Award: OCE-1537579

Intellectual Merit

Copepods are the most abundant multicellular animals on the planet.  They play important roles in the transfer of organic matter from primary producers to higher trophic levels including marine mammals such as whales and commercially important species such as finfish (cod) and lobsters. An important aspect of their availability to larger organisms is that they aggregate, forming densities that are much higher than the average concentrations found in the surrounding waters.  These patches form feeding “hotspots” that are crucial to the success of most fish and mammal species. The mechanisms for spatial aggregations of zooplankton are still poorly understood and remain a central issue in marine ecology. Understanding the fluid features and sensory cues that promote aggregation was the focus of this work.

At the scale of the copepod, the fine-scale flow features caused by turbulence forms the topography of the copepods environment. By deconstructing the response of copepods to turbulence we pursued a mechanistic understanding of copepod behavioral changes in and around turbulent flow features. The approach was novel because as part of this work we created a small turbulent feature (Burger’s Vortex) that could be held steady in space and time and rotate relative to gravity.  Using this tool, we investigated the effects of turbulence on swimming characteristics, escape behaviors and aggregation of copepods in or around the features.  This work was done using animals of different sizes, with different swimming patterns and different antennule architectures to determine how copepods exploit the shape and orientation of turbulent features.

What we found from this study.

1)     Copepods detect and respond to the turbulent features. Changes in their swimming characteristics help to maintain them in the vortex and provides a clear mechanism for how these small animals aggregate in response to flow.  This has 2 important implications. 

1. In nature this provides short lived patches of copepods that serve as local “hotspots” for feeding by copepod predators.
2. In aquaculture this provides a mechanism for aggregating live prey to enhance the feeding rates of culture fish.

2)     In this proposal we investigated the characteristics of the sensory system of different copepod species. To date, we are generating data sets for 3 species. The data is being arranged such that the 3D coordinates for each sensor morphology can be inserted into the fluid dynamics of the Burger’s Vortex (characterizing specific flow conditions) to determine the force and duration (work) acting on each seta. 

3)     Modeling results from this project has changed how the community models seta in flow fields. Previous work has relied on steady state conditions to model flow detection. The finding of this study suggests that setal motion in response to oscillatory flows never reaches steady state before the behavioral response time.  This is a fundamental shift in approach.

4)     The data from this grant has been presented at ICES 6th annual zooplankton conference (2016), ASLO 2016, 2017, 2019 and the American Physical Society in 2017, 2018, 2019.  High school students through the BLOOM program were introduced to sampling techniques and animal maintenance.  Information from this grant was also used in lectures for our High School Teacher’s science program.  Lectures included a discussion on small scale fluid motion, Reynolds numbers and the role of temperature in changing fluid viscosity. To date, we have submitted 1 manuscript.

Broader Impacts

The success of this project relied on complementary expertise in the areas of: sensory ecology, biological/physical interactions, and turbulence mechanics. Such interdisciplinary collaborations require the development of the lexicon for translating, sharing, and communicating biological, oceanographic, and engineering knowledge. This project has funded 3 HS students 2 undergraduate students and 2 PhD students.  The HS students were young men from a private HS for troubled teens.  This project has certainly made a difference in their life. The UG and PhD students associated with this work were all women.  Both PhD students are from underrepresented minorities.  One student is a classically trained engineer that has learned about biology.  The other is a biologist that learned about engineering.  The cross discipline training is key to creating a new generation of researchers that are versed in the language of both disciplines. All the students benefited from the interdisciplinary research between science, technology, engineering, and mathematics.  By working together as a team, we learned to use and develop innovative tools for examining fine-scale biological-physical-chemical signals in the sea, focusing on key members of the aquatic food web: the copepod. The work also targeted high school student educational programs and outreach through the Bigelow’s long running (31 years) high school program and our teachers workshop (10 years) that targets HS students and HS teachers respectively.  The results of this work were presented in both programs as an example of the interdisciplinary nature of science and the role that zooplankton play in marine food webs.

 

Last Modified: 01/30/2020
Modified by: David M Fields