Field-based Mesocosms: Construction and Deployment
In situ deployments for assessing impacts of chemical spills in coastal areas
This Storymap is intended as an instructional manual to guide you through the methods of construction and deployment of a field mesocosm. For more detailed background and project information please visit the NCCOS website .
Project Background & Introduction
Project Goals:
We are working to improve our ability to rapidly assess the impacts of oil spills by building on field and laboratory toxicity studies that were key to the Deepwater Horizon nearshore assessment.
Project Goals:
Our primary goal is to develop protocols for field-based mesocosms that are ready to use with future spills to reduce the potential loss of information during the immediate aftermath of these events. Our research will identify species and develop equipment best suited for field-based mesocosms.
Supplies Needed for Construction
The cages used are cylindrical 24” offshore bait pens with PVC coated 1” galvanized steel mesh and are available from a commercial vendor.
The cage must then be modified with a mesh that can retain the organism of choice.
The mesh used is a UV stabilized polyethylene available from a commercial vendor. These are listed as “Plastic netting standard duty”. The vendor we used lists three sizes in standard units at 1/4”, 1/8”, and 1/16” but other vendors may have different sizes if so desired.
The coarse 1/4" mesh is used for the outside cover of all cages and protects them from being punctured while deployed in the field. ↪
For cages containing small fish, the 1/8" mesh should be used for the primary cover. The pilot study focused on a Fundulus species. ↪
↩ For cages that will contain shrimp and other small invertebrates of interest, the 1/16" mesh should be used for the primary cover. A Palaemon species in the range of 15-32 mm was used during the pilot study.
A number of commercially available tools and materials are needed to attach the mesh securely to the frame.
4" and 18" cable ties are needed to secure the mesh for the fish cage.
4" cable ties are used to secure the lid when deploying animals in the field.
18" cable ties are needed to secure the mesh on the outside of the metal cage.
A pair of curved forceps are needed to help pull the cable ties through the mesh openings.
Nylon fishing line and sewing needles are needed to attach the mesh for the shrimp cage.
Use 50 lb test fishing line to secure the 1/16" mesh
A set of repair needles are also needed to secure the mesh on the outside of the metal cage.
All of the mesh for a cage can be precut before starting construction.
Using the appropriate mesh size (1/8" for Fundulus or 1/16" for Palaemon) for the desired organism, cut the piece for the external circumference of the cage (approximately 215cm x 72 cm). This will allow for a 4-5 cm overhang on the top and bottom of the cage.
Next cut two 75 cm square pieces of 1/4" mesh and two 75 cm square pieces of the appropriate mesh size for the desired organism that will be used for the top and bottom covers.
The 1/4" mesh should be the outermost layer of both the top and bottom of the cage regardless of the interior mesh size.
Regardless of the organism of interest, the smaller mesh should be the innermost layer of both the top and bottom of the cage.
Constructing the Fish Cage
Before attaching anything to the frame of the cage the existing wire lid and the metal used to attach it must be removed and discarded.
Line up the mesh pattern of the piece cut for the outer covering with the pattern of the wire frame and secure it with one of the 18" cable ties. Lining up the patterns will help ensure the mesh is attached as straight as possible.
Using 5-7 more 18" cable ties, finish securing one side of the mesh and trim off the end of the cable ties.
Tightly roll the mesh around the entire cage and secure it with a single 18" cable tie.
Add 8 or 9 more 18" cable ties evenly across the entire seam and trim off the excess.
Cut off the excess mesh on the ends so that you are left with 4-5 cm that will be tucked under the top and bottom covering if necessary.
To cover the top and bottom of the cage, use the precut pieces of 75 x 75 cm square mesh. This should be two layers with the interior mesh being the size appropriate for the organism to be contained. The outside mesh should be the rigid 1/4" mesh that will be in contact with the sediment.
The 4-5 cm overhang of the side mesh should be pressed down around the top/bottom edges to form a secure double layer around the circumference edge when the top/bottom mesh is attached.
18" cable ties should be used to secure the top and bottom edges by inserting from the outside of the cage and finished on the bottom, not the side.
Curved forceps can be used to help pull the cable ties through the mesh
Once each cable tie is inserted through the bottom a pair of forceps is useful to turn the tip of the cable tie at a 90 degree angle to come out of the side mesh. Then turn it back through the bottom mesh to complete.
Curved forceps can be used to help pull the cable ties through the mesh
Once the ends are secured, trim off the excess mesh around the edges.
The final step of the frame construction is to secure the bottom layer of mesh to the frame. This can be accomplished by using several cable ties spread out across the bottom and attached to the steel frame. When the cage is deployed in the field heavy silting can occur. This can be heavy enough to separate the mesh from the cage and compromise the deployment.
After all of the mesh has been attached to the cage, 3/4" PVC tubes must be cut that are about 60% of the height of the cage and attached to the outside.
PVC tubes are used to secure the cages to the sediment when deployed in the field.
Drill four holes at equal distance on each tube large enough to push an 18" cable tie through.
Insert cable ties through both sides of the pvc tube (this step eases the attachment process).
Attach the tube through the external mesh of the cage so that it is flush with the bottom and anchored by the metal of the cage skeleton. Secure the cable ties on the exterior of the cage.
Insert cable ties through both sides of the pvc tube (this step eases the attachment process).
4' pieces of rebar should be bent at a 90-degree angle using a small sledgehammer and bench vise. These will be used to secure the cages to the sediment.
Constructing the Shrimp Cage
The order in which the shrimp cage should be constructed is the same as described in the fish cage construction but the materials needed to secure it to the frame are different and are described in the supplies section above. This section only highlights the steps that are uniquely different in the construction of the shrimp cages.
Secure one end of the side mesh to the cage using a running stitch with double strung 50 lb test dacron fishing line and a 45 mm straight carpet needle.
Stitch used for securing the side mesh of the shrimp cage.
Fishing line used for sewing mesh.
Carpet needle for securing the side mesh.
Next, roll the mesh around the cage and overlap it, then secure the other end using the same technique as the first edge.
When the edge is complete, finish the stitch by turning it through the same hole twice and using a fisherman's knot through the loop created with the second turn to fully secure the thread.
We found the fisherman's knot to be the easiest way to secure the line. There are certainly other knots that can be used but an effective knot is critical.
Trim and fold the excess side mesh to the end of the cage and place it on top of the 75 x 75 cm mesh cutouts for the top/bottom. Remember to make sure the smaller mesh size is facing inward and the larger 1/4" mesh outward to be in contact with the sediment.
A single knot in the middle of the cage before starting will help hold the mesh in place.
Using an overcast stitch with a curved upholstery needle, sew approximately 8-inch sections on opposite sides to secure the top/bottom in place (pictured below).
Securing opposite sides first will help keep the mesh from shifting while working around the edge.
Curved upholstery needle.
Stretch the mesh across the top of the cage as you work around the edge to keep the mesh as tight as possible and repeat the 8 inch sections until complete. It is helpful to trim the excess mesh ahead of the stitch to access the edge of the cage for sewing.
Measure the distance from the top to bottom and cut a piece of the 1/4" mesh used for the bottom to fit over the exterior and prevent damage to the fine mesh. Pull tight and secure to itself with 18-inch cable ties. This piece will also serve as the attachment point for the PVC mounting tubes.
The final step of the frame construction is to secure the bottom layer of mesh to the frame. When the cage is deployed in the field heavy silting can occur. This can be heavy enough to separate the mesh from the cage and compromise the deployment.
Heavy silting can occur inside the cage, especially in the summer months.
This can be accomplished by using a running stitch through the bottom mesh and anchored to the steel frame in a pattern that gives enough attachment points to prevent the bottom from sagging.
Inside view of attachment points for the bottom mesh.
Constructing the Lid
After the top of the cage is secured you will need to cut out an opening with scissors equal to the size of the opening of the frame to access the interior.
Fish Cage:
The top of the cage will then need to be secured to the frame all the way around the perimeter of the opening. For the fish cage, 18" cable ties should be used.
Shrimp Cage:
The same result can be achieved for the shrimp cage using an overhand stitch.
Fish Cage:
Cut two layers of the same mesh used for the top/bottom in a square so that it overlaps the existing opening by 3-4 cm (approximately 31 square cm).
The lid of the fish cage should be two layers. The inside layer should be 1/8" mesh and the outside layer should be 1/4" mesh.
Fish Cage:
Secure the pieces together using 4" cable ties.
Fish Cage:
The cable ties should be spread out evenly around the edge of the lid.
Fish Cage:
These will be used to securely attach the lid to the top of the cage during a deployment.
Closeup of cable ties used to secure mesh lid together.
Fish Cage:
Once the lid is complete, align it on top of the cage and secure 5-7 cable ties per side to the ¼” mesh around the outside edge of the lid as pictured below.
Fish Cage:
The cable ties on the lid should be attached to the ones placed around the top of the cage with 6 of the 18" cable ties and tightened down in the field after the animals have been deployed into the cage.
Lid secured with cable ties.
Shrimp Cage:
For the shrimp cage, cut two pieces of mesh that are the same dimensions as the lid for the fish cage. You will also need one piece of the 1/16" mesh. Place the 1/16” mesh in between the two larger mesh sizes and secure all 3 together with cable ties running the entire perimeter of the lid.
Shrimp Cage:
The biggest difference between the two cage types when it comes to securing the lid is that the shrimp cage must be fitted with a running stitch around the outside edge of the lid.
Shrimp Cage:
Also, there should be a larger number of cable ties on each edge (~8-9) to secure the lid when working with smaller organisms to ensure they cannot escape.
Cable ties should be run underneath the stitching and attached to the top of the cage.
Tighten all of the zip ties around the edge after the animals have been placed inside.
Shrimp Cage:
Closeup of the cable tie loops used to secure the lid.
Closeup after the cable ties have been tightened.
Site Selection
01 / 03
1
Site Establishment
A preselected reference site should be established in each region (i.e. Southeast, Gulf Coast, Pacific Northwest) that will be used for assessments. The site should be shallow enough to access by foot to minimize gear loss and must be in contact with the sediment.
Prior to deploying animals, the deployment site or sites should have been fully vetted at low and high tides to properly place the cages.
2
Southeast Site
The pilot study took place in a relatively shallow, high-velocity creek near Charleston, SC. The average tidal range at this site is 6 ft.
3
Gulf Coast Site
The cages have also been deployed on the Gulf Coast in a relatively shallow, very low-velocity creek near Corpus Christi, TX. The average tidal range at this site is 1 ft.
Field Deployment
Collecting Animals:
Along the Atlantic and Gulf of Mexico Coasts, it is suggested to use a Fundulus species for the fish and a Palaemon species for the shrimp.
The cages as described here are made specifically for Fundulus in the range of 40-60 mm and Palaemon in the range of 20-30 mm. For other regions, organisms need to be in these size ranges in order for the method to work as designed.
Collecting Animals:
Organisms should be collected from a known uncontaminated site before dispersing to a potentially impacted site. Lab-raised animals or animals from other regions should not be used.
Shrimp can be collected using a dip net and walking along the marsh edge.
Fish species can be collected using minnow traps (or other suitable methods depending on the region).
Collecting Animals:
Test animals can be collected a day or two ahead of the deployment date and held in the laboratory.
Collecting grass shrimp for deployment.
20-30 mm grass shrimp ready to be counted into the cages.
Deploying Animals:
Animals should be pre-counted (25 Fundulus sp. per cage and 100 Palaemon sp. shrimp per cage) into buckets filled halfway with water from the deployment site. Using one bucket per cage will help organize dispersal.
Deploying Animals:
Carefully pour the buckets into the cages and secure the top with cable ties. Be sure to check each bucket and transfer all animals inside the cage.
Securing the Cages:
Cable ties should be run underneath the stitching for the shrimp cage or underneath the preplaced cable ties for the fish cage and attached to the lid as shown below.
Tighten the cable ties around all 4 sides of the lid after the animals have been placed inside.
Lid secured with cable ties and ready to be deployed in the water column.
Securing the Cages:
Arrange the cages in the water close together so they can be easily located but far enough apart so water can flow around them unobstructed.
Six cages deployed in Charleston, SC
Securing the Cages:
Make sure the bottom of the cages are in contact with the sediment, then secure them by pushing the 4' pieces of rebar through the PVC tubes and as far down into the sediment as possible. At least two tubes with rebar should be used but more can be mounted depending on the environment.
Securing the Cages:
The video shown is just a demonstration of the technique. In an actual deployment the cage should be deeper in the water column.
Retrieving Cages and Animals:
At the time of the desired endpoints, cages should be carefully removed from the water.
Retrieval should be done at or near low tide in order for the cages to be found most easily.
Working with one cage at a time, remove the rebar and carry the cage to an edge or sandbar so that there is enough water to keep the animals slightly submerged while counting.
Retrieving Cages and Animals:
Remove the lid by cutting the cable ties on three sides and if there is silt on the bottom carefully attempt to rinse as much of it out into the water as possible.
Nearly 4" of silt accumulated on the bottom of this cage in June 2020. Agitating the cage in the water to rinse it out is necessary before counting animals.
Retrieving Cages and Animals:
The contents of each cage should be carefully counted into buckets either using small nets or by hand.
Record all counts, cage conditions, and weather in the field notebook.
After all animals are counted they can either be returned to the water or brought back to the lab for further analysis.
QUALITY CONTROL/QUALITY ASSURANCE
Cages should be thoroughly inspected before each deployment to check for damage to the mesh, or seams. Cages should be tagged and numbered to monitor for individual defects that cannot be seen. If a single cage consistently performs poorly it should be removed from service.
Additional Resources:
NOAA's Office of Response and Restoration (OR&R) ARD Division
Contacts:
Paul Pennington: paul.pennington@noaa.gov
Pete Key: pete.key@noaa.gov
Blaine West: blaine.west@noaa.gov
James Daugomah: james.daugomah@noaa.gov
Product Disclaimer: Reference in this site to any specific commercial product, process, or service, or the use of any trade, firm or corporation name is for the information and convenience of the public, and does not constitute endorsement, recommendation, or favoring by the Department of Commerce or NOAA.
