The Maya understood the importance of the cenotes, but they could never have known that these flooded passageways were actually the beginning of subterranean rivers, all of which eventually flow out to the sea. Salt water, unlike fresh water, does not erode limestone, so most sea caves are created by the mechanical pounding of the waves. The rocky outcrops of New Zealand's Poor Knight Islands are riddled with sea caves and just like those in Borneo they have become important shelters for many species. After a day feeding in the open water vast shoals of demoiselle fish return to the caves, which they use as a refuge from predators. For these fish the caves are a nighttime retreat, but they're not the only commuters in here. There are other fish working to a different schedule.


玛雅人知道灰岩坑对于他们的重要性，但他们决不会知道，这些水坑实际上是一些地下河的起点，这些地下河一直流向大海。咸水与淡水不同，它不会腐蚀石灰岩，所以海上的绝大部分岩洞都是由海浪的机械冲击力形成的。新西兰普尔奈茨群岛的岩层有许多海岸岩洞，而且和加里曼丹岛的那些岩洞一样，这里也是多种动物的重要隐蔽场所。在宽阔的大海上觅食一天之后，大群的雀鲷回到岩洞中休息，它们在这里躲避食肉动物的攻击。对于这些鱼类来说，岩洞是夜晚休息之所，但它们并不是这里唯一的进出者。这里还有作息时间不同的其它鱼类。