ARMS

What are ARMS?

Autonomous Reef Monitoring Structures (ARMS) are a globally standardized sampling tool used in subtidal ecosystems worldwide, and coordinated by the Smithsonian Institution. They are generally used to evaluate ocean health by assessing temporal trends in poorly known subtidal cryptic species. Each unit is made up of a stack of PVC plates separated by small spacers, acting as a settlement structure and refuge for motile and sessile invertebrates, algae and benthic fish. ARMS’ are typically deployed for 6 months to 3 years with the goal of replicating the surrounding ecosystem to allow subtidal organisms to passively settle and grow on the structure. After retrieval, scientists collect individual and community genetic information, visually identify species, and quantify percent cover data from the ARMS. This data can be used to assess biodiversity and community composition.

What can the ARMS tell us?

Using ARMS combined with other established biodiversity surveys (e.g. visual dive surveys, environmental DNA sampling) allows for an in-depth analysis of biodiversity and community composition. These surveys help us to understand how different marine communities respond to changing ocean conditions, habitats, and restoration practices. Understanding these responses can help us predict community responses and implement strategies for future oceanic changes.

How are we planning to use ARMS?

In 2024, we conducted a pilot project north of Quadra Island, where we deployed multiple ARMS’ within a kelp forest and in the neighbouring urchin barren for a full year. The goal of the pilot study was to compare the biodiversity between kelp and urchin barrens and to determine necessary replication levels for future ARMS-related Sentinel projects. Comparisons were made using genetic barcoding, metabarcoding, and visual identification data collected from the ARMS at the end of the year-long deployment. 

Beginning in Fall 2025, we are working alongside community partners to expand the ARMS network across the Salish Sea in order to gain better understanding of kelp forest biodiversity across the region. We’re excited to expand this project throughout the Salish Sea and the neighbouring coastlines. ARMS have been deployed almost exclusively in tropical ecosystems, so we are eager to enhance our understanding of temperate subtidal cryptic biota using this method.

ARMS Gallery