The tropical Indo-Pacific seashores include the classic beautiful tropical beaches, but also host some of the most widespread plants and animals on the planet...
Many tropical seashores are simply the edge of the ancient and stable continental shelves where they meet the ocean. However, other more remote seashores have been created by extreme volcanic activities. Most of the oceanic islands are the result of land being thrust up relatively suddenly from depth due to land movement, and thus many tropical seashores have recent or ongoing volcanic activity. One of the best (and dangerous) places to climb the rim of an active volcano is the island of Tanna, in Vanuatu.
Among the more dramatic and interesting features along exposed coastlines are sea caves.
These are caused by the constant pounding of the ocean against the land. The hitting of constant waves all day and every single day has a huge cumulative effect. When the water hits the land it not only takes material off (the weathering), it also takes it away (the erosion). It is the particles that are carried in the water, (more so than the water itself) that acts as an abrasive and grinds away the material.
Weathering by water is not just due to simple physical battering. There is also weakening of the rock due to relatively fast and extreme changes in water and temperature where the sea water hits the land. When there is a rapid change in the volume of water seeping into the rock, and the water expands and contracts with re-hydration and dehydration, this hydration pressure weakens the rock. While the land above is consistently exposed to air and the land below constantly covered, the intertidal area is changing in temperature; it is exposed, then covered by cool water, then exposed and dried again in the tropical heat. Along the tropical coast there is also the addition of rain seeping into the rock through the heavy wet season rains, and then drying out again in the high heat of the summer sun. When temperatures change, they expand and contract the rock, and weaken in the process of thermal expansion.
Blowholes occur where holes have been weathered down into caves underneath a rocky coast. When waves hit the shore, the water in the underwater cave is forced into the small eroded gap and squeezed out and high into the air. One of the best places to see blowholes in the tropical Indo-Pacific is along the coast of Tonga at Mapu a Vaea.
Many visitors to the tropical seashore are disappointed when they first walk on a beach, due to the presence of large bits of hard coral and jagged remains of seashells, and they can be a nuisance for bare feet. While the main contributors of tropical beaches are the corals and ‘seashells’, there are also the remains of other obscure, unrelated groups, such as sponges, echinoderms, diatoms, foraminifers, and algae.
The sand of some tropical Indo-pacific beaches is stained pinkish from the broken down 'Organ-Pipe Coral', such as on Pink Beach on Komodo Island in Indonesia.
Some algae have calcified tissues, so when they break down these harder parts contribute to the beach sand.
When the green seaweed Halimeda breaks downs, the calcified harder parts of the alga can contribute to the beach sand. When there are larger areas or entire beaches made up of this, it is like soft piles of styrofoam snow flakes!
In an ecological sense, there are two main groups of plants that live along the seashore, which correlate with the two very different sides of the habitat. There are the plants that live in the ocean itself, or at least regularly “get their feet wet”. This includes the true marine groups, such as many seaweeds, as well as the sea grasses (to be covered in the section on Coral Reefs), and the intertidal plants, such as the mangroves (covered in various sections such as Australasian Mangroves and Indo-Malayan Mangroves). Then there are the land based plants that are covered here, many of which have adapted to live right on the seashore sand or rock, where they are exposed to sun, wind, and salt. There are many species that are characteristic of the tropical seashore, such as Goat's Foot Morning Glory, Beach Almond, Pandanus, and of course Coconut
The only mammals to be regularly seen in these habitats are flying fox, as bats can fly and disperse themselves to these remote islands.
In the north east of Australia is the muddy but birdy Cairns esplanade
North of Australia is Indonesia, with explosive Krakatoa.
More remote are the tropical Pacific islands. The Cook Islands include the stunning Aitutaki Atoll. North into the Micronesian islands is Palau. Out in the very remote eastern Pacific are the Pitcairn Islands.