On the northern coast of Indonesia's Sumba Island, a stand of mangrove trees appears to dip and sway to summon another dreamy sunrise. Walakiri Beach is gently sloped, so it's easy for a visitor to walk out into the knee-deep water to examine the extraordinary transitional zone of a mangrove ecosystem. Mangroves thrive here at the boundary between land and sea, growing in coastal salt water and low-oxygen conditions where other trees would quickly die. Their complex root systems filter out the salt and form a strong natural defense against storm surges, rising sea levels, and coastal erosion. Mangroves also create aquatic nursery habitats that support a highly diverse range of juvenile fish and crustaceans.