Transitions

Sea urchin on the beach: Whale Cove, Grand Manan Island. New Brunswick

It has been said that every spot on the Earth’s surface is an ecologic zone of transition, for at least one life form or one physical factor. If you walk 10 metres across the middle of a prairie wheat field, with flat grain extending almost to the horizon, it is hard to see what is changing, but you can be sure that there are transitions. On a shoreline on the other hand, the transitions are dramatic, often abrupt, and sometimes violent.  

Norman Aime (R) and me at the Churchill rocky shoreline site, summer of 2005 (photo © David Rudkin, Royal Ontario Museum)

When I traverse the modern shore of Hudson Bay and take a step from the cold hard quartzite into the even colder seawater, I am crossing the most elemental and complete kind of boundary on this planet. Salt water and dry land are arguably the two most different environments you can find in immediate proximity to one another. Fish and other sea animals live in a world where their body chemistry is very similar to that of the surrounding water; they breathe water and are buoyed up by it so that they are free of gravity. In my land world, I must carry my seawater-like chemistry around in a tough (though not always thick) skin, I breathe air, and each step of my hiking boot must counteract 190 lbs of gravity.

The transition from sea to land was a major evolutionary step for our fishy ancestors to undertake, and they hadn’t yet made this step when the ancient Churchill shore was being formed. So there were no amphibians, reptiles, or mammals on the scarp above that shore. The ancestors of insects had probably also not yet moved onto land, so no mosquitoes flew above the land surface, nor were there land snails. If snails had tried to move onto land before this time they would have found it a very inhospitable place, since there would have been no land plants for them to graze on, though there might have been lichens and algal scum on the bare rocks. The snails would have been quite happy to stay in the sea, though. There, they were surrounded by corals, sponges, seaweeds, trilobites, and squid-like cephalopods. Although none of these diverse animals belonged to the same species as those around today, together they make up an assemblage that we can easily recognize as a shallow-water, tropical biota.  

This diorama at the Manitoba Museum depicts an Ordovician seafloor in southern Manitoba (photo © The Manitoba Museum)

Since there was so little life on land at the end of the Ordovician Period, the transition zone represented by the ancient shoreline would have been extreme, in ways that we can only imagine. If I envision myself diving there, approaching the shore from the seaward side I can see silty sediment ploughed by worms and trilobites, then zones of dense, colourful corals extending upward into the intertidal zone. Lifting my head above water as I reach the shore, I can see … almost nothing. A sweltering Mars-like landscape of dark forbidding cliffs, with nearly no visible life. Sitting on the shoreline today considering this, I have to say that I prefer the modern Churchill land, even on a July day with a blasting northeast wind carrying cold sleet.   

I wrote this piece a few years ago. Sadly I won’t be getting to Churchill this year, though I will at least be doing some northern fieldwork before the end of the summer.