Microbial ecology of northern Gulf of Mexico estuarine waters.

Estuarine and coastal ecosystems are of high economic and ecological importance, owing to their diverse communities and the disproportionate role they play in carbon cycling, particularly in carbon sequestration. Organisms inhabiting these environments must overcome strong natural fluctuations in salinity, nutrients, and turbidity, as well as numerous climate change-induced disturbances such as land loss, sea level rise, and, in some locations, increasingly severe tropical cyclones that threaten to disrupt future ecosystem health. The northern Gulf of Mexico (nGoM) along the Louisiana coast contains dozens of estuaries, including the Mississippi-Atchafalaya River outflow, which dramatically influence the region due to their vast upstream watershed. Nevertheless, the microbiology of these estuaries and surrounding coastal environments has received little attention. To improve our understanding of microbial ecology in the understudied coastal nGoM, we conducted a 16S rRNA gene amplicon survey at eight sites and multiple time points along the Louisiana coast and one inland swamp spanning freshwater to high brackish salinities, totaling 47 duplicated Sterivex (0.2-2.7 µm) and prefilter (>2.7 µm) samples. We cataloged over 13,000 Amplicon Sequence ariants (ASVs) from common freshwater and marine clades such as SAR11 (Alphaproteobacteria), Synechococcus (Cyanobacteria), and acI and Candidatus Actinomarina (Actinobacteria). We observed correlations with freshwater or marine habitats in many organisms and characterized a group of taxa with specialized distributions across brackish water sites, supporting the hypothesis of an endogenous brackish-water community. Additionally, we observed brackish-water associations for several aquatic clades typically considered marine or freshwater taxa, such as SAR11 subclade II, SAR324, and the acI Actinobacteria. The data presented here expand the geographic coverage of microbial ecology in estuarine communities, help delineate the native and transitory members of these environments, and provide critical aquatic microbiological baseline data for coastal and estuarine sites in the nGoM.IMPORTANCEEstuarine and coastal waters are diverse ecosystems influenced by tidal fluxes, interconnected wetlands, and river outflows, which are of high economic and ecological importance. Microorganisms play a pivotal role in estuaries as "first responders" and ecosystem architects, yet despite their ecological importance, they remain underrepresented in microbial studies compared to open ocean environments. This leads to substantial knowledge gaps that are important for understanding global biogeochemical cycling and making decisions about conservation and management strategies in these environments. Our study makes key contributions to the microbial ecology of estuarine and coastal habitats in the northern Gulf of Mexico. Our microbial community data support the concept of a globally distributed, core brackish microbiome and emphasize previously underrecognized brackish-water taxa. Given the projected worsening of land loss, oil spills, and natural disasters in this region, our results will serve as important baseline data for researchers investigating the microbial communities found across estuaries.

Seasonal and environmental influences on recruitment patterns and habitat usage among resident and transient fishes in a World Heritage Site subtropical estuary.

This study investigated whether the fish communities inhabiting shallow non-vegetated habitats in two divergent bays in a subtropical World Heritage Site estuarine system differed according to wet (spring-summer) and dry (autumn-winter) seasons or polyhaline and mesohaline zones, within the broader objective of facilitating spatio-temporal management. Species richness (total of 74 taxa; total length, LT = 11-552 mm) and abundance (51 109 individuals) were mostly greater in the wet than dry season and in polyhaline than mesohaline areas. There was a major effect of rainfall on recruitment, particularly among transient fishes, which could be the result of enhanced survival of young via greater productivity (food resources) and protection from predators (via turbidity reducing visual cues). Salinity had strong interactive effects with rainfall and temperature in one bay, with greater species richness and overall abundances as well as large abundances of four key species [Anchoa januaria and Atherinella brasiliensis (pelagic residents), Cetengraulis edentulus (pelagic transient) and Diapterus rhombeus (demersal transient)] during the wet season in polyhaline areas; possibly reflecting a biodiversity hotspot that might be affected by distance to the estuary mouth and convergence hydrology. Regionally, the results support enforcing spatio-temporal restrictions to minimize anthropogenic activities within statutory (but not always enforced) protected areas. Globally, the data reiterate the need to identify and understand biotic and abiotic effects on estuarine ichthyofaunal distributions and abundances as a precursor to their management.

Zooplankton of an urban coastal lagoon: composition and association with environmental factors and summer fish kill

Zooplankton may be regarded as a sensitive tool for monitoring environmental variations in coastal lagoons due to their ability to immediately react to changes in the water column trophic features and salinity levels. As a coastal lagoon with a broad history of anthropic influence, Rodrigo de Freitas Lagoon (Rio de Janeiro, Brazil) is widely used for water sports and artisanal fishing. The present study aimed to expand the knowledge base about zooplankton in the Rodrigo de Freitas Lagoon by assessing the composition and time-spatial distribution of the major zooplankton groups. Samples were collected fortnightly from at four distinct sampling points August 2001 to July 2002. At each point, salinity, temperature, dissolved oxygen and water transparency were measured. During the study period, the lagoon behaved as an spatially homogeneous environment in what regards the abiotic variables. However, all these variables showed significant differences along the time, mainly related to seasonality (air temperature and rainy and dry periods). The zooplankton community showed low taxonomic richness, with the predominance of species commonly found in coastal lagoons, especially with mesohaline conditions, as well as those found in estuaries. An interesting fact was the rise in zooplankton abundance at all sampling points right after a fish kill event. Such increase was caused mainly by the Brachionus plicatilis O.F. Müller 1786 species. Thus, the zooplankton community was affected by physical and chemical factors, mainly by the dissolved oxygen decline event and variations in the influx of seawater into the lagoon. In addition, phytoplankton availability and fish predation pressure were suggested as important regulating factors of the zooplankton community.

Zooplankton of an urban coastal lagoon: composition and association with environmental factors and summer fish kill

Zooplankton may be regarded as a sensitive tool for monitoring environmental variations in coastal lagoons due to their ability to immediately react to changes in the water column trophic features and salinity levels. As a coastal lagoon with a broad history of anthropic influence, Rodrigo de Freitas Lagoon (Rio de Janeiro, Brazil) is widely used for water sports and artisanal fishing. The present study aimed to expand the knowledge base about zooplankton in the Rodrigo de Freitas Lagoon by assessing the composition and time-spatial distribution of the major zooplankton groups. Samples were collected fortnightly from at four distinct sampling points August 2001 to July 2002. At each point, salinity, temperature, dissolved oxygen and water transparency were measured. During the study period, the lagoon behaved as an spatially homogeneous environment in what regards the abiotic variables. However, all these variables showed significant differences along the time, mainly related to seasonality (air temperature and rainy and dry periods). The zooplankton community showed low taxonomic richness, with the predominance of species commonly found in coastal lagoons, especially with mesohaline conditions, as well as those found in estuaries. An interesting fact was the rise in zooplankton abundance at all sampling points right after a fish kill event. Such increase was caused mainly by the Brachionus plicatilis O.F. Müller 1786 species. Thus, the zooplankton community was affected by physical and chemical factors, mainly by the dissolved oxygen decline event and variations in the influx of seawater into the lagoon. In addition, phytoplankton availability and fish predation pressure were suggested as important regulating factors of the zooplankton community.

Zooplankton of an urban coastal lagoon: composition and association with environmental factors and summer fish kill

Zooplankton may be regarded as a sensitive tool for monitoring environmental variations in coastal lagoons due to their ability to immediately react to changes in the water column trophic features and salinity levels. As a coastal lagoon with a broad history of anthropic influence, Rodrigo de Freitas Lagoon (Rio de Janeiro, Brazil) is widely used for water sports and artisanal fishing. The present study aimed to expand the knowledge base about zooplankton in the Rodrigo de Freitas Lagoon by assessing the composition and time-spatial distribution of the major zooplankton groups. Samples were collected fortnightly from at four distinct sampling points August 2001 to July 2002. At each point, salinity, temperature, dissolved oxygen and water transparency were measured. During the study period, the lagoon behaved as an spatially homogeneous environment in what regards the abiotic variables. However, all these variables showed significant differences along the time, mainly related to seasonality (air temperature and rainy and dry periods). The zooplankton community showed low taxonomic richness, with the predominance of species commonly found in coastal lagoons, especially with mesohaline conditions, as well as those found in estuaries. An interesting fact was the rise in zooplankton abundance at all sampling points right after a fish kill event. Such increase was caused mainly by the Brachionus plicatilis O.F. Müller 1786 species. Thus, the zooplankton community was affected by physical and chemical factors, mainly by the dissolved oxygen decline event and variations in the influx of seawater into the lagoon. In addition, phytoplankton availability and fish predation pressure were suggested as important regulating factors of the zooplankton community.