Ekologija pojave sluzavog morskog snijega u sjevernom Jadranu

The development, aggregation, and senescence of amorphous marine snow aggregates in the northern Adriatic Sea off Rovinj, Croatia were investigated during an aggregation event from July to September, 1997. Aggregates and surrounding ambient water were sampled using SCUBA for bacterial and cyanobacterial abundance, dissolved oxygen, primary production, bacterial secondary production, dissolved organic carbon and dry weight measurements. Marine snow aggregates appear to be a rich protected environment that favors primary production and bacterial growth by making readily available marine organic moieties present in the gel’s matrix. Aged aggregates form two separate zones: an outer well oxygenated almost transparent gel-like zone, and a dark almost‑anoxic/anoxic central zone. The interstices of the aggregates contained high concentrations of dissolved organic carbon, especially in the central almost anoxic-anoxic zone, which can be correlated to microbial activity. When sinking below the pycnocline they efficiently bypass mid-water biota thus becoming an important component of the marine biological pump and a major mechanism for the movement of particulate and dissolved organic carbon towards the sea floor.U ovom radu je opisan razvoj, nakupljanje i starenje amorfnih nakupina morskog snijega u sjevernom jadranu tijekom jedinstvene pojave u smislu trajanja i veličine organskih nakupina tijekom ljeta 1997. Istraživanja su provedena od lipnja do rujna 1997. u sjevernom jadranu sa postajama uzorkovanja dvije nautičke milje od Rovinja, Hrvatska. Da bi se prikazao razvoj odvajanja unutrašnjih zona unutar čestica morskog snijega, SCUBA ronioci su uzorkovali nakupine sličnih oblika. Uzorci nakupina i mora oko agregata su prikupljeni za određivanje brojnosne koncentracije bakterija i cijanobakterija, mjerenje otopljenog kisika, primarne proizvodnje, bakterijske sekundarne produkcije, otopljenog organskog ugljika i suhe tvari. Čestice morskog snijega imaju karakteristike nezavisnih i samoodržavajućih i mogu značajno doprinijeti nakupljanju i taloženju novoproizvedene organske tvari iz vodenog stupca. U specifičnim uvjetima nakupine ne podliježu razgradnji, remineralizaciji ili kolonizaciji zooplanktona. Tijekom tonjenja ispod piknokline čestice učinkovito zaobilaze biološke zajednice srednjeg sloja vodenog stupca i tako postaju možda najvažniji čimbenik sekvestracije morske biološke pumpe i puta čvrstog organskog ugljika prema morskom dnu

Contribution of Zooplankton Lipids to the Flux of Organic Matter in the Northern Adriatic Sea

Analyses of particulate material collected by sediment traps moored at a location in the northern Adriatic Sea in 1991 revealed the presence of zooplankton fatty acids, even though zooplankton and other \u27swimmers\u27 killed by the trap\u27s preservative were carefully removed. Laboratory experiments were conducted to (1) prove the existence of zooplankton lipids within fecal pellets, (2) exclude the possibility of incomplete separation of swimmers and other material as eventual contamination with polyunsaturated fatty acids in fecal pellets, (3) evaluate the importance of zooplankton lipids to mass flux and (4) reveal the mechanisms which lead to excretion of undigested organic matter, in this case polyunsaturated fatty acids. Our results show that the main source of fatty acids found in mass flux were zooplankton lipid droplets inside fecal pellets. The predominant fatty acids of zooplankton fecal pellets were saturated acid 16:0, monounsaturated acid 18:1 and polyunsaturated acid 22:6. Lipid composition of fecal pellets was compared with those of zooplankton and phytoplankton. Aliquots of collected fecal pellets were stained with Nile Red in order to visualize lipid droplets within fecal pellets

Influence of Zooplankton Grazing on Free Dissolved Enzymes in the Sea

In the Northern Adriatic Sea, extracellular enzymatic activity was measured during a Lagrangian study following a drifting buoy for 40 h. Dissolved free enzymatic activity represented 20 to 70% of total activity depending on the type of enzyme. alpha- and beta-glucosidases exhibited a significantly higher free activity than proteolytic enzymes. In subsequent laboratory experiments we investigated the effect of zooplankton on the free enzyme pool. The 4-step approach included: (1) determination of the enzymatic activities in copepods (mainly Acartia clausi); (2) enzymatic activity in fecal pellets; (3) short- and long-term grazing experiments; and (4) degradability of free glucosidase in seawater. alpha- and beta-glucosidases, leu-aminopeptidase, lipase and chitinase were examined. Experiments in which zooplankton were selectively enriched revealed a significant increase in both particle-bound (due to the increase of bacterial density) and dissolved free enzymatic activity. Incubating water enriched in free enzymes released by zooplankton with natural bacterial consortia, we found that 70% of the original alpha- and beta-glucosidase activity remained after 22 h. The presence of microorganisms did not enhance the degradation of these enzymes as compared to autoclaved controls. We found that a considerable amount of free dissolved enzymes is lost by 0.2 mu m filtration using Nuclepore filters, thereby leading to an underestimation of dissolved enzymes by similar to 30% in our experiments. Based on our results we conclude that mesozooplankton contribute to the free enzymatic activity in natural waters especially during periods of high grazing activity

Potential role of acrylic acid in bacterioplankton communities in the sea

In order to test the role of acrylic acid in controlling bacterial metabolism we performed experiments with bacterioplankton originating from the upper mixed čayer of the northern Adriatic Sea

AI-Light Spectrum Replicator (LSR): A Novel Simulated In Situ Lab/On-Deck Incubator

In this communication, we present the prototype of a new simulated in situ lab/on-deck incubator, the light spectrum replicator (LSR), and a method for simulating the measured in situ HOCR light spectrum curves in incubation chambers. We developed this system using AI and genetic algorithms in an iterative fashion to find the best-fitting light spectrum in situ irradiance at different depths. The HOCR light spectrum measured at the depth and time of sampling was processed immediately, so the incubator is in a stable and ready condition by the time the samples inoculated with 14C were placed in sample holders (10 min after sampling). This incubator is intended to provide a reliable, fast, and easy-to-use tool for studying primary production based on the evaluation of the photosynthetic uptake of 14C. This system enables short incubation periods for small samples: we tested incubations of 5 mL samples during 15 min incubation periods. Our initial measurements taken using the prototype revealed a sufficiently good correlation between the on-deck measurements and in situ incubations. This prototype can be improved, as discussed in this text

Extracted Spectral Signatures from the Water Column as a Tool for the Prediction of the Structure of a Marine Microbial Community

In this communication, we present an innovative approach leveraging advanced Machine Learning (ML) and Artificial Intelligence (AI) techniques, specifically the Non-Negative Matrix Factorization (NMF) method, to analyze downward and upward light spectra collected by Hyperspectral Ocean Color Radiometer (HyperOCR, HOCR) sensors in the water column. Our work focuses on the development of a robust and efficient tool for unraveling the structure and activities of natural microbial assemblages in the ocean. By applying the NMF method to HyperOCR data, we successfully extracted five spectral signatures, representing unique patterns in the data. These signatures were instrumental in predicting the abundances of various microbial components, including bacteria, heterotrophic nanoflagellates, and picoeukaryotes, showcasing the potential of ML and AI in advancing oceanographic studies. To validate these methods, the study area included a shallow coastal area under the influence of freshwater inflow and an open offshore area with a depth of 100 m. The study sites in coastal and offshore waters (Kaštela Bay and Stončica Vis, respectively) had significantly different hydrographic and microbiological characteristics. Kaštela Bay had lower temperatures and salinity than the site on Vis. We have demonstrated prediction of the structure of the microbial community through application of different AI and ML methods with specific HOCR sensors