As part of the Shelfbreak Productivity Interdisciplinary Research Operation at the Pioneer Array (SPIROPA) Project, twelve grazing experiments were conducted during each of three research cruises (April of 2018, and May and July of 2019) in the Middle Atlantic Bight to estimate community zooplankton grazing and net phytoplankton growth rates. Stations where the experiments were conducted were strategically located in one of three key cross-shelf water mass regimes: (1) at the shelfbreak front, (2) inshore of the front in continental shelf water and (3) offshore of the front in slope water. Grazing incubations were performed on water sampled from the chlorophyll maximum, when present. The experiments included two "treatments": 1. whole water incubations and incubations on the <200 µm fraction of the plankton communinity.  All experiments were run in triplicate for 24 hours in flow-thru deck incubators and consisted of a dark treatment incubation and a light treatment incubation at a simulated 30% E0.

Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Daily zooplankton Grazing Experiments were conducted on each of three cruises as a component of the SPIROPA project. 12 experiments/Cruise, targeting 3 water mass regimes: shelf, shelfbreak front and slope waters.

Grazing experiment sample water was collected with a CTD/Niskin bottle rosette at depths ranging from surface (0 m) to 56m, targeting chl-a max if present. Two experimental treatments were incubated: 1. whole water to represent the entire plankton community and 2. <200 µm fraction of plankton community to estimate microzooplankton grazing impact.

Separate triplicate 4-liter jars of each treatment were concurrently incubated for 24 hrs. in two separate incubation conditions: Dark and Light (30% Eo) flow-through seawater deck incubators. After 24-hour incubations 3 liters of each replicate were poured through 15 µm sieves that were backwashed into 50 ml centrifuge tubes for a 30 ml final concentrate that was preserved in approximately 1% Utermöhl’s solution according to Guillard (1973) 

In the lab, zooplankton was identified to the lowest practical taxonomic level and quantified utilizing a dissecting microscope.

Website: http://science.whoi.edu/users/olga/SPIROPA/SPIROPA.html

Coverage: Shelf break south of New England, OOI Pioneer Array

NSF award abstract:

The continental shelf break of the Middle Atlantic Bight supports a productive and diverse ecosystem. Current paradigms suggest that this productivity is driven by several upwelling mechanisms at the shelf break front. This upwelling supplies nutrients that stimulate primary production by phytoplankton, which in turn leads to enhanced production at higher trophic levels. Although local enhancement of phytoplankton biomass has been observed in some circumstances, such a feature is curiously absent from time-averaged measurements, both from satellites and shipboard sampling. Why would there not be a mean enhancement in phytoplankton biomass as a result of the upwelling? One hypothesis is that grazing by zooplankton prevents accumulation of biomass on seasonal and longer time scales, transferring the excess production to higher trophic levels and thereby contributing to the overall productivity of the ecosystem. However, another possibility is that the net impact of these highly intermittent processes is not adequately represented in long-term means of the observations, because of the relatively low resolution of the in-water measurements and the fact that the frontal enhancement can take place below the depth observable by satellite. The deployment of the Ocean Observatories Initiative (OOI) Pioneer Array south of New England has provided a unique opportunity to test these hypotheses. The combination of moored instrumentation and autonomous underwater vehicles will facilitate observations of the frontal system with unprecedented spatial and temporal resolution. This will provide an ideal four-dimensional (space-time) context in which to conduct a detailed study of frontal dynamics and plankton communities needed to examine mechanisms controlling phytoplankton populations in this frontal system. This project will also: (1) promote teaching, training and learning via participation of graduate and undergraduate students in the research , (2) provide a broad dissemination of information by means of outreach in public forums, printed media, and a video documentary of the field work, and (3) contribute to improving societal well-being and increased economic competitiveness by providing the knowledge needed for science-based stewardship of coastal ecosystems, with particular emphasis on connecting with the fishing industry through the Commercial Fisheries Research Foundation.

The investigators will conduct a set of three cruises to obtain cross-shelf sections of physical, chemical, and biological properties within the Pioneer Array. Nutrient distributions will be assayed together with hydrography to detect the signature of frontal upwelling and associated nutrient supply. The investigators expect that enhanced nutrient supply will lead to changes in the phytoplankton assemblage, which will be quantified with conventional flow cytometry, imaging flow cytometry (Imaging FlowCytobot, IFCB), optical imaging (Video Plankton Recorder, VPR), traditional microscopic methods, and pigment analysis. Zooplankton will be measured in size classes ranging from micro- to mesozooplankton with the IFCB and VPR, respectively, and also with microscopic analysis. Biological responses to upwelling will be assessed by measuring rates of primary productivity, zooplankton grazing, and net community production. These observations will be synthesized in the context of a coupled physical-biological model to test the two hypotheses that can potentially explain prior observations: (1) grazer-mediated control and (2) undersampling. Hindcast simulations will also be used to diagnose the relative importance of the various mechanisms of upwelling. The intellectual merit of this effort stems from our interdisciplinary approach, advanced observational techniques, and integrated analysis in the context of a state-of-the-art coupled model. The project will address longstanding questions regarding hydrodynamics and productivity of an important ecosystem, leading to improved understanding of physical-biological interactions in a complex continental shelf regime. Given the importance of frontal systems in the global coastal ocean, it is expected that knowledge gained will have broad applicability beyond the specific region being studied.