As anyone who has bought or sold on eBay realizes, one person's trash regularly becomes another's treasure through the alchemy of the global flea-marketplace. This also applies to certain natural resources that are seemingly of little economic worth in one place and yet with globalization become priceless in another. The emergence of a booming sea urchin fishery in the western Atlantic in the late 1980s illustrates this phenomena, transforming a previously "valueless" species colloquially known as "whore's eggs" to green gold in a few short years. Yet just as quickly, the fishery appears to have collapsed.
Family members returning from Maine this summer have remarked at the virtual absence of urchin shells that once littered the rocks of Monhegan Island, and encountered no spiny accumulations beneath the ebbing tide. Researchers at UNH are actively trying to reestablish wild urchin beds where they have not rebounded from over-harvesting, yet it was not so long ago that urchins were roundly viewed as an ecological menace, creating barrens out of kelp beds and threatening vital fisheries.
When a native species comes to dominate a system in which in naturally occurs to such an extent that it overwhelms habitat and alters the composition and structure of natural communities, it is a good bet that something significant is missing from that ecosystem. Either predation has dramatically decreased, or some disturbance has eliminated the competition and opening up previously restricted ecological niches. When a species plunges from super abundance to scarcity in a short space of time, habitat destruction and overexploitation are often the culprits. The green sea urchin in the Gulf of Maine has experienced both extremes in quick succession in the space of a few decades.
Strngylocentrotus droebachiensis, the green sea urchin, is like an armored pot scrubber. It scours algae from rocky sub tidal regions where masses of urchins moving in a broad front through an area are capable of breaking down and consuming "all but the hardest coralline algae." If they were a terrestrial species, perhaps they would fill the niche of large ungulates, or even elephants, able to consume and process the coarse woody growth that is unavailable to other browsers and even alter habitats through their feeding. Their impacts are certainly disproportionate to their biomass, and for nearshore habitats in their circumpolar range research suggests urchins play a dominant role akin to a keystone species. Removal of the keystone, to follow this metaphor a step further, leads to rapid collapse.
Native species behave invasively within their home ranges in the absence of natural population checks. A number of species prey on green sea urchins at different stages of their life cycle, and in the Gulf of Maine these historically included vast numbers of cod. With the collapse of the cod fishery and the decline of other predatory fish, a significant check on urchin populations was removed from this system.
Other factors influencing urchin growth and die back are less well understood but include temperature variations and corresponding impacts on spawning conditions and the phenomena of urchins eating themselves out of house and home, rather like the impacts of elephants with restricted ranges on the systems that sustain them. Juvenile urchins rely on kelp forests for shelter from predators, while as adults they voraciously consume kelp and can transform kelp beds into barrens with their feeding. Some researchers conclude that a patchy mosaic of kelp and barrens habitats offers the best conservation outcome for urchins and kelp dependent species, as well as large numbers of the smallest and largest size classes of urchins.
Prior to 1987, sea urchins were a negligible part of the commercial fishery in the Gulf of Maine. Elsewhere, however, Japanese demand for urchin roe spawned intensive urchin harvests that also had a boom and bust character. On the west coast of North America, as in the Gulf of Maine, sea urchins were formerly despised as pests. According to the University of California, "quicklime (calcium oxide) was used to control sea urchins in commercial kelp beds and groups of recreational divers smashed sea urchins with hammers." The commercial fishery began in 1971, and for the next 10 years,
"landings increased rapidly, reaching nearly 25 million pounds in 1981. Prior to 1985, almost all landings were made in southern California with most sea urchins being harvested from the Channel Islands. Starting in 1985, the northern California fishery expanded rapidly and the total California landings peaked at about 52 million pounds in 1988."
By 1987, there were concerns that the California fishery was not sustainable, but by then several urchin species were in decline and harvests were down. The same pattern played out in Maine, which had not been considered a viable market until the mid 1980s when the yen gained sufficiently on the dollar to justify the transportation costs of live urchins to Japan. Urchin roe is in particular demand during the January holidays in Japan, when other urchin areas are closed for spawning. In Maine, however, the season includes the winter months, and seemingly overnight a green gold rush of urchin divers began in the Gulf of Maine.
Data from Maine show a rapid escalation in the urchin harvest between 1987 and 1993, when it peaked at 41 million pounds. The price per pound of roe has also increased, beginning at .16 cents in 1987 and rising to $1.44 in 2003. By then, however, the catch had dramatically fallen off. Part of the problem was high demand for urchins when sea urchin ecology and conservation needs were poorly understood. Catches are regulated by size and time of year but not by density of collection, and urchin barrens in the sub tidal regions of the lower Maine coast are quickly depleted by divers. Urchins need to be in close proximity to each other to spawn effectively, and they spawn in the summer when their predators are most active. A rising predator population of Jonah crabs and lobsters appears to have had a greater impact on scattered colonies of urchins. Green Sea urchins may also have been affected by disease during the same period that reproductive females were being aggressively removed from the population. Kelp beds regenerated rapidly but new barrens communities were not established by the diminished urchin population.
The result is a commercially important but unsustainable fishery driven by the enticements of a global market to over utilize a formerly low value species, and increased but belated interest in urchin conservation. Their role in maintaining an already compromised and complex coastal marine ecosystem has been altered, the full consequences of which are still unknown. The complex and synergistic impacts of pollution, temperature change, invasive species, over fishing and other disruptive factors on the marine environment remain are tremendous conservation challenge. As for the green sea urchin, the transition from "whore's eggs" to green gold and finally to threatened resource has played out countless times for other species and natural systems, a lesson we seem fated to perennially relearn.