Autonomous Reef Monitoring Structure (ARMS): Recovery and Processing

By Molly Timmers and Russell Reardon 

‘Reef Biodiversity: an Introduction’ posted on the 4th of February introduced coral reef diversity and the Autonomous Reef Monitoring Structure (ARMS).  This post will explore the recovery and processing of these platforms.

ARMS awaiting removal on left, encapsulated ARMS on right

An ARMS is a tool used to assess the lesser known and cryptic reef organisms. For the past two years, sessile and motile critters have been colonizing the open and closed ARMS layers.  One of our missions on this cruise has been to recover all the previously deployed ARMS for immediate shipboard and subsequent land-based processing.

We remove the ARMS from the benthos by attaching a milk crate lined with an 80 micron mesh over the center stack of plates comprising the structure.  A buoyed rope is then attached to the latching straps on the crate, and the whole unit is pulled to the surface.  The milk crate ensures that any recruited organisms within the ARMS will not fall out during transport.  Once on the surface and in the small boat, the milk crate encapsulated ARMS is placed within seawater-filled bins and transported back to the Hi‘ialakai.

Back on the ship, the ARMS is disassembled within a tub of seawater. The milk crate is detached, and each layer (plate) is removed individually.  The top and bottom of each plate is photographed to document the sessile organisms.  Once photographed, a paint brush is used to lightly sweep any motile organisms off the plates and into a bucket of seawater. The plates are then placed in ethanol to preserve the DNA for future molecular processing.

An example of a plate photograph

Once every layer has been photographed, brushed, and preserved, all of the buckets of seawater used during the processing are sieved into the following bins: 5 mm, 2 mm, 500 ?m, and 100 ?m.  The contents from the 2 mm, 500 ?m, and 100 ?m sieves are bulked and placed immediately into ethanol. Selected critters found within the 5 mm sieve are photographed, identified, and preserved individually while the remaining 5 mm organisms are bulked and placed in ethanol. 

The final task is to scrape the sessile organisms from the all the plates.  The scrapings are bulked and preserved.   In this manner, we are able to remove, preserve, and store all of the sessile and motile organisms that have recruited to the ARMS.

ARMS processing  in action. Upper left, disassembling; lower right, brushing;
middle, photography; lower right, sieving; upper right, scraping.

When we return to land, the contents will be sent to our partners at the Smithsonian, the Florida Museum of Natural History, and the Hawaiian Institute for Marine Biology who will begin the molecular processing and taxonomic archiving. Genetic sequencing will provide a relative index of diversity for each of our survey sites.  We will then be able to compare these indices among and between sites, islands, and regions. Ultimately, this process may allow us to detect and monitor changes in cryptic diversity in an effort to understand ecosystem shifts overtime.

Examples of invertebrates found within the ARMS