Notes on the herbivory on Buxbaumia viridis sporophytes in the Pyrenees

Buxbaumia viridis is a bryophyte whose gametophyte is highly reduced, while its sporophyte is relatively large, present all year round in its different phenological stages. In the Pyrenees, where the species is present in humid forests, especially pure Abies alba or mixed A. alba and Fagus sylvatica forests, the sporophytes mature in spring, losing their winter green colour. Herbivory has been detected on young capsules in spring. Observed damages are mainly of two types: cut setae, where capsule is completely lost and whose responsible organism has not been identified; and more frequently, torn capsules where sporal mass is partly gone, sometimes only part of the theca at the base of the capsule remains. The responsible organisms in the second type are young slugs (genus Arion), what have been observed in situ twice. The animal tears the capsule and scrapes with its radula the sporal mass from the inside. Between 1999 and 2014, we visited 40 localities with Buxbaumia viridis populations, located in Navarra and Huesca on the southern versant of the Pyrenees, and Pyrénées-Atlantiques and Hautes-Pyrénées on the northern versant, aiming to estimate the number of individuals. Grazing on B. viridis capsules has been detected in 28 of these localities (70%), proving that this consumption is not accidental. Regarding the grazing rate, 10 localities showed consumption less than 20% of the total sporophyte number, 14 a consumption ranging from 21 to 59%, and finally, 4 were over 60% of grazed sporophytes. This sporophyte consumption is so high that it might have an important incidence on the species conservation.