Biology subjects

Traboni, C.

Publications and source records attributed to Traboni, C..

2 recordsLinked to original sources

bioRxiv2025

Exploring the roles of trophic mode and microbial prey size in grazing pathways of tropical oligotrophic waters of the eastern Indian Ocean

Prey removal incubations were conducted in the Argo Basin (eastern Indian Ocean) to investigate the trophic ecology of the zooplankton community supporting Southern Bluefin Tuna larvae. Grazing and selectivity were evaluated considering prey trophic mode and size as food quality descriptors in copepod diets and compared with microzooplankton grazing. Copepod ingestion of eukaryotes ranged from 3.4 to 138 ng carbon (C) ind-1 d-1. Diet was dominated by mixotrophic (5-89%) and heterotrophic (0-84%) prey, with autotrophs contributing 2-17%. Nanoplankton provided the highest C intake to copepods (62-99%) rather than more abundant picoplankton (0.8-38%). No measurable reduction in chlorophyll a (Chla) concentration occurred from copepod grazing through food removal, suggesting a possible trophic cascade, although gut content revealed ingestion of 0.8 {micro}g Chla ind-1 d-1. Copepods showed moderate selection for picoplankton (E=0.3) over nanoplankton, perhaps due to faster consumption of nanoplankton by microzooplankton or ingestion of picoplankton aggregates. Ingestion of 15N (nitrogen)-labelled prey indicated copepod consumption of protistan consumers or small metazoans. We found significantly greater ([~]5-fold) copepod N consumption when using 1-2 {micro}m 15N-Synechococcus, compared to <1 {micro}m sized 15N-Prochlorococcus. Microzooplankton grazing on eukaryotes (0.07-2.5 d-1) and prokaryotes (0.3-2.1 d-1) greatly exceeded copepod grazing. Microzooplankton diet consisted mainly of heterotrophs (25-59%) and mixotrophs (13-41%), with lower autotrophic contribution (12-33%) of more nano- (95-98%) than picophytoplankton (2-5%) ingested. Overall, microzooplankton removed most of daily production (111%) in contrast to 7% for copepods. Our findings indicate that mixotrophy, intraguild grazing and nutrient channeling support the food web in this oligotrophic region.

ecology↗

bioRxiv2025

Acidic vacuole-containing organisms are a majority of the eukaryotic microbial community in oligotrophic Argo Basin waters (eastern Indian Ocean)

The Argo Basin of the eastern Indian Ocean in austral summer (February 2022) was characterized by warm (28.5-30.6{degrees}C), oligotrophic surface waters (nitrate and phosphate [≤]0.1 {micro}M), with relatively shallow mixed layers and deep chlorophyll biomass maxima. From euphotic zone depth-resolved samples analyzed by for DNA and acid vacuole staining (Hoechst and LysoTracker Green) by ship-board flow cytometry, we found that autotrophic populations were dominated by Prochlorococcus, followed by mixotrophs (58 and 28% of autotrophic community biomass, respectively), with only 14% obligate phototrophic phytoplankton (i.e., plastidic cells without acid vacuole fluorescence). Acid vacuole-containing microbes (mixotrophs and heterotrophs) were 34% of the microbial community, and 80% of the eukaryotic biomass. In shallow waters, the eukaryotic chlorophyll-containing community was comprised of pico-sized obligate phototrophs and mixotrophs (233-325 cells mL-1), nano-sized obligate phototrophs and mixotrophs (72 and 374 cells mL-1, respectively), with all groups increasing several-fold in the deep chlorophyll maxima. Mixotrophs were a higher proportion of the chlorophyll-containing community in the shallow nutrient-poor mixed layer, consistent with a nutrient-acquisition argument for their prevalence. Heterotrophic eukaryotes averaged 524 {+/-} 36 cells mL-1 in the euphotic zone, changing little with depth and showing a significant positive relationship with Prochlorococcus, but not any other group. In contrast, mixotrophs were positively correlated with heterotrophic bacteria, but not with Prochlorococcus. Overall, the high proportion of mixotrophs in the microbial community may channel more productivity to higher trophic levels than expected given the regions nutrient-poor status.

ecology↗