Growth and survival of juvenile red abalone (Haliotis rufescens) fed invasive macroalgae

Abalone is one of the most important small-scale fisheries in Mexico and is challenged by multiple stressors. For example, the loss of the native main food, Macrocystis pyrifera, and the subsequent takeover of non-indigenous algae species represent a major threat to abalone growth and survival. In Baja California, Mexico two introduced macroalgae, Undaria pinnatifida and Sargassum horneri have become common in the past decade with unknown consequences on native herbivores. In this work, we explored the effect of these invasive algae on the growth and survival of juvenile red abalone, Haliotis rufescens. One hundred and ten juvenile red abalone were tagged and fed with invasive algae U. pinnatifida and S. horneri, and a control with M. pyrifera. Then, the shell length, body weight, and survivorship were assessed monthly for 90 days. Results show that abalone fed U. pinnatifida had a total growth in length, weight, and survivorship, similar to those fed native M. pyrifera. In contrast, abalone fed S. horneri had significantly lower overall performance. Marine heatwaves and other climatic impacts are expected to favour the establishment of invasive species. These results may be relevant to inform local fisheries and management efforts in this area under future scenarios.