Seagrass-grazer interactions play a fundamental role in ecological processes by
regulating structure and functioning of plant communities. Within biotic connections,
herbivory is a crucial process because it involves the matter and energy transference from
primary producers to higher trophic levels, affecting the physical structure of the community
and ecosystem productivity. Contrary to previous beliefs, new insights suggest that grazing
may have an important impact on seagrass communities and that their grazers may be key to
understand seagrass food webs. Thus, the contrasting response found in previous research
may indicate that the susceptibility of seagrass species to be grazed may have a temporal and
spatial component and even within a community, a preferential consumption of some species
among others may exist depending on the palatability of their tissues. Therefore, the
assessment of the strength of the seagrass-grazers links and those mechanisms that regulate
this relationship, it is of crucial importance to increase our understanding on community and
ecosystem structure and dynamics. In addition, it is well known that seagrasses are living
under local and global threats, and consequently, there is a pressing need to include the global
change factors (eutrophication, acidification and warming) into the current experimental
approaches, in order to forecast the future responses of this fundamental community in the
changing world.
This PhD Thesis is structured in 6 chapters to answer particular questions about
seagrass-grazer interactions. In the first two chapters, the importance of hydrodynamics in the
seagrass-grazer interactions was studied, and it demonstrated how this abiotic factor acts as a
top-down regulator in the community. Moreover, seagrass acclimation to hydrodynamics
modulates intraspecific seagrass traits, and then seagrass palatability, influencing the selection
of leaves by consumers (chapters 2 and 3). On the other hand, eutrophication and the main
global change factors (i.e. warming and acidification) influenced positively Cymodocea nodosa
palatability through the alteration of leaf traits and by promoting the growth of epiphytes
(chapters 4 and 5). In the last chapter, we looked at the seagrass responses to biomass loss
promoted by herbivory, noting how the colonization states influences on the
compensation responses to herbivory in the fast-growing tropical species such as Halodule
wrightii.
The research presented in this PhD Thesis contributes to identify changes on
seagrass palatability under different environmental conditions and global change factors.
Particularly, this research displays how hydrodynamics modulate feeding behaviour of
consumers and how indirect effects of eutrophication and global change enhance
seagrass consumption by herbivores. In addition, this Thesis shows how
seagrass colonization states affect to compensatory responses derived by herbivore
damage.
The importance of considering biotic processes in conservation and management plans is
emphasized in order to enhance seagrass ecosystems resilience and to identify solutions to
support the maintenance of key ecosystem services provided by seagrass meadows to our
planet
