Sea Urchin Population Explosion in Southern California Coastal Waters

Abstract

Biscay which allows a 120 anticlockwise rotation of the Iberian peninsula between Eocene and Middle to Upper Miocene times. They refer several times to the fact that this va'ue is appreciably less than a rotation of 220, which they believe resulted from our paleomagnetic study of the Lisbon Volcanics (2).We must point out that in our paper (2) a post-Eocene rotation of 220 was not our unequivocal interpretation of the paleomagnetic data (3). As emphasized several times (2, 3), both graphically and otherwise, the accuracy of the paleomagnetic method is inherently limited. Therefore such precise interpretation (1) of our data is unwarranted. As stated in our abstract (2) and elsewhere, our conclusion is restricted to a belief that the rotation of the Iberian peninsula, which had previously been proposed by several authors using totally independent reasoning, may have occurrcd in part in post-Eocene times. This conclusion has been strongly challenged by Van der Voo (4), whose position is based on a large amount of paleomagnetic data from Paleozoic and Mesozoic rocks from Spain and Portugal. He and others prefer to think that the rotation ceased at the end of the Cretaceous period.We have reaffirmed our belief in the possibility of some post-Eocene rotation (5), but this has been repeatedly dismissed by Van (4) and probably could be used successfully on Acanthaster.The persistence of the high densities of sea urchins, long after they had eaten most of the food, has been puzzling. It seems unlikely that either the urchins or the coral-eating sea stars became "over efficient" as Chesher suggested (1). The urchins, and probably the sea stars, seem to be responding to unexpected and, with present knowledge, unpredictable events that follow environmental change by man. In the case of the urchins, the persisting high population densities may be the result of (i) destruction of their main predator, sea otters, during the close of the last century, (ii) depletion of an important competitor, abalone, during the past few decades, and (iii) enrichment of coastal waters with sewage effluent [amino acid enrichment from sewage adds significantly to the nutrition of urchins (5)

Aggregative feeding behavior in sea urchins leads to destructive grazing in a Nova Scotian kelp bed

“…Population outbreaks of sea urchins have repeatedly led to destructive grazing of kelp beds in temperate coastal regions (North & Pearse 1970, Breen & Mann 1976b, Hagen 1983, Johnson et al 2005, with dramatic implications for ecosystem productivity and services (Mann 1982). Kelps create 3-dimensional structure and provide food and habitat for a diverse fauna, including many ecologically or economically valuable species, such as fish, lobsters, and sea otters (Dayton 1985).…”

Population dynamics of coastal forests of Macrocystis pyrifera in Puerto Toro, Isla Navarino, Southern Chile

“…Grazing, especially by sea urchins, has been indicated to clear whole areas of kelp and subsequently prevent reforestation of barren areas (Aleem, 1956(Aleem, , 1973North, 1959North, , 1961McLean, 1962;Leighton et al, 1965;Neushul, 1965;Chapman, 1981). Biological or physical parameters affecting sea-urchin grazing activities therefore often result in sharp changes in kelp densities and sizes (North and Pearse, 1970;Lowry and Pearse, 1973;Estes and Palmisano, 1974;Breen and Mann, 1976;Mattison et al, 1977;Pearse and Hines, 1979;Duggins, 1980Duggins, , 1981Bernstein et al 1981). In southern California, however, Rosenthal et al (1974) found that storms and strong surge could produce kelp detachment, entanglement of drifting plants, and eventually clear whole areas which later showed increased juvenile settlement.…”

Overthrowing a regime shift: displacement of sea urchins by abalone in a kelp forest ecosystem

“…In addition loss of large predators and omnivores has resulted in declines in important trophic interactions within many kelp forest ecosystems (Dayton et al 1998). When left unconstrained, actively grazing sea urchins can convert multi-layered kelp forests into areas of coralline algal pavement (e.g., North and Pearse 1970, Simenstad et al 1978, Filbee-Dexter and Scheibling 2014 leading some ecologists to characterize sea urchin-kelp forest interactions as resulting in alternate stable states, regime shifts (Folke et al 2004, Petraitis and Dudgeon 2004, Estes et al 2011, or milestones of a declining ecosystem (Dayton et al 1998, Steneck et al 2004. Here the alternate regimes may persist for decades (Simenstad et al 1978, Scheibling et al 1999, Steneck et al 2002 and transitions among them have been triggered by sea urchin disease outbreaks Hines 1987, Scheibling et al 1999), physical disturbance from storms (Harris et al 1984, Ebeling et al 1985 and predation on sea urchins by sea otters, lobsters, crabs and large-bodied fishes (Estes et al 2004, Steneck et al 2004, Babcock et al 2010.…”

“…The two species are negatively associated at the scale of 25 m 2 in the shallow subtidal where their depth distributions overlap (Andrew and MacDiarmid 1999). The observed negative spatial associations among adults led early investigators to suggest that abalone and sea urchins competed for resources (North and Pearse 1970, Shepherd 1973a, Tegner and Levin 1982, Andrew and Underwood 1992. For example, Lowry and Pearse (1973) observed that when food was abundant, adult abalone displace sea urchins in crevices, demonstrating competition for space.…”