Blue Crab Babies and Microplastics

Posted Fri, 04/03/2020 - 09:19

Guest blog by Dr. Jonathan Cohen, Associate Professor of Marine Science, University of Delaware and Dr. Tobias Kukulka, Associate Professor of Marine Science, University of Delaware 

As warmer weather returns to the Atlantic coast, female blue crabs are waking up from a winter buried in the mud. They are making their way towards the open ocean where they release their offspring. These newly hatched spiny creatures, called “zoea larvae”, are smaller than a grain of rice. They’ll spend several weeks on a turbulent and windy voyage in the open, coastal ocean before returning to estuaries and coastal bays. Upon their return, they will eventually turn into adult crabs, and perhaps a crab cake once harvested. 

Microplastics, or plastic pieces smaller than 5mm in size, are commonly found in our ocean and coastal waters. Do the microplastics that these larval crabs encounter while drifting in the ocean affect their survival and ability to return to estuaries? With support from a NOAA Marine Debris Program Research grant, a team of University of Delaware (UDEL) marine scientists have joined forces to study this question. 

A view of a baby blue crab through a microscope that is smaller than a grain of rice.
Blue crab zoea larvae; each individual is smaller than a grain of rice. The small spines help protect the larvae from predators (Photo: Jonathan Cohen, University of Delaware).

In just a few months, the team will be onboard the UDEL’s coastal research vessel, (R/V) Joanne Daiber, conducting surveys for both larvae and microplastics in the Atlantic Ocean offshore of the Delaware Bay. These surveys will provide the data that physical oceanographer Dr. Tobias Kukulka, and graduate student Todd Thoman, need in order to test computer models they are creating, which predict how microplastics and crab larvae circulate in the coastal ocean. These models will tell the researchers how much microplastic exposure crab larvae may have on their ocean journey. At the same time, biological oceanographer Dr. Jonathan Cohen, and graduate student Hayden Boettcher, will be raising blue crabs in the laboratory. In these experiments, the team can control the amount of microplastics the blue crab larvae are exposed to, and if their survival, growth and energy consumption are affected. Together, the computer models and lab data will allow the team to predict how and if larval blue crabs are impacted by microplastics. From there, researchers can begin to understand whether microplastics have the potential to impact the blue crab fishery.

So what are researchers doing now to prepare for a busy field season? They are busy working on the computer models which will guide sampling activities and are replacing nets on the system used for collecting plastic and crab larvae. They are also calibrating the equipment used to measure the physics and chemistry of the water while sampling. Lastly, they are getting the lab ready to become home to thousands and thousands of crab larvae, which involves preparing the containers that will become homes for the larvae and microplastics to be used in the exposure experiments. It promises to be an exciting spring and summer as these scientists untangle the interactions of microplastics and blue crabs on the Atlantic coast!

Lab equipment that shows how plastic fibers are mind for the research project.
Microfibers are prepared for use in laboratory experiments by taking plastic thread, winding it around in a circle, freezing it, and then cutting it into very small pieces (Photo: Hayden Boettcher, University of Delaware).


Blue Crab Babies and Microplastics

Posted Fri, 04/03/2020 - 09:19

For citation purposes, unless otherwise noted, this article was authored by the NOAA Marine Debris Program.

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Tue, 04/28/2020 - 13:05

¡Hola! me encantan los cangrejos y me gustaría saber ¿cuándo y dónde estarán disponibles los resultados de esta investigación?

Great question! The project results will be available fall of 2021 at the earliest. Once available, we will have a new blog highlighting the results and these results will also be added to the project entry on the clearinghouse

Sandy Freeman

Fri, 05/01/2020 - 15:31

I am very interested in your research! Thank you for all you do! I was wondering if there is a specific time of year when the little baby crabs swarm the estuary banks? I was kayaking last year and saw an amazing site of them swarming and would love to witness it again! I just wasn't sure when and how long it occurs...I would not disturb them, just watch in awe! Thank you again

Thank you for your question! Our Research Analyst suggested the follow response and resources. Please reach back out if you have questions about this response. 

The best time to view the larval crabs would be over summer months. Crab zoea larvae are hatched near the estuary mouth and exported to the continental shelf, where they complete a loop out into the coastal waters, then due to winds, currents, and active swimming by the crab babies, they loop up and then back down into the Delaware Bay, with the aid of downwelling events. Crabs larvae are considered meroplankton, so essentially, as babies, they start off in the surface waters as plankton, then as they grow through different stages and reach a juvenile stage, they start to settle to the sea floor. A process that generally takes about 3 weeks in total. This whole process can occur in the Delaware Bay/coastal waters from May - August (female crabs will release larvae during this time frame).

For more information, please check out the project profile and clearinghouse entry and two additional papers that might be of interest:

Epifanio, C.E. 2007. Larval biology. In: V.S. Kennedy & L.E. Cronin, editors. The blue crab
Callinectes sapidus. Maryland Sea Grant. College Park, MD. pp. 513-533.

Epifanio, C.E., and J.H. Cohen (2016) Behavioral adaptations in larvae of brachyuran crabs: a
review. Journal of Experimental Marine Biology and Ecology 482:85-105.

Judith S Weis

Thu, 05/07/2020 - 12:16

If you are going to be sampling for microplastics with plankton nets, you will be missing most of the microplastics in the water, which are microfibers (that come off synthetic clothing in washing machines). Microfibers easily go through the holes in the nets. Whole water sampling ("grab" samples) are much more accurate. Also, in the lab experiments, are you planning to use microspheres for testing? These are very rare in the environment. You'd be much better using what is most abundant in the water, which is microfibers.