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 naturalist guide, Blanca, explains how native scalesia forest was attacked by brambles, suffocating the broccoli-like trees endemic to this biologically sensitive archipelago.

And then there were the feral goats, she continues, as we peer into a crater almost 700 metres deep, where the animals once resided. They too wreaked havoc on the delicate landscape. 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.

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 sexually ineffectual 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.

Protecting the islands' native residents is a daily struggle, science director Maria Jose Barragan Paladines tells me, on a private guided tour the centre.

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. In this case, survival of the fittest doesn't seem fair.

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 (GCT). 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.

But, admits Anne Guezou, outreach and education coordinator for the GCT, it's not that straightforward. Bans are only guidelines and no penalties have been put in place. In fact, when I landed at Baltra airport only days earlier and purchased a coffee in the neighbouring kiosk, I was presented with a plastic teaspoon, and several stores I pass continue to stock drink cartons with plastic straws.

These shortfalls shouldn't detract from the bigger picture, though; both the Ecuadorian authorities and residents of Galapagos have made great progress in protecting this UNESCO World Heritage Site.

A shining example is Isabela, one of the four inhabited islands, which now uses 100% renewable energy thanks to a new hybrid electricity generation system combining solar power and, bizarrely, a biofuel derived from a tropical nut.

Although only 1% of land is for human habitation, with the remainder devoted to National Park, tourism here has boomed in the last decade and there's even talk of direct flights launching from the mainland.

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, with a dining and lounge area in a modernist concrete building, that could have been masterminded by the Bauhaus school.

Entwined rose pearl trees form a tunnel leading to the entrance; their pom-poms of white flowers paving the way with a carpet of fallen petals. Very soon, after some strict negotiations with Isabela's Arnaldo Tupiza Tortoise Center and the promise of 24-hour surveillance, general manager Felipe de la Torre tells me a giant tortoise sanctuary will open on the property, with a view to eventually releasing the animals into the wild.

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 buzzy 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 and archways, where reef sharks navigate an aquatic maze and blue-footed boobies dance around pillars of cacti. 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, and a circus of rainbow wrasse, yellow-tailed surgeonfish and panamic sergeant major perform a somersault of colours before my eyes.

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 hare maturing into giant strides.

How to get there

Chimu Adventures (; 020 7403 8265) offers a 12-day land based 'Highlights of Galapagos, Guayaquil and Quito' tour, starting from £5,735 per person (two sharing). Includes a stay at Scalesia Lodge in luxury safari tents on Isabela Island, with a selection of daily excursions, transfers and internal flights.