Published online by Cambridge University Press: 26 August 2014
In many coastal areas substrate is the limiting resource for benthicorganisms. Some sessile species can be used as secondary substrate, reducingcompetition and increasing coexistence. In southern Chile, annualpopulations of Macrocystis pyrifera recruit and grow on theshells of Crepipatella fecunda. This study describesecological interactions between the kelp and the slipper limpet over anannual cycle. The degree of kelp overgrowth was established by collectingsporophytes and through in situ submarine photography overa 10 month period (starting when kelp recruits became visible and endingwhen sporophytes were no longer present). Changes in the biochemicalcomposition of the limpet tissue were also recorded by chemical analyses, toevaluate the potential effects (positive/neutral/negative) of kelp on C. fecunda nutritional condition. The results indicatethat both species coexist, although kelp overgrowth may cause a decrease incarbohydrates in C. fecunda tissues, restricted to theperiod when the kelp forest reaches its maximum biomass. Individually, theshort duration of the maximum overgrowth period and the size reached by C. fecunda females (up to 65 mm shell length) may enablerapid limpet recovery, avoiding competitive exclusion. On a populationlevel, the M. pyrifera annual cycle generates the needed‘break’ for C. fecunda populations, reducing the effects ofkelp overgrowth. Thus, in the view of the neutral effect of kelp overgrowth,together with the positive effect of C. fecunda on M. pyrifera recruitment described somewhere else, thisecological interaction can be categorized as commensalism.