Mesozooplankton and particulate matter responses to a deep-water frontal system in the southern California Current System

Abstract

We analyzed the abundance of mesozooplankton and suspended particulate matter across the deep-water "A-Front" in the southern sector of the California Current System. We characterized the A-Front with two novel devices, a free-fall Moving Vessel Profiler (MVP) and an Underwater Vision Profiler 5 (UVP5), together with quantitative bongo samples analyzed by ZooScan. The MVP permitted real-time visualization of vertical density structure, chlorophyll a fluorescence and particle size structure (from a laser optical particle counter) across the front to a depth of 200 m with the research vessel moving at 6 m s 21. The UVP5 quantified in situ vertical distributions from digital images of planktonic organisms and particles in profiles to 300 m. Both the MVP and UVP5 indicated that organic aggregates increased several-fold at the A-Front. The A-Front was a region of elevated abundance of mainly particle-grazing mesozooplankton, including calanoid copepods, Oithona spp., appendicularians and euphausiids, as well as a site of elevated ratio of nauplii copepod 21. In contrast, poecilostomatoid copepods, ostracods, chaetognaths and radiolaria, most of which are more carnivorous or omnivorous, were all elevated in abundance to the south of the front. We provide evidence that submesoscale fronts can be regions of locally elevated plankton abundance and production, as well sites of faunal transitions.

Seasonal Variation in Transport of Zooplankton Into the Arctic Basin Through the Atlantic Gateway, Fram Strait

“…The LOPC does not give any taxonomic information, and nets are not suited to capture marine snow or fragile zooplankton. Therefore, it is often unclear if transparent particles are marine snow or transparent zooplankton, and this varies in all likelihood regionally and seasonally (Ohman et al, 2012;Basedow et al, 2013). To separate zooplankton from other particles we followed the method developed by Espinasse et al (2017) that indicates the ratio of zooplankton to detritus among small (SEPs) and large (MEPs) particles by analyzing two simple indicators, the percentage of MEPs in all counts, and the mean AI of MEPs.…”

Ecological Transitions in a Coastal Upwelling Ecosystem

“…Ecosystem processes at fronts have attracted the interest of many previous investigators in the California Current System (e.g., Mackas et al, 1991;Haury et al, 1993;Venrick, 2000). A recent study in the CCE study domain revealed striking ecological changes at an oceanic frontal system (Landry et , Synechococcus, and total diatoms (taylor et al, 2012); bacterial carbon production rate (Samo et al, 2012); photograph of composition of net tows from 100-0 m (202 µm mesh); vertically averaged abundance of nauplii (free-swimming copepod larvae) per adult copepod and total calanoid copepods (Ohman et al, 2012a); vertical sections of acoustically derived estimates of euphausiid and fish acoustic backscatter (lara-lopez et al, 2012). in panel (d), stations are oriented from south (left) to north (right).…”

“…Vertical band delineates the front. Modified from the cover of the Journal of plankton research, September 2012 (see Landry, Ohman et al, 2012) maximum in diatoms was associated with elevated nitrate fluxes , peak phytoplankton variable fluorescence (Chekalyuk et al, 2012), elevated bacterial production (Samo et al, 2012), increased concentrations of organic aggregates (Ohman et al, 2012a), elevated abundance of calanoid copepods and of naupliar recruitment (Ohman et al, 2012a), and increases in both euphausiid and pelagic fish populations (Lara-Lopez et al, 2012). We hypothesize that such ecological "hot spots, " while …”

“…Vessel Profiler (Ohman et al, 2012a Institution of Oceanography (c) instantaneous rates of change of chl-a due to phytoplankton growth and micro-and mesozooplankton grazing for lagrangian drifter experiments (cycles). cycles are arranged from west (left) to east (right).…”

“…2007), dissolved oxygen McClatchie et al, 2010), windstress curl upwelling (Rykaczewski and Checkley, 2008), and plankton populations (Kahru et al, 2009;Lavaniegos and Ohman, 2007;Aksnes and Ohman, 2009;Ohman et al, 2012b) • Multidecadal variability associated with the Pacific Decadal Oscillation (PDO; Miller et al, 1994;Mantua et al, 1997;Di Lorenzo and Ohman, 2013) and the North Pacific Gyre Oscillation (NPGO; Di Lorenzo et al, 2008) • Interannual variability, dominated by the El Niño-Southern Oscillation (ENSO), that can be at least as strong as the temporal trends and multidecadal variations (Todd et al, 2011;Ohman et al, 2012a) where the PDO effect is modeled with a natural damping time scale set by the euphausiids' lifespan (Di . That is, the zooplankton are merely tracking changes in the physical environment (Hsieh and Ohman, 2006).…”