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?

Since Fall 2025, we have been 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 have anchored three ARMS per site across seven locations throughout the Salish Sea and the neighbouring coastlines. They will each remain anchored for approximately twelve months, allowing organisms to passively grow and collect on these units throughout the year.

In Fall 2026, scientific divers will carefully retrieve and transfer each unit for lab processing. We are fortunate to work alongside our community partners, who provide historical knowledge, data, and ground work to allow this expansive and comprehensive project to succeed. Previously, other research institutes have deployed ARMS almost exclusively in tropical ecosystems, so we are eager to enhance our understanding of temperate subtidal cryptic biota using this method.

ARMS Gallery