title for learn-about sections for chitons in A SNAIL'S ODYSSEY
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  Competitive interactions
  Topics of ecological interest in chitons include competitive interactions, considered here, and HABITAT PREFERENCES & ROLE AS HERBIVORES, GENETIC PATTERNS, and ORIENTATION & HOMING, considered in other sections.
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Research study 1

photograph of chiton Mopalia muscosaphotograph of limpet Lottia peltaOnthe central-California coast chitons Mopalia muscosa overlap in distribution with limpets Lottia pelta.  The 2 species shelter under cover of the brown alga Silvetia compressa and compete for algal foods growing there, in particular, the red algae Mastocarpus papillatus and Endocladia muricata.  The competition takes the form of active displacement, with the chiton shoving the limpet aside with its girdle.  Apparently, L. pelta is the only limpet species to be so excluded by Mopalia.  Connor 1975 Veliger 18 (Suppl): 9; see also Smith 1975 Veliger 18(Suppl): 57.

Research study 2

graph showing effects of chiton Katharina tunicata additions and removals on abundance of limpetsIn San Juan Island, Washington the black-leather chiton Katharina tunicata overlaps in distribution with at least 2 limpet species, Lottia pelta and L. scutum.  Katharina consumes both macro- and microalgae (diatoms), while the limpets eat mainly microalgae.  Experimental removal of all Katharina from 2 areas results in a significant rise in macroalgal cover and disappearance of the limpets over a 3-y period (see top graph). In contrast, experimental increase in chiton numbers at another site leads to greater abundance of limpets, and to greater reproductive output of both chitons and limpets (see bottom graph). These unexpected results are explained by the authors in this way: macroalgae outcompete diatoms for space on the rocks. The limpets depend upon the chitons to remove the macroalgae, thus allowing diatoms to grow and thereby providing food for the limpets. The authors describe the relationship of the 2 consumers as an “indirect commensalism”, in that one of the partners, the limpet, benefits from the association, while the other, the chiton, is not affected.  Dethier & Duggins 1984 Amer Nat 124: 205.

NOTE  the diet of K. tunicata in this area includes macroalgae including corallines, diatoms, and a variety of animal matter

NOTE  all chitons removed from the 2 experimental 25m2 plots (2900 individuals) are added to a third 25m2 plot. Data from replicate areas have been combined in the graphs for visual clarity