Hutchinson, N., and Williams, Gray A. (2003) An assessment of variation in molluscan grazing pressure on Hong Kong rocky shores. Marine Biology, 142. pp. 495-507.

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Abstract

Several methods of assessment have been used to document variation in grazing pressure on temperate rocky shores, although often these methods are applied without consideration of local conditions or species. In this study, a comparison was made between abundance counts of inactive molluscan grazers at low tide, direct observations of grazer activity and distribution throughout day and night tidal cycles, and records of grazing marks on wax discs, for the mid-shore of Hong Kong. The abundance of grazers found during low-tide counts varied among dates, sites and species. This method, however, did not record all grazer species that day/night observations showed to migrate from the low shore with the rising tide. Low-tide counts, therefore, underestimate grazing pressure (number of active grazers per unit area) and grazer guild (number of species). Grazing marks on wax discs also recorded a greater number of species than the low-tide counts of inactive grazers, and included grazers that were seen to migrate up shore during day/night observations. Certain limpet species, however, avoided the wax and did not leave grazing marks, showing this method to also underestimate grazing pressure. All methods showed grazing pressure to be variable at spatial scales of tens of metres or less and also temporally variable between sampling dates. The sole use of either low-tide counts or wax discs is likely to underestimate grazing pressure, due to variation in shore topography and grazer foraging behaviour, especially on shores with a narrow tidal range such as in Hong Kong. To gain a more accurate assessment of total grazing pressure, it is suggested that recording of grazing marks on wax discs should be used in conjunction with direct day/night observations.

Item ID:	45437
Item Type:	Article (Research - C1)
ISSN:	1432-1793
Keywords:	intertidal ecology; tropical rocky shore; herbivory; gastropod; mollusk; mollusc
Copyright Information:	© Springer-Verlag 2002
Date Deposited:	29 Aug 2023 01:10
FoR Codes:	31 BIOLOGICAL SCIENCES > 3103 Ecology > 310305 Marine and estuarine ecology (incl. marine ichthyology) @ 80% 31 BIOLOGICAL SCIENCES > 3109 Zoology > 310913 Invertebrate biology @ 20%
SEO Codes:	18 ENVIRONMENTAL MANAGEMENT > 1802 Coastal and estuarine systems and management > 180201 Assessment and management of coastal and estuarine ecosystems @ 50% 18 ENVIRONMENTAL MANAGEMENT > 1805 Marine systems and management > 180504 Marine biodiversity @ 50%
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