High-Resolution Sampling of a Broad Marine Life Size Spectrum Reveals Differing Size- and Composition-Based Associations With Physical Oceanographic Structure

Abstract

Observing multiple size classes of organisms, along with oceanographic properties and water mass origins, can improve our understanding of the drivers of aggregations, yet acquiring these measurements remains a fundamental challenge in biological oceanography. By deploying multiple biological sampling systems, from conventional bottle and net sampling to in situ imaging and acoustics, we describe the spatial patterns of different size classes of marine organisms (several microns to ∼10 cm) in relation to local and regional (m to km) physical oceanographic conditions on the Delaware continental shelf. The imaging and acoustic systems deployed included (in ascending order of target organism size) an imaging flow cytometer (CytoSense), a digital holographic imaging system (HOLOCAM), an In Situ Ichthyoplankton Imaging System (ISIIS, 2 cameras with different pixel resolutions), and multi-frequency acoustics (SIMRAD, 18 and 38 kHz). Spatial patterns generated by the different systems showed size-dependent aggregations and differing connections to horizontal and vertical salinity and temperature gradients that would not have been detected with traditional station-based sampling (∼9-km resolution). A direct comparison of the two ISIIS cameras showed composition and spatial patchiness changes that depended on the organism size, morphology, and camera pixel resolution. Large zooplankton near the surface, primarily composed of appendicularians and gelatinous organisms, tended to be more abundant offshore near the shelf break. This region was also associated with high phytoplankton biomass and higher overall organism abundances in the ISIIS, acoustics, and targeted net sampling. In contrast, the inshore region was dominated by hard-bodied zooplankton and had relatively low acoustic backscatter. The nets showed a community dominated by copepods, but they also showed high relative abundances of soft-bodied organisms in the offshore region where these organisms were quantified by the ISIIS. The HOLOCAM detected dense patches of ciliates that were too small to be captured in the nets or ISIIS imagery. This near-simultaneous deployment of different systems enables the description of the spatial patterns of different organism size classes, their spatial relation to potential prey and predators, and their association with specific oceanographic conditions. These datasets can also be used to evaluate the efficacy of sampling techniques, ultimately aiding in the design of efficient, hypothesis-driven sampling programs that incorporate these complementary technologies.

Metamorphosis of spiny lobsters (Panulirus argus and Panulirus guttatus) in the Yucatan Current as inferred from the distribution of pueruli and final stage phyllosomata

“…Differences in size and condition could also reflect variations in the quality and quantity of food. Phyllosomata are omnivorous but prefer gelatinous zooplankton (O'Rorke et al 2015 and references therein), which tends to be more abundant offshore near shelf breaks (Luo et al 2014; Greer et al 2020). Gelatinous zooplankton can accumulate dispersed microbial nutrients and make them available as larger prey for late stage phyllosomata, as suggested by analyses of fatty acids (Wang et al 2014; Briones‐Fourzán et al 2019).…”

Distributions of environmental parameters and fish at Humbold Bay, Jayapura

“…This environmental factor is very influential on the growth of plankton itself. The abundance of plankton can be utilized as a food source by small fish species, so the relationship between fish and plankton very significant [3][4][5]. The fish that eat plankton are small pelagic fish that generally live in the upper water column.…”

“…The results of the echogram analysis will be able to describe horizontally and vertically at the same time of the sounding conditions of plankton and fish. Research on the detection of plankton and fish using the hydroacoustic method has been done previously by [7] and [5].…”

Computationally efficient processing of in situ underwater digital holograms

“…Particle concentrations measured using a DIHM have been shown to be comparable to established methods, while counting more particles per recording (e.g., larger sample size) (Walcutt et al 2020). Recent technological advances have made underwater DIHM systems commercially available (Sun et al 2007), and as a result they have seen increasing use for marine particle measurements (e.g., Nayak et al 2018; Greer et al 2020; Walcutt et al 2020).…”

“…While these methods represent significant advances in DIH capabilities and have enabled analysis of larger data sets than previously possible, they still require computationally expensive high‐resolution reconstruction of the hologram prior to target detection and focusing. Most studies to date have used DIHM systems with relatively small imaging volumes (e.g., separation distances of 4 and 1.8 cm in Nayak et al (2018) and Walcutt et al (2020), respectively) and data sets (e.g., less than 1 h of data collected at 15 Hz analyzed in Greer et al (2020)). Processing schemes that avoid high‐resolution reconstruction would enable analysis of larger (e.g., long time series) data sets and data from larger imaging volume DIHMs.…”