Interaction Between Colaconema daviesii and the Microscopic Stages of the Giant Kelp Macrocystis pyrifera Shows Negative Consequences to Gametophytes and Young Sporophytes

Colaconema daviesii has been described as an epi-endophyte of red algae. However, it has also been observed in vitro to colonize thalli of Macrocystis pyrifera, a giant kelp classified as a foundational organism of coastal marine ecosystems. This study aimed to determine, through co-cultivations, how C. daviesii affects the early stages of M. pyrifera, specifically gametophyte and sporophyte development. Determined were growth, oogonia formation, and gametophyte fertility, as well as sporophyte growth rate and survival. The results showed that the presence of C. daviesii negatively altered oogonia production and gametophyte fertility. Moreover, the survival of young sporophytes in co-cultures decreased. These findings demonstrate that the early developmental stages of M. pyrifera could be susceptible to infestation by a filamentous red alga, with negative consequences on fitness.