Stirrings in the deep
by Ian Markham -- September 23rd, 2015
Towering beneath the churning, cold waves, kelp forests have inspired and astounded many with their grandeur and complexity. Even Charles Darwin was impressed by them remarking, “The number of living creatures of all orders, whose existence intimately depends on the kelp, is wonderful. A great volume might be written, describing the inhabitants of one of these beds of sea-weed.”
Diving in the Kelp forest mostly brings me a tranquility I find hard to come by elsewhere. Yet in my past three months working at the Hopkin’s Marine Station of Stanford University first as the teaching assistant in a kelp forest Ecology course and then as a diving technician, I have observed strange stirrings and shifts in the kelp forest that give me anxiety.
Monterey does not represent the typical environmental story of this modern age, that sad, steady decline since the dawn of industrial extraction. For a time it seemed it would provide perhaps one of the more dramatic examples of what we could do as a species systematically overexploiting one species after the next decimated everything from sea otters to whales to abalone to sardines. In the 1930s there were essentially no kelp forests left, the sardine horde had been pillaged, and the whales that were reported by French explorers to foul the very air of the bay with their ever-present breath had all but disappeared. But the amazing thing is that it came back. No, Monterey Bay is not one of those sad Lorax-esque warning cries but instead is an example of rebirth and new life better off now than it was 50 or 100 years ago. A hidden pocket of otters returning from the brink of extinction accompanied by protection, resource management, and tourism has revived the bay and its rich kelp forests. (Read: “The Death and Life of Monterey Bay” for the full story)
However, not all is well in this chilly paradise. There are concerning signs showing that this rich tapestry of life may be beginning to unravel once again.
As all environmental problems seem to be today, there is a mixture of issues that appear to be driving change in the kelp forests. Warm sea surface temperatures, making it far more pleasant for divers like myself, are likely taking a physiological toll on the kelp. Studies have shown that warm water reduces kelp reproduction, can decrease growth, and result in increased rates of herbivory by the insect-like amphipods and potentially the large numbers of snails on the Kelp. As the summer pushes on it seemed I could see this effect as instead of the typical late-summer thicket, the forest seemed to get rattier and thinner week by week with short often cut-off blades falling to pieces under grazing pressure.
What’s more, a mysterious disease has swept through and ravaged the populations of sea stars with unknown consequences to the kelp forest. This disease known simply as “sea star wasting” causes the critters to first contort their arms into knots as if trying to rip them off, then shrivel and literally drip off of the rocks in oozing heaps. All sea star species seems to have been affected but the more voracious predators like the sunflower or 20-arm starfish (Pyncnopodia helianthoides) and the ochre star (Pisaster ochraceous) have been hit hardest. Ochre stars are particularly noteworthy in that they are arguably one of the first species that woke the world up to the importance predators could have an ecosystem. In fact the term “keystone predators” known to all students of ecology was first coined by Bob Paine from looking at the effect of the sea stars in the intertidal. Without them muscles entirely overgrow the rocks to create a far simpler and less diverse habitat. Though perhaps not as obvious in their effect certainly the 20-arm starfish are an important part of kelp forest ecology. They are ravenous predators when seen in high-speed, careening about the sea floor vacuuming up snails and other invertebrates alike often with several in each arm waiting to be conveyed to their mouth in the center.
Fear has a powerful effect in the animal world. Some have suggested that seastars like wolves may have their biggest effect by changing they behavior of their prey species when they’re around. I’ve seen it myself in a lab context: if you put a seastar into a several-meter long seawater table with some snails at the far end, almost soon as the thing touches the water the poor little nails run for the hills and try to literally crawl out of the water just to escape the smell in the water of their nemesis. Chemical signaling is extremely important underwater and many species that we probably wouldn’t suspect are extremely sensitive to the cues given off by their predators and prey. In the kelp forest the presence of a seastar might mean that snails, young urchins and the like are forced off their favorite munching spots like reproductive blades and holdfasts and are relegated to high places where the heavy seastars can’t reach them.
Wasting disease struck hard and fast passing like a wave across the entire west coast a couple years ago. It took out an entire generation of several species leaving only juveniles and a scattering of adults. Some species like bat stars (batman’s choice for crime-fighting echinoderms) were less impacted. While others like the sunflower stars seem to have lost a complete generation. As far as I know and the folks I’ve discussed this with there’s not a single adult sunflower left between Baja and Alaska; not a single adult left in the Pacific kelp forests. Now, they’re not extinct. There are small juveniles that can be found. They recruited soon after the adults disappeared but no one really knows if those are even going to make it or if they’re wasting disease will strike again
The bizarre thing about sea star wasting is that it doesn’t seemed to be caused by a novel pathogen. Testing of historical specimens shows that it has been around for quite some time. So what suddenly cause it to wipe out the sea stars? We don’t really know, to tell the truth. Some will point to the high sea surface temperatures others will point to high sea star densities allowing for the disease to become an epidemic. But the fact that it occurred across multiple species, so completely across the entire range where very few factors are actually consistent makes it particularly bizarre.
In any case most all of the sea stars except for bat stars are gone. I haven’t seen papers published on this yet but I rather suspect that one of the big effects of losing me see stars is the predation of juvenile urchins. I suspect that the hungry 20 arm starfish and Pisaster rampaging around the ocean floor would probably snack happily on all of the young urchins that would settle on the forest floor. When young, the urchin tests and spines are soft enough to be dissolved by the voracious stars. Now, it could be a coincidence unrelated except by the ocean and conditions but sea urchins have had some incredibly successful recruitment these last few years in Monterey. It seems every crevice you look at is stuffed with urchins and the numbers are off the charts for some of the long-term data sets that we have both from the class and from groups like reef check who do citizen science diving. There’s enough that kelp forest ecologist who’ve known the place for 30 years say they’ve never seen so many and also concerned about the welfare of organisms like abalone who seem to compete for the same crevices.
Now urchins typically hide in crevices in fear of predators. In Southern California sheephead wrasse, wolf eels, spiny lobster’s and more would happily devour an urchin that gets too bold and leaves it’s crevice or at least they would before all of them were hunted to near functional ecological extinction. But the most voracious predator of urchins was always otters. When sea otter were eliminated from the California coast by a sequence of Russian and Spanish and American fur trappers, the urchin population exploded. Without the fear of otters urchins fill the crevices then spillover and run amok. They seem to switch into a behavior pattern where they rove aggressively across the ocean floor seeking hungrily for food. Acute attention to chemical cues means they soon find the nearest kelp. They then swarm over the holdfast (the equivalent of roots) and quickly devour the part that anchors it to the ocean floor leaving the rest to float off and die. They then charge to the next piece of kelp and as they do, form a horde that can quickly wipe out an entire kelp forest. The sort of classic thinking of predator prey dynamics would be that once they have eliminated their food source they would starve to death and eliminate themselves or reduce in numbers until their prey could return.
But urchins are amazing little monsters, capable of degrees of adaptation that most organisms are not. It is almost impossible to starve an urchin to death. They simply shrink absorbing their own test and grow smaller. The plates are designed so cleverly that they can simply adjust and refit to a smaller urchin as if they were babies again. Imagine if we could just get younger by not eating! I have seen these little monsters do incredible things including chew through solid plastic and withstand months of starvation as controls in my experiments.
So when an urchin population goes unchecked without predators it basically settles in to stay and what you have is what are now so common in Southern California without the otters: urchin barrens.
Thank goodness for the same fate did not fall the fall central California. After many years in which it was believed in the southern sea otters were extinct, a very small population was discovered along the coastline near Big Sur. With protection these otters then quickly expanded and began moving north scouring the ocean floor of its overabundant urchins. In their wake new kelp settled from the last remnants and kelp forests quickly regrew.
My worry is that this change is now beginning to reverse and erode that rebirth. Otter population have held stable and plateaued probably at a number well below their pre-pelting levels due to a number of factors. Several of the once most common abalone species have disappeared from the region under intense pressure of the industrial fisheries that once poach them. Moreover disease plagues the otter population particularly acephalon razor-headed hookworm and the disease that my own mother studied for many years called Toxoplasma. Now toxo has an amazing story in its own right but I can’t cover that here and do it justice. In brief, it’s a parasite that is “designed” to pass between cats and rodents and does so ingeniously by affecting rodents brains. It makes mice essentially attracted to the smell of cat urine and entirely devoid of fear. With this sort of mind control rodents will walk around in broad daylight and even seek out the areas where there are many cats. Once in a cat, the parasites multiply from a few hundred to billions of the environmentally resistant form called oosis. With a massive feral cat population in the Monterey bay area particularly surrounding Elkorn Slough, the feces of these animals washes into the watershed in high doses and then accumulate particularly it seems in the turban snails that some otters love will eat like popcorn. The parasite inside its mistaken host will proceed to settle into tissues of the brain affecting motility and fear centers seeminglyc causing them to get hit by boats and eaten by white sharks at my greater numbers than they would without the infection. As always in nature this is probably only one part of the problem that limits otter numbers but they simply aren’t as high as they could be.
Still though there are a lot of otters. Why are they not eating this huge abundance of urchins? Well it’s not really known but one factor might be the fact that otters are quite specialized in their diets by individual. Otters learn do you want to eat directly from their mothers. If mom has a taste for abalone pup has a taste for abalone, if mom has a taste for urchin then that’s what pups going to eat probably for the rest of its life. That said they eat so much and so often and are quite curious in a way that they will go for other unfamiliar food items but it may take them some time to adjust. Could just be a matter of time before some abalone specialist looks over at one of the few urchin specialists ands says to itself ‘hey wonder how those purple spiky things he’s eating tastes… I’m gonna try one!’ I certainly hope that’s the case but as it is right now it doesn’t seem to be happening quickly enough.
What you say then instead is areas much like in Southern California with holes in the kelp forest canopy opening above floor covered by hundreds of urchins. One of my dive sites that I used to frequent just a few blocks from Hopkins Marine Station called coral street used to be choked with kelp. At peak summer I would actually stop diving there because it was so difficult to force your way out on the surface. At present there is no forest, just urchins. A barren has formed and who knows how long it will stay.
To be honest I am afraid for my beloved kelp forest. Other openings, small at first have formed as well. And in the spots with thick kelp forests already I am beginning to see some of the marauding bands of urchins leave the crevices and find the nearest hold fasts.
The coming El Niño does not bring comfort to those of us who love the ocean. Though it does suggest the relief of this multi-year drought that is one of the worst in recorded history in California, it may spell doom for many marine organisms. The problem is that el Niño years disrupt the coastal winds and ocean currents that provide the upwelling which sustains this system. Typically strong winds create ocean currents that push water offshore and deep water from the Monterey canyon replace it bringing rich nutrients on which the plankton explode with life at the base of the food chain. When upwelling slows or stops this productivity stops as well and starvation begins. The black fishing cormorants that now cover the rocks are likely to die in large numbers. In the worst years dozens of stillborn pups are born on the beach surrounding Hopkins and even more than abandoned by their mothers as they can no longer sustain enough food to keep themselves sufficiently fat to nurse their small pups.
If the sea temperatures rise even higher than they already are before the el Niño and settle in perhaps for years the kelp forest may be in serious trouble. Combined with the onslaught of urchins who knows what will happen.
What can we do? It’s really quite hard to say. Most of what we could do would be indirect or we are doing it already. If some clever marketer could make a solid Pitch at selling the purple urchin not just the red urchin to the sushi market perhaps a small industry could burgeon in which humans could compensate for the predators which are no longer in the system. This seems to be partially the case in Southern California though the fishery is almost exclusively for the larger red urchins. Maybe some business’s unorthodox carbon offset could pay divers to go and scoop out hundreds of urchins since they are made of calcium carbonate and in in some sense are CO2 isinks which could be plucked from the ocean and redistributed potentially as fertilizer or additives for crops. The truth is I don’t really know and so I write this twiddling my thumbs and hoping that my predictions are wrong, that my fear is unfounded.
All I know is that while most Californians are waiting hopefully for this el niño to strike, I sit in fear and hope that it is a moderate one. Yes our parched land could use it but our oceans will really suffer if it is.
Kelp forests, however, are resilient. Unlike coral they grow quickly and can rebound given half a chance. Let’s hope they get it. Lest, I leave you with too much a sense of foreboding here are some fun sea lion shots to soften the blow.