Inorganic particulate suspensions and the feeding of ascidians

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Examination of Thin Layers of Phytoplankton and Zooplankton with Emphasis on Bioluminescence

Thin layers of plankton are commonly found in coastal environments, with a vertical scale ranging from centimeters to a few meters, but extending horizontally over kilometers. These layers are highly productive and can contain 50-75% of the total biomass of the water column2-4. A two-week study was conducted in San Luis Obispo Bay comparing a traditional sampling method, Niskin bottles, with a recent advancement, autonomous profilers. Diversity Indexes were calculated for all species sampled in both methods. T Tests were conducted to compare the diversity indexes between methods and were not statistically significant (P(T\u3c=t) one-tail=0.15). The abundance of a bioluminescent species, Noctiluca was compared at three different depths (shallow, within a spike in bioluminescence, and deep) and was found to be statistically significant (P(T\u3c=t) one-tail=0.0177 for the shallow depth vs. spike and P(T\u3c=t) one-tail=0.048 for the deep depth vs. spike). Future work could examine the vertical migration of phytoplankton and zooplankton throughout the night as opposed to one nightly sampling. This would allow interpretation of thin layers based on the behavior of the organisms comprising the layer, as opposed to the physical processes forming thin layers (as examined in this study)

The role of the extra cellular matrix on memory

forthcoming article published online at www.m-hikari.comInternational audienceWe expose first a biological model of memory based on one hand of the mechanical oscillations of axons during action potential and on the other hand on the changes in the extra cellular matrix composition when a mechanical strain is applied on it. Due to these changes, the stiffness of the extra cellular matrix along the most excited neurons will increase close to these neurons due to the growth of astrocytes around them and to the elastoplastic behavior of collagen. This will create preferential paths linked to a memory effect. In a second part, we expose a physical model based on random walk of the action potential on the array composed of dendrites and axons. This last model shows that repetition of the same event leads to long time memory of this event and that paradoxical sleep leads to the linking of different events put into memory

Seasonal and Interannual Variability of Phytoplankton Abundance and Community Composition on the Central Coast of California

Variations in the abundance and composition of phytoplankton greatly impact ecosystem structure and function. Within the California Current System (CCS), phytoplankton community structure is tightly coupled to seasonal variability in wind-driven coastal upwelling, a process that drives changes in coastal water temperatures and nutrient concentrations. Based on approximately a decade (2008-2018) of weekly phytoplankton measurements, this study provides the first characterization of the seasonal and interannual variability of phytoplankton abundance and composition in San Luis Obispo (SLO) Bay, an understudied region within the CCS. Overall, the seasonality of phytoplankton in SLO Bay mirrored that of the larger CCS; diatoms dominated the community during the spring upwelling season, whereas dinoflagellates dominated the community during the fall relaxation period. While we observed considerable interannual variability among phytoplankton taxa, of particular note was the absence of a fall dinoflagellate-dominated period from 2010 through 2013, followed by the return of the fall dinoflagellate-dominated period in 2014. This compositional shift coincided with a major phase shift of both the Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO). In addition to exerting a strong influence on the seasonality of phytoplankton community succession and transition between diatom- and dinoflagellate-dominated periods, the state of both the PDO and NPGO also influenced the extent to which environmental conditions (temperature and upwelling winds) could predict community type. These results highlight the importance of long-term datasets and the consideration of large-scale climate patterns when assessing local ecosystem dynamics

Seasonal controls on nearshore dissolved oxygen variability and hypoxia in a coastal embayment

Declining dissolved oxygen (DO) is emerging as an increasingly important stressor in nearshore ecosystems, and there is a growing need to better understand DO dynamics and hypoxia risk in this highly variable environment. In this study, we collected data from monthly cruises on the inner shelf, continuous nearshore moorings inside and outside a small coastal upwelling embayment (San Luis Obispo Bay in Central California), and weekly phytoplankton measurements inside the bay during the upwelling season. Nearshore DO was generally dominated by low-frequency synoptic variability, with increased DO variance near the surface relative to the bottom and inside the bay compared to outside. Two nearshore hypoxic regimes were identified. In the first regime, which occurred during periods of strong upwelling in the spring across all nearshore sites, the nearshore bottom water temperature-DO (T-DO) relationship was aligned with that found offshore, suggesting hypoxia was driven by the direct advection and cross-shelf exchange of low DO subthermocline waters from the shelf. This period also coincided with minimal water-column stratification, small vertical DO differences, and a diatom-dominated phytoplankton assemblage. In the second regime, which occurred during summer months and was characterized by weaker upwelling, strong stratification, and dinoflagellate-dominated phytoplankton assemblage, the near-bottom T-DO relationship inside the bay deviated significantly from that on the shelf offshore. These hypoxic events inside the bay were likely driven by localized respiration and lack of ventilation of bottom waters due to strong stratification. Collectively, these observations reveal a shift in the strength and magnitude of physical versus biological processes driving nearshore DO dynamics. The high spatiotemporal variability of DO dynamics in upwelling bays means that they are likely to be at the forefront of ecosystem impacts of and adaptions to climate change, and may act as sentinel systems or “canaries on the coast.

Evaluation of bio-optical inversion of spectral irradiance measured from an autonomous underwater vehicle

Autonomous underwater vehicles (AUVs) can map water conditions at high spatial (horizontal and vertical) and temporal resolution, including under cloudy conditions when satellite and airborne remote sensing are not feasible. As part of the RADYO program, we deployed a passive radiometer on an AUV in the Santa Barbara Channel and off the coast of Hawaii to apply existing bio-optical algorithms for characterizing the optical constituents of coastal seawater (i.e., dissolved organic material, algal biomass, and other particles). The spectral differences between attenuation coefficients were computed from ratios of downwelling irradiance measured at depth and used to provide estimates of the in-water optical constituents. There was generally good agreement between derived values of absorption and concurrent measurements of this inherent optical property in Santa Barbara Channel. Wave focusing, cloud cover, and low attenuation coefficients influenced results off the coast of Hawaii and are used to evaluate the larger-scale application of these methods in the near surface coastal oceans

MAPPING AGRICULTURAL LAND COVER FOR HYDROLOGIC MODELING IN THE PLATTE RIVER WATERSHED OF NEBRASKA

Throughout the western United States, natural resources managers are attempting to address the growing, and often competing, demands that municipal, agricultural and environmental interests have for water. The Platte River Cooperative Hydrology Study (COHYST) is a multi-agency effort that seeks to improve understanding of the ecology, geology, and hydrology of the Platte River watershed in central and western Nebraska. Information regarding the types, areal extent, and locations of crops (especially irrigated crops) is critical for estimating consumptive use of water. Digital land-cover and land-use datasets of the central and western Platte River valley have been prepared for four years: 1982, 1997, 2001, and 2005. Mapping was carried out using multidate Landsat satellite imagery in combination with ancillary geospatial data. The mapping was validated using field observations collected independently. Overall accuracy of the maps developed ranged from 74% to 82.7%. All land-cover maps and full documentation are available online at http://www.calmit.unl.edu/cohyst/

Coastal upwelling seasonality and variability of temperature and chlorophyll in a small coastal embayment

While the seasonality of wind-driven coastal upwelling in eastern boundary upwelling systems has long been established, many studies describe two distinct seasons (upwelling and non-upwelling), a generalized framework that does not capture details relevant to marine ecosystems. In this contribution, we present a more detailed description of the annual cycle and upwelling seasonality for an understudied location along the central California coast. Using both the mean monthly upwelling favorable wind stress and the monthly standard deviation, we define the following seasons (contiguous months) and a transitional period (non-contiguous months): “Winter Storms” season (Dec-Jan-Feb), “Upwelling Transition” period (Mar and Jun), “Peak Upwelling” season (Apr-May), “Upwelling Relaxation” season (Jul-Aug-Sep), and “Winter Transition” season (Oct-Nov). In order to describe the oceanic response to this upwelling wind seasonality, we take advantage of nearly a decade of full water-column measurements of temperature and chlorophyll made using an automated profiling system at the end of the California Polytechnic State University Pier in San Luis Obispo Bay, a small (~ 2 km wide near study site) and shallow (~ 10 m average bay depth) coastal embayment. Variability and average-year patterns are described inside the bay during the various upwelling seasons. Moreover, the role of the local coastline orientation and topography on bay dynamics is also assessed using long-term measurements collected outside of the bay. The formation of a seasonally variable upwelling shadow system and potential nearshore retention zone is discussed. The observations presented provide a framework on which to study interannual changes to the average-year seasonal cycle, assess the contribution of higher-frequency features to nearshore variability, and better predict dynamically and ecologically important events

Integrated measurements of acoustical and optical thin layers I: Vertical scales of association

This study combined measurements from multiple platforms with acoustic instruments on moorings and on a ship and optics on a profiler and an autonomous underwater vehicle (AUV) to examine the relationships between fluorescent, bioluminescent, and acoustically scattering layers in Monterey Bay during nighttime hours in July and August of 2006 and May of 2008. We identified thin bioluminescent layers that were strongly correlated with acoustic scattering at the same depth but were part of vertically broad acoustic features, suggesting layers of unique composition inside larger biomass features. These compositional thin layers nested inside larger biomass features may be a common ecosystem component and are likely to have significant ecological impacts but are extremely difficult to identify as most approaches capable of the vertical scales of measurement necessary for the identification of sub-meter scale patterns assess bulk properties rather than specific layer composition. Measurements of multiple types of thin layers showed that the depth offset between thin phytoplankton and zooplankton layers was highly variable with some layers found at the same depth but others found up to 16 m apart. The vertical offset between phytoplankton and zooplankton thin layers was strongly predicted by the fraction of the water column fluorescence contained within a thin phytoplankton layer. Thin zooplankton layers were only vertically associated with thin phytoplankton layers when the phytoplankton in a layer accounted for more than about 18–20% of the water column chlorophyll. Trophic interactions were likely occurring between phytoplankton and zooplankton thin layers but phytoplankton thin layers were exploited by zooplankton only when they represented a large fraction of the available phytoplankton, suggesting zooplankton have some knowledge of the available food over the entire water column. The horizontal extent of phytoplankton layers, discussed in the second paper in this series, is likely an important factor contributing to this selective exploitation by zooplankton. The pattern of vertical offset between phytoplankton and zooplankton layers was consistent between studies in different years and using different combinations of platforms, indicating the importance of the relationship between zooplankton layers and the fraction of phytoplankton within a layer at night within Monterey Bay. These results highlight the value of integrating measurements of various types of organisms to understand thin layers processes and the importance of assessing ecological interactions in plankton thin layers within the context of the properties of the entire water column, like the animals themselves do

Zooplankton Avoidance of a Profiled Open-Path Fluorometer

Significant avoidance of acoustically detected zooplankton was observed in response to a profiling instrument package. Avoidance decreased acoustic scattering from zooplankton averaged over the entire profile by more than a factor of 2, while the maximum avoidance decreased zooplankton acoustic scattering by a factor of 15 over the depth of some discrete scattering layers. Experimental manipulation of the profiler and its instruments revealed that an open-path fluorometer was triggering the avoidance. Avoidance occurred at an average of 8 m below the profiler with a range between 2 and 13 m. Effect range was positively correlated with the average attenuation coefficient of light over the effect range and consistently resulted in avoidance when light levels of approximately 0.013 µmol photons m−2 s−1 were received by the zooplankton. These results have important implications for the analysis of zooplankton data collected from platforms carrying open-path fluorometers and may also warrant careful interpretation of optical measurements from these packages