Earth Day is fast approaching. Shark populations are dwindling and, in some cases, nearing extinction. There are reports that the Great Barrier reef is losing its ability to recover from another bleaching incident. How are all these events related. Well, read on my friends.
Look at this picture of the plant we call Earth. See anything that strikes you? Like all that blue water? The Ocean covers over 70% of the plant, and yet we call it Earth Day. I won’t go into the history of Earth Day, you can do that for yourself. And yes, taking care of our precious “land plant” with recycling and other wonderful things is awesome. But what about “Mother Ocean”?
Well, in honor of Earth Day, let us consider the apex predator of the Ocean and what losing sharks means to us all. Sharks are often the top of the food chain in their eco system. They remove the weak, injured and sick of many different species. Sharks that reach adult hood have few predators. So, think of the Ocean as a huge food chain. Big fish eat smaller fish, and so on. But if we remove the apex predator what happens? Simply put, fewer apex predator mean more lower level carnivores which leaves fewer herbivores which then leaves more macro algae. I am sure as divers you have seen more algae on the reef. That algae is smothering the corals. And with less corals we have other issues coming from the sea.
For Earth day let us try and understand what this means. Studies of remote reefs have revealed ecosystems that are very different from those we know today. Yes, humans are creating major issues both on land and at sea.
A study of reefs in the Northwestern Hawaii Islands found that apex predators, including sharks, comprise over half of the fish biomass compared to less than 10% on reefs that are fished. On the unaltered reefs the sharks are bigger and populations of all species are far greater. Additionally the unaltered reefs are home to a larger variety of other species than regularly fished reefs.
The presence of sharks can also protect seagrass beds from over-grazing by dugongs and green sea turtles. These animals prefer to eat in the middle of a sea grass bed where the quality of food is the highest. But it is harder for them to escape a hunting shark from the middle of a large seagrass bed, so they stay on the outside when sharks are present. Seagrass beds are an important habitat for many fish and invertebrate species.
So for Earth day let us expand our thoughts to “Mother Ocean”