Oceanic ecosystems are dominated by minute microorganisms that play a major role in food webs and biogeochemical cycles . Many microorganisms thrive in the dilute environment due to their capacity to locate, attach to, and use patches of nutrients and organic matter . We propose that some free-living planktonic bacteria have traded their ability to stick to nutrient-rich organic particles for a non-stick cell surface that helps them evade predation by mucous filter feeders. We used a combination of in situ sampling techniques and next-generation sequencing to study the biological filtration of microorganisms at the phylotype level. Our data indicate that some marine bacteria, most notably the highly abundant Pelagibacter ubique and most other members of the SAR 11 clade of the Alphaproteobacteria, can evade filtration by slipping through the mucous nets of both pelagic and benthic tunicates. While 0.3 µm polystyrene beads and other similarly-sized bacteria were efficiently filtered, SAR11 members were not captured. Reversed-phase chromatography revealed that most SAR11 bacteria have a much less hydrophobic cell surface than that of other planktonic bacteria. Our data call for a reconsideration of the role of surface properties in biological filtration and predator-prey interactions in aquatic systems.

Salps are gelatinous planktonic suspension feeders that filter large volumes of water in the food‐dilute open ocean. Their life cycle allows periodic exponential growth and population blooms. Dense swarms of salps have a high grazing impact that can deplete the photic zone of phytoplankton and export huge quantities of organic matter to the deep sea. Previous studies described their feeding manner as mostly nonselective, with larger particles retained at higher efficiencies than small particles. To examine salp diets, we used direct in situ sampling (InEx method) of undisturbed solitary Salpa maxima. Aggregates (“chains”) of Salpa fusiformis and Thalia democratica were studied using in situ incubations. Our findings suggest that in situ feeding rates are higher than previously reported and that cell removal is size independent with ∼ 1 μm picoeukaryotes preferentially removed over both larger eukaryotes and smaller bacteria. The prey : predator size ratios we measured (1 : 104–1 : 105) are an order of magnitude smaller than previously reported values and to the best of our knowledge, are the smallest values reported so far for any planktonic suspension feeders. Despite differences among the three species studied, they had similar prey preferences with no correlation between salp body length and prey size. Our findings shed new light on prey : predator relationships in planktonic systems—in particular, that factors other than size influence filtration efficiency—and suggest that in situ techniques should be devised and applied for the study of suspension feeding in the ocean.

Ruppin's Estuarine and Coastal Observatory (RECO) is a Long-Term Ecological Research station positioned on the East Mediterranean shoreline between Tel-Aviv and Haifa, Israel. We present a comprehensive online database and an accompanying website that provides direct access to the physical, chemical, and biological characteristics of the local coastal marine ecosystem and the Alexander micro estuary. It includes three databases that are updated continuously since 2014: a) In situ stationary sensors data (10 min intervals) of surface and bottom temperature, salinity, oxygen and water level measured at three stations along the estuary. b) Monthly profiles and discrete biogeochemical samples (surface and bottom water) of multiple parameters at four stations located at the inland part of the estuary. Measured parameters include concentrations of chlorophyll-a, microalgae and bacteria (counted with a flow cytometer), Nitrate, Nitrite, Ammonium, Phosphate, total N, total P, particulate organic matter (POM), total suspended solids (TSS), biochemical oxygen demand (BOD), as well as Secchi depth in each station c) Bi-weekly profiles, chlorophyll-a concentrations and cell counts at two marine stations adjacent to the estuary, (1, and 7 Km from the estuary mouth, at bottom depths of 8 and 48 m). The database also includes historical data for the Taninim micro-estuary (2014–2016). The RECO observatory provides a unique data set documenting the interaction of highly eutrophicated estuarine water with the ultra-oligotrophic seawater of the Eastern Mediterranean. This combination results in sharp gradients of salinity, temperature, dissolved oxygen, and nutrients over very small scales (centimeters to meters) and therefore offers an important data set for the coastal shelf research community. The data set also provide a long-term baseline of the estuary hydrography and geochemistry with the hope to foster effective science-based management and environmental planning of this and similar systems.