I’m still trying to sort out my upgraded operating system vis a vis photos, so for our Bucket today let’s take a swim back into the Caribbean, in recognition of the vast and complex coral reef ecosystems that are declining worldwide as a result of destructive human activity. This generation of scuba divers may well be the last. Let me show you a bit of why they are so colorful and diverse.
A healthy coral reef has many different species of coral, which form the substrate of the community. Some are hard and slow-growing, like the knobby forms, while others are fast-growing branching forms, some of which are soft, like the waving gorgonians. Fast-growing species respond to quick changes, generating new habitat and food, while the slow-growing types are less vulnerable to physical damage and predation. With the range of species, a coral reef system is resilient to most environmental conditions, including violent storms. A varied substrate also provides food and habitat for a range of fish and invertebrates too: diversity feeds diversity. Ordinarily that variety means resilience in the face of changes.
Knobby corals form a three-dimensional “home” for mobile animals. During the daytime divers often see schools of fish floating quietly under their protection. This lack of activity is rest time for them; fish like these snappers are most active nocturnally, spreading out to feed on crabs and other invertebrates.
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One fascinating feature of reef ecosystems is the many forms of mutualism. While on land we usually think of animals as predators or prey, on the reefs there are also frequently interactions that benefit both, such as at feeding stations like the one below. On a healthy reef I’ll see these every hundred yards or so. Near a big hunk of coral or sponge, a large fish floats in stillness as many much smaller fish dart amongst its teeth and fins picking off parasites. The little fish are safe from predation at such times. There are many other associations of reef species like this, made possible by the high diversity of life in a relatively small area.
Some portions of the reef, especially shallow protected areas, are well suited for juveniles to grow up in relative safety. Snorkelers often see these baby fish, who look very different than the adult forms. The "disco fish” below, bright blue with silver spots, is a Yellowtail Damsefish. Coral reef ecosystems aren’t random assemblages. Even a casual diver will notice “neighborhoods”, each of which has a particular physical shape with a different variety of fish. The number of species is mindboggling.
As is the spectacular beauty, everywhere one looks. The colors and patterns of creatures leaves anyone who sees them speechless, terrestrial beings that we are. Coral reefs are richer in life than ecosystems we’re familiar with, especially in temperate latitudes. The vast numbers of fish coexisting in these small areas requires clues for species recognition and warning — it’s the diversity and concentration of life creates such glorious displays of beauty. Fish change in appearance as they mature, for reproduction time, when threatened, in greeting.
The strength of coral reef ecosystems depends on their capacity for diversity, structurally and in numbers of species. Biodiversity creates resilience, and reefs have persisted for millenia, varying in composition. But there’s a limit to resilience, when too many factors in the ecosystem are threatened at once, which is what we’re seeing now. A few outliers will survive for a while, with local protections like fishing, development and pollution management, but there is no protection from global climate change warming the water and increasing acidification. The scenes you see here and in videos are the tail end of a magnificent story, mostly hidden from us.
(For more information about reef ecology, visit coral.org/…, www.coral-reef-info.com/…, ocean.si.edu/….)
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The Bucket is now open for your reports from your natural neighborhood.