Posted on September 18 2018
People don’t go to the beach to see the kelp. The sun, the sand, the cool water, the people-watching, and a host of sports and games are what they came for. The kelp is just in the way. In some coastal towns, the Beach Dept. does “beach grooming,” to rake up all that nasty, fly-attracting, funny green/brown stuff so you don’t have to smell it, trip over it, or be grossed out by it. Thanks a bunch. In so doing, the well-intentioned gatherers completely starve a vital ecosystem of its nutrients. That pile of decomposing kelp, called beach wrack, is crucial stuff. No kelp, no amphipods or copepods to eat it; without them around, no food for the shorebirds. No kelp flies, either, but though they’re not popular, they and their larvae are part of the rolling cycle of beach life too. So don’t turn your nose up at a beach all “messy” with kelp. It’s a living beach, and a far more interesting and energized environment.
Of course, that nutritious kelp didn’t grow on the sand. It washed up after being torn off its rock anchor by wave action, or being chewed off at its base, or just snapping off in the current like the branches of a tree in a windy forest. Sometimes the pieces are the loose cuttings of a kelp-harvesting boat. Kelp grows thickly, like a land forest, though it can also be seen in singular strands, just like random trees standing alone. Some species can grow rapidly—one or two feet per day! At that rate, a massive wall of it can develop in relatively shallow water in front of a beach, smoothing out wind chop and improving wave conditions, for those who value such things. But beyond that, kelp forests are as rich as land forests for the habitat they provide to fish and invertebrates. Used for hiding, hunting, or to feed upon, countless species rely on a healthy stand of kelp to live successful lives. Kelp volume waxes and wanes with the season as heavy winter swell tends to rip out a good portion of spring and summer’s growth. Indeed, a kelp forest in a healthy environment can be totally destroyed by wave action in a few days, yet regenerate itself in just a few months. Unfortunately, changes of a different sort are upon the kelp forests of the world that will affect not only the algae itself, but its many dependents.
Kelp’s ability to inhabit a given seafloor is fairly temperature dependent. The kelp species that form large stands prefer colder waters. Though kelp can be found in tropical regions, there they grow in deeper, colder water layers and do not develop the “treetop” surface mats seen in chillier seas. Living in cold water provides a couple of advantages. Cold water from the deep carries more nutrient content, a supply line the kelp utilizes for its phenomenal growth rate. The low temperature also keeps certain hungry species at bay, specifically, urchins. Kelp isn’t a rooted plant, but an algae that takes its nutrients from the water. It secures itself to rocks or reefs on the bottom by means of a tightly gripping connection called a holdfast. Urchins love to forage on these holdfasts and once chewed through at their base, the long strands just drift away.
Urchins are fairly voracious, and they reproduce abundantly. Ideally, nature keeps its balance by providing a next-level predator to hold populations down. However, in some places, such as the Northern California coast, other factors have given the urchins a leg (or maybe a spine) up. Sea stars are urchin eaters, and they are the check on urchin numbers. But recently, viruses have weakened sea star populations, and left unmolested, urchin populations have exploded. An even higher level predator is missing in some places. Sea otters can down amazing volumes of urchins when they are present, but predation by killer whales sometimes thins otter numbers, giving the advantage to urchins again. Some species of lobster also prey on urchins and keep their numbers down, unless fishermen put too many lobster traps in place, and the balance tips toward urchins once more. Humans play a role as well—there is a huge market for urchin roe, called uni in Japanese, for use in sushi. Divers can pick a lot of urchins on their way to a big payday, though they concentrate their harvest on certain favored species, leaving other kinds of urchins behind, chewing away.
Many of these new conditions that favor urchin success have been put in place or aided by the ocean warming that results from climate change. The shifting range of warmer water has spelled not only trouble, but devastation for the kelp forests of east Tasmania. Armies of uncontrolled urchins expanding their territory as ocean water warmed, have created what are called “urchin barrens” where there is nothing much but wall-to-wall urchins, sometimes hundreds per square yard. Once the favored kelp has been gnawed away, urchins have to feed on whatever is left. First the lesser plants and algae go. Then, as urchins start to get desperate for food in their self-created wasteland, a physical transformation occurs. Their hard, calcareous mouthparts, called Aristotle’s Lantern for their distinctive shape, grow more stout. They do so to the point that they can grind though the shells of shellfish like barnacles, limpets and abalone. By the time they’re done scavenging for food, it’s all urchins, all the time, with nothing else on the seafloor. Somehow, urchin populations can persist in this state of starvation for years at a time, perhaps existing off drifting foodstuffs. In Japan, off the island of Hokkaido, they have hung on in these barrens for decades. As a further frustration, it seems that even a greatly reduced population of urchins in a barren is not enough to allow regeneration of kelp. It’s a rather desperate situation for kelp forests, and one to be avoided if at all possible.
The oceans are the Earth’s last frontier. In some ways we know more about space than we do about the 70 percent of our own planet covered in salt water. Losing kelp forests, like coral reef die-off, is just one of the more obvious tragedies of ocean habitat destruction, simply because such collapses are happening in nearshore waters. As our planet’s climate moves into uncharted territory, other unexpected and unfortunate scenarios are likely to further unravel our world. Go snorkel in a kelp forest while you can.
British Columbia has a lot of coastline, cold water, and some sizeable kelp forests. Go see ‘em! This travel map by MapArt will guide your journey. It’s available from Maps.com with a simple click.
caption: Large kelp forests are limited in their distribution.
source: Wikimedia Commons: Maximilian Dörrbecker(Chumwa) (CC by SA 2.0)
caption: Piles of kelp help energize the ecology of a healthy beach
source: Flickr: Ingrid Taylar (CC by 2.0)
caption: Beach hoppers, or amphipods, burrow under piles of kelp, and chow down.
source: Flickr: Ingrid Taylar (CC by 2.0)
caption: The kelp forest can grow as thick as a forest on land.
source: Wikimedia Commons: NOAA National Ocean Service (CC by 2.0)
caption: Mama sea otter grooms her newborn pup in the safety of the kelp forest canopy. By keeping the urchin population down, the kelp can flourish.
source: Wikimedia Commons: Mike Baird (CC by 2.0)
caption: California kelp beds are big enough to be seen from space, but their size has been diminishing.
source: Wikimedia Commons: NASA Earth Observatory image by Mike Taylor (Public domain)
caption: Purple sea urchins dominating the environment.
source: Flickr: Ed Bierman (CC by 2.0)