Grazing Drives Spatial Variation in the Abundance and Distribution Patterns of Autotrophs in Tropical Rocky Shore


Edison D. Macusi1,2*

1Aquaculture and Fisheries Group, Wageningen Institute of Animal Sciences, Zodiac, De Elst (Building no. 122) P.O. Box 338 6700 AH Wageningen University of Life, Wageningen, The Netherlands
2University of the Philippines Los Baños College, Laguna, Philippines

corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it. / This email address is being protected from spambots. You need JavaScript enabled to view it.



Grazing is known as a fundamental process that shapes the community structure of many rocky shores. In this study, the impact of molluscan grazing on autotroph assemblage at different scales in Hong Kong rocky shores were assessed to test whether grazing have different impacts at different spatial scales. The recruitment of various autotrophs in the grazer manipulation experiments were monitored regularly. Most of the treatment plots were colonized by various macroalgae with ephemeral erect algae increasing in abundance in various mollusc exclusion plots throughout the study period. Erect algal cover increased abundantly in shores during the coldest month of winter. The most conspicuous effect of grazing was at the two Stanley sites and to a lesser degree at the Cape d’ Aguilar that were reflected in the low values of chlorophyll a and autotroph covers in the control and grazer access plots. Complete exclusion was not possible in the two Stanley sites because of the high number of grazer intruders that entered the plots. This strong grazing pressure kept the algal cover in the exclusion and control treatments similar and dominated by encrusting algae throughout the experimental period. Because of this, it appears that the observed growth of erect algae in the mollusc exclusion plots and its patchy distribution near the sites and in rock pools support the hypothesis that molluscan grazers are the major causes of low settlement and recruitment of erect algae in these shores during winter.



Rocky shores have long been the favorite study site of many experimental ecologists understanding intertidal habitats for their presence along coastlines, ease of access to rock platforms, beaches, and organisms with short generational times, and ease of manipulation . . . . . . . . . .





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