Graduate Thesis Or Dissertation
 

The feeding ecology of the gumboot chiton, Cryptochiton stelleri (Middendorff, 1846)

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  • Investigations about the feeding ecology of a consumer can facilitate prediction of its effects on prey populations and the biological community. The aspects of feeding ecology that are important to predicting consumer effects include foraging movements, feeding preference and selectivity, and the effects of physical factors on foraging behavior and feeding rates. All of these aspects were investigated for a large invertebrate marine herbivore, Cryptochiton stelleri (Middendorff, 1846), the gumboot chiton. The movements of 252 Cryptochiton were observed during periods ranging from 1 to 512 days. Movements of subtidal chitons were significantly greater than those of intertidal chitons during the same time period. Movements of intertidal chitons on emergent substrata were not significantly different from those on submergent substrata. The home ranges of subtidal chitons were, in general, significantly larger that those of intertidal chitons. These patterns suggested that the impact of intertidal chitons on macroalgae will be more restricted in area than for subtidal chitons. Assuming that consumption rates are equal, the impact of an intertidal chiton would be more concentrated, thus causing a more patchy effect. The feeding behavior of Cryptochiton was examined by comparing laboratory preferences to selectivity calculated from actual availability and feeding observations in the field. Laboratory experiments indicated that Cryptochiton chiefly prefers perennial red algae such as Iridaea cordata and Cryptopleura spp. The most available algae in the field were Hedophyllum sessile, Odonthalia floccosa and ulvoids. The actual field diet was a mixture of all these species, which suggests that preference behavior interacted with availability to yield a diet that was different than that expected due to either factor alone. The effects of environmental harshness on the feeding behavior and consumption rates of the gumboot chiton, Cryptochiton stelleri were studied on the central coast of Oregon. Behavioral observations suggested that these chitons were much less active on substrata that were exposed at low tide than on submergent substrata. Intertidal chitons were much more active on low tides following heavy and medium wave action than following calm waves. Subtidal chitons were significantly more active during calm waves than during heavy wave action. Further, inclusion experiments indicated that grazing rates on Iridaea cordata were significantly higher at a wave-protected site than at an adjacent wave-exposed site.
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