A checklist of vascular epiphytes of El Cometa Lagoon , Pantanos de Centla Biosphere Reserve , Mexico

This study presents an updated checklist of vascular epiphytes found in the highly-conserved mangrove forest surrounding El Cometa Lagoon inside Pantanos de Centla Biosphere Reserve, Mexico. In order to perform this task, 25 sampling units were established at the study site and were visited at two stages, once in 2014 and next in 2016. Inside each sampling unit, all the epiphyte species found on host trees with a diameter at breast height 10cm were recorded. The complete epiphyte species list included 25 species belonging to 18 different genera. The richest family was Orchidaceae with nine species and the richest genus was Tillandsia with seven species. Additionally, the total epiphyte richness found in this study was among the highest reported for mangrove forests in Mexico. Epiphyte studies in mangrove forests are uncommon; therefore, this list is the first step to identify vascular epiphytes in the region and contribute to its proper conservation.

Mangrove forests are ecosystems of great economic and ecological importance in the tropical and subtropical coasts of the world (Tomlinson 2016).These ecosystems also harbour high functional diversity and productivity (Zaldívar-Jiménez et al. 2004;Rog et al. 2017).Mangrove forests are also very important ecosystems for carbon cycling dynamics because they are among the highest carbon sinks in terrestrial ecosystems (an average of 937tC ha -1 ) (Donato et al. 2011;Alongi 2012).
Mangroves are one of the most studied coastal ecosystems in the world (Rioja-Nieto et al. 2017).Nevertheless, few studies have evaluated the epiphyte ecology and diversity in mangrove forests (Gómez & Winkler 1991;Robertson & Platt 2001;Zotz & Reuter 2009;Cach-Pérez et al. 2013;Jiménez-López et al. 2017;Sousa & Colpo 2017).According to these studies, higher epiphyte diversity has been related to: The main objective of this study was to enlist the epiphyte species found in one of the most conserved subtropical mangrove forests in southern Mexico.The study was performed in a mangrove forest (Rzedowski 1978) located around El Cometa Lagoon inside Pantanos de Centla Biosphere Reserve (PCBR), Tabasco State, Mexico (Fig. 1).The dominant host trees were Rhizophora mangle L. and Bucida buceras L. (Jiménez-López et al. 2017;Solórzano et al. 2018).Two different time periods were required to obtain an adequate sampling of the forest, 10 days in July 2014 and 23 days in November 2016.The sampling units were concentrated on the southeast area of the lagoon where one of the most conserved parts of the forest can be found.Twenty 50×25 field plots (1,250m 2 each) and five transects of 50×5m (250m 2 ) were used to sample the vegetation.The 20 plots were arranged following two gradients, a distance-to-the-lagoon and distance-to-thebiggest-channel, while using a minimal distance of 100m between plots (modified from Sousa & Colpo 2017; Fig. 1).The remaining five transects were located in the vicinity of some of the previous plots in rich epiphyte areas, in order to increase the probability of registering most of the epiphyte richness of the site.Due to the reported correlation between host tree size and epiphyte richness in mangrove forests (Cach-Pérez et al. 2013), the biggest host tree individuals were expected to harbor most of the epiphyte richness.Therefore, epiphyte individuals were collected only from the host trees that had a diameter at breast height (DBH, breast height=1.30m)≥ 10cm (modified from Flores-Palacios & García-Franco 2006, 2008).
In order to identify the species, one to three epiphyte individuals that had a visible reproductive structure (i.e., either flower or fruit) were collected.When the individuals did not show any reproductive structure, they were collected and then grown ex situ in controlled conditions until they developed reproductive structures.Only afterwards the species was identified.Unfortunately, one species, Myrmecophila aff.tibicinis, did not show any type of reproductive structure during the study period; thus, its identity was not confirmed.
Every collected individual was pressed following conventional techniques (Lot & Chiang 1986) and was deposited in the HEM Herbarium of the Universidad de Ciencias y Artes de Chiapas.The species identity of every plant was determined using the specialized literature of Araceae (Croat 1983;Díaz-Jiménez et al. 2015), Cactaceae (Korotkova et al. 2017), Bromeliaceae (Ramírez-Morillo et al. 2004), Orchidaceae (Hágsater et al. 2005), and Polypodiaceae (Christenhusz et al. 2011; PPG I 2016) families and consulted with specialists (see Acknowledgements).Additionally, in order to obtain information about the vegetation types where each species can be found and their geographic distribution, the epiphyte collections at MEXU, HEM, CSAT, and UJAT herbaria were consulted.The scientific names of each recorded species followed Soto et al. (2007), while all species authors followed tropicos.org(https://www.tropicos.org)criteria.
In total, 25 epiphyte species (Appendix 1, Images 1 & 2) were reported.In terms of plant families, Orchidaceae was the richest family with nine species, followed by Bromeliaceae with eight species, and Polypodiaceae with four species (Appendix).The richest genus was Tillandsia L. with seven species, followed by Trichocentrum Poepp.& Endl.with two species.The number of species found in El Cometa Lagoon is equivalent to 17.13% of all the species reported in mangroves in Mexico (Carmona-Díaz & Hernández 2015).This means that in terms of vascular epiphyte richness, El Cometa Lagoon is currently ranked as the second richest mangrove forest in Mexico, after Sontecomapan (Magaña 1999;Valdez-Hernández 2000;Carmona-Díaz et al. 2004;Díaz-Jiménez 2007).
We suggest that Laelia anceps L., a previously reported species (INE 2000), should be eliminated from the epiphyte checklist of the mangroves found in the region.We think this species was misidentified, because it is typically found in oak-forests between 1500-2200 m (Hágsater et al. 2005)  has been unified as one species: Selenicereus undatus (Haw.)D.R. Hunt (Korotkova et al. 2017).It is worth mentioning that Bromelia pinguin L. (Bromeliaceae) and Trigonidium egertonianum Bateman ex Lindl.(Orchidaceae) were not reported in our study, but were listed in the previous checklists (INE 2000).Finally, the current checklist corrects some misidentifications made in previous studies (Jiménez-López & Domínguez-Vázquez 2017; Jiménez-López et al. 2017).
On one hand, it has been suggested that a higher host diversity results in a higher diversity of substrates, microclimates, and conditions available for the establishment of epiphytes (Cach-Pérez et al. 2013;Stein et al. 2014;Wagner et al. 2015).Therefore, this heterogeneity of conditions result in a higher niche variability that can host a higher epiphyte diversity.On the other hand, communities with highly variable host tree architecture and size have been associated with higher epiphyte richness (García-Franco 1996;Flores-Palacios & García-Franco 2006).Structurally homogeneous communities, however, have also been found to harbor high epiphyte richness (Sousa & Colpo 2017).In our study, host diversity was low, as two species, Rhizophora mangle L. and Bucida buceras L., were highly dominant (Solórzano et al. 2018).Thus, we consider this study as an example of a relatively homogeneous community in terms of diversity that harbors high epiphyte diversity.
Tillandsia was the genus with the highest species number; however, this was not surprising, as this species has been reported as tolerant to dry in high radiation conditions (Cach-Pérez et al. 2013;Chilpa-Galván et al. 2013).Physical conditions in mangrove forests (such as radiation, nutrients, and temperature) can be relatively extreme (Mikolaev et al. 2016).Mangroves usually eliminate salt through their leaves, which provokes a saline environment on the parts that epiphytes usually colonize (Tomlinson 2016).This salt condition can affect some epiphyte survival and growth rates (Zotz & Reuter 2009).Nevertheless, some epiphytes have adapted to survive under the saline conditions found in mangrove forests (Gómez & Winkler 1991).
No species was found to have a protected status under the Mexican legislation NOM-059-SEMARNAT-2010 (SEMARNAT 2010).Tillandsia brachycaulos, a frequently found species in this study, however, is included under the Least Concern category in the Red List (UICN 2017).This species was found preferably at low heights (1-2 m over ground height), where lower radiation and temperatures can be found (Mondragón et al. 1999;Cach-Pérez et al. 2013;Jiménez-López et al. 2017).