East Coast - The Intertidal
Welcome to the intertidal! That ever-changing, vibrant, life-filled strip between the high and low tide lines. For the next few weeks we’re going to be picking our way across both the Bay of Fundy’s expansive tidal flats and Nova Scotia’s rocky shores to explore the fascinating aspects of this ecosystem and meet some of the creatures who call it home.
EPISODE NOTES
The supralittoral or ‘spray zone’ only gets a passing mention in the episode but it’s worth pointing out that it’s home to some of the toughest animals and plants in the intertidal like barnacles, isopods and springtails. They have to be tough, because living in this zone exposes you to… just about everything. Heat, cold, rainwater, salt spray, intense sunlight plus predators from land, sea and air at the same time.
Filming the Bay of Fundy’s tides was mostly done from a classic vantage point: the small town of Alma at the edge of Fundy Provincial Park. The beach at Alma is one of those places where you can walk an incredible way out with the tide - but you’ve gotta be careful as it comes back in. There were a couple of photographers hanging out on a sandbar and focused so exclusively down their lenses that they didn’t notice the water was starting to surround them. I called some friendly warnings a few times and they waved me off, until they’d been trapped by the water and I got a little more emphatic. At that point they retreated back toward the shore, having to tromp through waist deep water to do so, acting like this was all part of the plan. Maybe it was. But they did not look like they were dressed to be in that deep.
I flip-flopped on the pronunciation of seiche, there are… variations. But I settled on the one I’d heard most often, backed by the authority of Merriam-Webster.
I also hedged my bets on how many billion tons of seawater enter the Bay of Fundy with every tide. Estimates differ pretty wildly (and that kinda makes sense, right? I can’t imagine how you would accurately measure that). But everyone seemed to agree that it’s at least a hundred billion tons. So I used the ‘at least’ dodge like I did in the migration series with stats like the arctic terns, who also have a pretty wild range of estimates on ‘migration length’.
Just like I knew saying ‘Alberta’s badlands are about as close as Canada gets to a desert’ was going to get me in trouble, I said ‘The foundation for almost every ecosystem is energy from the sun’ knowing people would ignore that all-important word. I guess I’m just saying: don’t @ me, sea vent bros.
TRANSCRIPT
The North Atlantic is deep and cold. The Atlantic coast of Canada can be barren and rugged.
But right where the two meet is a narrow strip, between the high and low tide lines, where nutrients from the sea wash up at the shore and life blooms around them. It’s a weird combination of high biodiversity in surprisingly harsh conditions. It’s called the intertidal and it’s where we’re gonna be poking around.
The intertidal is split into three major ‘littoral’ zones depending on how much time they spend underwater.
The upper littoral is only submerged at high tide.
The mid littoral has regular periods of both submersion and exposure.
And the lower littoral is submerged most of the time.
There’s also the supralittoral, or spray zone, which as you might guess is only splashed but never submerged by ocean water, except in storms or exceptionally high spring tides.
And there’s the sublittoral zone or neritic zone, the relatively shallow area extending out to the continental shelf with a maximum depth of 200 meters. This relatively small coastal layer actually has the greatest biodiversity and productivity in the whole ocean.
We’re gonna be spending most of our time in the mid and lower littoral zones - the place where receding tides can give you a glimpse into that undersea world.
But in Canada, you happen to be able to explore an expanse of the neritic zone on foot. Thanks to the Bay of Fundy, home to the highest (or, if you like, lowest) tides in the world.
Those tides are the result of a lot of coincidental factors at once. The bay is long, cone shaped, narrow and shallow, creating a funnelling effect on the water.
But it also has very conveniently timed ‘tidal resonance’. Water in any basin has a natural back-and-forth ‘sloshing’ motion also called a seiche. The timing of that motion is determined by the length and size of the basin, and the Bay of Fundy just happens to have a seiche that syncs with the tide, giving it a little extra oomph.
All that adds up to as much as 16 meters difference between high and low tide, the height of a five-storey building. Over a hundred billion tons of seawater flow in and empty from the bay twice a day - more than the combined flow of every freshwater river on earth.
In the tidal flats regions, that can mean that receding water exposes more than a kilometre of shoreline width. So you’re not just poking around a little strip of intertidal here. You’re striking out into the neritic zone. The line you’ll hear a lot is that you’re actually getting to ‘walk across the ocean floor’ - and get this totally unique view of what’s going on down there.
Across the Bay of Fundy’s tidal flats, and along the rocky shores of Nova Scotia, we’re also gonna be focusing in on tide pools.
Tide pools become little oases at low tide. When rock depressions or formations trap receding water they provide habitats with a whole lot going for them - though everything living in them is like a little Icarus.
The foundation for almost every ecosystem is energy from the sun.
That solar energy dissipates and scatters fast in water, so the shallower you are the more of it can be used and the more life you’ll find. Deeper than 200 meters, the limit of the neritic zone, and there’s no longer enough available for photosynthesis. That’s why life can be so vibrant there above that line, and drops off quickly with the continental shelf.
By that perspective it doesn’t get much better than a tide pool, the shallowest you can be while still being underwater. Of course, you’re constantly risking that solar energy overpowering your ecosystem by overheating the water or evaporating it completely.
But if you do get in that goldilocks zone, you’re in luck. You’ve got water to keep you going until the tide comes back in. The rocks give you natural protection. And you have a very reliable food delivery service. Every time the tide returns it beings you a new smorgasbord pulled up from deeper water.
So in these little rock pools, life concentrates and abounds. And over the next few weeks we’ll be picking our way across the Bay of Fundy’s exposed ocean floor and stopping at these little gardens of eden for a visit with just a few of the countless species who call them home.