In situ ichthyoplankton imaging system (<i>I</i>SIIS): system design and preliminary results

TLDR

Advances in acoustic and optical plankton samplers have enabled fine‑scale studies of plankton distribution, yet their limited sampling volume has confined them to abundant, small zooplankton and excluded rarer, larger ichthyoplankton and meso‑zooplankton. The authors present the In situ ichthyoplankton imaging system (I SIIS), designed to noninvasively sample large water volumes at very high resolution, thereby enabling quantitative measurement of rare plankton while also capturing more abundant taxa. I SIIS employs state‑of‑the‑art digital line‑scan cameras, high‑throughput data transfer, shadow‑photographic lighting, and a towed platform that delivers 68‑µm pixel resolution with a 20‑cm depth of field and 14‑cm field of view, and is integrated with environmental sensors such as CTD and fluorometers. Field trials demonstrated high‑resolution imagery and continuous quantitative imaging of over 70 L s⁻¹ for a 78‑minute run.

Abstract

Over the last two decades, there has been an accelerating advancement of acoustic and optical plankton samplers, opening many opportunities for fine‐scale studies of plankton distribution. To date, however, the imaging systems have been limited in the volume of water being sampled, thereby restricting their utility to quantifying highly abundant, small zooplankton like copepods, but not relatively rarer, larger ichthyo‐ and other meso‐zooplankton (e.g., larval decapods, salps, pteropods, ctenophores, etc.). Here we describe an imaging system, In situ ichthyoplankton imaging system ( I SIIS), that is capable of In situ (i.e., noninvasive) sampling of sufficiently large volumes of water at very high resolution, allowing quantitative measurement of these rare plankton, while at the same time also recording the smaller more abundant taxa. Capitalizing on state‐of‐the‐art digital line scan cameras and high‐throughput computer data transfer and storage, combined with shadow photographic lighting techniques, we have designed and built a towed system capable of imaging at 68‐micron pixel resolution, yet with up to a 20‐cm depth of field (with a 14‐cm field of view). This system is coupled with various environmental sensors (e.g., CTD, fluorometer), enabling the evaluation of fine‐scale, taxon‐specific distributions in relation to environmental conditions. Field testing demonstrated high‐resolution imagery of plankters, while quantitatively imaging &gt;70 L s −1 continuously for a 78‐min trial.