How will the ecosystems change? Glacial melting is shining a spotlight on the science of ecological succession. (via KnowableMag )
, Sandy Milner’s small team of scientists heads north, navigating through patchy fog past a behemoth cruise ship. As thefeeding grounds, distant plumes of their exhalations rise from the surface on this calm July morning. Dozens of sea otters dot the water. Lolling on backs, some with babes in arms, they turn their heads curiously as the boat speeds by. Seabirds and seals speckle floatingSome two hours later, the craft reaches a rocky beach where Wolf Point Creek meets the sea.
This spot — where Wolf Point Creek meets Muir Inlet — is a dynamic place. Once entirely icebound, Muir Inlet is now a watery expanse over 20 miles long. The inlet is part of the even more massive Glacier Bay that boasts more than a thousand glaciers — at least for now. Over the past 200 years, the glaciers here have receded rapidly as the planet has warmed. Alaskan glaciers are among the fastest-shrinking on Earth, making this place a natural laboratory for ecologists.
A historic painting of Muir Glacier, circa 1887/1888. Today, the glacier terminates on land and an alder- and willow-flanked creek meanders down to the waters of Muir Inlet.When the young Milner first arrived, there had been no studies of stream succession, he says. Glacier Bay seemed the perfect spot to start such a project.
En route to sample stream invertebrates at Wolf Point Creek, Sandy Milner’s team navigates through a dense alder thicket. Lush vegetation has grown up in the decades since Muir glacier melted and receded.So much has changed here, a point underlined as we push and shove our way through eye- and leg-poking alder thickets. First detected in the stream after the stream mouth emerged from glacial ice were larvae of chironomids, cold-loving midges. Later, other invertebrates came.
Pink salmon arrive to spawn in an Alaskan stream. Sandy Milner first spotted pink salmon at Wolf Point Creek in 1989. Since then, salmon numbers have exploded.After more than an hour of wading and bushwhacking, we arrive at the sampling site. Our quarry are macroinvertebrates — backboneless animals like midge, mayfly and stonefly that are visible to the naked eye.
Streams coming straight from glaciers are cold, nutrient-poor, turbid and fast-flowing. “All of this creates an ecosystem that is extremely hard to live in,” says Sudlow. So these newborn streams have very limited algal diversity, supporting mostly diatoms — species of small, single-celled algae with glass-like silica shells. Clinging tightly to rocks, “they can handle the worst conditions,” says Sudlow.
Succession as a theory has changed, and continues to change. As Ficetola explains, early work on succession was largely focused on plants. And it was proposed that succession led eventually to a “climax” community — a single stable endpoint based on an area’s climate and geography. Ecologists today recognize that succession is less predictable. Three different successional models dating back to the 1970s were put forward to explain how communities change.
Karson Sudlow and colleagues dislodge algae from rocks in a glacial stream. They use an electric toothbrush for a systematically timed scrub over a rectangular template.Milner has found that what matters most to stream life gradually shifts. Physical factors are the most important at first — especially water temperature and channel stability. Once the water warms, other factors may come into play.
Lakes above streams, including those fed by glaciers, help to regulate whether stream communities can remain stable and maintain the species gains made little by little. Flooding, Milner and colleagues found, acts like a stream time machine. A major flood in 2005 at Wolf Point Creek washed out species and reset stream life to a simpler community like the one in existence 15 years earlier.
They estimated from this exercise that glacier retreat will create over 6,000 kilometers of new Pacific salmon streams by 2100. That could mean, within the area that they studied, 27 percent more salmon habitat compared with today. “We hear so much about loss of salmon populations in the Pacific Northwest,” says Milner. But melting glaciers are “creating unique opportunities for new salmon populations to form.
But in the decade since protection, salmon preferences have changed. In three out of eight recent summers, returning salmon have found the Hanna and Tintina rivers dry. Now streams to the west, like Strohn Creek, fed by the rapidly melting Bear glacier near British Columbia’s Alaskan border, provide new, more favorable spawning habitat. So salmon have begun going there instead.
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