Foliose algal assemblages and deforested barren areas: phlorotannin content,sea urchin grazing and holdfast community structure in the Aleutian dragon kelp,Eualaria fistulosa

In the Aleutian Archipelago, two distinct organizational states of kelp forest communities exist, foliose algal assemblages and deforested barren areas. The canopy-forming kelp Eualaria fistulosa can be found in both states, although it is much less abundant in the deforested state. In contrast, sea urchins also occur in both states, but they are considerably more abundant in the deforested state. This study determined whether the protective phlorotannin content in E. fistulosa sporophylls that originated in foliose algal assemblages would differ from those that originated in deforested areas. We also examined sea urchin grazing rates on these sporophylls to determine whether there were any differences in grazing rates related to the origin of the sporophylls. Next, we determined whether taxon richness and abundance of E. fistulosa holdfast communities would differ depending on the origin of the holdfast. Our results showed that sporophylls that were collected in barren areas generally had higher phlorotannin content than sporophylls found in foliose algal assemblages, although phlorotannin content varied across the study area. Grazing rates on sporophyll tissue and holdfast community structure did not differ between foliose algal assemblages and barren areas. These results show that phlorotannin content is greatest in areas under high grazing pressure and that phlorotannins may possibly protect E. fistulosa and the holdfast communities from being grazed in barren areas.