambas estimaciones presentaron una tendencia de disminución anual del promedio de longitud. La pesca de C. articulatus puede considerarse como artesanal. La cantidad y tallas de captura se relacionaron con la temporada climática. Ante la falta de una estrategia de manejo sostenido del recurso, la pesca no regulada puede generar cambios poblacionales de la especie y afectar la estructura y dinámica de la comunidad de organismos intermareales.

ABSTRACT. Introduction: Black skipjack, Euthynnus lineatus, and Pacific sierra, Scomberomorus sierra, are of great economic importance in the small-scale fishery of the Tropical Eastern Pacific and in particular in the study area. Objectives: The objectives of the present study were to assess the diet components of E. lineatus and S. sierra, as well as to evaluate the niche width, trophic level, and trophic overlap between the two species, by size and season. Methods: Biological samples were obtained weekly from small-scale fishery catches in Bahía de Acapulco, Mexico. The E. lineatus sampling period occurred from October 2016 to October 2017, whereas S. sierra was sampled from October 2016 to June 2018. The Prey-specific Index of Relative Importance (% PSIRI) was used to evaluate the importance of each prey item in the diet of the predator. Levin´s index (Bi) was used as a measure of niche width. The Morisita-Horn index was used to evaluate diet overlap by size (juveniles or adults), by season (dry or wet), and between the two species. The trophic level (TL) of predators was calculated using the Cortés´ method. Results: A total of 262 E. lineatus stomachs were analyzed (42 % were empty and 58 % contained food) and a total of 209 S. sierra stomachs were analyzed (74.6 % were empty and 25.3 % contained food). Of the total E. lineatus specimens sampled, 107 were juveniles and 155 were adults. Black skipjack juveniles fed on five food items and adults fed on 13 food items. Of the total S. sierra specimens sampled, 75 were juveniles and 134 were adults. Pacific sierra juveniles and adults fed on five food items. The diet of the two species comprised fish, mollusks, and crustaceans. The two species showed narrow niche width. The diet of juvenile and adult E. lineatus presented differences with growth, contrary to what was observed for juveniles and adults of S. sierra. There were no significant differences in diet by season for both species. The trophic overlap obtained between the two species was low. The trophic level calculated for both species indicated that are tertiary consumers. Conclusions: Black skipjack and Pacific sierra are tertiary predators and present a specialist behavior, feeding mainly on fish from the families Engraulidae and Clupeidae. Although a degree of similarity in the dietary food components of these species was observed, there was not a high degree of interspecific competition for food.

A new haploporid trematode, Saccocoelioides lamothei n. sp., is described from the intestine of the Pacifi c fat sleeper, Dormitator latifrons (Richardson, 1844) from 2 coastal lagoons of Guerrero, Mexico. The new species is characterized by the presence of diffuse eye-spot pigmentation in the forebody, 2 sac-like caeca ending pretesticularly, ventral sucker pre-equatorial and miracidium with pigmented eye-spots in eggs. It differs from all other congeneric species by having a small, pyriform to slightly elongated body, a short but conspicuous prepharynx and sac-like caeca terminating pretesticularly, an extreme posterior position of the testis, a small spherical to elongated ovary, vitelline follicles irregular in shape and size and reaching the ovary level, the uterus extending from the testicular zone to the acetabular region, with numerous relatively large eggs.