MEPS 229:33-42 (2002)  -  doi:10.3354/meps229033

Grazing on intertidal microphytobenthos by macrofauna: is pheophorbide a a useful marker?

R. B. Ford*, C. Honeywill

Gatty Marine Laboratory, PO Box 349, Warkworth, New Zealand

ABSTRACT: This study critically evaluates the use of pheophorbide a as a marker pigment for macrofaunal grazing intensity in intertidal sediments. Based upon evidence from planktonic studies pheophorbide a has recently been used to quantify grazing in the sediments; however, no accurate tests have been made of the application of these planktonic concepts to the benthos. Laboratory and field examinations used the cosmopolitan species Arenicola marina, Corophium volutator and Hydrobia ulvae, as well as natural field assemblages from the Eden estuary, Scotland, to examine the relationship between grazing and pigment composition. Faeces from the 3 species were examined using high performance liquid chromatography and showed no sign of pheophorbide a, but all species showed concentrations of Œchlorophyll a-like¹ (chl a) grazing products. In laboratory manipulations, a negative relationship was apparent between grazer numbers and the concentrations of pheophorbide a and grazing products. In the field, pheophorbide a was rarely found but grazing products were present in consistently measurable amounts. When relevant physical and biological factors were regressed against grazing product concentration, a significant relationship was found with an adjusted R2 of 0.76. This multiple regression used 4 factors to predict chl a degradation concentration; however, the relationship was dominated by a positive relationship with chl a concentration and only 1 of the other 3 factors was directly related to grazing intensity. Neither pheophorbide a nor Œchl a-like¹ grazing products were found to be useful as marker pigments of macrofaunal grazing intensity in the intertidal system studied. This places doubt upon the use of pheophorbide a as a marker of macrofaunal grazing intensity in intertidal sediments in past papers, and discourages the use of any marker pigment in estuarine sediments without prior testing.

KEY WORDS: Intertidal sediments · Chl a · Pheophorbide a · Degradation · Grazing · Macrofauna · Microphytobenthos · Eden estuary · Scotland

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