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Seagrass Research in the Eastern Africa Region: Emphasis on Diversity, Ecology and Ecophysiology

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Seagrass Research in the Eastern Africa Region: Emphasis on Diversity, Ecology and Ecophysiology South Afnc"n Journal of Botany 2001 67 420-425 Copyrrgnt () NISC Pry LId Ponted "' South Arne" - All nghls reserved s o U'fI-fAtRTCAN JOUHNAL or BOTANY ISSN 0254-6299 Minireview Seagrass research in the eastern Africa region: emphasis on diversity, ecology and ecophysiology 1 SO Bandeira " and M Bjork2 , Depat1ment of Biological Sciences, Eduardo Mondlane University, PO Box 257, Maputo, Mozambique ' Botany Department, Stockholm University, 10691 , Stockholm, Sweden .. Corresponding author, e-mail: sband@zebra .uem.mz Received 7 April 2001 , accepted in revised form 8 June 2001 This paper presents a brief review of seagrass research ecophysiology and anatomy/histochemistry. Considering in the eastern African region , including Somalia, Kenya, this and the fact that eastern Africa with its 12 species Tanzania, Mozambique, eastern South Africa, is a region of high diversity of seagrasses, seagrass Seychelles, Comoros, Madagascar, Reunion and research in the region appears to be in its infancy. Apart Mauritius. Only about 60 references have been pub­ from the need for continued survey and mapping activ­ lished from this region since the 1930's, covering main­ ities, future research has to focus on the significance of ly seagrass diversity and ecology, and only about 30 of seagrass beds in the region, their role in the coastal these have been published during the last 10 years in ecosystem and how they are affected by various anthro­ international journals. These covered mainly ecology, pogenic changes. Introduction Seagrasses comprise a small taxonomic group of marine Seagrasses play an important ro le in shallow-water angiosperms with on ly about 50 species, which have a world ecosystems of both tropical and temperate zones. They wide distribution and have adapted to a life in seawater by have a high productivity, and the rate can be compared to the development of a specific morphology with an anchor­ that of crop plants (Drin9 1982, Larkum ef al. 1989). The age system made up of rhizomes and roots , air lacunae to seagrass beds increase the biodiversity of plants. animals , supply roots with oxygen. flowers with hydrophilous pollina­ fungi etc. in the areas where they occur (e.g. Oshima ef al. tion and. in some species. vivipary (Den Hartog 1970, 1999, Rindi et a/. 1999), act as a shelter for juvenile animals Larkum et a/. 1989, Elmqvist and Cox 1996). They have the and as nursery and foraging areas for many species (e.g. ability to take up nutrients by both roots and leaves (Stapel Harlin 1980, Larkum ef al. 1989). In addition , they trap nutri­ ef al. 1996, Pedersen et al. 1997, Hemminga 1998), and are ents (Gacia ef a/. 1999) and promote their recycling, as sea ­ mostly clonal plants with shoots (vertical rh izomes) arising grass decomposition is quite high (Newell ef al. 1984, from horizontal rhizomes below the ground. Most species Ochieng and Erftemeijer 1999). Seagrass meadows may have more or less flat linear leaves with parallel veins, also act both as sinks and sources for particles (e.g. Gacia except Halophifa spp., with petiolate leaves , and ef al. 1999, Koch 1999). Some of these particles, containing Syringodium isoetifolium (Aschers.) Dandy, with terete different nutrients, play an important ro le in seagrass growth leaves. Many of the intertidal seagrass species generally dy namics and nu trient budgets. The importance of seagrass have short stems, while plants growing subtldally may reach beds for littoral nutrient budgets is complex . as a number of considerable lengths. The ta llest seagrass species encoun­ models try to explain (e.g . Pergent ef al. 1994, Erftemeijer tered in the East African region is Thalassodendron cilialum, and Middelburg 1995, Pergent et al. 1997, Oshima ef al. which can measure up to 126cm in length . This was 1999). In Kenya , Ochieng and Erftemeijer (1999) estimated observed from a collection in Inhassoro (21 °32 'S, 35°12'E), that around 82 tonnes of dry weight of beach cast material southern Mozambique. Enhalus acoroides can also attain (d ispersed in about 10km of coastline) belonged to sea­ considerable length and was observed having up to 100cm grasses, most of it (c. 62 tonnes) were leaves of T. ciliatum . length in this region. The smallest ones are the th ree Senescent and detached leaves of T cilialum are also com­ species of the genus Halophila, the species H. minor nor­ mon in coastal areas and sand dunes, increasing the nutri­ mally only reaching less than 2cm height above bottom. ent content of these nutrient poor marginal areas. De Boer South African Journal of Botany 2001. 67: 420-425 421 (2000) es timated that the seagrasses such as Halodule covering the following main fields of research: Taxonomy wrightii Aschers. and Zostera capensis Setchel! were the and distribution (e.g. Isaac 1968, Bandeira 1997a, Spalding main nutrient source in the southern bay at lnhaca Island and Phillips 1998), ecology (e.g. Hemminga et al. 1994, contributing altogether with 490, 30 and 2 tones of C, Nand Duarte et al. 1996, Ochieng and Eritermeijer 1999), eco­ p, respectively. phys iology (e.g. Bjork et al. 1997, 1999, Beer and Bjork Economically, seagrasses can be utilised for paper pro­ 2000), anatomy and histochemistry (e.g. Barnabas 1982, duction , green manure, fl our (seeds of Zostera marina L. in 1983, 1991 , 1994) , ftowering and pollination (e.g. McMillan Mexico) and fodder. Thalassia hemprichH is used in salads 1980, Cox 1991) and feeding preferences (Mariani and in the Philippines (Cordero 1981). Seeds of Enhalus aco­ Alcoverro 1999). Pioneering publications on seagrasses in roides are eaten raw or boiled in the Philippines (Montano et the region are the ones by Moss (1937) , Cohen (t939), al. 1999) and reported to be used as food in periods of food Chasse (1962), tsaac (1968) which all covered mainty taxo­ scarcity in Kenya (Cox 1991) . Seagrasses are also used in nomical descriptions of seagrasses in Kenya, Madagascar traditional medicine in tnd ia (Parthasarathy et al. 1991). and Mozambique. The dominant part of seagrass research Overall economic value of seagrasses can be divided in use from the region covered the field of ecology (Figure 1) . Work value (e.g. direct/indirect uses and/or benefits to humans), from the period 1991-2000 indicates that most recent and existence va lue (abstract values not necessarily related research on seagrasses was performed in Kenya, Tanzania, to human benefits or use) . Th ese values are good indicators Mozambique and South Africa (Figure 2). Examples of of the ecological and economical losses when seagrass important references per country are given in Table 1. habitats are destroyed (Thorhaug 1990, Costanza et al. 1997, NSW Fisheries 1997). In money terms, this overall Diversity of sea grasses in eastern Africa seagrass value has been estimated by Costanza et al. (1997) to t 9 004USD ha ' year '. Twelve seagrass species occur in the eastern African The present study presents a review of seagrass research region, grouped in three fami lies: Hydrocharytaceae with the performed in the eastern African region. Emphasis is given species Enhalus acoroides (U.) Royle, Halophile minor to studies on seagrass diversity and ecology. We have (Zoll.) den Hartog, H. ovalis (R . Br.) Hoo k. f., H. stipulacee based the review on research work from the region and it (Forsk.) Aschers. and Thalassia hemprichii (Ehrenberg) covers published research in the eastern African countries Asherson; Zosteraceae with Zostera capensis Setchell and including the istand states tocated in the western tndian Cymodoceaeae with Cymodocea rotundata Ehrenb. et ocean viz: Somalia, Kenya, Tanzania, Mozambique, eastern Hempr. ex Aschers. , C. serrulata (R. Br.) Aschers. et South Africa, Seychelles, Comoro, Madagascar, Reunion Magnus, Halodule uninervis (Forsk.) Aschers. in Bossier, H. and Mauritius. wrightii Ascherson, Syringodium isoetifolium (Ascherson) Dandy and Thalassodendron cilia tum (Forsk.) den Hartog. History of seagrass research in the western Indian These 12 species comprise about a fifth of the worfds total Ocean seagrass species. This is quite diverse if compared with some other seagrass areas such as the Mediterranean Sea Around 60 published references (see bibliography in re fer­ with fou r spe cies and eight species in the Caribbean Sea ence list) on seagrasses have been published in the region with the Gulf of Mexico and Florida. However, Western 30 'C Seychelles F? ~• 25 •:a• 20 ,"a. South Africa a.• 15 •a. Mozambique '0, 10 ,c• E 5 z" Tanzania 0 ..0 "'. Kenya ~~ ~~. c:!l' o 2 4 6 8 10 12 number or papers published (1991-2000) Figure 1: Number of papers per subject groups pub li shed in the Figure 2: Number of publications per country in the period eastern African region 1991-2000 (grid bars indicate publica ti ons In international journals) 422 8andelra and Bjork Table 1: Examples of important seagrass references given per Halodule uninervis, Halophila minor, H. ovaJis, H. stipulacea, country Syringodium isoe tifolium , Thalassodendron cilia tum and Thalassia hemprichii (Isaac 1968, McMillan 1980). Frequent Country : Reference flowering occurs in a few species such as Halophila ovalis, and Kenya Isaac 1968 Syringodium isoetifolium , Thalassia hemprichii McMillan 1980 Tha/assodendron cilia tum. Cox 1991 Coppejans et a/ 1992 Seagrass ecology and ecophysiology Hemminga el al. 1995 Wakibya 1995 The ecological sea grass research in the region has mainly Duarte et al. 1996 covered asp ects of distribution, structure and productivity Uku et al. 1996 (e.g . Duarte 1996, Bandeira 1997b), tolerance to salinity Ochieng and Erttemeij er 1999 (e .g. Adams and Bate 1994a), seagrass associated with Tanzan ia Semesi 1988 seaweeds (e.g. Coppejans et al. 1992), and seagrass epi­ Bjork et al. 1997, 1999 phytes (Semesi 1988, Leliaert et al. 2001, Uku and Bjork in Beer and Bjork 2000 Schwarz et al. 2000 this volume). Leliae rt et al.
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