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.

The anthropogenic discharges of inorganic nutrients impact water quality, affecting the macroinvertebrate assemblage and food safety. The main objective of this study was to examine the seawater quality and macroinvertebrate dynamics in muddy habitats of Buenaventura Bay, Colombian Pacific. Macroinvertebrates were captured using artisanal trawl nets during different seasons and along four sampling sites. Multivariate analyses (canonical correspondence analysis and generalized additive model) were used to assess the effects of variations in nitrite, nitrates, phosphate concentrations, and physicochemical variables (salinity, pH, dissolved oxygen [DO], temperature, and total dissolved solids [TDS]) of water on the macroinvertebrate assemblage. Richness was the highest at sites with high salinity and temperature and low concentrations of nitrites and TDS. The densities of the commercial shrimp species Xiphopenaeus riveti and Rimapenaeus byrdi were the highest at sites with higher DO and alkalinity, and lower nitrate concentrations. The swimming crab Callinectes arcuatus was dominant at sites with low water quality. In summary, in the transitional season and at the inner sites of Buenaventura Bay, it was observed the lowest water quality due to high nitrate concentration. High nitrate concentration was highlighted as the main anthropogenic factor that could decrease the capture of target macroinvertebrate species for food and livelihoods of artisanal fishermen and their families. Thus, macroinvertebrate communities may be vulnerable to increased inorganic nutrient inputs, which could affect estuarine water quality and ecosystems services.