September 11, 2013 | 3
Pandas, lions, and elk and their ilk often find their way onto the covers of conservationists’ marketing materials. But I think relying exclusively on big furry animals (industry codename: charasmatic megafauna) means they are missing out on some potentially awesome spokes-creatures. Take this little guy.
How can you resist that face? And his requests are so modest! He asks only that you stop mechanically grooming beaches, piling erosion-stopping rip-rap on them, and, oh, I don’t know, maybe stop turning perfectly nice sandy shore into smog-choked megacities. Is that so hard?
OK. Maybe we can just start with a little less beach grooming. Look at that face! Come on!
You’ve probably encountered the crustaceans called isopods before — little animals with shield-shaped shells of overlapping plates, supported by two long rows of scuttling legs. They curl up into balls when disturbed, and go by various names: “pill bugs”, “roly polies”, or “wood lice”. Among the Deep Sea News crew, giant isopods have practically achieved cult status (who could forget Isopocalypse 2010 or the 2009 album “Songs About Giant Isopods”?) And of course, there’s the one isopod to rule all our nightmares, Cymothoa exigua. Yup. The parasitic one that eats fish tongues, then latches on to the stump to replace them.
But there are many other isopods in the world. Perhaps 10,000 described species, in fact, found on land and at sea. Alloniscus perconvexus prefers the teeny-tiny strip in between. And that is the root of its troubles.
That space is in dry beach sand, just above the reach of high tide. One problem for these creatures, from the conservation perspective, is that this strip of real estate probably appears to most people to be an extremely thin desert with a great view. But as it happens, an astounding variety of organisms live in beach sand, wet or dry. Most of them are microscopic. So strange as it might seem, aside from perhaps shorebirds and perhaps crabs, Alloniscus is the charasmatic megafauna of its ecosystem.
These are Alloniscus‘s little houses. Like hobbits, they live in holes.
For millennia, the little isopod had this sandy home pretty much to itself. Then, surely without meaning to, the people of southern California went on a hole-crushing bender of unprecedented proportions.
First, they obliterated big beaches to make ports in places like Los Angeles and Long Beach.
Then, they started “grooming” lots of beaches with mechanical rakes starting in the 1960s. They did this to make the beaches look nicer and to give a more even surface for spreading a towel or picnic blanket.
Here’s what they use to do it. You can imagine what this thing does to those little holes — and their occupants.
45%, or 161 km of southern California mainland beaches are now groomed, and where this is true, these little isopods are absent despite the presence of relatively wide, sandy beaches.
People also, quite understandably, like to drive jeeps, dirt bikes, and ATVs up and down the beach. But when foot or tire meets hole, it’s a bad scene for isopods. Driving on burrows potentially crushes the homeowner. During years of heavy off-road vehicle use at southern California’s Ormond Beach, one scientist found no upper beach isopods in multiple surveys from 1971 to 1978.
Beach erosion has also greatly contributed to the isopod housing crisis. Sand that would otherwise reach the coast has been getting trapped behind the dams of western reservoirs. One estimate suggests 1.02 million cubic meters of sand per year for the last 50 years that otherwise would have fed southern California beaches got trapped behind such dams (where it will eventually cause problems of its own). As a result, beaches shrank. The highest-ever recorded concentration of the beach isopod Tylos punctatus was 31,000 isopods per meter of shoreline in the late 1960s at a place called Carlsbad Beach. It was not detected there at all in 2010, 2011, or 2012. Erosion had replaced the sand with cobbles.
The human response to the erosion problem has compounded the situation for isopods. Two favored anti-erosion techniques are armoring beaches with big piles of rocks and other debris; and dumping lots of sand all at once to “nourish” them. Both options may smother or blockade holes.
Here’s what a beach looks like before and after armoring.
You can see how sand isopods might have an issue with this.
Today, according to a study by David Hubbard, Jenifer Dugan, and a team of scientists at the University of California, Santa Barbara published in June, more than 27%, or 120 km, of wave-exposed southern California beaches are armored. One population of T. punctatus boasted 713 isopods per meter of shoreline in a 2002 survey of Broad Beach near Mailbu. After the beach was armored with rock and “geotextile revetment”, isopods could not be detected by sampling in 2010 (though they did find a plucky holdout in debris on the surface).
Hubbard and Dugan’s team set out to sample populations of these two isopods at beaches across Southern Californiain 2010 and 2011 to see what effect all these changes had actually had. That found that both Alloniscus perconvexus and Tylos punctatus populations are fragmented and in decline across their ranges. They have been eradicated from 64% (14 sites) and 57% (16 sites), respectively, of the beaches they were found at 100 years ago.
The few mainland beaches that they remain at tend to be remote, restrict vehicle access, and require a hike or stairs to get to. They are often narrow “pocket beaches” backed by bluffs. But yet again, the isopods will soon face another housing crisis even here: these pocket beaches are those most vulnerable to sea-level rise. Of the 450 km of southern California coast, less than 10% has the potential to support isopods if the shore sees 1.4 m of sea level rise by 2100.
And the isopods are not alone in their predicament. Hubbard and his co-authors suggest that many of southern California’s sandy beach invertebrates — things like flightless beetles and little shrimp-like creatures called amphipods — have suffered the same population declines and fragmentation as the beach isopods for more or less the same causes. More than 50% of them share a characteristic with isopods that make them vulnerable: they don’t make swimming or floating larvae that could more easily disperse long distances to help fill in big distribution gaps. The adults are also generally flightless, and you can tell by looking at the beach isopods that, while cute, they are not great at beach hopping. So any actions we take to help isopods could potentially help a larger group of animals who share their home and who help keep the hidden beach ecosystem humming.
And there is cause for hope in southern California. People with authority could take action to help transplant isopods and other small beach animals to more suitable habitat as the waters rise. We could limit vehicle or foot traffic at more sandy beaches. We could come up with better solutions to the problem of shore erosion than simply building an ugly wall. But probably the easiest, most effective thing that could be done to both give isopods their homes back, avoid the threat of sea level rise, and still let people enjoy the shore, the authors say, is also the simplest: stop grooming beaches.
Because, given a chance, these isopods aren’t helpless. Though they clearly do not possess the beach-storming capabilities of Operation Overlord, if they hold a nearby beachhead, they’re not entirely lacking in that department either. Ormond Beach, the place where off-road vehicles eliminated (or nearly did) beach isopods in the 1970s, vehicles were banned in the 1980s. Just to the south lay the protected beaches of Mugu Naval Air Station. More than ten years later in 1996, Hubbard resurveyed the site and found T. punctatus. In 2009 and 2011, he found both species.
Hubbard D.M., Dugan J.E., Schooler N.K. & Viola S.M. (2013). Local extirpations and regional declines of endemic upper beach invertebrates in southern California, Estuarine, Coastal and Shelf Science, DOI: 10.1016/j.ecss.2013.06.017
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