# Satellite view reveals tide-fed biodiversity in Guinea-Bissau

> Eighty-eight islands and islets spread across Guinea-Bissau's coast, then seem to enlarge as the sea pulls back. A July 17 NASA Earth Observatory release uses a Landsat 8 image to show that daily transformation in the Bijagós Archipelago. The image was acquired...

Canonical URL: https://www.argo.net/satellite-view-reveals-tide-fed-biodiversity-in-guinea-bissau/
Byline: NASA Earth Observatory
Published: 2026-07-25T11:15:03+00:00
Categories: News, Oceans

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Eighty-eight islands and islets spread across Guinea-Bissau's coast, then seem to enlarge as the sea pulls back. A July 17 [NASA Earth Observatory release](https://science.nasa.gov/earth/earth-observatory/a-tide-fueled-trove-of-biodiversity-in-guinea-bissau) uses a Landsat 8 image to show that daily transformation in the **Bijagós Archipelago**. The image was acquired on November 28, 2025, by the satellite's **Operational Land Imager**. At relatively low tide, pale sandflats and mudflats spread around green islands and dark blue channels. NASA describes the scene as a view of coastal habitat that helps sustain birds and sea turtles.

The striking image is a snapshot, while the living system follows a repeating tidal schedule. Water moves through sandy channels twice each day, covering and uncovering broad flats beside mangroves. That rhythm brings food within reach for wildlife and then changes the places where animals can feed, shelter, or travel. The archipelago's value comes from this linked mosaic of shore, shallow sea and forest, as well as from the forces that build and reshape it.

![Source_thumbnail_1](https://www.argo.net/wp-content/uploads/2026/07/source_1.jpg)

## A coastline that changes by the hour

Low water exposes **intertidal mudflats** and sandflats that were hidden only hours earlier. In a satellite image, the exposed ground makes the islands look much larger. As the tide returns, water covers those surfaces again and threads through the channels. The change is especially vivid from orbit because land, shallow water and deeper water reflect light differently. On the ground, it is the ordinary timetable that organizes each day's opportunities for the animals living along the coast.

Intertidal habitat lies between the usual high- and low-water marks. It is a demanding place for organisms because temperature, saltiness, waves and exposure can shift quickly. Yet the [intertidal zone](https://oceanservice.noaa.gov/facts/intertidal-zone.html) can be rich in life. Worms, crustaceans, mollusks and small fish use its sediments and shallow pools. When the flats emerge, birds can reach prey that water had kept out of view.

Along the Bijagós shore, **mangrove forests** add another layer to the tidal landscape. Their roots help hold sediments in place and create sheltered water among the trees. NASA reports that manatees, dolphins and schools of fish move closer to the islands at high tide, with fish entering deeper into the mangroves. The same water that reveals feeding flats at low tide also connects these protected spaces as it rises.

Orbiting sensors provide a useful record of that changing pattern, especially when images are compared across dates and tidal conditions. The November view shows broad exposed flats, but it cannot show every channel's depth or the number of animals below the water. Local observations, field surveys and tidal measurements remain essential for those details. The satellite perspective contributes something different: a wide view of habitat extent that would be difficult to assemble from one place on shore.

## Why the tide runs so high

The scale of the water-level swing helps explain why the scene looks so dramatic from space. A 2025 paper in *Estuarine, Coastal and Shelf Science*, [Tidal amplification and distortion in Guinea-Bissau, West Africa](https://doi.org/10.1016/j.ecss.2025.109318), examined the regional tide. Its authors found that the area can experience a **tidal range** of up to 7 meters, or 23 feet. NASA contrasts that with roughly 1 meter in many other parts of the West African coast.

The researchers linked that amplification to the region's **wide, shallow shelf** and to the shape of the estuary. Those features can alter the way a tidal wave travels toward land. Water moving over a shallow seabed can slow and pile up, while a narrowing or shaped coastal setting can further change its height and timing. The study examined tides rather than the abundance of particular animals. Its result supplies physical context for the enormous area that appears and disappears around the archipelago.

Measurements from space also played a role. The team used **satellite altimetry** data from the NASA and CNES TOPEX/Poseidon mission and from Jason-1 and Jason-2 to help validate its findings. Altimeters measure the height of the sea surface from orbit. The long record from [TOPEX/Poseidon](https://sealevel.jpl.nasa.gov/missions/topex-poseidon/summary) and later missions gives coastal scientists another way to compare models with observed water levels. Landsat offers a different kind of evidence, a detailed view of the shore's changing surface.

A tidal range describes the difference between high and low water, so it captures the vertical scale of a cycle rather than the full story of each tide. Winds, weather, river flow and the shape of local channels can still affect conditions at a particular place and time. The 2025 analysis addresses the large-scale processes behind the regional pattern. Its 7-meter figure helps readers interpret the sweeping change visible around the islands in the Landsat scene.

## Feeding grounds on the East Atlantic Flyway

Every exposed flat can become a feeding area. UNESCO estimates that the archipelago supports about **870,000 migratory shorebirds**, making it one of West Africa's most important feeding areas on the **East Atlantic Flyway**. This migration route links Arctic and northern European breeding regions with African wintering grounds. Birds arriving along the route depend on dependable places to refuel and the Bijagós flats supply prey in a setting renewed by the tide.

That bird count belongs to the broader [Coastal and Marine Ecosystems of the Bijagós Archipelago](https://whc.unesco.org/en/list/1431/), which UNESCO inscribed on the World Heritage List in 2025. UNESCO calls it the only active deltaic archipelago on Africa's Atlantic coast. River sediments, coastal currents, upwelling and tides meet there. Together they create conditions that support a large variety of coastal habitats and species, from the open flats to the forested shore.

For a shorebird, the important detail is often small enough to miss in a satellite view. A probing bill finds a buried worm. A bird picks a crustacean from wet sediment. Each successful meal depends on the timing of exposure, the amount of prey in the flat and safe space to feed. The Landsat image cannot count those animals. It shows the expansive habitat that makes such feeding possible and helps explain why this coastline is so important at a continental scale.

The two scales belong together. Bird surveys establish how many migrants use the region, while satellite images reveal the shape and distribution of the places they use. Repeated imagery can also show where flats, channels and vegetation lie during different conditions. That information can help frame questions for fieldwork. NASA's image is therefore most powerful as a landscape view, placing wildlife observations within the dynamic geography of the archipelago.

## Sea turtles and a protected island refuge

The archipelago also supports large numbers of **green sea turtles**. NASA notes that tens of thousands move inland toward sandy beaches during the nesting season. A major nesting concentration occurs on tiny **Poilão**, within João Vieira and Poilão Marine National Park. Sandy beaches, productive nearby waters and the wider protected archipelago all matter to turtles at different stages of their lives. The satellite image captures part of that connected coastal setting, including the waters and shorelines around the nesting beaches.

Hatchlings face danger as soon as they emerge. NASA describes nighttime runs toward the water while crabs, lizards and birds hunt near shore. In shallow water, jacks, barracudas, groupers and snappers are among the predators. Tuna, mackerel, sharks and rays pose further risks offshore. NASA cites estimates that fewer than 1 percent of green turtle hatchlings reach adulthood. Such figures summarize a long and hazardous life cycle and survival can vary with place and conditions.

World Heritage recognition draws attention to the archipelago's extraordinary natural value, while its habitats remain dynamic. Tides keep moving sediment, water and food through the system every day. Protecting a place like this involves the beaches where turtles nest, the waters they cross, the mudflats used by birds and the mangroves that line the islands. The satellite view brings those connected habitats into one frame.

Seen from hundreds of kilometers above Earth, the November 2025 Landsat scene makes the boundary between sea and land look temporary. For the archipelago's wildlife, that moving boundary is a source of food, a travel route and a sheltering network. NASA's 2026 feature brings that daily process into view while pointing to the ecological importance of Guinea-Bissau's tidal flats, mangroves, beaches and islands.