Yassandra Marcela Barrios Castro is talking to a small group of fishermen on the shore of Tierra Bomba, an island off the coast of Cartagena in northern Colombia. She's the only woman in the group, and the men, all around her father's age, are gesticulating wildly at her. But the 19-year-old remains calm and self-composed, as she explains how destructive their practice of blast fishing is to the reef and its inhabitants.

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The fishermen of Tierra Bomba have been using dynamite to fish for decades and it isn't easy to be told they're doing it all wrong — particularly by a teenager.

"It is very easy for men to dismiss me because I am a girl," says Yassandra. "And age is something that's respected here, so for a young woman to stand up and say that an old tradition is wrong, and is damaging the ocean… well that's not an easy task."

Destroying the island's livelihood

Yassandra lives in Boca Chica, on the south coast of Tierra Bomba. The island is surrounded by coral reefs and its 9,000 human inhabitants rely heavily on the ocean for food. But blast fishing and trawling are tearing apart the very ecosystems that provide the community with a living.

"There are a lot of people here who are not conscious of what their actions are doing," Yassandra says. "They are damaging the ocean and I'm so worried that it will be forever."

Many islanders struggle to make ends meet and there are few educational opportunities. Biologist Valeria Pizarro says this makes it hard to engage the population in environmental issues.

"The people here have more pressing problems," says Pizarro, who has been researching Colombia's Caribbean reefs for decades.

That makes Yassandra, who is studying marine biology at Sinu University in Cartagena, something of an exception.

"I want to know what is happening in the ocean at a deeper level," she says. "The course gives me another, more profound, perspective."

Yassandra is the only woman on her program and travels two hours by boat each day to attend. What she learns, she wants to share with those who haven't had the opportunity to get a formal education, so she organizes community discussions to engage locals in the environmental threats they face.

"I'm trying to explain that if we protect the reef and our ocean then more people will come to see it, and it may bring some money to our island," she says. "And also, if we completely destroy the reefs then we will have nothing to fish at all."

Changing cultural attitudes

Warm, smiling and full of energy, Yassandra has a knack for winning people over. Which is fortunate, given the culture she's up against. Pizarro says women here get used to being ignored, interrupted, and having men take credit for their ideas.

"If you want to speak, to be heard and to make a change you have to have a strong personality and be able to deal with gossip and being called 'hysterical,'" Pizarro says. "You have to be able to speak loudly, and be brave enough to interrupt."

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The issues Yassandra is raising also touch on a point of male duty and pride: bringing in a decent income to support the family. It's all very well telling people their work has environmental consequences, but, Pizarro admits, "change is very difficult when you are poor."

"I always struggle to 'demand' a change from people who are living one day at a time," Pizarro says. "I know overfishing is a big issue for any marine ecosystem, but how can I ask someone that has no money to feed his family to stop fishing?"

The real challenge is to offer alternatives. And there are local projects attempting to do just that. One is a diving school where Yassandra is also a student.

From fishing to tourism

The Paraiso Dive Cartagena, as the school is called, is teaching young people on Tierra Bomba to dive. The hope is that one day they will be able to earn a living as diving instructors and guides instead of from fishing. 

Colombia boasts 2,900 kilometers (1,800 miles) of coastline. Its Caribbean and Pacific Ocean waters are home to 2,600 marine species, including 155 corals and six of the world's seven turtle species. All this is a major draw for tourists, but most diving instructors and tour guides aren't locals, and that's something Paraiso Dive wants to change.

The diving school also teaches conservation. Researchers come here from all over the world, and often start reef-monitoring projects. When they return home, they can employ locals to continue their fieldwork, thanks to that training.

Christina Kuntz, co-owner of the diving school says she wants to offer young people a way of making a living from the reef without damaging it. "It's really important if you're trying to dissuade people from overfishing that you offer them an economically viable alternative," she says.

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But again, it's harder for female students than their male peers. "The women here have to deal with ingrained sexism," Kuntz says. "They're expected to just stay at home, and are not given the same chances as men."

Yassandra is one of four young women on the diving course. "For them to say, 'yes, I can dive and I know how all this equipment works,' well, that's a pretty big deal,'" Kuntz adds.

A new generation demands change

Breaking new ground in activism and potentially the workplace, Kuntz says Yassandra is "important for females, for Afro-Colombians, for island communities, for marine biologists, and for scuba divers,"

And for the environment she is trying to protect, which is now under pressure from climate change as well as overfishing. Coral cover on Caribbean reefs has decreased from an average of 50 percent to just 10 percent.

"Coral reef degradation and climate change in general will affect marginalized island communities like Tierra Bomba first, so people like Yassandra are critical to protecting such communities and the ecosystems on which they depend," Kuntz says.

Once qualified, Yassandra will be the only marine biologist on the island. "I am part of a new generation that wants to protect my island," Yassandra says. "If I can find a way to join people together to protect our reefs, then our island is going to have a bright future."