It is likely that harmful algal blooms have increased in frequency, intensity, and geographic distribution in the last decades in response to anthropogenic activities. The Galápagos Islands are renowned for their exceptional biological diversity; however, marine dinoflagellate communities have not been represented in biodiversity assessments. Therefore, this study aims to provide key information about dinoflagellate diversity and abundances, with special attention to harmful species, during a weak La Niña event in the Galápagos Marine Reserve (GMR). The study was performed during March–April 2017 and four transects were conducted at four Islands (Santa Cruz, Santa Fé, Seymour, and Pinzón) representing the southern region of the GMR. Water net samples were collected at 2, 5, and 10 nautical miles (nm) from the coast, at a total of 48 sampling sites. The presence of toxic species, and their cell abundance was estimated in seven transects at 0, 15, and 30 m of depth. A total of 152 taxa belonging to 7 orders, 22 families, and 38 genera were registered. The number of taxa found is almost three times higher than the maximum observed in previous studies. Dinoflagellate species richness among stations ranged between 53 and 23 taxa and was higher in northern sites. From the applied cluster analysis, five dinoflagellate assemblages were identified as a discrete community structure, one was found only in Santa Fé Island, which is probably related to the presence of the Equatorial Undercurrent (EUC). Regarding cell abundance estimations, low abundances were registered throughout the sampling sites and no blooms were detected. Higher abundances were registered in the northern transects coinciding with one of the most productive areas of the archipelago, situated north of Santa Cruz. Among the identified taxa, 19 of them were potentially toxic, including epiphytic species, allowing the possibility of blooms in benthic areas. This study presents the first record of several dinoflagellate species in the area (both non-toxic and harmful species) and thus, emphasizing the need for the implementation of phytoplankton monitoring programs by the government to prevent potential ecological, sanitary and economic impacts in the GMR.

The environmental quality of mangroves is influenced by multiple factors, among which shrimp aquaculture currently plays a major role. This study describes the alterations of natural conditions of mangrove systems that house shrimp farms in the northern Ecuadorean coast. Water, sediment quality and the structure of benthic assemblages of four sectors with different proportions of mangroves and shrimp ponds are described. The samples were collected at the confluence of mangrove drainages or tidal creeks, as well as in the modified drainages for shrimp farm infrastructures towards navigable channels, during the dry and rainy seasons. Shrimp farm drainage water had a 17% higher dissolved oxygen concentration and 2.5 times higher total ammonium and phosphorus compared to mangrove drainage water. The sediment in the latter decreased their total organic matter and nitrogen content by 44% and 53%, respectively, slightly increasing the pH level and increasing the ammonium content by 93%. Furthermore, the redox profiles were different between the types of drainages. The soft-bottom benthic assemblages involved 56 species in the study area and exhibited a variety of sectoral structures, with better indicators of ecological status in sectors with fewer shrimp farms. Finally, improvements are suggested for monitoring the environmental quality of shrimp farms in Ecuadorean mangrove systems.

Illegal gold mining is on the rise in the tropical Andes. The Santiago-Cayapas watershed is located in the north of the Pacific basin of Ecuador, in the Chocó biogeographical region. It is recognized for its high biodiversity, as 62 fish species have been described in the area, and because it contains two of the largest protected areas in the Pacific coast of Ecuador: the mangroves of the Cayapas and Mataje Rivers and the Cotacachi-Cayapas Ecological Reserve. Open-pit gold mining has been described in the area since 2006 and most mining fronts operate illegally and lack any environmental control. Heavy-metal concentrations and fish communities were studied in streams that drain active and abandoned mines, in larger rivers located downstream of the mined areas and in control sites without mining activities. Open-pit mining causes a reduction of dissolved oxygen concentrations and an increase of water temperature, turbidity, and concentrations of Al, Cr, Co, Cu, Fe, Mn, and V. Fish abundance decreased in streams that drain active mines, however, metrics of taxonomic diversity remain unchanged among the study sites. The response of fish communities to open-pit gold mining was complex and driven by the pollution tolerance of each species, the presence of specific adaptions to turbid waters, and changes in the fishing pressure as locals avoid fishing activities in mined areas. Finally, streams that drain abandoned mines showed chemical characteristics, metal concentrations, and fish communities that were similar to control sites, but maintained higher water temperatures than control sites.

Mangrove sediments serve as paleoenvironmental records of organic matter and nutrient accumulation. Ecuador, the world’s largest producer of whiteleg shrimp Penaeus vannamei in brackish waters, lost 43% of its continental mangroves between 1969 and 1999. Currently, more than 70,000 hectares of shrimp farms operate in estuaries with mangroves and within mangrove reserves. Variations in mangrove coverage and the extent of shrimp farms are described for the period 1996–2020 for two mangrove reserves, REMACAM and RVSMERM, with an observed increase in the extent of shrimp farms in both reserves. Four sediment cores obtained from mangrove drains and drains transformed into shrimp farm infrastructures were analyzed to observe the impact of this activity on the cumulative changes in total organic carbon (TOC) content and total nitrogen (TN) content, the fractionation of stable isotopes δ13C and δ15N, as well as the TOC/TN ratio. The mangrove drains in REMACAM had 3.8 times more TOC and 2.3 times more TN than drains transformed into shrimp farms in RVSMERM, with lower TOC/TN ratios. The organic matter in sediments from sectors with a higher proportion of shrimp farms mainly came from particulate organic matter of freshwater and freshwater algae compared to mangrove drains. Increases in TOC and TN content were recorded in all analyzed sectors, which could be attributed to the cumulative impact of population growth, the development of other agricultural crops, and continental deforestation, despite the fact that proportionally, the highest increases occurred in the sector with a greater influence of shrimp farms.

Gold mining activities are often suspected to increase mercury pollution-associated with human health and ecological risks in aquatic ecosystems. The objective of this study was to quantify total mercury (THg) concentrations in fish from four different sampling sectors along the Cayapas River watershed that varied according to different exposure levels to artisanal and small-scale gold mining (ASGM) activities. We analyzed 142 samples from eight freshwater fish species ( Bryconamericus dahli , Brycon sp. , Brycon dentex, Chaetostoma marginatum , Pimelodella modestus , Rhamdia quelen , Gobiomorus maculatus , and Mesoheros festae ). Potential human exposure and health risks from fish consumption in three population groups (children, women, and men) was also evaluated to estimate intake rates and determine fish consumption with minimal risk to the population’s health. We found different THg concentrations among feeding habits and sampling sectors. Carnivorous fish species ( Pimelodella modestus , Rhamdia quelen , Gobiomorus maculatus , and Mesoheros festae ) showed higher THg concentrations (0.063 ± 0.021 µg.g ^-1 ) and periphyton-feeder species ( Chaetostoma marginatum ) revealed the lowest levels (0.018 ± 0.007 µg.g ^-1 ). Downstream sites showed the highest levels of THg compared to the other upstream sites, despite some sites being directly impacted by ASGM activities. Regarding human exposure, no significant potential health risk was found for the exposed population over a lifetime. However, the THg of a Rhamdia quelen sample slightly exceeded the FDA-EPA Hg reference value in fish across all sites, representing a potential risk for children. Our results suggest that the THg concentrations in the studied fish species are independent of ASGM activities. The accumulation rates may be due to other parameters such as land uses, local hydrology, fishing pressure or natural habitats modification. Further ecological and physiological studies, including spatial and seasonal distribution of Hg in the surface sediment, water column and fish species, should be investigated to assess and modulate the impacts of the ASGM in the Santiago-Cayapas watershed compared with other land uses that contribute to the Hg inputs, bioaccumulation, and biomagnification in ichthyofauna.