Sea otters, sea urchins and algae

When Europeans settled the Alaskan coast in the 19th century, they created a trade in sea otter pelts that led to the disappearance of the species in the region. In the absence of the otters, the sea urchins they love swarmed. They have eaten up all the kelp, the large brown seaweed that can grow to tens of metres in length and line the coasts of the North Pacific. The kelp forests have disappeared, leaving small fish unprotected and the coastline bare to the ocean waves. This “ecological cascade” is an emblematic example of the massive impact of the extermination of a single species on an entire seascape.

Fortunately, the transformation is reversible: as soon as otters were reintroduced to Alaska in the late 1960s, they went back to fishing for sea urchins. Where they thrive, the kelp forests are less ferociously browsed, and gradually recover. All’s well that ends well? Not completely, because, apart from sea urchins, otters love to eat shells. They bring them to the surface and, floating comfortably on their backs, they smash them with pebbles. From the shore, otters can easily be seen treating themselves to a platter of seafood, then grooming themselves vigorously with their offspring. Even the most hardened of scientists describe the sight as “wonderfully adorable”. The First Peoples of southern Alaska, whose livelihoods include shellfish harvesting, are not entirely enchanted. Local communities see the otters as competitors, and have obtained hunting licences, greatly reducing the populations of the small marine mammals near the village of Sitka in the Alexander Archipelago.

Is it impossible for fishermen and otters to live together? Researchers from the University of California at Santa Cruz have been looking into this question (1) . For three decades, they have studied otters, sea urchins and kelp near Sitka and in Torch Bay, an uninhabited area in southern Alaska. They have traced the ups and downs of the ecological cascade associated with otters: with them come kelp forests. However, beyond these major trends, they identified a mosaic of coastal micro-habitats, within which otters have very restricted territories: females spend their entire lives within a 10-25 km radius, and the animals avoid areas where they are likely to encounter their predators, killer whales and great white sharks.

In the infinite landscapes of Alaska, an ecological balance is therefore likely to be established naturally; local communities do not necessarily have to choose between otters and shellfish, ecotourism and fisheries. As the authors of the study note, this hypothesis is reinforced by “archaeological evidence that indigenous people in the Pacific Northwest had access to distinct areas where shellfish and sea otters were abundant”.
(1) Gorra et al. (2022) Southeast Alaskan kelp forests: inferences of process from large-scale patterns of variation in space and time. Proc. R. Soc. B 289: 20211697.

The flycatcher and COP26

As COP26 draws to a close, with little hope for a real transformation of our ways of doing things, let’s take a look at past climates and their impacts on wildlife. We are living in the Quaternary Era, which began 2.58 million years ago; a straw in the history of the Earth, but a period with a particularly tormented climate: no less than 50 climatic oscillations of varying magnitude and duration, and between 8 and 10 ice ages in the last 800 000 years alone. Many of the species we see, including the smallest birds, existed millions of years ago. I find it absolutely fascinating that they have come through all these crises, adapting to dramatically changed temperatures and landscapes.

This is what colleagues have shown in a recent study led by Vera Warmuth from the University of Munich (1). The scientists looked at the genetics of the black flycatcher, a passerine bird weighing about ten grams and smaller than my hand, which nests in forests, parks and gardens in Eurasia, feeding on insects. The research team determined the DNA mutations in different flycatcher populations from Spain to Norway. The frequency of these mutations allowed them to date the exact moment when these populations split from each other. They found that these divergences correspond closely to major climatic events, including global temperature fluctuations sometimes exceeding ten degrees.

This was the case approximately 130,000 years ago, with an abrupt period of cooling that turned European forests into tundra and damaged flycatcher populations. At the end of this episode, around 110,000 years ago, flycatchers recolonised the spaces that were once again habitable, with distinct populations in the Iberian Peninsula compared to the rest of Europe. This early differentiation of Iberian flycatchers is surprising, as it was previously thought that it only appeared after the very last ice age, some ten thousand years ago. As Jacques Blondel, a specialist in the evolution of birds at the CNRS, confirms, “today’s biodiversity is a legacy of the climatic oscillations that have punctuated the last two million years. The study by Warmuth and colleagues has the great merit of specifying the tempo and mode of this differentiation with the help of a precise example.

The flycatchers in my area are currently wintering in sub-Saharan Africa and I cannot ask them about the posturing of COP26. It is highly likely that the ongoing warming will again transform their ranges and affect their population sizes. Recent studies show that it is already disrupting their migration, forcing them to return to Europe about ten days earlier (2). In their nesting areas, they will find landscapes devastated by intensive agriculture and modern forestry, where the insects essential to their survival are becoming rare.

(1) Warmuth, Vera M., et al. (2021) “Major population splits coincide with episodes of rapid climate change in a forest-dependent bird”. Proceedings of the Royal Society B. 288.1962: 20211066.

(2) Helm, Barbara, et al. (2019) “Evolutionary response to climate change in migratory pied flycatchers”. Current Biology 29.21: 3714-3719.

Environmental chronicle : The snow bunting, feathered flake

As every year since 2004, our team from the CNRS and the French Polar Institute Paul-Emile Victor has been on the east coast of Greenland, in Ukaleqarteq, to study the animals (end). Today, the snow bunting.

At 4 a.m. they wake me up again. I can hear their little paws drumming above my head. Although they weigh only 35 grams, they make a hell of a racket. A whole family of snow buntings is hunting for insects and spiders in the permanent Arctic summer sun. Around 4 a.m. the sun comes out from behind the mountain and warms the dark shingled roof of our Greenlandic hut.

This sudden rise in temperature animates the invertebrates, which the buntings chase frantically. Several groups of four or five youngsters are accompanied by their mothers, from whom the youngsters beg for food with loud chirps.

The young buntings were born two weeks earlier in a rock crevice, a nest carefully chosen by their parents to be out of reach of ermines and foxes. These highly secure quarters are rare, and the males return from migration as early as April to guard their chosen nest and wait for the previous year’s mate.

They then face near-winter conditions, with temperatures often close to -30°C and blizzards that completely cover the birds huddled in the wind. They move around and rest in small groups but, unlike the penguins in Antarctica, they do not huddle together to better cope with the cold: they prefer to shiver, lying in the snow or in a rocky crevice, a few dozen centimetres apart.

Incredible buntings, which alone among the passerines (1) have managed to colonise the very high latitudes in the north of the globe. They nest all along the coasts of the Arctic as far north as Greenland, thanks to an extraordinary metabolism and sometimes a little help from humanity. In the cold, the buntings come close to the houses, to take advantage of the bread crumbs but also to peck at the grasses that surround the Inuit villages.

This vegetation is fertilised by the faeces of the inhabitants and the sled dogs, which are themselves mainly fed with the products of hunting marine mammals, birds and fish. Indirectly, some snow buntings are thus saved from the polar cold by the abundant marine resources of the Arctic.

These buntings, satisfied with the service, spend the whole winter in Greenland. The others migrate from West Greenland to the Great Lakes region of North America, or from East Greenland to the northern Caspian Sea in Russia. These long-distance journeys are made at high altitude and at night, using the Earth’s magnetic field as a compass. But navigation is not without its faults and some get lost, like this beautiful male that appeared in the Chausey Islands (Normandy) in the spring of 1994, which was already calling me towards Greenland.

(1) Small birds belonging to the order Passeriformes, which includes more than half of the 10,000 bird species.

Environmental chronicle

In Brittany, gannets are on the decline

September 2021: There are plans for a marine extension to the natural reserve of the Sept-Iles archipelago in Brittany. This marine extension may include a quiet zone, closed to marine traffic between April and August each year. The quiet zone will be essential for rafts of northern gannets and other seabirds, the Sept-Iles being the most important seabird breeding area in metropolitan France. Unfortunately, this plan for a quiet zone is meeting the fierce opposition of local recreational sailors, who see the plan for a marine extension to the Sept-Iles terrestrial reserve as an attempt to their “freedom”. I wrote a tribune in Libération, explaining why this marine extension and the quiet zone are essential for seabird conservation: En Bretagne, les fous de Bassan battent de l’aile.

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