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Hermit Crab Shell Exchange – Nanaimo, British Columbia

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Enjoy this video by Garrett Clement with his voice over and the hermit crab’s adventures in Nanaimo, British Columbia.

Hermit crabs are anomuran decapod crustaceans of the Paguroidea superfamily that have evolved to safeguard their delicate exoskeletons by occupying empty scavenged mollusk shells. Hermit crabs come in over 800 different species, the majority of which have an asymmetric abdomen hidden by a tight-fitting shell. The non-calcified abdominal exoskeleton of hermit crabs necessitates the use of an exogenous shelter system. Hermit crabs must use shelter made by other organisms to avoid being defenseless.

Sea to Sky

Hermit crabs differ in size and shape from a few millimetres long carapaces to Coenobita brevimanus, which can live for 12–70 years and grow to be the size of a coconut.

Hermit crabs require larger shells as they mature. Due of the scarcity of adequate complete snail shells, fierce competition for shells often occurs among hermit crabs. The proportional abundance of gastropods and hermit crabs, matched for size, determines the availability of empty shells in any particular location. The population of creatures that prey on gastropods while leaving the shells intact is an equally important concern. To acquire access to the shell they prefer, hermit crabs housed together may fight or murder a competitor. Fighting over empty shells will, on the other hand, lessen or disappear if the crabs are of different sizes.

Liquid Diving

When seashells aren’t accessible, hermit crabs will make do with tin cans, custom-made shells, or any other form of garbage, which is typically fatal to the crabs (as they can climb into, but not out of, slippery plastic debris). This can even generate a fatal chain reaction, as a dead hermit crab would send out a signal to alert others that a shell is available, drawing even more hermit crabs to their deaths.

By H. Zell – Own work, CC BY-SA 3.0

Dive Report

Site Highlights:

This site although quite uninspiring in its topography still has a lot to offer. Located off Cottam Point in Nanoose bay it sits between Vancouver Island and Mistaken Island. One of the main draws is the Sealions that often pass through this passage. Also, plentiful in macro life such as Grunt Sculpins and Giant Nudibranchs. If that wasn’t enough, Octopus are sited here on a regular basis. This site takes patience and a slow pace to fully appreciate. However, every time I visit it finds a new way to surprise me.


Although this site is not deep bottoming out at 18m it is still advisable to exercise caution and dive at slack tide. Current has been known to rip through the gap potentially pushing divers into the bay.

Dive Log:

Date: Feb 20, 2021
Dive Site: Cottam Point
Location: Nanoose Bay, BC
Water Temperature: 7°C
Visibility: 20m
Dive Time: 50 mins
Max Depth: 14m

Best Time to Visit:

January – February


Octopus, Sealions, Grunt Sculpin Giant Nudibranchs

Who to Call:

Brenda from Nanaimo Dive Outfitters

Garrett Clement

Thanks Garrett Clement – follow Garrett’s dive videos on YouTube



About Author

Kathy is the owner of Kirk Scuba Gear, a passionate Scuba Diver, Ocean Advocate and Managing Editor of The Scuba News Canada

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