beach coast coastline colors colours dune-flora dunes flora grass grasses green greenery growing growth levels low tide natural ocean ocean edge ocean waterline plants receded receding receding tide rough salt-resistant sand sand-dunes Sandbar scrub tidal tides vegetation water waterline glistening glossy high-tide mangrove-growth mangroves ocean-edge ocean-waterline rocks rocky root-network Roots security strength strong support tide aerial aerial roots layers mangrove growth pebbles root network birds gulls pelicans seabirds seagulls waterbirds backdrop background coastal conservation conserve conserving contrast contrasting cultivation environment environmental foliage leafy leaves light nature path track sand dunes