J Rudi Strickler

Weihs [1] mentioned that the swim-and-sink behaviour of copepods was better known as the hop-and-sink behaviour. The biological reality, however, is that the two behaviours are different. Bainbridge [3] referred to the swimming of the calanoid copepod Calanus finmarchicus as ‘hop and sink’but provided no further description of the behaviour. Later on, Strickler [4] used ‘hop and sink’to describe the jerky swimming pattern displayed by cyclopoid copepods and provided a detail description and kinematic analysis of the behaviour. Here, we present one of his high-speed Schlieren videos of a cyclopoid copepod in hopand-sink together with its path speed as a function of time (electronic supplementary material, video S1; figure 1). Each hop starts with the cyclopoid beating its two antennules (A1) and culminates with the cyclopoid sequentially beating its four pairs of swimming legs along with its urosome [5]. Each …

A common question in the aquatic sciences is that of how zooplankter movement can be modeled. It is well-established in the literature that there exists a randomness to this movement, but the question is how to characterize this randomness. The most common methods for doing this involve the random walk and correlated random walk (CRW) models. Here, we present a time series model that allows a better description the randomness in Daphnia motion when the amount of time that elapses between observations of their position is small. Our approach is adaptable to description of tracks of a multitude of animal species through re-estimation of model parameters. The model we propose uses information about how the animal moved during the previous two time intervals to explain how it moves currently. We demonstrate that the proposed model provides better predictive accuracy and fit than do the CRW and …

“The material called “Auftrieb” has been investigated by zoologists and botanists since the groundbreaking contributions by Johannes Müller. It has been investigated and collected many times with fine, permeable nets. This material is—besides Müller’s interest in its systematics and anatomy—without any doubt of great importance to the metabolism of the seas.This contribution tries to get a closer look at this metabolism. It turns out that the name “Auftrieb” is not sufficiently comprehensive and descriptive, therefore, I have preferred to name this material “Halyplankton”(1). However, since we are only talking about the oceans here, the shorter term “Plankton” will be sufficient. It is defined as “everything that floats in water, regardless of whether it is high or low in it, and whether it is dead or alive.”

Microcystis is the predominant genus of harmful cyanobacterium in both Lake Erie and Saginaw Bay of Lake Huron and has the capacity to regulate the buoyancy of its colonies, sinking under certain conditions while floating towards the surface in others. Understanding the factors that control buoyancy is critical for interpretation of remote sensing data, modeling and forecasting harmful algal blooms within these two systems. To determine if Microcystis colony buoyancy in the two lakes responds similarly to diurnal light cycles, colony buoyant velocity (floating/sinking terminal velocity in a quiescent water column) and size were measured after manipulating the intensity of sunlight. Overall, there were more positively buoyant (floating) colonies in Lake Erie while most of the colonies in Saginaw Bay were negatively buoyant (sinking). In Lake Erie the colonies became less buoyant at increased light intensities and were …

Nutrient acquisition is crucial for oceanic microbes, and competitive solutions to solve this challenge have evolved among a range of unicellular protists. However, solitary solutions are not the only approach found in natural populations. A diverse array of oceanic protists form temporary or even long-lasting attachments to other protists and marine aggregates. Do these planktonic consortia provide benefits to their members? Here, we use empirical and modeling approaches to evaluate whether the relationship between a large centric diatom, Coscinodiscus wailesii, and a ciliate epibiont, Pseudovorticella coscinodisci, provides nutrient flux benefits to the host diatom. We find that fluid flows generated by ciliary beating can increase nutrient flux to a diatom cell surface four to 10 times that of a still cell without ciliate epibionts. This cosmopolitan species of diatom does not form consortia in all environments but frequently …

With the increased use of digital holography to observe biological events in three dimensions the need for autofocusing becomes essential. We introduced a modified image quality evaluation technique as a focus criterion in the reconstruction of digital holograms. The method employed was initially proposed by [Wang et al. (2008)] to evaluate image inpainting quality from three aspects: luminance, definition, and gradient similarity. We considered these criteria for automatic focusing, individually and in combination. Our numerical simulation and experimental results obtained from 96 holograms of planktonic organisms show that the combined approach provided more accurate results compared to the individual metrics. We propose the use of such combined criterion to implement autofocusing algorithms for serial holograms, such as from observations of performances of plankton behavior.

A body with mechanical sensors may remotely detect particles suspended in the surrounding fluid via controlled agitation. Here we propose a sensory mode that relies on generating unsteady flow and sensing particle-induced distortions in the flow field. We demonstrate the basic physical principle in a simple analytical model, which consists of a small spherical particle at some distance from a plate undergoing impulsive or oscillatory motion. The model shows that changes in pressure or shear on the plate can be used to infer the location and size of the sphere. The key ingredient is to produce strong shear or strain around the sphere, which requires careful tuning of the viscous boundary layer on the moving plate. This elucidates how some organisms and devices may control their unsteady dynamics to enhance their range of perception.