Declines in coastal macrozooplankton communities within a recent climate and ocean tipping point in the Tropical South Atlantic.

This study investigated whether variations in climate and ocean drivers on global, regional, and local scales affected macrozooplankton communities in a coastal protected area in Tamandaré Bay (northeastern Brazil). For this purpose, bimonthly field campaigns were carried out from June 2013 to August 2019. A significant tipping point (point of change, p < 0.001), with an abrupt increase in SST, was detected in the TSA (Tropical South Atlantic) index. This indicates the existence of a climate regime shift in the Tropical South Atlantic during the 2015/16 El Niño (EN) event. Extreme rainfall events were observed in Tamandaré Bay after this EN event, in 2017, 2018, and in 2019 (and more recently, in 2022). This extreme rainfall led to low-salinity events, increased variability in salinity, and significantly lower abundances in the period after the strong EN event, for socioeconomically relevant penaeid shrimp postlarvae and several other zooplankton groups (e.g., copepods, appendicularians, anomuran hermit crab larvae, and chaetognaths). We found a significant relationship between SSTs in the TSA region and penaeid shrimp recruitment in the study area, located leewards of the TSA index area. The decline in shrimp postlarvae and other macrozooplankton may be due to a combination of factors, such as climate and ocean shifts (atmospheric easterly waves disturbances, winds, precipitation, salinity) and possibly increasing marine pollution (related to extreme rainfall events, that convey macro- and microplastics, and pollutants from the continent). Cnidarian medusae and fish eggs were among the few "winners" of this ecosystem regime shift. Changes in climate, ocean, macrozooplankton, and shrimp postlarvae abundance evidence a relevant climate, ocean and ecosystem regime shift in this region with a tipping point during 2015/16 "Godzilla" El Niño. Possible future consequences in the context of persistent warming in the TSA region and the currently ongoing record strength 2023/24 EN event are discussed.

Influence of microplastics and biogenic particles on the size spectra of tropical estuarine and marine pelagic ecosystems.

Size spectra analysis has been widely used to study pelagic ecosystems worldwide. It has a solid theoretical and empirical basis and can be used to provide useful information on ecosystem structure and trophic efficiency. The objective of this study was to obtain complete Normalized Biovolume Size Spectra (NBSS), including zooplankton, microplastics, and other suspended particles, along an estuary-shelf gradient. Plankton net samples (300 µm mesh) were obtained in the Rio Formoso Estuary, in Tamandaré Bay and on the continental shelf off Tamandaré, Brazil, during two years (from April/2013 to May/2015). Particles were identified by image analysis (ZooScan) and infrared spectroscopy (FTIR). Generally, NBSS slopes were close to -1 (i.e., between -1.09 and -0.85), except for NBSSz (zooplankton only) in the Estuary (-1.59) and in the Bay (-1.44), where the steepest slopes were observed, due to the importance of small-sized zooplankton in these areas. The NBSSz slope was significantly steeper in the Estuary and in the Bay than on the Shelf. The inclusion of particles into the NBSS (NBSSp) turned the slope significantly less steep in the Estuary and in the Bay. Intercepts were significantly higher in the Estuary than in the other areas, after including particles in the analysis (NBSSp), due to the extremely high total volume of biogenic particles in the estuary. The most relevant impacts of microplastics were detected within the larger size classes (> 2.60 mm Feret length, > 0.58 log10 mm3). In the Estuary, large-sized microplastics were similarly important (in terms of volume) as zooplankton. Large-sized polyethylene and polypropylene were more relevant in the Bay, large-sized nylon fibers on the Shelf (in the rainy season). The present study, a pioneering effort towards a synthetic analysis of zooplankton, microplastics, and other particles, highlights the importance of including non-living particles in size-based studies and ecosystem models.

Seasonal and diel variations in the vertical distribution, composition, abundance and biomass of zooplankton in a deep Chilean Patagonian Fjord.

Comau Fjord is a stratified Chilean Patagonian Fjord characterized by a shallow brackish surface layer and a >400 m layer of aragonite-depleted subsurface waters. Despite the energetic burden of low aragonite saturation levels to calcification, Comau Fjord harbours dense populations of cold-water corals (CWC). While this paradox has been attributed to a rich supply of zooplankton, supporting abundance and biomass data are so far lacking. In this study, we investigated the seasonal and diel changes of the zooplankton community over the entire water column. We used a Nansen net (100 µm mesh) to take stratified vertical hauls between the surface and the bottom (0-50-100-200-300-400-450 m). Samples were scanned with a ZooScan, and abundance, biovolume and biomass were determined for 41 taxa identified on the web-based platform EcoTaxa 2.0. Zooplankton biomass was the highest in summer (209 g dry mass m-2) and the lowest in winter (61 g dry mass m-2). Abundance, however, peaked in spring, suggesting a close correspondence between reproduction and phytoplankton spring blooms (Chl a max. 50.86 mg m-3, 3 m depth). Overall, copepods were the most important group of the total zooplankton community, both in abundance (64-81%) and biovolume (20-70%) followed by mysids and chaetognaths (in terms of biovolume and biomass), and nauplii and Appendicularia (in terms of abundance). Throughout the year, diel changes in the vertical distribution of biomass were found with a daytime maximum in the 100-200 m depth layer and a nighttime maximum in surface waters (0-50 m), associated with the diel vertical migration of the calanoid copepod family Metridinidae. Diel differences in integrated zooplankton abundance, biovolume and biomass were probably due to a high zooplankton patchiness driven by biological processes (e.g., diel vertical migration or predation avoidance), and oceanographic processes (estuarine circulation, tidal mixing or water column stratification). Those factors are considered to be the main drivers of the zooplankton vertical distribution in Comau Fjord.

A fresh look at microplastics and other particles in the tropical coastal ecosystems of Tamandaré, Brazil.

Plankton organisms, biogenic particles, inorganic mineral particles, and microplastics are the four main components of particulate organic matter in aquatic ecosystems. We propose a new index, the Relative Microplastics Concentration (RMC, in %), considering that microplastics are more deleterious when food is scarce. A total of 112 plankton net samples were collected in estuarine, coastal and shelf environments of Tamandaré, Brazil. Particles were identified by image analysis (ZooScan) and FTIR. Higher concentrations of total microplastics, PP (Polypropylene) and PE (Polyethylene) in the estuary indicate an oceanward decreasing gradient from terrestrial sources. Higher concentrations of nylon fibres were found offshore. Yet, RMC indicated that the Bay had the most severely impacted ecosystems (RMC: 2.4% in the estuary, 5.1% in the Bay, and 2.0% on the shelf), for total microplastics and PP & PE. Shelf ecosystems were most severely impacted with nylon fibres. RMC analysis provided a new perspective into the impact of microplastics on tropical coastal food webs.