Facilitation between two introduced species in Patagonia: a mechanistical approach

PEREYRA, PATRICIO; SAAD, J. F.; GASTALDI, MARIANELA; DE LA BARRA, PAULA; GONZALEZ, RAÚL C.; NARVARTE, MAITE ANDREA

Puerto Madryn

Congreso; Congress of Marine Bioinvasions; 2018

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 structuralcomplexity, 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 bellow mature U. pinnatifida in November 2017 to promote spores settlement (n=20 for each treatment). In March 2018, we attached collected S. clava individuals ofwith similar size to tiles with the one adult mimics and attached them to tiles (n = 20) to test for biologicaleffects (i.e. 1 adult mimic (c) vs. live individuals). In May 2018 we retrieved all the experimental units. We found that more U. pinnatifida settled on alive S. clava than on (c), showing that S. clavamay 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.