Autonomous Reef Monitoring Structures (ARMS) Deployment


Deployment Equipment

QTY Description
1 (3)* ARMS with base plate attached
4 (12)* Heavy duty 24" cable ties
4 (12)* Heavy duty 36" cable ties
2 (6)* Weights (capped PVC pipe with lead inside)**
4 (12)* 3/8" x 24" stainless steel threaded rods with a chisel point on one end***
1 Sledge hammer per diver
1 Gear bag
1 Drop line with buoy
1 Camera
1 GPS
  • *Number in parentheses is the quantity required for one survey site of 3 ARMS.
  • **This is optional but helps in high wave energy environments and overall in stabilizing the ARMS units.
  • ***Bring extra stainless steel threaded rods (if a rod is bent during installation, it must be replaced with a new rod). There are other installation methods that range from drilling eye-bolts and using cables or zip ties to connect the unit to heavy anchors. You can improvise based on budget, wave exposure, and habitat.
Figure 1: ARMS deployment gear.
Figure 1: ARMS deployment gear.

Weight Attachment

One method to help stabilize the ARMS unit on the benthos is to add weights to the device. Prior to deployment, you can attach a PVC pipe weight to each handle using two 24" zip ties per side. It is best to thread each 24" zip tie through the handle space twice such that each zip tie forms two loops around the PVC weight. Ensure that the zip ties are tightened around each end of the PVC pipe weight so that the weights are securely attached to the ARMS.

Figure 2: Zip tying the weights to the ARMS unit (left) and a deployed ARMS unit with attached weights (right).
Figure 2: Zip tying the weights to the ARMS unit (left) and a deployed ARMS unit with attached weights (right).

Deployment

NOAA deploys ARMS in sets of three on hard bottom forereef habitats at depths of 10-15 meters. Individual ARMS units within a survey site are placed 2-4 meters apart.

Lowering the Equipment

Figure 3: ARMS equipment ready for lowering off of the small boat.
Figure 3: ARMS equipment ready for lowering off of the small boat.

In order to minimize adverse impacts to the coral reef habitat, we lower all of the ARMS equipment to the bottom using the buoyed drop line. The bitter end of the line is run through one handle of each of the 3 ARMS and clipped back to itself. The tool bag is clipped to the line just above the ARMS.

A free-diver briefly surveys the desired survey area for an appropriate sandy / rubble location into which the equipment can be lowered from the support boat. Once the free diver finds a suitable location, hand signals and/or voice commands are used to direct the support vessel over the appropriate location in which to lower the equipment.

Once the equipment is lowered, the surface buoy attached to the drop line marks the dive location. Divers need only follow the drop line down to the equipment to begin ARMS installation.

Figure 4: ARMS being lowered off of the small boat (left). Figure 5: ARMS lowered into a rubble patch (right).
Figure 4: ARMS being lowered off of the small boat (left). Figure 5: ARMS lowered into a rubble patch (right).

Installation

Figure 6: Using a sledgehammer to pound in the stakes.
Figure 8: Zip tying the stakes to the ARMS unit.
Figure 7: Zip tying the stakes to the ARMS unit.

Divers look for rubble or bare patches of substrate in which to install the ARMS so as to minimize any collateral damage to the coral reef habitat. ARMS are installed approximately 2 to 5 meters apart as the topography allows.

If installing ARMS units with stainless steel shanks, drive a stake using a sledge hammer through each corner hole of the base plate. If possible, stakes should be installed perpendicular to the substrate to facilitate ARMS removal at a later date by simply lifting it vertically off the stakes.

However, sometimes it is not possible to achieve a perpendicular orientation of the stakes. This is not a problem. Just be sure to hammer in the stakes to at least half of their length in whatever orientation allows this. Stability of the ARMS base plate is ultimately more important than stake orientation.

Once the stakes are driven into the substrate through the holes in the base plate, use the 36" heavy duty zip ties to secure the base plate to the stakes.

Thread a zip tie through a corner of the base plate and take multiple wraps around the stake before securing. Repeat for the remaining corners. A correctly installed ARMS unit should feel securely attached to the substrate with very little play (lateral or vertical) when manipulated by the diver.

If for some reason the stakes cannot be installed through the corner holes of the base plate, they may be installed through the handles at opposing angles (crossed). Similarly, use the 36" heavy duty zip ties to secure the base plate to the stakes.

Alternative Installation Methods

In hard bottom habitats, such as basalt, that are challenging to pound in stakes, you can alternatively use heavier weights to secure the ARMS unit to the benthos or a pneumatic drill to install eye bolts. Zip ties would be used to secure the weights to the base plate (see below) and in drilling, zip ties secure the base plate to the eye bolts.

ARMS secured to benthos with 70 lbs weights ARMS secured to benthos with 70 and 40 lbs weights ARMS secured to benthos with 40 lbs weights
ARMS units secured benthos using weights. Long weights shown are 70 lbs each and the shorter weights are 40 lbs each.

Photography

Figure 6: Two installed ARMS units at a site.
Figure 8: Two installed ARMS units at a site.

Document the site with photos of the surrounding habitat as well as the deployed ARMS. If there is a particular sponge, algae, tunicate, bryozoans etc that is prevalent at the site, take a close-up image to document.

GPS

Mark a GPS point of the site. Make sure to swim over the spot and get the point directly above the ARMS.