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1. Selective and differential feeding on marine prokaryotes by mucous mesh feeders

   https://doi.org/10.1111/1462-2920.16334  

   Thompson, Anne W. ; Sweeney, Carey P. ; Sutherland, Kelly R. ( January 2023 , Environmental Microbiology)

   Microbial mortality impacts the structure of food webs, carbon flow, and the interactions that create dynamic patterns of abundance across gradients in space and time in diverse ecosystems. In the oceans, estimates of microbial mortality by viruses, protists, and small zooplankton do not account fully for observations of loss, suggesting the existence of underappreciated mortality sources. We examined how ubiquitous mucous mesh feeders (i.e. gelatinous zooplankton) could contribute to microbial mortality in the open ocean. We coupled capture of live animals by blue‐water diving to sequence‐based approaches to measure the enrichment and selectivity of feeding by two coexisting mucous grazer taxa (pteropods and salps) on numerically dominant marine prokaryotes. We show that mucous mesh grazers consume a variety of marine prokaryotes and select between coexisting lineages and similar cell sizes. We show thatProchlorococcusmay evade filtration more than other cells and that planktonic archaea are consumed by macrozooplanktonic grazers. Discovery of these feeding relationships identifies a new source of mortality for Earth's dominant marine microbes and alters our understanding of how top‐down processes shape microbial community and function.

    

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2. Diet and trophic interactions of a circumglobally significant gelatinous marine zooplankter, Dolioletta gegenbauri (Uljanin, 1884)

   https://doi.org/10.1111/mec.14926  

   Walters, Tina L. ; Lamboley, Lauren M. ; López‐Figueroa, Natalia B. ; Rodríguez‐Santiago, Áurea E. ; Gibson, Deidre M. ; Frischer, Marc E. ( December 2018 , Molecular Ecology)

   Gelatinous zooplankton play a crucial role in marine planktonic food webs. However, primarily due to methodological challenges, the in situ diet of zooplankton remains poorly investigated and little is known about their trophic interactions including feeding behaviour, prey selection and in situ feeding rates. This is particularly true for gelatinous zooplankton including the marine pelagic tunicate,Dolioletta gegenbauri. In this study, we applied an 18S rRNA amplicon metabarcoding approach to identify the diet of captive‐fed and wild‐caughtD. gegenbaurion the midcontinental shelf of the South Atlantic Bight, USA. Sequencing‐based approaches were complimented with targeted quantitative real‐time polymerase chain reaction (PCR) analyses. Captive‐fedD. gegenbaurigut content was dominated by pico‐, nano‐ and micro‐plankton including pico‐dinoflagellates (picozoa) and diatoms. These results suggested that diatoms were concentrated byD. gegenbaurirelative to their concentration in the water column. Analysis of wild‐caught doliolids by quantitative real‐time PCR utilizing a group‐specific diatom primer set confirmed that diatoms were concentrated byD. gegenbauri, particularly by the gonozooid life stage associated with actively developing blooms. Sequences derived from larger metazoans were frequently observed in wild‐caught animals but not in captive‐fed animals suggesting experimental bias associated with captive feeding. These studies revealed that the diet ofD. gegenbauriis considerably more diverse than previously described, that parasites are common in wild populations, and that prey quality, quantity and parasites are likely all important factors in regulating doliolid population dynamics in continental shelf environments.

    

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3. Oscillations in the near-field feeding current of a calanoid copepod are useful for particle sensing

   https://doi.org/10.1038/s41598-019-54264-1  

   Giuffre, Carl ; Hinow, Peter ; Jiang, Houshuo ; Strickler, J. Rudi ( November 2019 , Scientific Reports)

   Calanoid copepods are small crustaceans that constitute a major element of aquatic ecosystems. Key to their success is their feeding apparatus consisting of sensor-studded mouth appendages that are in constant motion. These appendages generate a feeding current to enhance the encounter probability with food items. Additionally, sensing enables the organism to determine the position and quality of food particles, and to alter the near-field flow to capture and manipulate the particles for ingestion or rejection. Here we observe a freely swimming copepodLeptodiaptomus sicilisin multiple perspectives together with suspended particles that allow us to analyse the flow field created by the animal. We observe a highly periodic motion of the mouth appendages that is mirrored in oscillations of nearby tracer particles. We propose that the phase shift between the fluid and the particle velocities is sufficient for mechanical detection of the particles entrained in the feeding current. Moreover, we propose that an immersed algal cell may benefit from the excitation by increased uptake of dissolved inorganic compounds.

    

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4. A comparison between Zooglider and shipboard net and acoustic mesozooplankton sensing systems

   https://doi.org/10.1093/plankt/fbz033  

   Whitmore, Benjamin M ; Nickels, Catherine F ; Ohman, Mark D ( July 2019 , Journal of Plankton Research)

   Abstract Some planktonic patches have markedly higher concentrations of organisms compared to ambient conditions and are <5 m in thickness (i.e. thin layers). Conventional net sampling techniques are unable to resolve this vertical microstructure, while optical imaging systems can measure it for limited durations. Zooglider, an autonomous zooplankton-sensing glider, uses a low-power optical imaging system (Zoocam) to resolve mesozooplankton at a vertical scale of 5 cm while making concurrent physical and acoustic measurements (Zonar). In March 2017, Zooglider was compared with traditional nets (MOCNESS) and ship-based acoustics (Simrad EK80). Zoocam recorded significantly higher vertically integrated abundances of smaller copepods and appendicularians, and larger gelatinous predators and mineralized protists, but similar abundances of chaetognaths, euphausiids, and nauplii. Differences in concentrations and size-frequency distributions are attributable to net extrusion and preservation artifacts, suggesting advantages of in situ imaging of organisms by Zooglider. Zoocam detected much higher local concentrations of copepods and appendicularians (53 000 and 29 000 animals m−3, respectively) than were resolvable by nets. The EK80 and Zonar at 200 kHz agreed in relative magnitude and distribution of acoustic backscatter. The profiling capability of Zooglider allows for deeper high-frequency acoustic sampling than conventional ship-based acoustics. 

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5. Body size‐ and season‐dependent diel vertical migration of mesozooplankton resolved acoustically in the San Diego Trough

   https://doi.org/10.1002/lno.11993  

   Gastauer, Sven ; Nickels, Catherine F. ; Ohman, Mark D. ( November 2021 , Limnology and Oceanography)

   Diel vertical migration (DVM) is a common behavior among marine organisms to balance the trade‐off between surface feeding opportunities and predation‐related mortality risk. Body size is a master trait that impacts predation risk to both visual and nonvisual predators. Acoustic measurements from the autonomousZoogliderrevealed size‐dependent DVM behaviors in the San Diego Trough. Dual frequency (200 and 1000 kHz) backscatter, in conjunction with physical properties of the ambient water and optical imaging of zooplankton, were recorded during 12Zooglidermissions over 2 yr. Acoustic size‐categories were identified based on the theoretical scattering properties of dominant taxonomic groups identified optically by the Zoocam. Acoustic modeling suggests that the measured acoustic backscatter in this region is largely dominated by copepods, with appreciable contributions from other taxa. We found that larger organisms migrated deeper (245–227 m) and faster (> 20 m h⁻¹) compared to smaller organisms (156 m, > 15 m h⁻¹). Larger organisms entered the upper layer of the water column later in the evening (0.2–1.5 h later) and descended into deeper water earlier in the morning (0.4–3.7 h earlier) than smaller‐bodied organisms, consistent with body size‐dependent visual predation risk. The variability in daytime depths occupied by small, intermediate, and large‐bodied backscatterers was related to the depth of the euphotic zone, again consistent with light‐dependent risk of predation.

    

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