Colony Structure and Seasonal Differences in Light and Nitrogen Modify the Impact of Sessile Epifauna on the Giant Kelp Macrocystis pyrifera (L.) C Agardh |
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Authors: | Christopher D Hepburn Catriona L Hurd Russell D Frew |
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Institution: | (1) Department of Botany, University of Otago, 569001 Dunedin, New Zealand;(2) Department of Chemistry, University of Otago, 569001 Dunedin, New Zealand |
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Abstract: | The presence of the stoloniferous hydroid Obelia geniculata (L.) had no effect on the pigment concentration or nitrogen status of underlying blade tissue of the giant kelp Macrocystis pyrifera (L.) C. Agardh. The sheet-like colonies of the bryozoan Membranipora membranacea (L.) markedly reduced the pigment concentration of colonized blade tissue, but only during winter. Reductions in pigment
concentration are most likely a result of damage to underlying tissue due to some factor related to the presence of bryozoan
colonies on blade surfaces. Blade tissue colonized by M. membranacea also had higher δ15N signatures than surrounding bryozoan-free tissue, possibly indicating the provision of nitrogen to M. pyrifera by bryozoan colonies. Results show that seasonal changes in nitrogen and colony size can strongly modify the effect of epifauna
on macroalgae they colonize. Unlike bryozoans, hydroid colonies provided no barrier to nitrogen uptake by colonized M. pyrifera tissue and enhanced ammonium uptake was observed for tissue colonized by O. geniculata during nitrogen limitation. Epifauna with stoloniferous growth forms such as hydroids are more likely to have benign or even
mutualistic relationships with macroalgae they colonize than the sheet-like colonies of bryozoans. |
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Keywords: | ammonium bryozoan hydroids kelp Macrocystis nutrient uptake |
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