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Abstract Doliolids have a unique ability to impact the marine microbial community through bloom events and filter feeding. Their predation on large eukaryotic microorganisms is established and evidence of predation on smaller prokaryotic microorganisms is beginning to emerge. We studied the association between microorganisms and wild‐caught doliolids in the Northern California Current system. Doliolids were collected during bloom events identified at three different shelf locations with variable upwelling intensity. We discovered doliolids were associated with a range of prokaryotic microbial functional groups, which included free‐living pelagic Archaea, SAR11, and picocyanobacteria. The results suggest the possibility that doliolids could feed on the smallest members of the microbial community, expanding our understanding of doliolid feeding and microbial mortality. Given the ability of doliolids to clear large portions of seawater by filtration and their high abundance in this system, we suggest that doliolids could be an important player in shaping the microbial community structure of the Northern California Current system. 

Abstract Ctenophores are numerically dominant members of oceanic epipelagic communities around the world. The ctenophore community is often comprised of several common, co-occurring lobate and cestid genera. Previous quantifications of the amount of fluid that lobate ctenophores entrain in their feeding currents revealed that oceanic lobates have the potential for high feeding rates. In order to more directly examine the trophic role of oceanic lobate ctenophores, we quantified the encounter and retention efficiencies of several co-occurring species (Bolinopsis vitrea, Ocyropsis crystallina, Eurhamphea vexilligera and Cestum veneris) in their natural environments. Encounters and predator–prey interactions were video recorded in the field using specialized cameras and SCUBA techniques. The lobate species encountered, on average, 2.4 prey per minute and ingested 40% of these prey. This translated to an estimated ingestion rate of close to 1 prey per minute. Cestum veneris and most of the lobate species retained prey as efficiently as the voracious coastal lobate predator Mnemiopsis leidyi, suggesting that these oceanic species have a similar predation impact in their environments as M. leidyi does in coastal ecosystems. Hence, quantified in situ predatory-prey interactions indicate that epipelagic ctenophores have a significant impact on oceanic ecosystems worldwide. 

Abstract Eastern boundary systems support major fisheries of species whose early stages depend on upwelling production. However, upwelling can be highly variable at the regional scale, leading to complex patterns of feeding, growth, and survival for taxa that are broadly distributed in space and time. The northern California Current (NCC) is characterized by latitudinal variability in the seasonality and intensity of coastal upwelling. We examined the diet and larval growth of a dominant myctophid (Stenobrachius leucopsarus) in the context of their prey and predators in distinct NCC upwelling regimes. Larvae exhibited significant differences in diet and growth, with greater seasonal than latitudinal variability. In winter, during reduced upwelling, growth was substantially slower, guts less full, and diets dominated by copepod nauplii. During summer upwelling, faster-growing larvae had guts that were more full from feeding on calanoid copepods and relying less heavily on lower trophic level prey. Yet, our findings revealed a dome-shaped relationship with the fastest growth occurring at moderate upwelling intensity. High zooplanktivorous predation pressure led to above average growth, which may indicate the selective loss of slower-growing larvae. Our results suggest that species whose spatio-temporal distributions encompass multiple regional upwelling regimes experience unique feeding and predation environments throughout their range with implications for larval survivorship. 

The Northern California Current (NCC) system is a productive coastal ecosystem with a mosaic of temporal and spatial features. The phytoplankton community plays a crucial role in supporting the rich ecosystem and economically important fisheries of the NCC. Our study integrates data across two years (2022-2023) and multiple transects to investigate the community composition of two major phytoplankton groups in the NCC: picocyanobacteria and photosynthetic picoeukaryotes (PPE). The abundances and cell sizes of the phytoplankton were measured using flow cytometry. We found PPE present at similar concentrations in both summer and winter, while picocyanobacteria were much more abundant in the summer than the winter. The relationship between the picocyanobacteria and PPE varied across on- to off-shore transects with different coastal bathymetry. Abundances of both picophytoplankton increased with distance from shore. Cell size also varied along these gradients. Sampling during a marine heatwave in summer 2023 revealed a shift towards smaller picophytoplankton. Overall, these data reveal a dynamic microbial community underlying a productive coastal system, which could inform management decisions and future ecosystem models in the context of climate change and marine heat waves. 

Eastern Boundary Systems support major fisheries whose early life stages depend on upwelling production. Upwelling can be highly variable at the regional scale, with substantial repercussions for new productivity and microbial loop activity. Studies that integrate the classic trophic web based on new production with the microbial loop are rare due to the range in body forms and sizes of the taxa. Underwater imaging can overcome this limitation, and with machine learning, enables fine resolution studies spanning large spatial scales. We used theIn-situIchthyoplankton Imaging System (ISIIS) to investigate the drivers of plankton community structure in the northern California Current, sampled along the Newport Hydrographic (NH) and Trinidad Head (TR) lines, in OR and CA, respectively. The non-invasive imaging of particles and plankton over 1644km in the winters and summers of 2018 and 2019 yielded 1.194 billion classified plankton images. Combining nutrient analysis, flow cytometry, and 16S rRNA gene sequencing of the microbial community with mesoplankton underwater imaging enabled us to study taxa from 0.2µm to 15cm, including prokaryotes, copepods, ichthyoplankton, and gelatinous forms. To assess community structure, >2000 single-taxon distribution profiles were analyzed using high resolution spatial correlations. Co-occurrences on the NH line were consistently significantly higher off-shelf while those at TR were highest on-shelf. Random Forests models identified the concentrations of microbial loop associated taxa such as protists,Oithonacopepods, and appendicularians as important drivers of co-occurrences at NH line, while at TR, cumulative upwelling and chlorophyllawere of the highest importance. Our results indicate that the microbial loop is driving plankton community structure in intermittent upwelling systems such as the NH line and supports temporal stability, and further, that taxa such as protists,Oithonacopepods, and appendicularians connect a diverse and functionally redundant microbial community to stable plankton community structure. Where upwelling is more continuous such as at TR, primary production may dominate patterns of community structure, obscuring the underlying role of the microbial loop. Future changes in upwelling strength are likely to disproportionately affect plankton community structure in continuous upwelling regions, while high microbial loop activity enhances community structure resilience.