Saturday, 15 August 2020


Devonian Coral, Kootenay Rockies, BC

This fellow is a coral from a Devonian reef site near the Bull River in the Kootenay Rockies. 

Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically live in compact colonies of many identical individual polyps. Corals species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.

A coral group is a colony of myriad genetically identical polyps. Each polyp is a sac-like animal typically only a few millimetres in diameter and a few centimetres in height. A set of tentacles surround a central mouth opening. Each polyp excretes an exoskeleton near the base. Over many generations, the colony thus creates a skeleton characteristic of the species which can measure up to several meters in size. Individual colonies grow by asexual reproduction of polyps. 

Corals also breed sexually by spawning: polyps of the same species release gametes simultaneously overnight, often around a full moon. Fertilized eggs form planulae, a mobile early form of the coral polyp which when mature settles to form a new colony.

Modern coral reefs begin to form when free-swimming coral larvae attach to submerged rocks or other hard surfaces along the edges of islands or continents. As the corals grow and expand, reefs take on one of three major characteristic structures — fringing, barrier or atoll. Back in the Devonian, reefs were formed from corals and stromatoporoids which formed on top of carbonate banks.

Modern Thriving Coral Community
Corals reappeared during the Devonian period, around 410 million years ago. It is around this time that they began to form extensive reef systems. 

These early coral reefs were predominantly composed of coral-like stromatoporoids (reef-forming sponges), tabulate corals (mounds, branches, and organ shapes), rugose corals (horn-shaped), and predecessors of the modern-day coralline algae (encrusting multi-coloured algae seen on rock surfaces). 

It was towards the end of this period that scleractinian or ‘stony’ corals first appeared that populate coral reefs today. 

350 million years ago corals briefly disappeared from the geological record. The reason for this is not clear but evidence points towards rapid fluctuations in sea levels and a rapid reduction in atmospheric carbon dioxide. It has been a long stretch of good conditions for corals but with global warming, we are beginning to alter our oceanic conditions and not to the liking of our beautiful corals.