Phenotypic plasticity in a mutualistic association between the sponge Haliclona caerulea and the calcareous macroalga Jania adherens induced by transplanting experiments. I: morphological responses of the sponge |
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Authors: | José Luis Carballo Enrique Ávila Susana Enríquez Leonardo Camacho |
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Institution: | (1) Laboratorio de Ecología del Bentos. Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Apartado Postal 811, Mazatlán, 82000, Mexico;(2) Laboratorio de Fotobiología. Unidad Académica Puerto Morelos. Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Apartado Postal 1152, Cancun, 77500, Mexico;(3) Postgrado en Ciencias del Mar y Limnología, UNAM, Mazatlán, Mexico |
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Abstract: | The mutualistic association between the sponge Haliclona caerulea and the calcareous red macroalga Jania adherens is conspicuous on shallow rocky regions of Mazatlán Bay (eastern tropical Pacific, Mexico). Transplanting experiments were
carried out to examine the morphological responses of the association to an environmental depth gradient. Simultaneously,
we conducted caging experiments to examine the effects of predation (mainly by angelfishes) on association morphology. For
this, we transplanted specimens of the association from a control area at 3 m depth to depths of 1 and 5 m, and measured the
morphological responses in the association (macro- and microstructure) from the three sites before and after 103 days. The
association had the capacity to adjust both macro and micromorphologically, and both external morphology and body structure
changed significantly with depth. The specimens grown at 1 m developed a larger surface area of attachment, higher organic
density and higher inorganic content than the control specimens at 3 m, and the organisms grown at 5 m depth. We also detected
significant differences in the aquiferous system of the sponge, which developed smaller and more numerous oscula at 1 m than
at 5 m depth. These differences seem to be consistent with the wave movement as one of the main regulatory factors of the
morphology of the association. However, the spicules from H. caerulea were most slender in shallow water, which is not consistent with increasing robustness in the face of greater wave force.
The algal skeleton supplied up to 27% of the total inorganic structure of the association; thus, algal contribution significantly
reduces the energy costs of spicule production, specifically under high wave exposure, when H. caerulea requires structural reinforcement relative to organic content. The contribution of the sponge to the association (as ratio
Si to CaCO3) increased significantly from 3 to 5 m (12% in the uncaged specimens and 22% in the caged specimens), showing that the mutualistic
relationship decreases with depth. The production of sponge branches in caged individuals was the most notable difference
from uncaged morphs, which could suggest the effect of predators like angelfishes. However, branches could also be a response
to the reduction in water movement and irradiance inside the cages. Sponges are known to show morphological acclimation in
response to habitat variation, but this is the first study to show it in a sponge living in association with a macroalga. |
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