Three fish assemblages (functional groups according to estuary use) were examined, which presented different responses to environmental variations, mainly associated to the dry and rainy seasons and high and low salinities and temperatures in the Buenaventura Bay estuary, Colombia, Tropical Eastern Pacific. In total, 4674 individuals were collected, belonging to 69 species of 29 families. The most abundant species was Sphoeroides trichocephalus (35% of the total density). The assemblage of estuarine-resident fishes showed high tolerance to environmental variations since these were present all along the estuary and throughout the year. The assemblage of marine estuarine-dependent species was associated with the rainy season and low salinities and temperatures. The assemblages of marine estuarine opportunist fishes were associated with areas of higher environmental variability in both seasons, dry and rainy. Fish species belonging to the same functional group showed variations in their response to environmental changes which evidenced complex spatial and temporal dynamics. Understanding these changes is necessary to generate effective management plans based on scientific ecological knowledge, which include environmental impacts present in this estuary such as microplastics, heavy metals, and effects of dredging, and their effects on the ecosystem.

In tropical estuaries, fish diversity varies spatially and temporally due to behavioral processes such as reproductive migrations, predator avoidance, and foraging, which are affected by water quality. Eutrophication is one of the main factors affecting water quality in estuaries. The objective of this study was to determine variation in fish assemblage explained by fluctuating water quality in the Buenaventura Bay. Fish were captured using artisanal trawl nets during the wet, dry, and transitional seasons at four sampling sites. Additionally, alkalinity; phosphate, nitrite, and nitrate concentrations; dissolved oxygen; pH; temperature; and suspended solids were measured. Multivariate analysis was used to assess the effect of water quality on fish assemblage. In Buenaventura Bay, the assemblage composition of Pseudupeneus grandisquamis, Daector dowi, and Citharichthys gilberti was affected by nitrate concentration. Moreover, large fish biomasses were associated with high nitrite concentration, intermediate salinity, and low dissolved oxygen, suggesting that these estuaries are dominated by species tolerant to poor water quality. Species richness was associated with low nitrate and phosphate concentrations, more suitable water quality indicators, and intermediate temperatures. These results suggest that the deteriorating water quality of estuaries as a result of the anthropogenic impact could increase dominance and decrease richness, resulting in structural changes of fish assemblages.

The environmental health of Buenaventura Bay, a highly impacted tropical estuary, is influenced by numerous human activities, including mining upstream. Large-and small-scale fishing plays an important role in the local economy, so we investigated the dynamic processes of bioaccumulation of mercury at basal trophic levels. Four samples were taken at each of the four locations in Buenaventura Bay during each of the four seasons of 2015. We measured the total mercury content (T-Hg, dry weight) in sediments and in muscle tissue across 17 macroinvertebrate species. The most abundant were the blue crab (C. arcuatus) and the mantis shrimp (S. aculeata aculeata). Blue crab showed an average muscle T-Hg value exceeding the limit of 0.2 g•g-1 , which is the maximum T-Hg level suggested for food consumption by vulnerable humans and populations: pregnant women, children, and the community that feeds from this source of protein on a daily basis. It was found that, 6.22% of individuals exceeded the 0.5 g•g-1 level, which is the maximum T-Hg level suggested for food consumption by the general population: the population that consumes it sporadically. Significantly high values of T-Hg in blue crab and mantis shrimp occurred during low salinity conditions in the estuary, suggesting that Hg mainly originates from river runoff during the rainy season. Nevertheless, the biota-sediment accumulation factor (BSAF) was favored in high salinity, which could mean greater availability of Hg for higher levels of the estuarine food web in the dry season and in marine waters. In general, the T-Hg levels in some samples exceeded 0.2 g•g −1. Therefore this pollutant must be monitored due to its biomagnification potential and as a threat to human health, especially that for the local population of fishermen and their families.

Buenaventura bay is characterized by a great dynamic of environmental variables. There is descriptive information concerning the distribution of macroinvertebrates in the bay and its habitat, however it is necessary to document on its dynamics in relation to environmental variables. The objective of the present work was to determine the espatio-temporal variation in the structure and composition of macroinvertebrates and their relationship with the environmental variables. Four sampling (April-June-September-November) were carried out throughout 2015, in four stations (Estuary River-Internal Estuary-External Estuary-Marine Estuary). At each station three samples of sediments, physicochemical variables of the water and macroinvertebrates were collected. A total of 532 individuals were found in 17 species and 9 families. The abundance varied from 0.7±1.2 to 29.7±7.4 individuals per trawl and the richness varied from 0.3±1.2 to 4.7±1.2 species per trawl. The multiple regression analysis suggests an influence of the variables salinity and percentage of clayson the structure and composition of macroinvertebrates in the bay. The abundance and richness of macroinvertebrates was higher when the salinity conditions prevailed in the estuary.

Introducción: La dinámica de las condiciones ambientales influencia la variación del alimento disponible para los organismos estuarinos, afectando el consumo de alimento de los organismos bentónicos como los lenguados, esenciales para establecer y monitorear la calidad ambiental en estos ecosistemas. Objetivo: Determinar los hábitos tróficos de tres especies de la familia Achiridae en la Bahía de Buenaventura, Pacífico colombiano. Métodos: Los peces se recolectaron por medio de pesca de arrastre artesanal. Así mismo, en laboratorio se determinó la dieta de cada una de las especies y se calcularon diferentes índices tróficos, registrando diferencias en los hábitos alimentarios entre estas especies. Resultados: Se recolectó un total de 159 peces del género Achirus, siendo la especie más abundante Achirus klunzingeri (98), luego Achirus mazatlanus (44) y finalmente Achirus scutum (17). La dieta de A. scutum se basó en detritos, la de A. mazatlanus en detritos y peces y la de A. klunzingeri en crustáceos y peces. Los individuos de A. klunzingeri presentaron diferencias en su dieta entre la zona interna y externa del estuario, en la zona interna los peces fueron la presa principal y en la zona externa fueron los crustáceos. Las especies A. klunzingeri y A. mazatlanus presentaron ingesta de microplásticos, principalmente fibras alargadas e incoloras presentes en individuos de todas las tallas. La dinámica de los hábitos tróficos de A. klunzingeri, se relacionaron con algunas variables ambientales, como temperatura, trasparencia y oxígeno disuelto. Por ejemplo, estas tres variables presentaron correlaciones negativas con el ítem peces, y positivas para la categoría crustáceos. Conclusión: Se evidenció que estas especies son generalistas y que las condiciones ambientales no solo influenciaron la dinámica del consumo alimentario, sino que también, determinaron la presencia de los microplásticos.