RIPE, juicy and delicious in jam, fresh blackberries are a joy for foragers. But in the Galapagos Islands, they only leave a sour taste in the mouth.

Following a trail around the twin sinkholes of Los Gemelos on Santa Cruz Island, my guide, Blanca, explains how native scalesia forest was attacked by brambles.

Feral goats, she continues, as we peer into a crater almost 700m deep, where the animals once resided, too wreaked havoc on the delicate landscape too. Yet when they disappeared, one of their food sources, blackberries, flourished.

In a scenario akin to the ‘Old Lady Who Swallowed A Fly’, it’s just one of the many unfortunate chain reactions caused by disrupting nature, a problem the Galapagos Islands know only too well. Unwittingly or not, invasive species were introduced to this far-flung Ecuadorian archipelago, 600 miles off the west coast of South America, by humans, who – some might argue – were the most damaging addition of them all.

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It’s a dichotomy environmentally-conscious visitors to Galapagos now face. As much as we want to witness the unique creatures and plants that thrive on these volcanic outcrops in the Pacific Ocean, our mere presence potentially does them harm.

One organisation hoping to restore and maintain balance is the Charles Darwin Foundation, an NGO set up in 1959, which celebrates its diamond anniversary this year.

The visitor centre on Santa Cruz is also the resting place of Lonesome George, the Pinta Island giant tortoise, whose death in 2012 marked the extinction of his sub-species.

I was lucky enough to see George alive shortly before he died, now the embalmed wrinkled rarity stares back at me from a glass cabinet in a humidity and temperature-controlled room, which visitors can only enter for six minutes at a time. What could be interpreted as a macabre showpiece turns out to be something far more chilling – an example of what might happen to other island inhabitants unless we all take note.

The latest major threat is the philornis downsi fly, whose larvae hatch in the nests of mangrove finches and crawl into the nostrils of young chicks. The number of these feathered creatures, found only on Isabela island, now stands at less than 100, making them the most endangered bird in Galapagos. Another issue is plastics, currently the scourge of our wild planet. Debris is not only potentially poisonous when ingested by birds and marine creatures, it also carries invasive algae in its crinkles and folds.

Influenced by three ocean currents, Galapagos has become a dumping ground for rubbish washed into the sea, and beach clean-ups are one of the key priorities for the Galapagos Conservation Trust. Over the course of last year, plastic bags, straws and Styrofoam cups were banned, part of a growing movement to make the Galapagos Marine Reserve plastic-free.

Although only one per cent of land is for human habitation, with the remainder devoted to National Park, tourism here has boomed in the past decade and there is even talk of direct flights launching from the mainland.

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For now, though, it’s the wild island – a sentiment perfectly summed up in the four (canvas) walls of Scalesia Lodge, a collection of luxurious safari-style tents pitched on platforms in the forested highlands. The largest of the archipelago’s 19 islands and scores of islets, Isabela is a mass of twisted lava and five active volcanoes, including Sierra Negra, which erupted last year.

There are no roads in the northern sector, with several landing sites accessed only by expedition cruise ships, but the south has a community of bars at Puerto Villamil, overlooking flamingo-filled lagoons and beaches sprawled with marine iguanas.

One of the area’s geological wonders is Los Tuneles, a series of flooded lava tunnels. Nearby, an area has been designated for snorkelling, presenting some excellent opportunities for marine wildlife viewing. Green sea turtles casually glide alongside me, unperturbed by the human-shaped obstacle in their path. Duck-diving into a cave, I discover a shiver of white-tipped reef sharks sleeping and circling. Again, not one of them seems to notice I’m there.

But the best surprise comes in the smallest form – a male Pacific seahorse, anchored to the seabed by its prehensile tail. Like a cartoon caricature, it doesn’t look real – a fantasy form only nature could create.

It’s proof, that sometimes little things can have the greatest impact. When it comes to conservation on the Galapagos Islands, baby steps are maturing into giant strides.