It’s the Tiny Fish That Are Important

Many of us are thrilled by the bigger marine life -- the mantas and the sharks -- when we go diving, but there has been a visible increase in the interest in the minutiae of life on the reef, probably driven by the popularity of macro photography.

Now Isabelle Cote of Fraser University in Canada makes the point that it is the tiny fish that hide in nooks and crannies that are actually among the most important inhabitants of the reefs. That's because they supply much of the food that supports the larger, more visible animals.

Cote's colleague, Simon Brandl, has been studying these cryptobenthic reef fish--- those less than 5mm (or a quarter-of-an-inch long), and when he looked at surveys of plankton near reefs, he was surprised to find 70 percent of fish larvae were cryptobenthic species.

Larger fish may produce more eggs overall, but these have yolks that allow them to float in the planktonic soup for weeks, dispersing over large distances. By contrast, the eggs of smaller fish develop fast so that the larvae stay close to the reefs, eventually outnumbering those of their bigger contemporaries.

This makes them an important food source for other animals. They live fast and die young. Their mortality rate can be as high as 70 percent per week. The research team think these findings could explain Darwin's paradox -- how coral reefs so rich in life can thrive in nutrient-poor waters, or how Darwin put it: "How these oases of life occur in oceans that might otherwise be deserts."