The influence of light attenuation on the biogeomorphology of a marine karst cave: a case study of Puerto Princesa Underground River, Palawan, the Philippines

Coombes, M. A., La Marca, E. C., Naylor, L. A. , Piccini, L., De Waele, J. and Sauro, F. (2015) The influence of light attenuation on the biogeomorphology of a marine karst cave: a case study of Puerto Princesa Underground River, Palawan, the Philippines. Geomorphology, 229, pp. 125-133. (doi: 10.1016/j.geomorph.2014.10.007)

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Abstract

Karst caves are unique biogeomorphological systems. Cave walls offer habitat for microorganisms which in-turn have a geomorphological role via their involvement in rock weathering, erosion and mineralisation. The attenuation of light with distance into caves is known to affect ecology, but the implications of this for biogeomorphological processes and forms have seldom been examined. Here we describe a semi-quantitative microscopy study comparing the extent, structure, and thickness of biocover and depth of endolithic penetration for samples of rock from the Puerto Princesa Underground River system in Palawan, the Philippines, which is a natural UNESCO World Heritage Site. Organic growth at the entrance of the cave was abundant (100% occurrence) and complex, dominated by phototrophic organisms (green microalgae, diatoms, cyanobacteria, mosses and lichens). Thickness of this layer was 0.28 ± 0.18 mm with active endolith penetration into the limestone (mean depth = 0.13 ± 0.03 mm). In contrast, phototrophs were rare 50 m into the cave and biofilm cover was significantly thinner (0.01 ± 0.01 mm, p < 0.000) and spatially patchy (33% occurrence). Endolithic penetration here was also shallower (< 0.01 mm, p < 0.000) and non-uniform. Biofilm was found 250 m into the cave, but with a complete absence of phototrophs and no evidence of endolithic bioerosion. We attribute these findings to light-induced stress gradients, showing that the influence of light on phototroph abundance has knock-on consequences for the development of limestone morphological features. In marine caves this includes notches, which were most well-developed at the sheltered cave entrance of our study site, and for which variability in formation rates between locations is currently poorly understood.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Naylor, Dr Larissa
Authors: Coombes, M. A., La Marca, E. C., Naylor, L. A., Piccini, L., De Waele, J., and Sauro, F.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Geomorphology
Publisher:Elsevier B.V.
ISSN:0169-555X
ISSN (Online):1872-695X
Copyright Holders:Copyright © 2015 Elsevier B. V.
First Published:First published in Geomorphology 229:125-133
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher.

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