scubaseason

Common Spider Crab

Maja brachydactyla

Sighting evidence at The Gully, St. Abbs Head

Large spider crabs aggregate in The Gully in late summer and autumn when they moult in groups, a behaviour that reduces predation risk by overwhelming potential predators with numbers. Aggregations of dozens can cover the gully floor in August and September, their spiny carapaces camouflaged with attached algae and sponge fragments. Outside aggregation season, individuals forage singly on the gully walls, picking off hydroids and soft invertebrates.

Evidence at this site

No confirmed records on file at this site

Common Spider Crab is listed as a curated species here based on historical reports.

How is this calculated?

Sighting evidence is compiled from iNaturalist observation records within a set proximity radius, filtered for quality-grade observations. “Last confirmed” is the date of the most recent research-grade record. Record count covers a rolling 24-month window. Confidence reflects record count, recency, and consistency of seasonal signal.