Brief introduction about mangrove ecosystems
Mangroves are the only trees that are capable of thriving in salt water and form unique intertidal forests at the edge of land and sea. Mangroves, defined as ‘tree, shrub, palm or ground fern, generally exceeding one half meter in height, and which normally grow above mean sea level in the intertidal zone of marine coastal environments, or estuarine margins’ (Duke, 2006), constitute one of the most threatened ecosystems (Farnsworth& Ellison, 1997; Valiela et al., 2001; Alongi, 2002; Duke et al., 2007). Due to the widespread distributions of most mangrove tree species few are listed on the IUCN Red List of Threatened Species™ (Polidoro et al., 2010), and many others are listed as ‘least (global) concern’. Yet, both mangrove species and entire mangrove ecosystems are locally threatened throughout their distribution range despite their numerous goods and services.
Mangrove ecosystems provide habitats for numerous animals and micro-organisms (Cannicci et al., 2008; Nagelkerken et al., 2008), live in close interaction with the mangrove vegetation (Bouillon et al., 2004; Kristensen et al., 2008). Mangrove forests provide essential functions and services to coastal populations, such as protection of the coastal zone (e.g. Badola & Hussain, 2005; Dahdouh-Guebas et al., 2005b; Olwig et al., 2007; Barbier et al., 2008; Kaplan et al., 2009) and a variety of timber and non-timber forest products (Bandaranayake, 1998, 2002; Walters et al., 2008).
Many mangroves have been degraded over time as evidenced by numerous retrospective research approaches (Dahdouh-Guebas & Koedam, 2008; Ellison, 2008). Next to direct anthropogenic degradation (Farnsworth & Ellison, 1997; Alongi, 2002), also indirect degradation such as cryptic ecological degradation (Dahdouh-Guebas et al., 2005a) threatens the survival of individual mangrove trees and vegetation assemblages. ‘Cryptic ecological degradation’ (sensu Dahdouh-Guebas et al. 2005a) indicates that introgressive mangrove-associated vegetation or minor mangrove species such as Acrostichum aureum L. slowly start to dominate a forest at the expense of typical, functional, valuable and functional true mangrove species (qualitative degradation) but without loss of spatial extent (no change or an increase in area). In addition, climatic change events such as sea-level rise (Gilman et al., 2008) threaten mangrove ecosystems worldwide.
It becomes increasingly more important to understand the early drivers in mangrove dispersal (Di Nitto et al., 2008, Triest, 2008), mangrove establishment (Krauss et al., 2008), adult mangrove growth and development (Komiyama et al., 2008), regenerative constraints (Bosire et al., 2005), and vegetation dynamics (Berger et al., 2008) in order to design mangrove recovery programmes (Kairo et al., 2001; Bosire et al., 2008).
Mangroves are distributed world-wide in all continents with tropical and subtropical coasts and occur in 124 countries and territories. FAO (2007) estimates a total area for mangroves of 15.6 to 19.8 million hectares. The northern extension limits of mangroves are in Japan (31ºN) and Bermuda (32ºN) and the southern extension limits are in South Australia (38.75ºS) and the east coast of South Africa (32.6ºS) (Tomlinson, 1986). In some countries mangroves are not native such as in the Hawaiian Islands, but since the early 1900's, at least six species have been introduced there (Kathiresan & Bingham, 2001). Also in countries with mangroves exotic mangrove species have been introduced; for instance Nypa fruticans (Thunb.) Wurmb., a mangrove species endemic to the Indo-West-Pacific region only, was introduced in West-Africa (Spalding et al., 1997). Inversely, some other species have gone extinct in some countries, such as Bruguiera gymnorrhiza (L.) Lamk. in Yemen or Heritiera littoralis Dryand. in Bangladesh (loc. cit.).
To document and analyse the historic loss and current extent of mangrove ecosystems and mangrove biodiversity around the world, the Mangrove Reference Database and Herbarium has been created.
Justification of the Mangrove Reference Database and Herbarium
Species lists per country can be easily found but a global overview of the exact local distribution and biodiversity of mangrove species (on the level of mangrove estuaries, bays or lagoons) is still lacking. Yet, it is urgently needed because in some sites mangroves may display a strong dynamism in space (e.g. Dahdouh-Guebas et al., 2002), and in time (Dahdouh-Guebas et al., 2000; Fromard et al., 2004).
Distribution data per country are often not representative for all mangrove sites within the country that may differ significantly with respect to climatic, oceanographic, anthropogenic and other factors driving local mangrove species composition. As (Jayatissa et al., 2002) demonstrated, highly resolved and correct distribution data on a local scale are essential in the light of biogeographical studies, remote sensing, in situ conservation or management, and restoration ecology of mangrove forests. Many global initiatives aim at global distribution maps, which may be correct on a global administrative level. However their country-wide distribution maps or tables are seldom applicable in the field as the species representative on the (administrative) scale of a country are not present in each and every mangrove site. In addition, Jayatissa et al. (2002) and Dahdouh-Guebas et al. (2005a, 2005b) cautioned for the consequences of an erroneous use of the term ‘true mangrove species’.
The overall aim of this online database is to generate global or regional maps on mangrove distribution and composition that are correct on the scale of specific lagoons or even parts of a lagoon, and to perform further research on the past, current and future diversity and distribution of mangrove plant species in view of their ecological and socio-economical functions, goods and services.
Specific objectives of the Mangrove Reference Database and Herbarium
The specific objectives of the Mangrove Reference Database and Herbarium, detailed in the sections History and Framework and Data holdings and methodology of the Mangrove Reference Database and Herbarium, are to:
History and Framework of the Mangrove Reference Database and Herbarium
The Mangrove Reference Database was started in 2001, when the Flanders Marine Institute (Vlaams Instituut voor de Zee - VLIZ) created the Flanders Marine Data and Information Centre (VMDC). This centre became an integral part of international networks such as UNESCO’s IOC Project Office for International Oceanographic Data and Information Exchange (IODE), OBIS, ESF Marine Board, MARS, EMODNET and other European networks. VMDC hosts the Mangrove Reference Database on its server and develops ICT tools to ease its use.
Since universities in Brussels and Flanders (Belgium) had played a long-standing role in research on mangrove ecosystems, at the origin focused on Kenya and Sri Lanka, but since then expanded to single case-studies or long-term projects in Mexico, Brazil, Mauritania, Gambia, Cameroon, Tanzania, Kenya, India, Malaysia, Vietnam and China, the idea seemed justified to start the current database collaboration with VLIZ, coordinated by the Université Libre de Bruxelles (U.L.B.) and the Vrije Universiteit Brussel (V.U.B.).
The larger framework of the Mangrove Reference Database involves also a real and virtual Mangrove Reference Herbarium coordinated by the U.L.B. The real herbarium consists of herbarium sheets of each and every true mangrove species of the world and is hosted at the U.L.B. (herbarium acronym BRLU), the V.U.B. (BRVU), and the National Botanic Garden of Belgium (BR), each institute currently making its own efforts to aid the realisation of this a complete true mangrove species collection. While currently distributed among these institutes, all located within a few kilometers of one another, we aim at establishing the complete mangrove reference herbarium collection in a single location. The virtual herbarium consists of scanned herbarium sheets with tools for high definition online viewing and is hosted on the Mangrove Reference Database and Herbarium website in collaboration with the Belgian Biodiversity Platform.
Data holdings and Methodology of the Mangrove Reference Database and Herbarium
All existing mangrove literature sensu lato records are browsed for true mangrove plant species lists and geographic coordinates, a dynamic task as, in order of importance, (1) new peer-reviewed papers continue to appear in scientific literature, (2) older papers and (3) grey scientific literature (e.g. university dissertations) are still in the process of being inserted, and (4) researchers and others world-wide continue to upload species lists, the latter of which are subject to higher quality control. Where such studies are estimated to provide exhaustive species lists, e.g. as part of a vegetation structure study, remote sensing study, etc., they were georeferenced using geographic coordinates or maps provided by the authors, or by existing gazetteers. The Mangrove Reference Database and Herbarium also links to the complete reference of the respective literature record, which is important in a historic research context. All studies in which the mangrove plant species lists proved impossible to be georeferenced below country-level are currently excluded from the database. This does jeopardize the integrity of the database, since country-wide information was included through global sources that were included (e.g. Spalding et al., 1997). All the studies that focus on a single species without reporting other species present in the area (e.g. studies on the extraction of biochemical substances from a particular species) are currently excluded as well, but they will be integrated at a later stage. In parallel to the introduction of literature records into the database, we also integrate historic mangrove distribution data through herbarium records. While giving credit to the herbarium reference numbers of all collaborating institutions (see collaborations) species identity, place and year of collection are given.
Descriptions of mangrove species are mainly based on Tomlinson (1986) and Duke (2006), but it is worth emphasizing that the database’s mangrove plant species list is focused on what are considered to be true mangrove plant species on a global scale, but that the database is dynamic and can be expanded where needed. The idea is not to provide exhaustive species lists of mangrove associates. As indicated above through the papers by Jayatissa et al. (2002) and Dahdouh-Guebas et al. (2005a, 2005b), the scientific interest in distinguishing true mangrove plant species (both major and minor components as defined by Tomlinson 1986) lies in the socio-ecological functionality of the species, e.g. representatives of the Rhizophoraceae are more vulnerable, more valuable and more functional than mangrove-associate species. Therefore their conservation is of prime importance.
The resulting distribution maps emphasize georeferenced points, but also indicate polygons for a particular country, representing the country-level information in studies that cannot be georeferenced below country-level or other global databases.
The Mangrove Reference Database and Herbarium is part of a larger database and IT platform called ‘Aphia’, hosted by VLIZ. Aphia (not an acronym, but a random fish genus) is also the taxonomic IT platform used by the World Register of Marine Species (WoRMS), which is now a collection of over 20 global, regional and thematic taxonomic databases. The data in the Mangrove Reference Database and Herbarium is therefore immediately reflected on the WoRMS website. The data stored in Aphia are also contributed to other global initiatives such as the Encyclopedia of Life (EoL), the Global Biodiversity Information Facility (GBIF), the Global Names Index (GNI) and the distribution data will be contributed to the Ocean Biogeographic Information System (OBIS), which is the information component of the Census of Marine Life (CoML).
The Aphia system provides password-controlled access to the database for ‘editors’ to validate, add, edit and/or remove information directly via the web interface. Access to the taxonomic information is restricted to recognized taxonomic editors, whereas literature references, distribution records, images, specimen details, etc… can be added by the academic staff involved in the coordination and maintenance of the database (after inquiring a personal login). The information is directly available to interested readers and researchers with access to the internet.
Finally, we refer to the present website for updated descriptions on database holdings, operation and maintenance.
Collaborating Institutions so far
We thank the following institutes (in alphabetic order) for logistic support, photographs or access to herbarium records (official herbarium codes between brackets). We encourage other institutes with mangrove herbarium or distribution records to take contact in order to join the collaboration list below.
We also thank the following people (in alphabetic order) for their help in synthesizing the information from the herbarium records : Henk BEENTJE (Kew), Hugues DE GERNIER (ULB), Caroline LAROYE (ULB), Sophie LEGUIL (ULB), Assumpta MUKANDERA (ULB) as well as all authors of our publication :
MASSÓ I ALEMÁN, S., C. BOURGEOIS, W. APPELTANS, B. VANHOORNE, N. DE HAUWERE, P. STOFFELEN, A. HEUGHEBAERT & F. DAHDOUH-GUEBAS, 2010. The ‘Mangrove Reference Database and Herbarium’. Plant Ecology and Evolution 143(2): 225-232.
How to cite
Usage of data from the Mangroves Database in scientific publications should be acknowledged using the following paper:
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Cannicci, S., D. Burrows, S. Fratini, S.Y. Lee, T.J. Smith III, J. Offenberg & F. Dahdouh-Guebas, 2008. Faunistic impact on vegetation structure and ecosystem function in mangrove forests: a review. Aquatic Botany 89(2): 186-200.
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Di Nitto, D., F. Dahdouh-Guebas, J.G. Kairo, H. Decleir & N. Koedam, 2008. How does sea level rise affect mangrove propagule establishment ? An experimental study using digital terrain modelling. Marine Ecology Progress Series356: 175-188.
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Prof. Dr. Farid DAHDOUH-GUEBAS
Laboratory of Systems Ecology and Resource Management
Laboratoire d'Écologie des Systèmes et Gestion des Ressources
Département de Biologie des Organismes
Faculté des Sciences
Université Libre de Bruxelles - ULB
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Laboratory of Plant Biology and Nature Management
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