Seagrass meadows are among the most threatened ecosystems on earth, raising concerns about the equilibrium of coastal ecosystems and the sustainability of local fisheries. The present review evaluated the current status of the research on seagrasses and submerged aquatic vegetation (SAV) habitats off the coast of Brazil in terms of plant responses to environmental conditions, changes in distribution and abundance, and the possible role of climate change and variability. Despite an increase in the number of studies, the communication of the results is still relatively limited and is mainly addressed to a national or regional public; thus, South American seagrasses are rarely included or cited in global reviews and models. The scarcity of large-scale and long-term studies allowing the detection of changes in the structure, abundance and composition of seagrass habitats and associated species still hinders the investigation of such communities with respect to the potential effects of climate change. Seagrass meadows and SAV occur all along the Brazilian coast, with species distribution and abundance being strongly influenced by regional oceanography, coastal water masses, river runoff and coastal geomorphology. Based on these geomorphological, hydrological and ecological features, we characterised the distribution of seagrass habitats and abundances within the major coastal compartments. The current conservation status of Brazilian seagrasses and SAV is critical. The unsustainable exploitation and occupation of coastal areas and the multifold anthropogenic footprints left during the last 100 years led to the loss and degradation of shoreline habitats potentially suitable for seagrass occupation. Knowledge of the prevailing patterns and processes governing seagrass structure and functioning along the Brazilian coast is necessary for the global discussion on climate change. Our review is a first and much-needed step toward a more integrated and inclusive approach to understanding the diversity of coastal plant formations along the Southwestern Atlantic coast as well as a regional alert the projected or predicted effects of global changes on the goods and services provided by regional seagrasses and SAV.

Ephemeral macroalgal blooms have been increasing in frequency and abundance worldwide. We investigated the variability of drift macroalgae abundance in a shallow bay of the Patos Lagoon Estuary (PLE) in southern Brazil to determine the influence of climate and hydrology on the onset and magnitude of blooms. During the study period (January 2004 to May 2007), three growth cycles were observed and differed in timing, magnitude and persistence. Macroalgal biomass (mostly Ulva species) varied annually and interannually (3 g DW m⁻² to 432.7 g DW m⁻²), peaking during the spring and summer. On an annual scale, macroalgal blooms occurred after reductions in freshwater discharge and associated decreases in water level and increases in salinity and retention. These hydrological parameters were influenced by precipitation which, in turn, is affected by the El Niño Southern Oscillation. On an interannual scale, the largest bloom was observed during a weak-moderate El Niño year. No direct relationship was found between biomass peaks and water nutrient concentrations, but tissue nitrogen content indicated no nitrogen limitation. However, a trend of increasing phosphorus concentration (resulting in decreased DIN:DIP ratios) may be associated with the largest bloom observed. Under favourable hydrological conditions for growth, wind action affected the algal transport in shallow areas, thereby controlling the magnitude and persistence of the blooms. The macroalgal abundance found in the PLE was comparable to that found in temperate eutrophic lagoons, highlighting an algal-dominated period triggered by the combined effects of climate and hydrological factors in a post-El Niño period.

Estuaries are among the most productive aquatic ecosystems and provide important ecological and economic services in coastal areas. However, estuarine systems have been threatened worldwide by natural and anthropogenic impacts acting on local, regional, and global scales. Long-term ecological studies contribute to the understanding and management of estuarine functioning and provide the baseline information for detection changes and modeling of predictive scenarios. Here, we describe long-term data on the biodiversity and physico-chemical parameters obtained from 1993 to 2016 for the Patos Lagoon estuary and adjacent marine coast (PLEA), in southern Brazil. We report 8 datasets containing 6972 sampling events with the occurrence and abundance records of 275 species (kingdoms: Bacteria, Protozoa, Chromista, Plantae, and Animalia) of functional groups plankton, benthos, and nekton. Datasets also include 22 190 abiotic records. The database is published in the Global Biodiversity Information Facility (GBIF) repository (see Sect. 3 “Data availability” and Table 3). The present compendium represents one of the most comprehensive and longest datasets from primary producers to top predators in an estuarine coastal system in South America, and their availability will be an important contribution to the understanding and predictability of estuarine dynamics around the world.

The ongoing environmental crisis, driven by biodiversity loss and climate change, raises concerns about the impacts on marine systems and human well-being. These environments provide crucial ecosystem services valued at approximately USD 74.5 trillion·year⁻¹ globally. Seagrasses support fisheries, protect coasts, help mitigate climate change, maintain biodiversity, provide food security, and enhance water quality. However, comprehensive assessments of seagrass ecosystem services (SESs) and their impacts are lacking. Focusing on the Brazilian southwest Atlantic, our aim is to bridge this gap and identify key research areas for improved management decisions. Our literature search employed n = 19 paired terms for seagrass in Brazil. We screened 30,351 search returns for 394 relevant documents. Research on SESs has grown over time, and most research has focused on provisioning and supporting ecosystem services: 79.7% of documents mentioned at least one SES, while 24.5% of the documents provided evidence of observed SESs; 31.5% only provided information on expected SESs. Provisioning services were the most observed and expected. Coastal urbanization (54%) and marine food provisioning (17%) were the main drivers impacting SESs. Terrestrial food and material provision (9%) and climate change (8%) were also significant drivers. This study provides key recommendations aimed at fostering further research and management strategies to consider the complete ensemble of ecosystem services for a range of seagrass bioregions, to better understand the provision of and impacts to seagrass services and human well-being at the global scale.