Adaptations to barnacle fouling in the mangroves <Emphasis Type="Italic">Kandelia obovata</Emphasis> and <Emphasis Type="Italic">Aegiceras corniculatum</Emphasis> |
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Authors: | S W Li Benny K K Chan |
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Institution: | (1) The Swire Institute of Marine Science, Division of Ecology & Biodiversity, School of Biological Science, The University of Hong Kong, Pokfulam Road, Hong Kong;(2) Biodiversity Research Center, Academia Sinica, Taipei, 115, Taiwan |
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Abstract: | Mangrove trees planted for restoration or rehabilitation often fail to show satisfactory survivals. Although it is generally
assumed that barnacle fouling is a factor in mangrove mortality, the sub-lethal response of mangroves to this fouling is not
known. In the present study, we compare the leaf morphology (stomata density, leaf thickness, percentage thickness of palisade
layer and number of hypodermal layers), lenticel density and the plant fitness (number of flowers or droppers per tree) between
mangroves fouled by the acorn barnacle Fistulobalanus albicostatus (the fouled group, number of barnacles ~ 120 individuals per tree) and non-fouled mangroves (the control group). We observed
55 Kandelia obovata from three locations, two in Hong Kong (n = 35, fouled 25 and control 10) and one location in Taiwan (n = 20, fouled 10 and control 10). Aegiceras corniculatum (n = 45) was observed from two sites in Hong Kong, one on the east coast (n = 20, 10/10) and one on the west coast (n = 25, 10/15). In seedlings (K. obovata
n = 10, 5/5), fouling density did not affect leaf morphology. In mature trees, however, leaves from fouled trees had significantly
higher density of stomata and stem lenticel, a lower percentage thickness of leaf palisade layer and more layers of lower
hypodermis in the leaves, probably for compensating the impeded gaseous exchange functions of the lenticels. The number of
droppers and flowers on fouled mangroves was significantly lower. It is possible that after compensating for respiratory stress,
the plant had less energy available for reproduction. Although there was no obvious barnacle-induced mortality in this study,
barnacles appear to be related to a reduction in plant fitness. This may induce sufficient stress that over time fouled mangroves
cannot sustain viable populations. |
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