Long Term Faunal Changes at Hopkins Marine Station

Our impetus for historical studies of the intertidal zone at Hopkins Marine Station (HMS) was the observation by Charles Baxter, a Stanford University lecturer, that intertidal species composition had changed dramatically since his arrival at HMS in the late 1970s. In spring 1993, we relocated the original brass bolts that marked an intertidal transect established by W.G. Hewatt in 1931

Figure 3.1. Map of Monterey Bay, California.

(Hewatt 1934, 1937) at HMS (Fig. 3.2A, B).The transect runs for 98.8 m perpendicular to shore from high to low intertidal zone. Hewatt had recorded the abundance of invertebrates in over 100 square-yard plots along this transect. Between 1993 and 1995 we resurveyed 57 of the square-yard (0.84 m2) plots in the exact location of Hewatt's plots in order to compare abundances of inverte-brates.We had sufficient data to quantitatively compare 62 species, representing a range of intertidal taxa, trophic levels, and life-history strategies. Changes in these species are shown in Figure 3.3. Almost all species changed in abundance, with 46 species showing a significant change in abundance (paired i-test, P < 0.05), but there was no overall direction of change, with 24 species increasing and 22 decreasing.

In contrast, a very strong pattern of change appears when species are considered by their geographic range. We assigned each species to a geographic range category based on its range relative to the study site in Monterey Bay as reported in the most comprehensive guides to the fauna (primarily Brusca 1980, Morris et al. 1980,

Hewatt Transect Hopkins
Figure 3.2. Photos of investigators on Hewatt's transect. (A) W. G. Hewatt ca. 1932. (B) Raphael Sagarin 1998.

Ricketts et al. 1985). Species with a northern limit south of Cape Mendocino, California, were considered southern species. Those with a southern limit north of Point Conception, California, were considered northern species, and those with boundaries extending

V Q Irt

Figure 3.3. Plot of density in 1995 vs. density in Hewatt's study in 57 paired plots for 62 species. Solid symbols are species that showed a significant change in abundance between the two studies (paired t-test, P < 0.05).

Log(Hewatt Density +1)

Log(Hewatt Density +1)

Figure 3.3. Plot of density in 1995 vs. density in Hewatt's study in 57 paired plots for 62 species. Solid symbols are species that showed a significant change in abundance between the two studies (paired t-test, P < 0.05).

* Cosmopolitan

Log(Hewatt Density +1)

Figure 3.4. Plot of density in 1995 vs. density in Hewatt's study in 57 paired plots for 62 species. Solid symbols are species that showed a significant change in abundance between the two studies (paired t-test, P < 0.05). Open symbols are nonsignificant changes. Southern species: circles. Northern species: squares. Cosmopolitan species: triangles. Ap: Acanthina punctulata (snail); Ac: Alpheus clamator (shrimp); Ae: Antho-pleura elegantissima (anemone); Aec: Anthopleura elegantissima (anemone, clonal form); Ax: Anthopleura xanthogrammica (anemone); Cl: Calliostoma ligatum (snail); Cc: Corynactis californica (anemone); Ca: Crepidula adunca (snail); Ch: Lepidochitona (Cyanoplax) hartwegii (chiton); Ev: Erato vitellina (snail); Fv: Fissurella volcano (limpet); Lh: Leptasterias hexactis (sea star); Oc: Ocenebra circumtexta (snail); Pc: Petrolisthes cinctipes (crab); Pt: Pseudomelatoma torosa (snail); Ss: Serpulorbis squamigerus (tube snail); Ts: Tectura scutum (limpet);Tr: Tetraclita rubescens (barnacle). Adapted from Sagarin et al. 1999.

beyond these points in both directions were considered cosmopolitan species.

Division of species in this manner reveals a dramatic range-related pattern of species' abundance changes (Fig. 3.4). Almost all southern species (10 of 11) increased in abundance, whereas most northern species (5 of 7) decreased. Cosmopolitan species showed no trend, with 12 increasing and 16 decreasing.

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