Biogeomorphological inheritance: The legacy of past landforms constrains future tropical coastal landscapes

Abstract

Coasts are some of the most dynamic environments on Earth. Coastal systems comprise physical environments together with a biological component, and, for much of the world, a human element, which in many cases imposes anthropogenic stresses. The biological component is especially prominent in the tropics, and the biogeomorphology of these coasts is dominated by the role played by key organisms: corals, which form impressive coral reefs, and mangroves, which fringe low-energy shorelines. Whereas the present is the key to the past, the past also sets the stage on which future changes play out. Coral reefs have played a prominent role in deciphering the trajectory of past sea-level change, and modern reefs are often founded on older Pleistocene reefs. Inheritance is apparent both at the scale of interglacial highstands and in terms of the Holocene landforms that characterise reef-top habitats. The stratigraphy of mangrove environments reveals their more passive response to sea-level rise, constrained by accommodation space provided by the prior topography. The suite of landforms that have developed during the past few millennia have resulted in a variable coastal landscape. Tidal incursion into low-lying terrain enables mangrove establishment, re-occupying former channel courses. The trajectory of past landform change has been contingent on biogeomorphological history, and the future response of these tropical systems will also reflect in part the legacy of their geomorphological evolution. The role of inheritance is investigated with respect to reef and wetland environments, illustrating how past coastal landforms predispose future response.