Author: BBC World Service

Coastlines around the world are changing, causing serious problems for the many communities living near the sea, as well as vital and fragile coastal ecosystems.

In the second of a two-part special on coastal erosion, CrowdScience explores the best ways to tackle this problem. Presenter Caroline Steel visits the Caribbean island of Puerto Rico to see the various methods they use to protect their coasts.

First up: ‘riprap’ – rocks strategically placed to keep the encroaching sea at bay. The problem is, while it protects the area immediately behind the rocks, riprap can exacerbate erosion nearby.

But there are other, more nature-friendly solutions, including sand dune restoration. Caroline picks up her shovel and helps to re-plant dunes, destroyed in the past by erosion as well as sand extraction for the construction trade. The roots of these plants stabilise the dunes, while building boardwalks prevents further damage from humans.

Nature also offers the perfect offshore protection against coastal erosion: coral reefs. These are the first line of defence in absorbing the power of the ocean’s waves. Down on the beach, we see for ourselves just how effective they are. The reefs face threats, but restoration plans are afoot. We visit a nursery that grows corals to plant out on the reefs – and find out about corals’ surprising cannibalistic tendencies in the process.

Featuring: Professor Robert Mayer - Director of Vida Marina, Center for Conservation and Ecological Restoration, University of Puerto Rico Nada Nigaglioni - Biology student, University of Puerto Rico Ernesto Diaz - Caribbean Regional Manager at TetraTech Dr Stacey Williams - Executive Director, ISER Caribe

Presenter: Caroline Steel Producer: Hannah Fisher Editor: Cathy Edwards Production Co-ordinator: Liz Tuohy Studio Manager: Emma Harth

(Photo: Coast restoration measures at Ultimo Trolley Beach, Puerto Rico. Credit: BBC)

Join the Unexpected team as they journey beyond the borders of reality to ask why we believe in the illogical.

After a fraudulent psychic dupes 1.3 million Americans, panellist Camilla Mota turns to history for insight into how scientists debunk such con artists. The Unexpected library harbours secrets of paranormal experimentation and dead air live on the BBC, and panellist Phillys Mwatee reveals why our beliefs win out over hard evidence written in ink. Nevertheless, in a world rife with conspiracy and vaccine hesitancy, Melissa Kapulu from the KEMRI-Wellcome Trust Research Programme in Kilifi, Kenya, shares the fascinating scientific obstacles faced in the quest to eradicate malaria from Africa once and for all.

Also hear how a Nigerian pastor and super-star has been making Melissa's job much harder, and life on fake mars. Presenter: Alex Lathbridge, Phillys Mwatee and Camilla Mota Producer: Harrison Lewis, Alex Mansfield and Noa Dowling

Friday, April 13th 2029 – mark it in your calendar. That’s the day an asteroid the size of an aircraft carrier will fly past Earth, closer than some satellites. Don’t worry – it will miss, but it’ll will pass so close to Earth that it will be visible to the naked eye of 2 billion people, particularly in North Africa and Western Europe.

Roland Pease this week attended the Apophis T-5 Years conference at the European Space Research and Technology Centre (ESTEC) in the Netherlands, meeting astronomers scrambling to get missions up to the object to learn what kind of threats such asteroids might pose to us in the future and to discuss the science of planetary defence.

NASA’s OSIRIS-APEX, a follow-on to OSIRIS-REx, will study the physical changes due to the gravitational forces from the Earth as it closely passes us by. But will there be an armada of spacecraft sent to monitor Apophis? The European Space Agency hope to gather support for their own mission, RAMSES.

Presenter: Roland Pease Producer: Jonathan Blackwell

Image Credit: JPL/Caltech

Around the world, coastlines are constantly changing due to the power of waves, currents and tides. Coastal areas are also some of the most heavily populated and developed land areas in the world. So it’s not hard to see how the natural process of coastal erosion can cause serious problems for us.

It’s an issue that’s been bothering CrowdScience listener Anne in Miami Beach, Florida. She can see the beach from her window and wonders why after every storm, several trucks arrive to dump more sand on it.

In this first of two programmes, CrowdScience visits Anne’s home in south Florida and finds out how erosion threatens Florida’s famous beaches. Caroline Steel speaks to geoscientist Dr Tiffany Roberts Briggs and hears why it’s such a problem for this tourist-reliant state. Tiffany explains the delicate balance between natural processes and human infrastructure.

Meanwhile, the Caribbean island of Puerto Rico declared a state of emergency in April 2023 due to coastal erosion. Caroline witnesses the impacts of erosion first-hand, as Ruperto Chaparro shows her abandoned houses crumbling into the sea.

But how can we quantify the rate of erosion? Dr Kevian Perez in the Graduate School of Planning at University of Puerto Rico explains the methods they use to monitor Puerto Rico’s coastlines, and how they are evaluating the effectiveness of different mitigation methods.

However, some of the methods used to protect coastal communities from the encroaching sea have done more harm than good. So what are the best ways to tackle this problem? That’s what we’ll be exploring in next week’s programme.

Presenter: Caroline Steel Producer: Hannah Fisher Editor: Cathy Edwards Production Co-ordinator: Liz Tuohy Studio Manager: Steve Greenwood and Bob Nettles

Featuring: Dr Tiffany Roberts Briggs, Associate Professor at Florida Atlantic University Ruperto Chaparro, Director of Sea Grant Programme, University of Puerto Rico Anabela Fuentes Garcia, Villa Cristiana community leader Dr Kevian Perez, researcher at the Coastal Research and Planning Institute of Puerto Rico at the Graduate School of Planning

(Photo: Puerto Rico after Hurricane Maria. Credit: Orlando Sentinel/Getty Images)