WATER WONDERS
Examining our marine ecosystems
Examining Cape Breton’s marine ecosystems.
Today, Cape Breton Island cradles a huge, saline lake: a “sea” inside and an ocean outside the land we call home.
But Unama’ki was not always an island and Pitu’paq was not always an estuary. Melting glaciers at the end of the last ice age (about 10,000 years ago) caused the global sea level to rise from about 120 m below the present level. It flooded into the Bras d’Or Lake and the Canso Strait about 6,000 years ago, creating the island’s shorelines on which we now find ourselves. For example, the valleys through which the Sydney River, Leitches and Balls creeks flowed were inundated, creating the forked tongue of the Sydney Harbour that has served maritime interests for hundreds of years.
Because the ice sheet was kilometres thick and extended hundreds of kilometres beyond our present shorelines, what is now sea was then land, so all of our marine ecosystems are young. But there was enough time for the instincts of many migratory marine species (such as salmon and needle fish) to drive them up against the impermeable wall of the Canso Causeway in expectation of passage between the Gulf of St. Lawrence and the Atlantic Ocean but to the delight of excited predators such as gannets, whales and humans.
The worst thing we can do to marine ecosystems is to disconnect them from each other. Water connects all the world’s ecosystems, and we meddle
with those linkages at our peril.
The spectacular flooding event connected the new Bras d’Or estuary to a diversity of marine water bodies that surround the island: the Gulf of St. Lawrence to the west and north, the Cabot Strait, Sydney Bight, and Laurentian Channel to the east, and the Eastern Scotian Shelf to the south. The connections make the 1,200 km2 Bras d‘Or Lake a hotspot of aquatic biodiversity that, with its 2,400 km2 watershed, was deemed worthy of Global recognition as a Biosphere Reserve in 2011 under the UNESCO’s Man and the Biosphere program.
Each of the surrounding marine ecosystems has its own distinct environments and habitats for marine life that sustains itself and us: sponges, corals, shellfish and vast stocks of groundfish abound in the highly productive waters between here and Newfoundland and on the Scotian Shelf. The latter is home to Canada’s newest marine protected area on the St. Anns Bank just east of Scatarie Island
(itself a Provincial Wilderness Area surrounded by rich fishing grounds). The gulf, itself an extension of the St. Lawrence River estuary, adds abundances of oysters, scallops, shrimp, crab, eels, herring, tuna, seals and whales) to the mix of biodiversity.
Species living and visiting in the much less productive Bras d’Or estuary are mainly a subset of what is outside (especially in the gulf) including jellyfish, oysters and cod, as well as transient rarities such as ocean sunfish and leatherback turtles.
The lake also has its peculiarities, including fresh-saltwater crossover species like brown trout, salmon and eels; invasive species such as green crabs and a particularly nasty oyster parasite; as well as some relict species of shrimps and worms that can only be found elsewhere in the Arctic. Hundreds of barrachois ponds along the Bras d’Or shoreline form a necklace of nested, mini-ecosystems that are unique in their variety of forms and functions, providing a habitat buffer between the land and the lake in many places.
It is largely the pattern of water currents driven by winds, tides and coastal runoff that define the distributions of life forms and productivity of these marine ecosystems. Currents carry nutrients, plankton and the reproductive stages of hundreds of species form sources to sink locations, and also mix water between the seabed and the surface of the water column. The massive outflow of the St. Lawrence River moves surface waters out of the gulf through the Cabot Strait (some flows into the Bras d’Or Lake), while deep, near bottom currents through the Cabot Strait replace some of that water.
The Labrador Current also has a diversion into the gulf, which exits to the northwest Atlantic
past Cape Breton, carrying a great deal of ice in spring. The convergence of flows out onto the Scotian Shelf forms the headwaters of the Nova Scotia current, which flows southeast along the coast of the province from Glace Bay to Pubnico. The warm waters of the gulf stream, well to the south in the northwest Atlantic Ocean, sometimes extend onto the Scotian Shelf to mix with the cold waters and enrich the diversity of species on the various banks that support our great fisheries.
The hydrodynamic connections between all of our marine ecosystems mean that none may be considered in isolation when trying to understand their ecology, manage our exploitation of their resources, and predict how anthropogenic climate change and coastal interventions will affect their resilience. We need to know their ability to continue to provide the many ecosystem goods and services on which we have built so much of our culture and economic development.
The ocean is a foreign, dangerous and opaque realm for most people, so the unknowns greatly exceed the knowns about our wonderful marine heritage. We need more local scientists committed to marine ecosystem research and management.
“The ocean is a foreign, dangerous and opaque realm for most people, so the unknowns greatly exceed the knowns about our wonderful marine heritage.”
On a personal note, near the end of a long career conducting research in many of the world’s oceans, I count myself privileged to have the opportunity
to study in the ocean sector at Cape Breton University.