EFFECTS OF FEEDING PRESSURE AND LOW-LIGHT STRESS ON THE PERFORMANCE OF ANTIHERBIVORE DEFENSES IN THE TWO RED ALGAE Gracilaria edulis AND Gracilaria salicomia FROM THE MALAY PENINSULAR
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Date
2009
Journal Title
Journal ISSN
Volume Title
Publisher
Journal of Sustainability Science and Management
Abstract
The objective of this study was to test for the inducibility of an anti-feeding defense
in two red macroalgal from the coast of the Malay Peninsular as a response to grazing pressure.
Whether the defense capacity in these seaweeds is generally impaired by low-light stress was also
investigated. Aquaria with blackened walls connected to a :flow-through water system were used
as Experimental Units (EUs). Different light regimes were established using layers of black gauze
material and clear perspex lids, mounted on top ofthe EU. The gauze allowed the stepwise reduction
of ambient light. Six different light levels with eight replicates each were realised. The growth
rates of algal exposed to different light levels were calculated using a linear regression analysis.
Using outdoor mesocosm facilities, three fully-factorial experiments were realised during which
low-light stress on different algae-grazer combinations was induced: 1) the red algae Gracilaria
edulis with the sea hare Aplysia sp., 2) G. edulis with the abalone Haliotis diversicolor, and 3)
Gracilaria salicornia with H diversicolor. For each combination, 48 aquaria were used, while in
a control group of another 48 tanks, algae were kept in the absence ofherbivores. Following lowlight and feeding-stress induction, herbivore consumption on algal material was assessed in feeding
assays with living thalli fragments. Negative effects of light reduction on algal growth rates was
observed in both experiments with G. edulis and in one trial with G. salicornia, while general
effects of low-light stress on seaweed palatability were absent in our study. By contrast, for some
herbivore-algal combinations, significant differences in consumption were detected on previouslygrazed and ungrazed algal material, that indicates the presence of an inducible defense. G. edulis
and G. salicornia produced defenses when exposed to grazing by the gastropod Aplysia sp. and H
diversicolor, respectively. In contrast, G. edulis showed no response to H diversicolor. Our findings
show that inducible defenses generally exist in the two investigated Gracilaria species, but vary
with the identity ofherbivores. Surprisingly, algal palatability was not affected throughout all lowlight regimes, contrasting the widespread notion that defensive traits in seaweeds are dependent
on metabolic energy. Thus, it appears that low-light stress effects play only a minor role on the
performance of antiherbivore defenses in these two red algae.
Description
Keywords
Antiherbivore defense, red algae, grazers, low-light stress, palatability