Coastal sand dune vegetation: a potential source of food, fodder and pharmaceuticals

K R Sridhar and B Bhagya

Microbiology and Biotechnology, Department of Biosciences, Mangalore University,
Mangalagangotri 574 199, Karnataka, India
sirikr@yahoo.com

Abstract

Coastal sand dune (CSD) flora has a wide range of applications in nutrition, medicine, industry and agriculture. The native people are intimately associated with dune vegetation for a variety of traditional benefits particularly food, fodder, health, soil fertility and recreation. Temperate CSDs comprise of mainly the members of Poaceae, while tropics with Asteraceae, Cyperaceae and Fabaceae and Poaceae. Many CSD legumes meet the protein and energy requirement of rural population and livestock. Canavalia maritima is a major strand legume with pantropical distribution. Tender pods and seeds are edible after boiling or roasting in Northern Australia, while seeds are important source of dietary protein in West Africa and Nigeria. Canavalia cathartica is another wild legume with wide distribution throughout CSDs of tropical Asia and Africa. Seeds of CSD Canavalia serve as potential source of proteins, carbohydrates, amino acids, fatty acids and energy. The CSD legumes of west coast of India are useful as green manure, mulch, cover crop, pasture, fodder, oil and medicinal value. The strand plants possess several bioactive compounds of human, veterinary and industrial importance.

The CSD vegetation is under severe threat mainly due to global warming and human interference and thus needs stringent restoration measures for sustainable use for coastal rural development.

Keywords: bioactive compounds, Canavalia, coastal sand dunes, disturbance, fodder, food, nutrition, restoration, traditional knowledge, vegetation, wild legumes

Introduction

Animal husbandry plays an important role in rural development and economy of developing countries. Nutrition is one of the most critical constraints to increase animal productivity in developing countries (ILRI 1995). Perpetual gap exists between the demand and supply of digestible crude protein and total digestible nutrients to livestock in Asian continent (Singh et al 1997). One of the challenges to uplift the livestock production is to increase the quality of legume-based pasture diets (Poppi and Mclennan 1995). The use of forage legumes as ruminant feed has increased in tropics to meet the protein deficiency. However, supplementation of animal protein for monogastric animals is expensive and not affordable by farmers (Umoren et al 2005). Feed supplementation with wild native legumes is economically viable and provides additional proteins, minerals and energy during dry season. Over the past few decades, research has been directed to evaluate nutritional qualities of underexplored legumes adapted to different habitats (Siddhuraju et al 1995, 2000, Vijayakumari et al 1997, Makkar et al 1998).

Coastal sand dunes (CSD) constitute a variety of habitats and vital ecological and economic importance (Maun and Baye 1989, Martinez et al 1997). Growth, survival and heterogeneity of CSD vegetation spatially and temporally influenced by environmental factors such as temperature, desiccation, low moisture retention, sand erosion, sand accretion, salinity and salt spray (Watkinson and Davy 1985, Maun 1994). Among the dune disturbances, burial is the most important factor followed by salt spray, which influences the distribution of dune plant species (Maun and Perumal 1999). Studies on CSD vegetation, restoration and stabilization confined mainly to temperate regions (Sylvia and Will 1988, Sylvia 1989, Koske and Gemma 1997). Several microflora adapted to strand environment live independently or mutually with vegetation (e.g. rhizobia, Frankia, mycorrhizas). The CSD flora has a wide range of economic value (e.g. nutritional, medicinal, industrial, agricultural) particularly for rural coastal population. The native people intimately associated with dune habitats are dependent on vegetation for a variety of benefits (e.g. food, fodder, health, soil fertility, recreation). The purpose of this review is to project the nature of vegetation on CSDs; nutritional value and bioactive potential of selected dune plants; traditional knowledge of native coastal dwellers on the use of dune plants in human health, veterinary and agriculture; threats to dune vegetation due to human interference and restoration measures with emphasis on Southwest coast of India.

Dune flora

Ammophila(American beach grass) is a major dune building grass adapted to temperate US Atlantic coast has highly influenced the coastal geomorphology and plant community structure (Maun and Baye 1989). Ammophila breviligulata adapted to CSDs becomes senescent on dune stabilization and replaced by other species. Ammophila arenaria (European beach grass or marram grass) is native to European CSDs and deliberately cultivated to stabilize the dunes (Seabloom and Wiedemann 1994). Desmoschoenus spiralis and Scirpoides nodosa are native plants species on the CSDs of New Zealand. The foredune complexes of New Zealand comprise of Calystegia soldanella, is a cosmopolitan prostrate species consists of long rhizomes capable of forming sand mounds. This plant species grow in association with Elymus farctus and Leymus arenarius and tolerate inundation of seawater. Uniola paniculata (sea oats) is a semitropical C4 perennial grass dominates the foredunes of southeastern US Atlantic and Gulf coasts (Hester and Mendelssohn 1987). It is also widely distributed in Bahama Islands and some parts of Cuba. Chamaecrista chamaecristoides is a shrubby legume endemic to Mexico and partly to the Pacific coast (Martinez and Moreno-Casasola 1998). It grows on mobile dunes, increases the biomass significantly on sand covering, fixes nitrogen and facilitates the succession of associated flora.

The dominant tropical coastal sand dune vegetation belongs to the Asteraceae, Cyperaceae, Fabaceae and Poaceae (Moreno-Casasola 1988; Arun et al 1999, Rao and Sherieff 2002). Most tropics and warm temperate shores consist of Ipomoea pes-caprae (Convolvulaceae) (St John 1970). It is a stoloniferous perennial creeping strand species confined to the Indian Ocean establishes along with 73 typical beach plant species in the Gulf of Mexico and tolerates sand erosion, accretion and inundation (Britton and Morton 1989, Devall 1992). Ipomoea brasiliensis is pantropical except for the Indian Ocean (Fosberg and Sachet 1977), while Ipomoea imperati confined to beaches and several islands (Leonard and Judd 1999). In addition to Ipomoea spp., CSDs of east coast of Africa consists of 156 plant species with Gramineae (17 species) and Papilionaceae (16 species) (Musila et al 2001). Stable sand dunes support higher richness and diversity of plant species than disturbed dunes. Dune plants of different microenvironments within the dunes are adapted to exploit nutrient pulses from rain and salt spray and exhibit different growth responses. They have more plasticity in allocation of biomass, wherein significantly high biomass will be allocated to roots than aerial tissues under most unfavourable conditions facilitates dune stabilization.

Indian subcontinent has a coastline of about 7516 km long with 2.1 million km² exclusive economic zone and 0.13 million km² continental shelf (Khoshoo 1996).The coastal zone is one among the 10 biogeographically important habitats of the Indian subcontinent (Rodgers and Panwar 1988). The CSD biogeographic regions of the Indian subcontinent have been divided into eight subdivisions (Pakistan, Kutchchh and Northwest Kathiawar, Southern Kathiawar-Gujarat, Konkan, Malabar, Coromandel-Circar, islands between India and Sri Lanka, Utkal and Bengal, Andaman and Nicobar Islands) (Rao and Meher-Homji 1985). A variety of psammophytic strand vegetation exists on the CSDs of the Indian Subcontinent (e.g. mat-forming creepers, prostrate/erect herbs and sedges, climbers, plants with perennating organs, scrubs, trees) (Rao and Meher-Homji 1985). Strand and associated flora of Indian CSDs consist of 154 species belonging to 108 genera and 41 families (Arun et al 1999, Rao and Sherieff 2002). Based on the number of species in each family, Fabaceae stands the highest (24 species) followed by Poaceae (22 species), Asteraceae (15 species) and Cyperaceae (13 species) (Table 1).

Among the species of Fabaceae, frequency of occurrence of Canavalia maritima was highest (44.4%) followed by Canavalia cathartica (22.2%), Crotalaria verrucosa (18.1%), Derris triflorum (16.7%), Erythrina indica (15.3%) and Crotalaria retusa (12.5%) (Table 2). Economic value of some nitrogen fixing CSD legumes of Southwest coast of India has been given in Table 2.

The CSD vegetation withstand xeric and saline conditions probably due to association with a variety of stress-tolerant bacteria (e.g. nitrogen fixing) (Will and Sylvia 1990, Chen et al 2000, Arun and Sridhar 2004), endophytic fungi (Beena et al 2000, Seena and Sridhar 2004), endo- (Sturmer and Bellei 1994, Koske and Gemma 1997, Kulkarni et al 1997, Beena et al 2000, 2001, Bhagya et al 2005, Arun and Sridhar 2006) and ectomycorrhizae (van der Heijden et al 1999, Ashkannejhad and Horton 2005). These stress-tolerant microbes will be of immense value to domesticate CSD plants having forage and veterinary potential.
 

Food and fodder

Varieties of strand plants are useful as food or fodder. The whole plants of Cakile edentula serve as forage, its powdered roots with other flours used in bread preparation and the leaves are used in salads (Maun et al 1990). Mucuna and Sesbania of west coast of India are useful as fodder (Arun et al 1999, Arun 2002). Pods and seeds of Mucuna pruriens and Sesbania bispinosa are edible (Anonymous 1986, Arun et al 1999). Seed accessions of Sesbania bispinosa collected from Southern India possess adequate quantity of minerals, essential amino acids and essential fatty acids (Pugalenthi et al 2004). Canavalia maritima is one of the major mat-forming creepers of CSDs of southwest India (Arun et al 1999, Beena et al 2001, Seena and Sridhar 2006). The young pods and seeds consumed on boiling or roasting in Northern Australia, while seeds serve as source of dietary protein in West Africa and Nigeria (Abbey and Ibeh 1987). The whole plant is used as feed for rabbits in the southwest coast of India. Similarly, Canavalia cathartica is another wild ancestral form of Canavalia gladiata widely distributed in tropical Asia, Africa (Purseglove 1974) and southwest coast of India (Arun et al 1999, 2003). This legume is also known from Kenya, Seychelles, Tanzania, Japan, Taiwan, Bangladesh, Cambodia, Indonesia, Malaysia, Myanmar, Papua New Guinea, Philippines, Sri Lanka, Thailand, Vietnam, Australia and Hawaiian Islands (http://www.ars-grin.gov/cgi-bin/npgs/html/taxon.pl?310991). In view of economic value, agrobotanical, nutritional, antinutritional properties and bioavailability of proteins of Canavalia maritima and Canavalia cathartica of CSDs of southwest coast of India have been documented.

Canavalia cathartica and Canavalia maritima are perennial, stoloniferous herbaceous plant species withstand dry conditions of tropical CSDs (figure 1 a, b).

Canavalia cathartica yield larger and heavier pods than Canavalia maritima. The pods of Canavalia spp. are smooth, elongated, thick-walled and green turning yellow on ripening during October-November on the southwest coast of India. Dry seeds of Canavalia maritima are small, oval, bulged, bright orange to maroon with short hilum (figure 1 c), while Canavalia cathartica are large, oval, flattened, brownish black and occasionally striated with long hilum (figure 1 d) (Table 3).

Raw seeds of Canavalia cathartica possess highest crude protein (35.5%). Roasting and cooking decreased protein as well as crude fiber, while elevated crude lipids and total carbohydrates (Table 4).

The dietary guidelines published by USDA/HEW (1980) emphasize on increasing the amounts of dietary fiber in daily diet. As Canavalia seeds are excellent source of dietary fibers, it helps to prevent certain intestinal diseases (Hellendoorn 1979). Crude fiber promotes fast transmission of food through bowel (Van Soest 1975, Cummings 1978). The food containing high dietary fiber protects against atherosclerosis on binding to bile salts (Kritchevsky and Tepper 1968). The energy of raw and thermally processed Canavalia seeds (1520 and 1630 kJ/100 g) is higher than many cultivated legumes (1358.3-1426.2 kJ/100g (Kuzayali et al 1966).

There is a clear gap in our knowledge on vitamins, starch, sugars, dietary fiber, toxins and enzymes of Canavalia seeds. Canavalia seeds are known for several minerals, but it should be considered in conjunction with bioavailability (Table 5).

Cooking lowered sodium, which is nutritionally advantageous in view of recommended low sodium intake in the diet. High quantity of potassium in Canavalia seeds is beneficial to those who take diuretics to control hypertension and suffer form excessive excretion of potassium through body fluids. Zinc and manganese meet the NRC/NAS (1989) requirements for infants, while phosphorus, magnesium, iron, copper and calcium are inadequate. Fatty acid composition of seeds reveals that palmitic and stearic acids are high in raw seeds of Canavalia maritima, while stearic acid in Canavalia cathartica (Table 6).