Facilitation between two introduced species in Patagonia: a mechanistical approach

PATRICIO PEREYRA; SAAD, JUAN FRANCISCO; MARIANELA GASTALDI; PAULA DE LA BARRA; RAÚL GONZALEZ; MAITE NARVARTE

Puerto Madryn

Congreso; Xth International Conference of Marine Bioinvasions; 2018

CENPAT

Positive interactions are increasingly studied in marine environments. We were recently able to document a novel interaction between two introduced species, the clubbed tunicate Styela clava and the macroalga ?wakame? Undaria pinnatifida, in which the presence and abundance of U. pinnatifida was favored by the occurrence of S. clava. We inquired if this was due to a biological effect (i.e. presence of S. clava vs. an inanimate, erect substrate), or if it was due to a greater added complexity, either in total area available for settlement or in height (i.e. increasing access to light). To test this, we made mimics of synthetic rubber that copied adult (10 ± 3 cm) and juvenile (3 ± 1 cm) individuals of S. clava, and arranged them in four different groups of structural complexity, from higher to lower complexity: (a) 5 adult mimics, (b) 5 juvenile mimics, (c) 1 adult mimic and (d) 1 juvenile mimic. We deployed them (n = 20 for each treatment) in an inner channel of San Antonio Bay below mature U. pinnatifida in November 2017 to promote spores settlement. In March 2018, we collected S. clava individuals with similar size to the adult mimics and attached them to tiles (n = 20) to test for biological effects. In May 2018 we retrieved all the experimental units. We found that more U. pinnatifida settled on alive S. clava than on mimics, showing that S. clava may offer additional benefits than only more area for settlement. We also found a larger number of U. pinnatifida per area in adult than in juvenile mimics, but the density of mimics did not affect the response, showing that U. pinnatifida takes more advantage at settling on adult than on juveniles mimics, possibly related with greater access to light.