Canopy-forming gelidiales from the canary islandsmorphology, reproduction and historical evolution of their populations

Resumen

In the Canary Islands occurrence of 16 species of Gelidiales is currently accepted. Among these, Gelidium canariense, G. arbuscula and Pterocladiella capillacea are the only canopy-forming species. Additionally, these macroalgae are important primary producers on exposed rocky shores in the islands, which highlights the relevance and importance of the Gelidiales to the benthic marine communities in the archipelago. In chapter 1 a detailed review about previous studies of the species of Gelidiales in the Canary Islands is presented. This chapter serves as an introduction of this thesis, as it identifies any knowledge gap on the studies of Gelidiales in the archipelago and, in combination with conclusions based on previous studies, the chapter forecast future changes to the marine ecosystems, as well as, conservation and recovery plans for their populations. Among the three dominant and habitat-forming Gelidiales in the archipelago, Gelidium canariense is the only endemic species growing in wave-exposed upper sublittoral communities in the north rocky shores of the western islands. This perennial macroalgae is easily recognizable by its unique overall appearance and blackish colour, however, some diagnostic features of the male and female gametophytes were poorly known or yet undescribed. In chapter 2 we aimed to fill this knowledge gap in the morphology and phenology of the species. We also analyzed the morphological variables that best explain the morphotypes, as well as, their spatial and temporal variations according to life-cycle phases. All this information is pivotal for further comparisons with available material of the TFC Phyc (Universidad de La Laguna-SEGAI) which, eventually, will help us understand the historical evolution of this endemic species. Recently, G. canariense and G. arbuscula have been classified as vulnerable species in the List of Wild Species under Special Protection Regime and Spanish Catalog of Threatened Species. The attachment to and colonization of a new substratum by spores is one of the most important processes in the life cycle of benthic marine algae. In particular, spore settlement and development are bottlenecks for resilience of several habitat-forming macroalgae species. Hence, a detailed description of the tetraspore germination of G. canariense and G. arbuscula is presented in chapter 3. In this chapter the tetraspore germination and the growth curve of the primary rhizoids for one week of these vulnerable Gelidiales from the Canary Islands is performed for the first time. The spore germination pattern is common in the Gelidiales species according to old references. However, the time intervals of the initial stages of spores for different Gelidiales species has not been examined and it may be essential for the sustainability of the species. Species vulnerability to global warming and changes in ultraviolet radiation may depend on both ecological and geographical characteristics as well as, the ability of organisms to adapt to new conditions or successfully disperse and migrate to existing suitable habitats. According to observational historical data, populations of G. canariense have suffered an extensive decline in recent decades. Nevertheless, no previous studies have supported this observation with accurate data or characterized the relationship of this species with environmental changes. Hence, our goal in chapter 4 was to provide useful data for analyzing the conservation status of this species. In particular, we evaluated changes in the distribution of the endemic macroalga G. canariense during the last 30 years in the north coast of Tenerife and we determined the variation in macroalgae assemblages dominated by G. canariense over the last decade in the island. Finally, we explored whether these changes correlate with the actual trends of some climatic variables in a scenario of global environmental change. Understanding and forecasting the effects of climate change on vulnerable species are of main concern to biologist and ecologist. Herbarium collections are consider real witnesses to biodiversity changes as they can gather information that goes back since decades to centuries. In chapter 5 we assess long-term changes in the size of the thallus and reproductive effort of the asexual individuals (sporophytes) of all specimens deposited in the herbarium TFC Phyc (Universidad de La Laguna-SEGAI) of G. canariense, G. arbuscula and P. capillacea. Furthermore, we study the effects of the increase in sea water temperature and incident light in net primary production and we also study the effect of extreme desiccation on the relative water content and net primary production of the three species of Gelidiales. This combination of historical morphological changes with experimental studies will enable us to elucidate possible major drivers on the progressive changes that these species are facing at individual and population levels. Finally, the genetic sequencing of herbarium specimens also provides a new tool to asses historical evolution of populations in macroalgae. Hence, in chapter 6 we perform the first genetic study of historical specimens of the herbarium TFC Phyc of G. canariense. Particularly, we study the genetic variability of the endemic species over the last 40 years in Tenerife using the mitochondrial intergenic marker cox2-3. We also assess the genetic diversity at the mesoscale (<100 km) i.e., between two localities on the north coast of Tenerife and at the macroscale (>100 km) using specimens collected on the island of La Palma using cox2-3 spacer. In this chapter we want to establish a baseline (i.e., extraction method, PCR protocol for mitochondrial markers, level of DNA degradation of herbarium samples) of the genetic characterization of G. canariense that can be used in future molecular studies to better understand the genetic strategy of populations of this vulnerable species.