Setting up & Tending the Farm
Introduction
You’ve picked a seaweed species to cultivate and done your research on where to put your seaweed farm. You’ve applied for a license or lease to farm seaweed at your selected site and the application has been approved by the Maine Department of Marine Resources (DMR). And most recently, you’ve created a plan for obtaining your own seed for the upcoming season. With all of this taken care of a few months before grow-out begins, it’s time to get out on the water to prepare your site for its first crop of seaweed.
Setting up a kelp farm
In the world of aquaculture equipment and farm construction, seaweed farming tends to be on the simpler side of things. There are numerous designs for seaweed farms depending on the species, the harvest method, and the size of the crop. Generally speaking, seaweed farms come down to one basic premise: seaweed grows on a suitable substrate that is suspended below the surface of the water and anchored in place. Whether the substrate used is long lines wrapped with seed string, a net directly inoculated with spores, or a wooden raft with seed string fastened to it, the concept remains the same: create an artificial, easily seeded, and easily harvestable attachment place for seaweed to grow.
Farm design and biology
The techniques used for farming seaweed, come from understanding the biology of the species being cultivated.
Image credit: Jaclyn Robidoux, Maine Sea Grant
In Maine, the common setup for all farmed kelp is to use single long lines or an array of long lines suspended several feet under the surface, held in place by moorings or anchors on either end. There are many variations on farm designs, and no two farms will look identical, since farm design is unique to farm sites and operations. Long-lines are horizontal lengths of poly line, often between 400 and 1,000 ft, with seed string wrapped around them. Each end of the horizontal longline is attached to mooring systems held in place by anchors or concrete blocks. Systems with multiple long-lines, sometimes referred to as arraysDiagram of a kelp long line array.
can be attached to a spacer to maintain the shape at either end before being attached to the mooring lines. Depending on the configuration, horizontal longlines may be continuous lines or they may be broken into segments of 200 ft and attached end to end to form a single line that parallels the ocean surface. Between each segment are droppers– depth maintenance systems constructed out of buoys, PVC, and weights– that are, used to maintain the long line at an optimal depth of around 7 ft (~2 m).
Image credit: Jaclyn Robidoux, Maine Sea Grant
When setting up multiple parallel kelp lines, there should be enough space between the moorings that their associated long lines are not in danger of tangling. Typically people have ten feet at a minimum between kelp lines for sugar kelp and winged kelp. Skinny kelp can grow over ten feet and more space between lines may be required.
Image credit: Jaclyn Robidoux, Maine Sea Grant
When you begin preparing your site to farm seaweed, the process starts with setting up the moorings. Mooring systems are used at either end of each kelp longline, and moorings should be set well in advance of the planned seeding date. The mooring buoys should be observed over several tide cycles to determine if the moorings are correctly spaced and aligned. In Maine, all buoys associated with your farm, including mooring buoys, are required to have “SEA FARM” painted on them with three inch letters.
Seeding a kelp farm
The second stage of setup for a kelp farm is deploying long-lines. This aspect of farm construction can happen at the same time as seeding or before seeding, depending on the technique that is used to transfer inoculated seed string to the poly line. If you plan to setup long-lines at the same time as seeding, you may want to prepare gear such as long-line segments and droppers ahead of time to ensure a smooth and efficient seeding process.
Prepping long line and droppers
Making long lines
Long line segments are fairly easy to make. Starting with a spool of 7/16 inch poly rope (or similar), measure out 200 ft segments and cut the line into pieces. Then fuse the ends of each line segment with heat to prevent fraying and make knot tying easy. Finally, coil the line segments so they will be easy to transport and won’t tangle.
Making dropper buoys
Making depth control droppers, or depth maintenance systems, is also fairly straightforward. Droppers are used to keep kelp lines 2 meters (7 ft) below the surface, which is the optimal depth for growing sugar kelp. Droppers consist of a buoy, a 7ft PVC spacer, and a weight. When the kelp on the long line is small, the dropper buoy keeps the line from sinking too deep. As the seaweed grows and the kelp stipes fill with air and begin to float, the weights keeps the long line from coming to the surface. Droppers are placed in 200 ft intervals along the long line when new line segments are started.
Buoy used to keep the kelp longline afloat if it begins to get heavy.
Seven feet of line threaded through a PVC tube to keep the long line at the appropriate depth.
Attachment point where the dropper buoy is spliced into the longline.
Weight on the dropper to keep the kelp longline from floating to the surface as the kelp holdfasts become more buoyant.
Once all of the farm equipment has been prepared and seed spools are ready to be transferred to their grow-out sites, it is time to begin seeding and deploying kelp lines. Seeding happens during November and early December as this is when nursery grown seed is mature enough to be moved without impacting its survival. Seeding should be done around a low tide on a calm day– preferably overcast but without rain.
Seeding begins with the transfer of seed spools from the nursery to the farm. Whether you grow your own kelp seed or purchase seed spools from another source, you have to take care when transporting seed not to shock the juvenile kelp by significantly altering their ambient water temperature or leaving them exposed to the open air for too long. Reusing the settling tubes from the inoculation stage of nursery growth is a good system for careful transport of seed spools.
Seed spool transport
Seed spools with kelp seedlings growing on them are placed in settling tubes filled with cold, sterile seawater. These tubes can be packed upright into coolers or ice baths to keep seed cold for several hours without damaging the kelp seedlings.
Before heading out to the farm you should make sure to have all of the gear you will need to deploy long lines, including:
- your seed spools
- your pre-cut 200 ft segments of poly line
- the appropriate number of droppers
- any other lines, buoys, or anchors that you may need for your chosen mooring system
You will also want to have two or three people on the boat to handle both seeding and steering the vessel at the same time.
On your way out to the farm site, you and your crew should determine which way the wind is blowing, which way the current is flowing, and what the direction of your boat’s net movement is without the motor. If possible, you should begin seeding from the upwind/up-current side of the farm so the boat will drift naturally toward the location of the opposite mooring.
Once you are in position at the first mooring, long line deployment begins with threading the first segment of polyline through one of the seed spools and attaching it to the mooring system. Then you take one end of the seed string and tie it securely to the long line. At this point, you should be holding the seed spool with locking pliers to control the rate it unravels onto the long line while your other crew member slowly begins backing the boat toward the corresponding mooring at the other end of the farm. The seed string will begin to unwind and wrap around the long line. As the long line passes through the seed spool, there should be tension on the line to achieve tight, even wraps of the seed string. As the seed string is unraveling, be aware of prolonged exposure of the seed to cold or windy conditions that may freeze or dry the delicate blades, particularly if seeding late or in winter conditions. Occasionally submerging the spool or gently pouring seawater over it can help prevent this.
Once the next line segment is ready to go and threaded with the second seed spool, the new seed string is fastened to the long line and the process of unwinding the seed spool while maintaining tension on the long-line begins again. This process is repeated until you reach the mooring system at the opposite side of your lease and the final long-line segment is attached to the mooring. It is common for long-lines to be a total of 1,000 ft long– containing 5 line segments and 3 droppers.
Once all of the long lines on a farm are deployed and tied off at their moorings, the last task is to tension the lines to prevent tangling. This is easiest to do at low tide on a calm day and will depend on which mooring system you use. For moorings with deadweight anchors, you will need to use block and tackle to tension the lines. Meanwhile, for moorings with claw anchors, you can drag the anchor line on the mooring to reposition the anchor and tension the long-line.
Bock and Tackle
Block and tackle are mechanical advantage systems that can be used to tension long lines. They are used to create slack in one portion of a line so that portion can be tied again with more tension.
Image credit: Hussellvs
Tending to the seaweed farm
Kelp grow-out on the farm takes about six months. During this time, there is still some need to handle the crop, though time spent tending the farm is usually limited by weather. There are a couple farm maintenance tasks which are critical to stay on top of during grow-out:
- Observing and correcting crossed or tangled long-lines
- Monitoring and maintaining proper depth of long-lines
The farm should be monitored on a weekly or biweekly basis between the time you seed the lines to the time you harvest to make sure everything is in order. Additional checks on long-lines are also advised after storms, high wind events, and cold snaps where ice may become a factor. It’s important to keep records of the growth on your farm beginning at seeding and over the course of the season, especially if you plan to farm seaweed year-after-year or are hoping to grow and sell a certain volume. Simple photo logs can help visually capture growth and color, monthly measurements of blade length or weight can help understand the biomass, and short notes about each long-line’s productivity (“good growth,” “bald spot in the middle of the line, 200ft-400ft”) can help farms identify areas that grew well or pin-point where things might have gone wrong.