MARERENI, Kenya — The scorching afternoon sun stretches across the semiarid landscape of Marereni, in Kenya’s Kilifi county, where salt and sea shape both the land and the lives that depend on it. Known for its extensive salt mining operations, this remote settlement lies at the heart of the country’s north coast salt belt. Yet beyond the glint of salt pans, Marereni is also home to one of the coast’s most vital ecosystems: a mosaic of fringing, estuarine and creek mangrove forests that support rich biodiversity. This is the stunning backdrop to the site of restoration projects aimed at both revitalizing these important mangroves — and the communities that tend to them.

In recent years, Marereni’s mangroves have been disappearing due to conversion pressure for solar salt works, aquaculture and human settlement, according to information from the Kenyan government’s National Mangrove Ecosystem Management Plan 2017-27. The plan underscores that the loss of mangrove cover significantly weakens coastal protection, leaving shorelines more susceptible to erosion, storm surges and rising sea levels. This not only heightens the vulnerability of inland areas and infrastructure to climate-related risks but also disrupts vital marine ecosystems, degrading crucial breeding and nursery grounds for fish, crustaceans and other species, leading to declining fish stocks and reduced biodiversity.

For coastal communities, such as those in Marereni, the loss of mangroves threatens their very livelihoods. Many depend on mangrove ecosystems for fisheries, fuelwood, construction materials and a range of other vital services. As the mangroves vanish, so do economic opportunities, exacerbating poverty and food insecurity in these communities.

Since 2022, a California-based nonprofit organization called Seatrees (formerly known as Sustainable Surf/SeaTrees) has been working with communities in Marereni to restore and protect coastal and marine ecosystems as a natural solution to climate change. This follows similar work the organization began in 2020 in another coastal location called Mida Creek.

“As a fisherman, I saw the value in joining this initiative,” says Emmanuel Gona, from Muyu wa Kae village in the Marereni project area, who has worked with these efforts since 2020. “Restoring and planting mangroves helps boost fish populations, which means better catches — and a better income for people like me.”

Most of Seatrees’ projects globally have been funded through traditional means, including corporate and individual donations and grants. But in 2024, Seatrees started offering donors the option of buying $3 “biodiversity blocks,” each of which represents a single tangible conservation action: planting one mangrove tree on site in Marereni.

Seatrees touts these “blocks” as part of the world’s first marine biodiversity credit program, designed to restore and protect natural marine ecosystems that historically have been relegated to the sidelines of conservation funding. Despite covering more than 70% of the globe and playing a crucial role in regulating the Earth’s climate, the ocean remains an afterthought in global conservation funding. According to a 2022 U.N. report, marine protected areas globally receive approximately $980 million annually — roughly 4% of the $23 billion allocated to terrestrial protected areas each year.

“There’s a dual crisis that the world is in right now — climate change and biodiversity loss. And these two things are deeply intertwined. Yet, the ocean has been largely missing from that story,” says Michael Stewart, a director and co-founder of the organization.

The concept of marine biodiversity credits comes on the heels of recently developed land-based biodiversity credit programs, which fund projects such as forest conservation and species habitat restoration. They work by assigning financial value to measurable conservation outcomes, allowing buyers to support specific biodiversity gains in exchange for standardized biodiversity credits. These credits can then be used by companies or individuals to meet voluntary environmental targets or demonstrate a commitment to biodiversity stewardship. But they remain a controversial funding mechanism, with some critics saying they risk becoming tools for greenwashing if not rigorously monitored and could distract from the need for stronger regulation and direct environmental action. The difference between Seatrees’ biodiversity credits and ordinary online donations remains somewhat nebulous.

When asked, Kevin Whilden, co-founder and director of Seatrees, says the goal of their project is to shift conservation financing away from one-time donations and toward a long-term, scalable model. “Instead of treating initiatives such as tree planting or coral reef restoration as isolated projects, our biodiversity blocks promote continuous stewardship, aligning with the 2030 U.N. Sustainable Development Goals.”

On the ground in Marereni, so far, Seatrees has issued 300,000 marine biodiversity credits totaling $900,000, mostly through individual buyers and small companies. A Seatrees count earlier in 2025 showed they had already planted 190,000 mangrove trees, with 30,000 new trees planted each month. Seatrees estimates all 300,000 mangrove biodiversity blocks will be planted by July.

Restoring Marereni’s mangroves

In Muyu wa Kae, a fisherman mends his net beneath the shade of a swaying coconut tree, the breeze carrying whispers of the retreating waves. Along the shore, wooden boats rest on the damp earth, waiting for the tide’s return, while tiny crabs scuttle in and out of their burrows, dotting the exposed seabed near the mangrove trees.

Muyu wa Kae is an area within the Seatrees restoration site, which covers 600 hectares (1,483 acres). The work here is carried out in partnership with a local NGO called Community Based Environmental Conservation (COBEC). Seatrees sends funding to COBEC, which implements projects on the ground. (The two groups also partner on mangrove planting in Mida Creek, which isn’t part of the marine biodiversity credits initiative.)

COBEC’s approach goes beyond just planting trees. The organization works directly with local communities, ensuring they benefit from restoration efforts. “You can’t implement conservation projects without community participation,” says Edward Mwamuye, COBEC’s program manager. “We invest in livelihood enhancement programs such as smart agriculture, beekeeping and small businesses.”

Community members form their own groups and turn mangrove restoration into a livelihood by establishing and maintaining mangrove nurseries. COBEC and Seatrees support the groups by providing some materials used in growing propagules, which group members nurture over the course of several months until they are ready for planting. COBEC then purchases the saplings for its Seatrees project sites, where mangroves have been degraded from tree cutting for fuel and home construction, sand deposition or livestock grazing. (The nurseries also sell to other organizations.) With the income earned, some groups are able to start small side businesses such as goat rearing.

Currently, there are more than 30 project groups in Marereni involving 640 community members (218 men, and 422 women). These groups cultivate four species of mangrove native to the Kenyan coast: Rhizophora mucronata, Avicennia marina, Ceriops tagal and Bruguiera gymnorrhiza. This initiative has become the primary income source for participating community members.

Zena Hamisi, chairperson of the Neema Muslim Women Group in Marereni’s Mto wa Mawe Creek, says the project has uplifted her and her fellow members. “COBEC has held our hand and supported us to a point where we now earn income,” she says. Each sapling sells for 20 shillings (about $0.15). Half the earnings are shared among group members and the other half go into a savings account for other income-generating projects. For example, Hamisi says her group members used their savings to buy a maize shelling machine that they rent to farmers during harvesting season.

Hamisi stresses the impact of mangrove restoration on local livelihoods, particularly fishing: “Marereni residents’ main source of income is fishing, and when mangrove numbers declined, fish catches also went down. Since we started restoring them, we have seen improvement.” However, illegal mangrove cutting remains a problem, and she calls for more education. “Some people know it’s wrong but still cut them, saying these trees, even if cut down, will just regenerate,” she says.

Hamisi says she believes Seatrees’ work with COBEC is impactful but suggests increased engagement. “More community members should be educated about them. They should visit Kenya regularly, monitor progress and support us in long-term projects such as crab cage farming.” She warns that environmental projects have a time limit. “Once the trees are restored, what next? Sustainable projects such as crab cage farming could provide income for generations.”

One strategy Seatrees and COBEC use to address illegal deforestation — a major obstacle to mangrove restoration — is COBEC’s Treeducation Scholarship Fund. The initiative offers 300 scholarships over 10 years to members of local communities, aiming to support school fees and the establishment of woodlots to grow non-mangrove trees that could be cut as an income source, helping to shift the logging pressure away from mangrove forests.

“The plan is to maintain and expand the education fund throughout the [10-year] lifespan of the biodiversity blocks project,” says Orion McCarthy, Seatrees’ science lead.

Gona, the Muyu wa Kae fisherman, says that before the restoration efforts, fishers barely caught fish worth 500 shillings (less than $4) per day, but now they can make between 900 and 1,000 (up to $7.75). “The improvement is clear, especially if you go fishing at night,” Gona says. Research has proven that mangroves often support rich fish and crustacean communities.

However, Gona acknowledges that men’s participation in the conservation effort remains low. His group has only 10 men and 27 women. “Some see this work as women’s work or think it’s for lazy people. In our group, even if we sell 3,000 seedlings, each member only gets about 1,000 [Kenya shillings], which is not enough. People need alternative livelihoods.” He suggests that better communication about the project’s importance and better financial incentives could encourage more men to join.

Measuring and monitoring

Seatrees relies on what it calls a “basket-of-metrics” to assess biodiversity improvements and the success of restoration work across its project sites in Marereni and Mida Creek. This includes field surveys by trained COBEC staff to measure mangrove species diversity, root density, canopy cover, juvenile tree density and the height and diameter of mangroves within representative 10-by-10-meter (32-by-32-foot) plots, each containing roughly 200 seedlings, in order to estimate aboveground biomass. They also assess crab and snail diversity and abundance. Scout patrols cover a range that extends across 1,248 hectares (3,084 acres). In addition, Seatrees collaborates with Ocean Ledger, a London-based remote sensing company, to analyze satellite imagery showing height, canopy cover and aboveground biomass of mangrove trees in a much larger area than COBEC can access on the ground. The two data sources — field assessments and satellite data — are used together, with each helping to validate and strengthen the findings of the other.

Julius Sila, a mangrove restoration coordinator and GIS expert at COBEC, says assessments happen both before and after restoration work. The baselines are established using comparative data from nearby areas that are considered pristine versus heavily degraded. Then, he says, “after restoration, we will revisit these sites annually [for 10 years], using designated 10-by-10-meter plots for long-term monitoring. By comparing these data points over time, we can determine the extent of biodiversity uplift.” If they find poor survival rates, the area will be replanted with new mangrove seedlings to replace those that failed to establish.

Baseline data for the Marereni site were initially collected between May and September 2024, before planting began in October. The first round of biodiversity data collection is set for October 2025, with findings expected in early 2026. Results will be publicly available.

Globally, despite widespread investment in mangrove restoration, survival rates remain low, according to a 2022 study, due to inappropriate site selection, limited community engagement and planting in unsuitable hydrological or sedimentary conditions. Yet Seatrees and their partner COBEC report a survival rate of around 80% for their planted mangroves. According to Sila, this outcome is due to addressing the root causes of degradation before planting begins, matching species to the right site conditions and using scientific assessments such as soil salinity tests to guide planting. “If all these are addressed, expect success,” Sila says.

Project challenges

Conditions on site in Marereni have presented multiple challenges. Sila says hydrological changes have hindered restoration efforts in Marereni. “Mangroves thrive in creeks with low wave activity and consistent water exchange from the ocean,” he says. “However, sedimentation has altered the ecology of these creeks, creating obstacles for the restoration process.”

The issue arises when creek water becomes stagnant due to blocked pathways, preventing proper tidal flow. “Mangroves are typically submerged in water for about six hours during the tidal cycle. However, due to hydrological changes and sand deposition, some inlet creeks become blocked. This disruption leads to water stagnation or even drying out of mangroves,” Sila says.

Stagnant water, combined with high temperatures and evaporation, becomes increasingly saline, which can cause mangroves to dry up and die. Additionally, beach erosion displaces sand, which can bury young planted sites, hindering their growth.

Another pressing concern is the pollution caused by underground seepage of saline water from nearby salt pans, which border the extensive mangrove forest in Marereni. “Not all of the ponds meet the required standards. This leads to underground seepage, which negatively impacts the surrounding environment, including the mangroves,” Sila says, adding that they do not yet have funds to address such issues.

Still, despite these challenges, Seatrees and COBEC remain committed to restoring Marereni’s mangrove forests and ensuring long-term sustainability — and the local communities say they remain committed as well.

Banner image: Emmanuel Gona, a fisherman and community scout from Muyu wa Kae village in Marereni, says he believes conserving and restoring mangrove ecosystems is key to boosting fish populations. Image by Juliet Ojwang.

Citation:
Lovelock, C. E., Barbier, E., & Duarte, C. M. (2022). Tackling the mangrove restoration challenge. PLOS Biology, 20(10), e3001836. doi:10.1371/journal.pbio.3001836