The best scientific questions, by definition, lead researchers down unexpected paths. The investigations of UC San Diego professor and NRS faculty reserve manager Kaustuv Roy are a case in point: though Roy's research initially focused on how certain marine fauna are responding to global warming, his line of inquiry expanded to reveal surprising new information about the health of California's intertidal zone. Now, it turns out, his findings have implications for conservation practices as well as for basic science.
Roy's research began with his realization that temperature increases, if accurately projected for the next few decades, would far exceed anything that had been observed in historic times or even estimated in recent geologic times.
To discover what effect these changes were having on living creatures, Roy and his graduate students turned to the intertidal zone just down the hill from their San Diego campus. Not only was this local intertidal zone convenient, it also provided a geologic context. Researchers working with specific species at low tide had only to climb the bluffs above the beach to compare their contemporary species with the community as it existed during the Pleistocene Epoch, 11,000 to 125,000 years ago. "The fossil deposits from the Pleistocene intertidal community are surprisingly similar to what's found along the coast today," Roy notes. "Eighty percent of the modern species are represented in the fossil records in sufficient quantities to estimate relative abundances and sizes."
The geologic record provides an important context for interpreting present-day changes along the coast. Species' ranges, for example, have changed continually to adapt to a changing environment. Fossil evidence clearly indicates that, during the late Pleistocene, many species ranged a full degree further south than they do today. And, during the last interglacial period, many southern species ranged at least a degree further north.
Home, home on the range
The fossil record proved especially valuable when Roy began looking at Acanthinucella spirata. Today this common snail is found from mid-Baja California up to Tomales Bay, 40 miles north of San Francisco - and much of this geographic range is covered by the fossil record. However, further investigations by Roy revealed, within this range, important differences between the species as it existed in prehistoric times and as it now exists contemporary times.
For one thing, genetic variation in the northern population is now much less than that found south of Point Conception. After studying both the genetic data and the fossil record, Roy and his colleagues theorized that northern populations of the snail became extinct at some point, and then the area had been recolonized by a small number of individuals from the south during the last 12,000 to 30,000 years.
The lack of genetic diversity in the present-day northern population would seem to indicate that it is not as healthy as the southern population. Yet, when morphological diversity is also measured, the finding is that species form and structure are much more varied in the north than in the south. Apparently, after the snail recolonized its former territory, a new form evolved with much thicker, shorter, and broader shells.
This discovery has implications for resource managers who usually focus on conserving the most genetically diverse populations of threatened species in the belief that genetic diversity will help a species withstand future environmental changes. Roy's study suggests that conservation criteria should be expanded to include morphologic as well as genetic diversity.
That was then, this is now
Roy's research, with its paleontological focus, naturally drew him toward extensive use of museum collections. In addition to fossils, many museums also hold collections of contemporary specimens collected 50, 80, or 100 years ago. What Roy discovered from working with these collections was that contemporary specimens collected in the mid-twentieth century and earlier differ in two distinct ways from what today's researchers see in their field surveys: (1) many species no longer range as widely as they once did, and (2) individual representatives of these same species now tend to be smaller than individuals in past times.
Regular encounters with beach visitors backed up this observation. Older people who approached the field crews almost invariably spoke about how much California's coast had changed since they were young - species they were used to seeing had disappeared, and the size of those that remained was much smaller. Such encounters were so frequent, Roy began to worry he was working in a system so out of balance it might invalidate his scientific work. He explained: "If we're losing species at particular sites, or if sizes and population numbers are changing, then ecological relationships are changing as well. How much of the change is natural? This is where we run our experiments and do our empirical work. If the system is so far from equilibrium, even on a scale of 150 years, then we really need to keep that in mind. If everything is half the size of what those individuals were 150 years ago, then we've got a problem, both from a conservation and a scientific perspective."
Measuring a mirage
Roy began to worry that what he'd thought was his ideal laboratory had already become a victim of the "shifting baseline syndrome" identified by fisheries biologist Daniel Pauly in 1995. Pauly used the term shifting baseline syndrome to refer to a disturbing trend in resource management where each generation of scientists "accepts as a baseline the stock size and species composition that occurred at the beginning of their careers, and uses this baseline to evaluate changes. When the next generation starts its career, the stocks have further declined, but it is the stock at that time that serves as the new baseline. The result obviously is a gradual accommodation of the creeping disappearance of resource species..." (D. Pauly, "Anecdotes and the shifting baseline syndrome of fisheries," Trends in Ecology and Evolution 10(10), p. 430 (1995).)
It was at about this point that Roy decided to try to quantify the health of the intertidal and the changes occurring there. Working with Paul Dayton, of UC San Diego's Scripps Institution of Oceanography, and David Lindberg and James Valentine, of UC Berkeley, he began to collect and organize an online database that would provide a baseline for detecting local extinctions, diminished body sizes, and morphological changes. They named their group Conservation and Biodiversity of the Rocky Intertidal of Southern California (CBRISC); supported by a grant from the UC Marine Council, they began to compile their data. Nowadays the database includes more than 4,100 historical records, drawn from a wide variety of sources and dating back to 1869. These records cover intertidal mollusk species found at 301 localities throughout southern California.
Fossil records and museum collections provide the geologic perspective for the database. Records of archaeological explorations of Native American middens provide the early human record. The personal observations of early European explorers, nineteenth- and twentieth-century naturalists, and amateur collectors offer first glimpses of the impact of modern civilization. And these observations are amplified by data drawn from a wide range of scientific publications, from the Edward "Doc" Ricketts classic, Between Pacific Tides, to recent doctoral dissertations.
The database has grown sufficiently inclusive to help guide current CBRISC field research, as teams return to locations previously surveyed to identify local extinctions, changes in community composition, and size shifts in individual species.
The prodigal snail returns
The database is shedding new light on the health of the intertidal. It has shown, for example, that southern California has an abundance of extralimital species, invasives that have moved into the area from beyond their historic ranges. Mexacanthina lugubris, for example, has become the most common intertidal snail in San Diego. Its historic northern limit was Ensenada in northern Baja California, but, in 1976, it started showing up at Point Loma National Seashore in San Diego. Earlier this year, La Jolla was thought to be the snail's new northern limit, but now Roy has begun finding it in Orange County. Though the speed of the invasion seems rapid, in a sense M. lugubris is simply returning home: the fossil record indicates it was found throughout southern California during the Pleistocene.
Roy is intrigued at what prompted this recolonization. Is M. lugubris simply moving up the coast in response to warmer water and air temperatures? Or did something happen to the California species that is being replaced by this species? Has the southern California intertidal become a "sink habitat," where mortality exceeds reproduction? If so, how much of the destruction is natural and how much has been caused by humans?
Losing at hide-and-seek
Roy's curiosity led him to investigate the impact human collecting has on body sizes of the intertidal mollusks. Body size is an important indicator of a community's well-being, because many animals, especially mollusks, are long-lived (20 to 30 years), and body size correlates directly with reproductive capacity.
Previous studies in Chile, Australia, and South Africa have shown that human collecting can dramatically impact the size frequency distribution of exploited species (those that people eat). These studies were conducted by comparing protected intertidal zones with public areas. All showed that, in human exclusion zones, exploited species had significantly larger body sizes, while control species (those that humans didn't eat) were not significantly larger even where they were protected.
Roy decided to conduct a similar study that would also include a historic perspective from the database. For exploited species, he chose Lottia gigantea (owl limpet) and Tegula aureotincta (gilded turban snail), while, for nonexploited species, he chose Acanthinucella spirata (a small predatory snail) and Fissurella volcano (a small limpet). CBRISC crews surveyed sites from southern Los Angeles County to the U.S.-Mexican border, including the NRS's Scripps Marine Reserve in San Diego County. At almost every location, they found significant size declines in all species, exploited and nonexploited, over three time periods: pre-1960, 1960 to 1980, and current (1981 to present).
Their next challenge was to identify the cause of these declines in size. Possibilities included human disturbance, warmer water temperatures, and poor field survey techniques. To eliminate the latter two possibilities, the CBRISC field crews surveyed the one site in southern California with an enforced human exclusion zone, the rocky intertidal at Cabrillo National Monument at Point Loma. By using the same crews and techniques, in an area with similar habitats, they would be able to isolate human disturbance as the cause of the size changes.
The findings were dramatic. All four species, even those not known to be exploited, were significantly larger at protected Point Loma than anywhere else along the coast. In fact, specimens for two of Roy's four species were even larger than the specimens found in museum collections.
It seems humans are impacting the sizes of intertidal mollusks in southern California - and in a major way. What's more, the effect is pervasive and can be seen not only in species that are directly exploited by humans, but also in those that are not. "If you enforce existing laws," Roy notes, "you can minimize the loss somewhat. The bad news is that most laws are not being enforced anywhere in southern California."
But Roy is still a bit puzzled over why inconspicuous, nonexploited species have declined. He suspects that either they are being affected by human trampling (see page 5 sidebar, "Is California's intertidal zone being loved to death?"), eaten by an unknown group, or being taken by indiscriminate poachers. Anecdotal discussions with Fish and Game wardens seem to indicate that poachers often prefer to wipe an area clean quickly rather than spend a lot of time focusing on particular species, all the while exposing themselves to greater risk of being caught at their illegal activities.
What it all means
What does Roy's work reveal about the health of the intertidal? He fears the entire system may be in a slow-motion collapse that will be difficult to reverse. What he discovered about the exploited Lottia gigantea provides insight: "This species lives at least 30 years, and individuals change sex as they grow. A 50-mm specimen can be 18 to 20 years old. At about 40 mm, they change from male to female. At many sites, we no longer find large Lottia gigantea, and we don't know what impact this is having on sex change. Are they changing earlier in response to human impact? Looking down the road, is the species going to be in trouble when the individuals who are 20 years old now start crashing?"
The CBRISC database continues to open new lines of inquiry. And Roy is looking to increase his survey range, expanding northward to the Channel Islands and central California. In addition, he's considering including more species in upcoming size surveys to find out if his current four choices are exceptions. Then there's the possibility of conducting more studies that integrate both historical data and quadrat-scale comparisons.
"CBRISC takes up a lot of our time because it's so darn interesting," Roy notes with a smile. "But given the results we have already, it's important that we continue. If we don't, we'll never know what the system is going to look like 10, 15, or 20 years from now. And without knowing this, we'll never be able to manage it." - JB
For more information, contact:
Kaustuv Roy
Biology / 1254 Biology Bldg. 0116
University of California, San Diego
La Jolla, CA 92093-0116
Phone: 858-822-0559
Email: kroy@ucsd.edu |
