Ecology of west Iberian kelps: Laminaria ochroleuca and Saccorhiza polyschides living near their distributional limits

Tese de Doutoramento, Ecologia (Ecologia das Populações), Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015

This thesis focused on the understudied western Iberian kelps. Chapter I focused on population dynamics. With exception of L. hyperborea, shallow kelp forests seemed to be self sustainable, although highly impacted by extreme environmental conditions. With further climate change, it might be expected that the shallower population will become younger and dependent on spore dispersal from the subtidal. In Chapter II the resilience of shallow L. ochroleuca populations was studied. In one of the sites, canopy was completely removed during a storm. Results indicate that extensive removal hampers the population’s ability to recover as it stripes the area from individuals big enough to produce spores. In addition, the lack of protection offered by the canopy hampers recruitment. S. polyschides has different life histories across latitudes. At the poleward range, individuals are able to overwinter and recruit year-round, while low-latitude macroscopic sporophytes are seasonal. While this difference has commonly been attributed to temperature limitations, chapter III shows that temperature does not offer an explanation for the different life histories, raising the novel hypothesis that such difference was caused by nutrient limitations at low-latitudes. Chapter IV focused on the microscopic development of L. ochroleuca and S. polyschides. While they showed similar temperature limitations, S. polyschides showed overall lower mortality and quicker development, despite showing more vegetative growth by the gametophytes when compared to unicellular L. ochroleuca female gametophytes. As both L. ochroleuca and S. polyschides can be found in shallow areas, their thermal stress responses were compared by exposing recruits of the two species, from the geographical edges of distribution of L. ochroleuca, to repeated heat shock, simulating low tides. Recruits of L. ochroleuca from the low latitude areas were the most resistant, while no differences were observed between S. polyschides from the two latitudes.

The projects PTDC/AACCLI/109108/2008 and EXCL/AAG-GLO/0661/2012, the French Research Agency ANR Biodiversity Project: ANR BDIV 012. The work was also aided by ASSEMBLE remote access grant nº 227799.