Gitai Yahel

How flow moves through porous structures like sponges has long intrigued physical and biological scientists. Despite sponges having specialized cells that function as biological pumps, their porous bodies are proposed to passively take advantage of ambient currents via ‘inducedflow’. This hypothesis relies on the fact that flow external to perforated or tube-like structures drives flow through the structure, but much of the support for this comes from work on dead specimens. A modern understanding of sponge morphology and physiology however, shows that sponges possess a sophisticated sensory system, even in their canals. We used custom flow and oxygen sensors at a 175m deep sponge reef to test the hypothesis of current-induced passive flow through living glass sponges. Evidence to support a passive flow hypothesis was only found in one of six individuals that filtered more water during periods of higher ambient current. As expected, all individuals stopped pumping independently of ambient currents, illustrating their control over pumping using the well-described electrical conduction system. However, at higher ambient currents, sponges removed 30% less oxygen, suggesting a mechanism by which the sponge senses the ambient flow rates and reduces the metabolic expenditure of filtration. The underlying mechanism by which this happens remains unknown, but it may involve a feedback loop through the canals, potentially via primary cilia that have been shown to sense flow in other sponges. Our experiments reveal that while sponges can take advantage of ambient flow, water movement through these animals is controlled by their complex physiology.

10th Sponge World Conference, 25-30 June 2017, Galway, Ireland.-- 1 pageThe contribution of DOM to sponge feeding is now well documented1, 2 and uptake of labile DOC occurs in both high (HMA) and low (LMA) microbial abundance sponge3. In contrast, considerable DON uptake and nitrate excretion are observed only in HMA species. We used in situ and laboratory techniques to measure the dissolved and particulate nitrogen fluxes mediated by HMA and LMA sponges and constructed a partial ni- trogen budget for 14 sponges species from four different oceanic areas: North-East Pacific, North Sea, North- West Mediterranean Sea, and the Red-Sea. Regardless of the oceanographic settings, HMA sponges exhibited high plasticity in their ability to use the available dissolved nitrogen compounds. Under normal oxygenated conditions, NH4+ levels are low and most of nitrate excreted by HMA sponges is derived from full oxidation of DON; when NH4+ concentrations are high, its uptake represent an addition to the nitrification rates. The ubiquity of nitrification among the different geographical zones and the high rates of nitrate production as- sociated with HMA sponges suggest that it represents a relevant process for energy income and potentially microbial production within these sponges. We discuss the energetic consequences of these results considering the contribution of full oxidation of the organic matter for the sponge holobionts and the consequences for nutrient cycling. Our data suggest that the HMA sponges are unique among the metazoans in their nutritional plasticity and their ability to take advantage of the entire range of reduced compounds available in the water, provide them with a relevant additional energy sourcePeer Reviewe

Suspension feeders, including ascidians (Phylum Chordata, Class Ascidiacea), experience a dilute prey field composed of extremely small particles. The filtration apparatus of ascidians is based on a mucous-mesh that is continuously secreted and ingested. The rate and metabolic cost of this mesh secretion has not been quantified to date. We used video boroscopy to quantify the mucous-mesh production rate of the solitary ascidian Herdmania momus under different food and temperature treatments. H. momus individuals with an average (±95% CI) biomass of 30.7 ± 1.1 mg and a branchial sac area of 10.3 ± 1.2 cm2 produced an average of 276 ± 33.5 cm2 of mucous-mesh h-1, corresponding to a median turnover rate of 625 ± 82 mesh d-1. Since the mean mesh mass was 2.44 ± 0.58 mg, this production rate corresponds to roughly 50 ± 8 times the individual’s biomass per day. Food concentration had no detectable effect on mesh production rate, whereas a temperature difference of ~9°C (20 vs. 29°C) moder...

Sponges are commonly divided into high (HMA) and low (LMA) microbial‐abundance species according to the bacterial biomass in their tissue. These two groups reflect distinct aquiferous structures and feeding strategies. In the NW Mediterranean coralligenous community, HMA and LMA sponges are often packed in dense, multispecies assemblages that cover many pinnacles and overhangs. We investigated the metabolism of HMA and LMA species that cohabitate the coralligenous community by sampling in situ the inhaled and exhaled water. Sponges consumed plankton, dissolved organic carbon (DOC), and ammonium in relation to their abundance in ambient water. The plankton retention efficiency was high for all species. DOC was the main source of C for the sponge species, accounting for ∼ 90% of the examined sources. Nitrogen fluxes markedly differed between the two groups: plankton was the main source of nitrogen for LMAs that excreted dissolved organic nitrogen (DON) and ammonium. The nitrogenous wa...

Monthly surveys of water properties along the estuary. These surveys include water column CTD profiles of temperature, salinity, dissolved oxygen, chlorophyll fluorescence, and turbidity (OBS). Profile data are accompanied by Secchi depth measurements and discrete water samples collected by a horizontal Niskin bottle near the surface and near the bottom. Water samples are analyzed for the concentrations of Phosphate, Nitrate, Nitrite, Ammonium, Total and particulate nitrogen and phosphorus, total suspended solids, particulate organic matter, biological oxygen demand, chlorophyll-a, cell counts of nano and pico planktonic algae and non-photosynthetic bacteria.

Bi-weekly surveys of water properties at two marine stations ~1 and 6.6 Km from the estuary mouth at bottom depths of 8 and 48 meters. These surveys include water column CTD profiles of temperature, salinity, dissolved oxygen, chlorophyll fluorescence, and Turbidity (OBS). Profile data are accompanied by discrete water samples collected by a Niskin bottle at 10 m depth, these samples are analyzed for the concentrations of chlorophyll-a and pico and nano planktonic algae and non-photosynthetic bacteria.

How flow moves through porous structures like sponges has long intrigued physical and biological scientists. Despite sponges having specialized cells that function as biological pumps, their porous bodies are proposed to passively take advantage of ambient currents via ‘inducedflow’. This hypothesis relies on the fact that flow external to perforated or tube-like structures drives flow through the structure, but much of the support for this comes from work on dead specimens. A modern understanding of sponge morphology and physiology however, shows that sponges possess a sophisticated sensory system, even in their canals. We used custom flow and oxygen sensors at a 175m deep sponge reef to test the hypothesis of current-induced passive flow through living glass sponges. Evidence to support a passive flow hypothesis was only found in one of six individuals that filtered more water during periods of higher ambient current. As expected, all individuals stopped pumping independently of ambient currents, illustrating their control over pumping using the well-described electrical conduction system. However, at higher ambient currents, sponges removed 30% less oxygen, suggesting a mechanism by which the sponge senses the ambient flow rates and reduces the metabolic expenditure of filtration. The underlying mechanism by which this happens remains unknown, but it may involve a feedback loop through the canals, potentially via primary cilia that have been shown to sense flow in other sponges. Our experiments reveal that while sponges can take advantage of ambient flow, water movement through these animals is controlled by their complex physiology.

In the version of this Letter originally published, the authors incorrectly stated that primers 28F-519R were reported in ref. 54 to underestimate the abundance of SAR11 in the ocean. This statement has now been amended in all versions of the Letter.

Constructing the Suez Canal connected the Red Sea and the Mediterranean Sea, allowing rapid marine bio-invasion. Over the last century, several bivalve species have invaded the Levantine basin, yet their distribution and impact on the benthic community have not been thoroughly studied. Large-scale benthic surveys along the rocky substrate of the Israeli Mediterranean coastline indicate that invading bivalves now dominate the rocky environment, reaching densities of tens to hundreds of individuals per m2. No native bivalve specimens were found in any of the transects surveyed. The small-scale ecological effects of the established invading populations on the benthic community were examined using in-situ exclusion experiment where all invading bivalves were either physically removed or poisoned and kept in place to maintain the physical effect of the shells. Surprisingly, the experimental exclusion showed little measurable effect of bivalve presence on the invertebrate community in clo...

Sponges play a key role in the transfer of energy and nutrients into many benthic ecosystems, and the volume of water they process is an important regulator of these fluxes. Theoretical scaling relationships between sponge volume, osculum cross-sectional area, and pumping rates were recently proposed and confirmed for small sponge specimens in the lab. To examine how these relationships apply to field populations we measured, in situ, the pumping rate (PR) of 20 species representative of different morphologies and host types (high- and low-microbial-abundance, HMA and LMA) from temperate and tropical regions. The total oscula area (∑OSA) increased allometrically with sponge volume (V) exhibiting similar exponents (∑OSA=aVb, b ranging 0.6–0.7) for all species, except for tropical HMAs (b = 0.99). Osculum flow rate (OFR) also increased allometrically with OSA and oscula of the same size pumped at the same rate irrespective of sponge volume. As a result, and in contrast to former repor...

The vast majority of organic matter in the world ocean is found in the dissolved pool. However, no evidence has been demonstrated for direct uptake of bulk dissolved organic matter (DOM) by organisms other than bacteria and some invertebrate larvae. The total organic carbon (TOC) is 10–30 % higher in coral reefs than in adjacent open waters. The dissolved organic carbon (DOC) accounts for �90 % of the TOC. Using a new in situ technique for clean sampling of the seawater inhaled and exhaled by benthic suspension feeders, we measured directly the removal of DOC in the symbiont-bearing reef sponge Theonella swinhoei. The sponge removed up to 26 % (mean � SD: 12 % � 8%) of the TOC (dissolved and particulate) from the water it filtered during a single passage through its filtration system. Most of the carbon gained by the sponge was from the dissolved pool (10 � 7 �mol C L �1), an order of magnitude greater than the carbon gained from the total living cells (phytoplankton and bacteria) t...

Max Planck Institute for Marine Microbiology, Bremen, Germany, 2 Institut de Ciències del Mar, Consejo Superior de Investigaciones Cientifícas (ICM-CSIC), Barcelona, Spain, Centre d’Estudis Avançats de Blanes, Consejo Superior de Investigaciones Cientifícas (CEAB-CSIC), Girona, Spain, 4 School of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel, 5 Faculty of Marine Sciences, Ruppin Academic Center, Michmoret, Israel, Department of

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,...

Micro-estuaries in semi-arid areas, despite their small size (shallow depth of a few meters, length of a few kilometers, and a surface area of less than 1 km 2) are important providers of ecosystem services. Despite their high abundance, tendency to suffer from eutrophication and vulnerability to other anthropogenic impacts, such systems are among the least studied water bodies in the world. In low tidal amplitude regions, micro-estuaries often have limited rate of sea-river water exchange, somewhat similar to fjord circulation, caused by a shallow sandbar forming at the coastline. The long-term study, we report here was inspired by the idea that, due to their small size and low discharges regime, relatively small interventions can have large effects on micro-estuaries. We used a stationary array of sensors and detailed monthly water sampling to characterize the Alexander estuary, a typical micro-estuary in the S.E. Mediterranean, and to identify the main stress factors in this aqua...

Oceanic ecosystems are dominated by minute microorganisms that play a major role in food webs and biogeochemical cycles 1. Many microorganisms thrive in the dilute environment due to their capacity to locate, attach to, and use patches of nutrients and organic matter 2,3. 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 µ m 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. Culture-independent molecular techniques have revealed that a relatively small number of groups dominate marine microbial communities 4. Among these, Pelagibacter ubique and other members of the SAR11 clade are most ubiquitous, comprising 15-60% of the total bacteria in the upper ocean 5,6. The mechanisms underlying the extraordinary success of the SAR11 bacterial clade in open ocean ecosystems have been vigorously debated in recent years. Adaptation to resource competition has been suggested as one plausible mechanism since P. ubique exhibits a high surface-to-volume ratio coupled with a small and streamlined genome, containing high-affinity transporters that enable efficient metabolism in an oligotrophic environment 7. While these traits indicate a potential for fast growth, the measured in-vitro growth rate of P. ubique is low (0.04− 0.58 day −1) 8. Other mechanisms, including low viral infectivity, 'cryptic escape' through reduced cell size, and elaborated K-strategy defense mechanisms have been suggested, but with the discovery of widespread 'pelagiphage' viruses infecting SAR11, these mechanisms are now considered less likely 9. Many organisms, particularly suspension feeders, feed on bacteria , and grazing is considered a prominent mortality factor for in the ocean. Although top-down control and differential grazing pressures can potentially shape the composition of the oceanic microbial community 10,11 , to date, little is known about grazing resistance of specific marine bacteria 12. Hence, low mortality might be an additional explanation for the high abundance of SAR11 12. To test for differential grazing efficiency for different bacteria we first focused on benthic tunicates (ascidians). These common filter feeders resemble planktonic tunicates in their use of mucous nets to filter bacteria and phytoplankton. We chose ascidians as a model organism because their strainer-like filtration apparatus is relatively simple compared to their planktonic counterparts 13 and their inhal-ant and exhalant siphons are sufficiently large to allow direct sampling of the water before and after filtration. We used the InEx VacuSIP method 14 (Fig. 1a, Supplementary Information movie S1) to cleanly collect the water inhaled and exhaled by ascidians in situ and calculated the removal efficiencies of different microorganisms. Cell counts made with a flow cytom-eter indicated that the ascidian Microcosmus exasperatus efficiently retained photosynthetic algae, coccoid picocyanobacteria and bacteria with high nucleic acid content (52%-82%, Fig. 1b), however different taxa were retained with significantly different efficien-cies (Friedman test, P < 0.001). Notably, low nucleic acid bacteria , with which SAR11 clade is usually associated 15 , were removed at significantly lower efficiency (18 ± 10%, CI95%, P < 0.05, RM ANOVA, Fig. 1b). To taxonomically identify the retained and non-retained bacteria phylotypes, we extracted DNA from the microbial community in the inhaled and exhaled water and measured the relative frequencies of different bacterial phylotypes based on 16S rRNA metabarcoding analysis by SILVAngs (Fig. 1c). The ambient microbial cell count in the water inhaled by the ascidians was 8.5 × 10 5 ± 3.1 × 10 5 cells mL −1 with 20 phylotypes (clustered at 98% identity) accounting for 92% of the total 16S rRNA gene reads sequenced. SAR11 clade and picocyanobacterial phylotypes accounted for 33% and 44% of the total reads, respectively (pink and

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 : 10 4-1 : 10 5) 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.

Benthic suspension feeders play essential roles in the functioning of marine ecosystems. By filtering large volumes of water, removing plankton and detritus, and excreting particulate and dissolved compounds, they serve as important agents for benthic-pelagic coupling. Accurately measuring the compounds removed and excreted by suspension feeders (such as sponges, ascidians, polychaetes, bivalves) is crucial for the study of their physiology, metabolism, and feeding ecology, and is fundamental to determine the ecological relevance of the nutrient fluxes mediated by these organisms. However, the assessment of the rate by which suspension feeders process particulate and dissolved compounds in nature is restricted by the limitations of the currently available methodologies. Our goal was to develop a simple, reliable, and non-intrusive method that would allow clean and controlled water sampling from a specific point, such as the excurrent aperture of benthic suspension feeders, in situ. Our method allows simultaneous sampling of inhaled and exhaled water of the studied organism by using minute tubes installed on a custom-built manipulator device and carefully positioned inside the exhalant orifice of the sampled organism. Piercing a septum on the collecting vessel with a syringe needle attached to the distal end of each tube allows the external pressure to slowly force the sampled water into the vessel through the sampling tube. The slow and controlled sampling rate allows integrating the inherent patchiness in the water while ensuring contamination free sampling. We provide recommendations for the most suitable filtering devices, collection vessel, and storing procedures for the analyses of different particulate and dissolved compounds. The VacuSIP system offers a reliable method for the quantification of undisturbed suspension feeder metabolism in natural conditions that is cheap and easy to learn and apply to assess the physiology and functional role of filter feeders in different ecosystems.