Developing the knowledge base needed to sustainably manage mesopelagic resources

Recent estimates suggest that the mesopelagic zone could contain a total fish biomass of 2-19.5 gigatonnes, roughly equivalent to 100 times the annual catch of all existing fisheries. In addition to the possibility of direct consumption of mesopelagic species, there is interest in their use for fishmeal, as a source of dietary supplements for humans, and to bio-prospect pharmaceuticals. All of this, and the demands for a global food supply that can feed an ever-growing population, has driven interest in the mesopelagic. Thus, accurate quantification of the biomass of mesopelagic resources, their nutritional and genetic composition, their links to other components of the food web, to other oceanic realms and to biological and chemical oceanographic processes and cycles, are the focus of growing research activity. This information is needed to ensure the sustainable management of these resources. In this introduction, we summarize the contributions included in this theme set and provide some “food for thought” on the state-of-the-art in research on the mesopelagic, including identifying the knowledge that must be generated to support its sustainable management (e.g. the effect that extracting significant biomass might have on the pelagic ecosystem and the flow of material and energy through it

Fishing in the Dark: A Pursuit-Diving Seabird Modifies Foraging Behaviour in Response to Nocturnal Light Levels

Visual predators tend not to hunt during periods when efficiency is compromised by low light levels. Yet common murres, a species considered a diurnal visual predator, frequently dive at night. To study foraging of murres under different light conditions, we used a combination of archival tagging methods and astronomical models to assess relationships between diving behaviour and light availability. During diurnal and crepuscular periods, murres used a wide range of the water column (2–177 m), foraging across light intensities that spanned several orders of magnitude (103–10−10 Wm−2). Through these periods, they readily dived under conditions equivalent to ambient moonlight (∼10−4 Wm−2) but rarely under conditions equivalent to starlight (∼10−8 Wm−2). At night, murres readily foraged during both moonlit and starlit periods, and diving depth and efficiency increased with nocturnal light intensity, suggesting that night diving is at least partially visually guided. Whether visually guided foraging is possible during starlit periods is less clear. Given the dense prey landscape available, random-walk simulations suggest that murres could benefit from random prey encounters. We hypothesise that murres foraging through starlit periods rely either on close-range visual or possibly nonvisual cues to acquire randomly encountered prey. This research highlights the flexibility of breeding common murres and raises questions about the strategies and mechanisms birds use to find prey under very low light conditions

Gene expression and epigenetic responses of the marine Cladoceran, Evadne nordmanni, and the copepod, Acartia clausi, to elevated CO2

Characterizing the capacity of marine organisms to adapt to climate change related drivers (e.g., pCO2 and temperature), and the possible rate of this adaptation, is required to assess their resilience (or lack thereof) to these drivers. Several studies have hypothesized that epigenetic markers such as DNA methylation, histone modifications and noncoding RNAs, act as drivers of adaptation in marine organisms, especially corals. However, this hypothesis has not been tested in zooplankton, a keystone organism in marine food webs. The objective of this study is to test the hypothesis that acute ocean acidification (OA) exposure alters DNA methylation in two zooplanktonic species—copepods (Acartia clausii) and cladocerans (Evadne nordmanii). We exposed these two species to near-future OA conditions (400 and 900 ppm pCO2) for 24 h and assessed transcriptional and DNA methylation patterns using RNA sequencing and Reduced Representation Bisulfite Sequencing (RRBS). OA exposure caused differential expression of genes associated with energy metabolism, cytoskeletal and extracellular matrix functions, hypoxia and one-carbon metabolism. Similarly, OA exposure also caused altered DNA methylation patterns in both species but the effect of these changes on gene expression and physiological effects remains to be determined. The results from this study form the basis for studies investigating the potential role of epigenetic mechanisms in OA induced phenotypic plasticity and/or adaptive responses in zooplanktonic organisms.publishedVersio

Advancing the link between ocean connectivity, ecological function and management challenges

Ocean connectivity is a dynamic and rapidly evolving field of research in marine science, partly because there is an increasing demand for information on connectivity that informs effective assessment and management of marine resources. Achieving this will require a better alignment between ocean connectivity tools and developments and the needs and challenges of assessments and conservation. For these reasons, the ICES Journal of Marine Science solicited contributions to the article theme set (TS), Beyond ocean connectivity. We briefly summarize the nine articles that appear herein, grouping them into four general topics: methodological advances, population dynamics and assessment implications of connectivity, spatial and management implications, and connectivity in ecosystem processes. We also discuss the challenges facing ocean connectivity research if it is to effectively support advancing fisheries assessment frameworks and integrated ecosystem approaches. We hope that the contributions included in this TS serve to convince managers and fisheries scientists of the need to incorporate results from research on connectivity

The three-dimensional prey field of the northern krill, Meganyctiphanes norvegica, and the escape responses of their copepod prey

In the north Atlantic, Meganyctiphanes norvegica feeds predominantly on copepods, including Calanus spp. To quantify its perceptual field for prey, and the sensory systems underlying prey detection, the responses of tethered krill to free-swimming Calanus spp. were observed in 3D using silhouette video imaging. An attack–which occurred despite the krill’s being tethered—was characterized by a pronounced movement of the krill’s antennae towards the target, followed by a propulsion and opening of the feeding basket. Frequency distributions of prey detection distances were significantly different in the light vs. the dark, with median values of 26.5 mm and 19.5 mm, respectively. There were no significant differences in the angles at which prey were detected by krill (relative to the predator’s longitudinal body axis) in the light vs. the dark. Prey detections were symmetrically distributed on either side of the predator, in both light and dark. However, significant asymmetry was found in the dorsal–ventral direction with 80% of the prey detections located below the midline of the krill’s body axis and, given the placement and orientation of the compound eyes, presumably outside its visual field of view. This indicates that, at least under these conditions, vision was not the main sensory modality involved in the detection of active prey by M. norvegica. However, under some circumstances, vision may provide supplemental information. Avoidance responses of copepod prey were nearly twice the velocity of their nominal background swimming speed (153 ± 48 and 85 ± 75 mm s−1, respectively), on average taking them 43 ± 16 mm away from the predator. This is far beyond the krill’s perceptual range, suggesting that the escape reaction provides an effective deterrent to predation (although perhaps less so for free-swimming krill). This information can be used to parameterize models that assess the role of krill as predators in marine ecosystems

Advancing the link between ocean connectivity, ecological function and management challenges

“Ocean connectivity” is a dynamic and rapidly evolving field of research in marine science, partly because there is an increasing demand for information on connectivity that informs effective assessment and management of marine resources. Achieving this will require a better alignment between ocean connectivity tools and developments and the needs and challenges of assessments and conservation. For these reasons, the ICES Journal of Marine Science solicited contributions to the article theme set (TS), “Beyond ocean connectivity.” We briefly summarize the nine articles that appear herein, grouping them into four general topics: methodological advances, population dynamics and assessment implications of connectivity, spatial and management implications, and connectivity in ecosystem processes. We also discuss the challenges facing ocean connectivity research if it is to effectively support advancing fisheries assessment frameworks and integrated ecosystem approaches. We hope that the contributions included in this TS serve to convince managers and fisheries scientists of the need to incorporate results from research on connectivity

Light Primes the Escape Response of the Calanoid Copepod, Calanus finmarchicus

The timing and magnitude of an escape reaction is often the determining factor governing a copepod’s success at avoiding predation. Copepods initiate rapid and directed escapes in response to fluid signals created by predators; however little is known about how copepods modulate their behavior in response to additional sensory input. This study investigates the effect of light level on the escape behavior of Calanus finmarchicus. A siphon flow was used to generate a consistent fluid signal and the behavioral threshold and magnitude of the escape response was quantified in the dark and in the light. The results show that C. finmarchicus initiated their escape reaction further from the siphon and traveled with greater speed in the light than in the dark. However, no difference was found in the escape distance. These results suggest that copepods use information derived from multiple sensory inputs to modulate the sensitivity and strength of the escape in response to an increase risk of predation. Population and IBM models that predict optimal vertical distributions of copepods in response to visual predators need to consider changes in the copepod's behavioral thresholds when predicting predation risk within the water column