Biology subjects

Bahlburg, D.

Publications and source records attributed to Bahlburg, D..

3 recordsLinked to original sources

bioRxiv2024

A circadian clock drives behavioral activity in Antarctic krill (Euphausia superba) and provides a potential mechanism for seasonal timing

Antarctic krill is a species with fundamental importance for the Southern Ocean ecosystem. Their large biomass and synchronized movements, like diel vertical migration (DVM), significantly impact ecosystem structure and the biological carbon pump. Despite decades of research, the mechanistic basis of DVM remains unclear. Circadian clocks help organisms anticipate daily environmental changes, optimizing adaptation. In this study, we used a recently developed activity monitor to record swimming activity of individual, wild-caught krill under various light conditions and across different seasons. Our data demonstrate how the krill circadian clock, in combination with light, drives a distinct bimodal pattern of swimming activity, which could facilitate ecologically important behavioral patterns, such as DVM. Rapid damping and flexible synchronization of krill activity indicate that the krill clock is adapted to a life at high latitudes and seasonal activity recordings suggest a clock-based mechanism for the timing of seasonal processes. Our findings advance our understanding of biological timing and high-latitude adaptation in this key species.

ecology↗

bioRxiv2023

Intercomparison of growth models for Antarctic krill (Euphausia superba): towards a generalised understanding

Antarctic krill is a key species of the Southern Ocean, impacted by climate change and human exploitation. Understanding how these changes affect the distribution and abundance of krill is crucial for generating projections of change for Southern Ocean ecosystems. Krill growth is an important indicator of habitat suitability and a series of models have been developed and used to examine krill growth potential at different spatial and temporal scales. The available models have been developed using a range of empirical and mechanistic approaches, which provide alternative perspectives and cross-validation of analyses of the key processes influencing krill growth. Here we undertake an intercomparison of a suite of the available models to understand their sensitivities to major driving variables. This illustrates that the results are strongly determined by the model structure and technical characteristics, and the data on which they were developed and validated. Our results emphasize the importance of assessing the constraints and requirements of individual krill growth models to ensure their appropriate application. The study also demonstrates the value of the development of alternative modelling approaches to identify key processes affecting the dynamics of krill. Of critical importance for modelling the growth of krill is appropriately assessing and accounting for differences in estimates of food availability resulting from alternative methods of observation. We suggest that an intercomparison approach is particularly valuable in the development and application of models for the assessment of krill growth potential at circumpolar scales and for future projections. As another result of the intercomparison, the implementations of the models used in this study are now publicly available for future use and analyses.

ecology↗

bioRxiv2023

An open and lightweight method to analyze the vertical distribution of pelagic organisms using echogram screenshots

Multifrequency echosounders are versatile devices commonly used in commercial fisheries, fisheries science and biological oceanography for the detection, quantification and even identification of organisms suspended in the underlying water column. They produce data that is rich in information, but can be tedious to process, often relying on expensive commercial software. The aim of our overarching research project was to analyze the vertical distribution of Antarctic krill swarms (Euphausia superba) in different seasons and regions in order to learn more about their behavioral ecology and ecophysiological adaptation. Therefore, we only required visual information on the distribution of krill swarms as well as metrics that characterize their vertical position. Instead of using storageintensive raw acoustic data, we developed a simple method to extract the relevant information from screenshots taken automatically on board a commercial krill fishing vessel during its operations. Using screenshots instead of raw data reduced the amount of data by a factor of >1000 (3 TB of raw data vs. 2.8 GB of screenshots for 8 months of observations) while preserving the information needed to carry out our seasonal behavioral analyses. In this study, we present the workflow and demonstrate that our method produces qualitatively and quantitatively similar results to using raw data, while being much less demanding in terms of computation and data storage. The code for the data processing is written in the open source programming language R, publicly accessible and therefore, provides a useful resource for other scientists interested in the dynamics of vertical biomass distributions from echosounder data.

ecology↗