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MEPS prepress abstract   -  DOI:

Seasonal changes in facilitation between an ascidian and a kelp in Patagonia

Andrea Evangelina Arcángel*, Emiliano Alexis Rodríguez, Paula de la Barra, Patricio Javier Pereyra, Maite Narvarte

*Corresponding author:

ABSTRACT: Positive interactions may change in outcome over time and depending on which of the interacting species is studied. We explored the seasonal patterns of facilitation between Styela clava and Undaria pinnatifida by following their association for a complete sporophytic phase. In addition, we investigated how the relationship affected the morphometric parameters of U. pinnatifida, and if the association had a negative outcome for S. clava. We performed monthly surveys in San Antonio Bay (Argentina) for nearly one year to evaluate U. pinnatifida’s density (both the total and mature individuals exclusively) on different substrates to determine whether U. pinnatifida was more closely associated with S. clava than with inert substrates (i.e., consolidated and nonconsolidated). Moreover, we compared the morphometry of U. pinnatifida between substrates (S. clava vs. rock) and collected S. clava individuals overgrown by U. pinnatifida and classified them by their holdfast’s coverage to assess their condition (dead or alive). A higher total density of individuals of U. pinnatifida was associated with S. clava than with other substrates from autumn to spring. Undaria pinnatifida individuals growing on S. clava were smaller than those growing on rock. Finally, the probability of S. clava dying increased for individuals with higher holdfast coverage, although the scarcity of dead individuals found suggested a negligible influence. Our findings suggest, whereas U. pinnatifida clearly benefitted from this interaction by appearing earlier on the field and presenting higher densities that could benefit the population when associated to S. clava, for S. clava the relationship was more neutral.