WELCOME TO THE 17 TH INAUGURAL LECTURE UNIVERSITY OF UYO

1. UNIVERSITY OF UYO WELCOME TO THE 17TH INAUGURAL LECTURE UNIVERSITY OF UYO WELCOME TO THE 17TH INAUGURAL LECTURE UNIVERSITY OF UYO by PROFESSOR IMOH E. UKPONG (Professor of Biogeography) ..Biogeographer, Mangrove Ecologist &Vegetation Scientist, Coordinator Uniuyo/Lancaster Higher Education Link and Former Dean of Social Sciences… DEPARTMENT OF GEOGRAPHY & REGIONAL PLANNING UNIVERSITY OF UYO NIGERIA

2. MANGROVE FORESTS UNDER THREAT?

3. DEDICATION This Inaugural Lecture is dedicated to ALL RESEARCH SCHOLARS and lovers of Knowledge.

4. MANGROVE FORESTS UNDER THREAT? AN EVALUATION OF THE INTEGRITY OF MANGROVE ECOSYSTEM FUNCTIONING PROFESSOR IMOH E. UKPONG (Professor of Biogeography) …Biogeographer, Mangrove Ecologist & Vegetation Scientist, Coordinator Uniuyo/Lancaster Higher Education Link and Former Dean of Social Sciences… DEPARTMENT OF GEOGRAPHY & REGIONAL PLANNING UNIVERSITY OF UYO NIGERIA

5. 1.0. INTRODUCTION Definition of Mangrove • The term mangrove generally applies to: • An association of trees [including associated micro-organisms e.g. bacteria, fungi, algae, and fauna, e.g. molluscs, crabs, shrimps and fish] which live in wet, loose soils in tropical tide waters. The term also applies to certain species of trees which occur in such an association. • “Mangrove” is normally restricted to those species of trees which possess either pneumatophores or viviparous fruits or both (these are coping mechanisms due to the extreme environmental factors of high salinity, fluctuating water saturation and anaerobic substrates). • The word “mangrove” is used when reference is made to individual kinds of trees, while the word “mangal” may be used with reference to the swamp forest community. • The mangrove flora is very specialized and consists of shrubs and trees of relatively few genera and about thirty species. • Two classes of plants make up the mangrove vegetation: • Genera and higher taxa found only in the mangrove habitat • Species that belong to genera of inland plants but which have become adapted to life in the swamps.

6. Table 1.1: Some families, genera and species represented in mangrove vegetation (after van Steenis 1962, Chapman 1976)

7. Mangroves are best developed in extent and variety of trees when bordering the coastal margins of the tropical rain forest. Geographically, two broad groups of mangroves are recognized: 1.2 General distribution pattern Europe N. America Africa South East Asia S. America Australia Fig 1.2 World distribution of mangroves • The Indo-Pacific mangrove region extending from East Africa through Southeast Asia to New Zealand and the Southern Archipelago of the pacific from Samoa. • The West Africa-Americas mangrove region extending from the Atlantic coast of Central Africa, through West Africa and America, excluding Hawaii but including the Galapagos Islands (Ding Hou 1960, van Steenis 1962).

8. 1.3. The Biogeography of mangroves • Mangrove habitat is exclusively tropical, subtropical and tidal • The habitats have soil or sediment that are waterlogged, saline or of variable salinity • Mangroves occur in river estuaries, lake shores or marine shorelines • The habitat contains a variety of plant species. About 54 species in 20 genera belonging to 16 families constitute true mangroves • Evolutionary convergence has resulted in increased adaptations of species to variable salinity, tidal inundation and anaerobic soils. • Red mangroves (Rhizophora spp) prop themselves above the water level with stilt roots and breath through lenticels. Fig 1.3 Red mangroves (Rhizophora spp)

9. 1.3. The Biogeography of mangroves: Contd. • Red mangroves have impermeable roots which act as ultra-filtration mechanism that exclude sodium salt from the rest of the plant • Black mangroves (Avicennia spp) occur on higher topography and posses pneumatophores or aerial breathing roots covered with lenticels Fig 1.4 Black mangroves (Avicennia spp)

10. 1.3. The Biogeography of mangroves: Contd. • Between 90% - 97% of salt is excluded at the roots of Avicennia spp before water uptake into the mangrove tissues (the remaining salt accumulate in old leaves which are then shed or are safely stored in cell vacuoles) • White or Grey mangroves (Laguncularia racemosa) secrete salt directly from glands located at the leaf base. • There are about 18 million ha of mangroves in the world. Thirty-five percent occurs in SE Asia. Indonesia alone has 4.5 million ha. Fig 1.5 White or Grey mangroves (Laguncularia racemosa)

11. 1.3. The Biogeography of mangroves: Contd. • Nigeria contains the third largest area of mangroves in the world • Indigenous species in Nigeria are Rhizophora racemosa, Rhizophora mangle,Avicennia africana and Laguncularia racemosa which generally occur in this order along the zonation gradient from the river channels inland to the lowland freshwater swamp forest. Fig 1.6 Nigerian shoreline Showing Mangrove Vegetation

12. 1.3. The Biogeography of mangroves: Contd. • Mangrove area estimates in Nigeria has however remained a subject of debate, e.g. estimates of 540,000 ha (Allen 1965); 999,400 ha (Environmental Management Project 1977); 973,000 ha (FAO, UNEP, 1980,1981); 972,826 ha (FAO 1980); 670,000 ha (Hughes to Hughes 1982); 709,800 ha (Moses 1985); 997,700 ha (Environmental Management Project 1995); 1,051,500 ha (Spalding, Alasco & Field 1997); 1,050,000 ha (Aizpuru, Achard and Blasco 2000) have all been cited in the literature. For e.g. it is not likely that the national level of mangrove area in Nigeria could have increased from 540,000 ha (Allen 1965) to 1,050,000 ha (Aizpuru et. Al. 2000)!! • Most estimates are actually extrapolations. Available literature on the sources and projects for these estimates point to the lack of interest by researchers and environmentalists in verifying the accuracy of data/information for Nigerian mangroves • However, the estimates offered by Geomatics International in the Environmental Management Projects of 1977 (999,400 ha) and 1995 (997,700 ha) are perhaps the most authentic, having been based on remote sensing analysis. • Nevertheless, to say that the national level of mangrove has decreased by only 1,700 ha in 18 years appears to be an underestimate. We believe that between 15,000 - 20,000 ha of mangroves are lost yearly to various uses in Nigeria • Obtaining accurate mangrove area estimate for Nigeria is a challenge to our GIS experts. We believe that it is possible to more accurate estimates of the mangrove area.

13. 2.0. THE MANGROVE SWAMPS OF SE NIGERIA 2.1 General Characteristics: Fig 2.1 Mangrove Swamps in SE Nigeria

14. THE MANGROVE SWAMPS OF SE NIGERIA:General Characteristics: • The alluvial mangrove swamps with luxuriant forests are found in the inter-tidal marginal estuaries of the Cross River[810km2], Kwa Iboe River[50km2], and Imo River[196km2]. • The swamps stretch approximately from longitude 7030 to 8030 East. • Between the Cross River in the east and Imo River to the west, the coastline is about 170km long • The sandy coastal ridges along the Atlantic shoreline also carry mangroves, but mainly stunted, shrubs and strand species. • Semidiurnal tides alternate twice daily and cause tidal flow of the sea in and out of the mangrove swamps during high and low tides. • Tidal flushing may extend for more than 20km upstream from the estuarine mouth e.g. from the Cross River estuary up to Creek Town. • At high tide average depth of water is approximately 6 metres. • Tidal amplitude is low, being approximately 2.01m at spring tides and 1.07m at neap tides (measured at Tom Shot Point at the month of the Cross River estuary). • Mean salinity value (for the Cross River) is 10.80 PPT(Ramanathan 1981). However, a range of 2.8PPT at Calabar to 9.5PPT at the mouth of the estuary has also been reported (NIOMR 1986).

15. THE MANGROVE SWAMPS OF SE NIGERIA:General Characteristics Contd. • Wider salinity gradients ranging from 2.3PPT to 33.35PPT occur during the rainy season due to freshwater inputs (Ramanathan 1981). • Extensive mangrove growth occurs in the estuarine swamps of Imo River, Kwa Iboe River and Cross River. However, the Cross River swamp is the most complex in terms of species diversity. Species found include Avicennia africana, Rhizophora racemosa, Rhizophora mangle, Rhizophora harrisonii and Lagunchularia racemosa. • The important associes are Nypa fruticans, Raphia spp, Conocarpus erectus, Pandanus candelabrum, Phoenix reclinata and Acrostichum aureum • The Atlantic coastal sand ridges which separate the estuarine mangrove swamps from the ocean are themselves not continuous separated from each other by ebb-flood channels that permit ocean tides to inundate and flush the swamps. • Mangrove species on the beachridge sands occur as strand and shrubs usually not more than 1m tall e.g. A. avicennia and R..racemosa.. Strand associes include Sesuvium portulacastrum, Ipomoea sp., Paspalum vaginatum, Hibiscus tilaceus, Triumfettarhomboideae and Cyperus articularis.

16. 2.2. Estuarine processes and landforms associated with mangrove growth in SE Nigeria. • The estuaries of SE Nigeria are all positive estuaries, i.e. freshwater inflow from upland streams exceeds outflow caused by evaporation. Therefore surface salinities are lower within the estuaries than in the open sea. This salinity gradient favours mangrove growth. • Due to subsidence and incision of the coastal areas of Nigeria during the ice age, the coastal sedimentary belt has drowned river estuaries. But due to recent sedimentation, bars or silt deposits which favour mangrove growth have developed along the mouths these estuaries • The major source of sediment is therefore the hinterland catchment and tributary rivers that empty their waters through the estuaries into the Atlantic Ocean • The Cross River (flowing over Precambrian Basement and Cretaceous – Tertiary Sedimentary rocks) is particularly endowed with sediments more that the Imo and Kwa Iboe Rivers, which account for the differences in the sizes of the estuarine swamps. • Within the estuaries, the substrates are different from that of the adjacent marine coast. Marine coasts are typically of sandy nature, while the estuarine areas are dominated by inter-tidal mudflats. • Differences in substrates and sedimentation account for the relative luxuriance of mangroves between the estuaries and the marine coasts.

17. 2.3. Physiographic mangrove habitats: • In SE Nigeria, mangrove species occurrences are identifiable with a number of physiographic habitats. The morphology of the habitats are shaped by the various fluvial processes that operate on the swamp landscape. • The habitats identified and generalised flood tolerance sequence of species are: i) Distributary channel habitat (DC) (R, racemosa > N. fruticans > A. africana > R. mangle > P. reclinate > Raphia)

18. 2.3. Physiographic mangrove habitats: Contd. ii) Point – bar habitat (PB) (R. racemosa > A.africana > R. mangle > N. fruticans > R. harrisonii > Raphia spp > P. candelabrum)

19. 2.3. Physiographic mangrove habitats: Contd. iii) Braided channel habitat (BC) (N. fruticans > R. racemosa > P. candelabrum > A.africana)

20. 2.3. Physiographic mangrove habitats: Contd. iv) Interdistributary basin habitat (ITD) (R.racemosa > A. africana > N. fruticans > R.mangle > D.lunatus > P.reclinata)

21. 2.3. Physiographic mangrove habitats: Contd. v) Wooded levee habitat (WL) (A.africana > R.racemosa > N.fruticans > R.mangle > R. harrisonii)

22. 2.3. Physiographic mangrove habitats: Contd. vi) Tributary creek habitat (TC) (A. africana > N. fruticans > R.racemosa > T.rhombodeae)

23. 2.3. Physiographic mangrove habitats: Contd. vii) Inter-riverine creek habitat (IRC) (A. africana > R.racemosa > P. candelabrum > R.mangle > R. hookeri).

24. 2.3. Physiographic mangrove habitats: Contd. viii) Beachridge strand habitat (BR) (A. africana/ R.racemosa/S. portulacastrum/I. Cairica/Remeira maritina) Mangrove species distribution and relationships among the hysiographic habitats are shown on Tables 3.2(a) and 3.2 (b) and 3.2(c), while soil properties in the habitats are shown in Table 3.3.

25. Table 3.2(a) Density of overstorey mangrove species and associes (Density in stems/hectare) and significance of ANOVA tests among the physiographic habitats, (n): not significant, p > 0.10; (*) p > 0.05; (**) p > 0.025. The habitats are: DC = Distributary channel; PB = Point-bar; BC = Braided channel; ITD = Interdistributary basin; WL = Wooded levee; TC = Tributary creek; IRC = Inter-riverine creek; BR = Beachridge. Parenthesis indicate number of stands in each habitat

26. Table 3.2 (b): Density of understorey mangrove species and associes (Density in stems/hectare) and significance of ANOVA tests among the physiographic habitats, (n): not significant, p > 0.10; (*) p > 0.05; (**) p > 0.025. The habitats are: DC = Distributary channel; PB = Point-bar; BC = Braided channel; ITD = Interdistributary basin; WL = Wooded levee; TC = Tributary creek; IRC = Inter-riverine creek; BR = Beachridge. Parenthesis indicate number of stands in each habitat Physiographic Habitats Specie s DC PB BC ITD WL TC IRC BR (understorey) (10) (8) (13) (16) (13) (6) (9) (5) Avicennia africana (**) 230 260 38 231538 183422300 Nypa fruticans (**) 110 38 381310 117 0 0 Rhzophora racemosa (*) 270425 108306 130 67 178 280 Rhizophora mangle (n) 270 225 100 150 308 117 187 0 Triumfetta rhomboideae (*) 0 0 0 13 180 183 0 0 Other stems 125 25 61 225 31 50 11 20

27. Table 3.2(c) Density of groundlayer mangroves and saplings (Density in stems/hectare) and significance of ANOVA tests among the physiographic habitats, (n): not significant, p > 0.10; (*) p > 0.05; (**) p > 0.025. The habitats are: DC = Distributary channel; PB = Point-bar; BC = Braided channel; ITD = Interdistributary basin; WL = Wooded levee; TC = Tributary creek; IRC = Inter-riverine creek; BR = Beachridge. Parenthesis indicate number of stands in each habitat. Physiographic Habitats Species DC PB BC ITD WL TC IRC (Groundlayer) mangroves (**) 160 1325 362 2692092 2367 333 Nypa saplings (*) 90 125 515 150 323 150 33 Raphia spp (*) 20 138 0 44 26 17 12 Pandanus spp (*) 20 25 154 50 6 34 22 Other saplings 30 15 0 19 8 43 39 ______________________________________________________________________

28. Table 3.3: Soil properties in mangrove physiographic habitats, sample size was 2 replicates/10 x 10m quadrat. The significance of F – test for variation among the habitats is indicated by (n) not significant (*): p < 0.05; (**): p < 0.01; (***): p < 0.001 Physiographic Habitats Sample pH Sand Silt Clay Org Soluble CO3 Chloride ( ) > = number size % % % carbon sulphate me/100mg % of quadrats % me/100mg DC (10) 20 5.4 32.9 45.7 21.4 7.2 0.12 8.2 2.4 PB (8) 16 6.3 30..3 50.5 19.2 6.6 0.10 8.6 2.7 BC (13) 26 5.0 17.0 56.6 26.4 12.2 0.1 10.0 3.3 ITD (16) 32 5.5 30.9 36.4 32.7 7.9 0.0 9.3 2.3 WL (13) 26 6.6 27.0 51.8 21.2 9.9 0.10 7.6 3.6 TC (6) 12 5.9 35.2 34.4 30.4 7.2 0.05 10.9 2.5 IRC (9) 18 6.4 66.5 22.5 13.0 5.1 0.12 7.3 4.2 BR (5) 10 5.6 70.6 23.4 5.9 4.2 0.18 13.6 4.4 Significance (***) (**) (**) (*) (**) (*) (*)

29. Observations: • We were able to establish the fact that some mangrove species selectively occur and dominate over others on certain physiographic habitats. • We were also able to establish the fact that the flood tolerance order of species or generalized zonation sequence vary, depending on habitat morphology. • We were able to link substrate composition, both the physical and chemical properties, to variation in species occurrence and habitat morphology. • It is therefore clear that mangrove habitats posses unique environmental and morphological properties to which the species show varying levels of adaptation • We were therefore confident to recommend habitat classification as the basis for demarcating mangrove forests for management purposes, e.g. creation of mangrove reserves and for establishment of nurseries on natural sites.

30. 2.4. Some species identified in the mangrove and strand zone in SE Nigeria are: Chrisobananus orbicularis Caparis spp Clerodendrum ligustrinum Cocos nucifera Drepanocarpus lunatus Diodea maritima Dononia viscosa Desmoncus spp Dalbergia spp Euphorbia glaucophylla Eugenia coronatus Elecocaris spp • Avicennia africana • Acrostichum aureum • Acantus ebracteatus • Andropogon spp • Alternanthera spp • Bravaisia tubiflora • Bucida spp • Cactus afer • Concarpus erectus • Cyperus maritimus • Cyperus articulans • Canavalia rosea

31. 2.4. Some species identified in the mangrove and strand zone in SE Nigeria Contd: Finbristylis obtusifolia Hibiscus tilaceus Hibiscus tuoratensis Heteropogon spp Heliotropium curassavicum Hamelia nodosa Helicania spp Ipomoea cairica Ipomoea pescaprae Impereta cylindrica Jacquinia spp Lagnncularia racemosa Mariscus ligulatus Malaviscus arboreus Mutingia calabura Nypa fruticans Nectandra spp Phoenix reclinata Paspalum viguiatum Pandanus candelabrum Philozerus vermicularis Phyllantus foliosa Panicum repens Panicum maximum Psychotria spp Rhizophora racemosa Rhizophora mangle Rhizophora harrisonii Raphia vinifera Raphia hookeri Rhabdahenia spp Sesuvium portulacastrum Sporobolus viginicus Selaginella spp Stenotaphurm secndatum Sophora spp Scirpus sp Sarcostemma spp Solanum sp Triumfetta rhombiodeae Tillandsia sp Vossia cuspidata

32. 3.0. ECOLOGICAL STATUS OF MANGROVES In assessing the ecological status of mangroves, the apparently simple zonation and succession pattern of species have always been cited. These two related concepts were central to our thinking and we had to look at them very critically. 3.1. The concept of vegetation zonation in mangroves is based on the observation that: • Mangroves are mono-specific along shorelines. They occur nowhere else except along saline or brackish shorelines • The species are mono-dominant and display banded structure from the shores inland, for e.g., on the Nigerian shoreline, R. racemosa fringe the channel margins, followed by R. mangle and/ A. africanna away from the channels. • Indeed such discrete zonation would imply abrupt changes in environmental conditions between the species zones • But since the swamp landscape is constantly disturbed by flocculation, tidal flushing and other fluvial processes, there is bound to be overlap in environmental conditions, which should result in overlap in the species zones

33. Fig. 3.1: Idealized Sequence of Species Zonation

34. Therefore, there should be gradation between species zones rather than discrete and tidy zonation. • Since there is overlap in species niche relations, zonation per se cannot be said to exist in mangroves [ This was like standing the traditional concept of mangrove zonation on its head. It sounded strange at the time but we held onto our conviction] • The implication is that there is vegetation continuum or floristic gradation in the mangroves. • Using a continuum index ordination, we asked a conceptual question and submitted a rather radical thesis to the Hungarian Academy of Sciences in 1990 (see Ukpong, Imoh (1992) Is there vegetation continuum in mangrove swamps?Acta Botanica Hungarica 37 (1-4) pp 151 –159. Fig. 3.2: Continuum Index Ordination for Mangroves

35. 3.2. The theory of vegetation succession in mangroves: • Succession is a process of vegetation development from initial establishment on a bare surface, till it grows to become a mature or climax vegetation. The climax is supposed to be the most mature or steady state form of that vegetation • In the case of mangroves, initiation takes place when seedlings are established along shorelines. Apparently, the species zones should represent the stages of mangrove development towards the stable climax. But where is the climax? Is it the last mangrove zone or the adjacent non-mangrove community? • In the literature, there appears to be no agreement as to whether mangrove species zones are stages in the development of mangrove towards the climax or stable community, • Consequently, the literature abound with numerous tidy mangrove succession schemes for every possible swamp segment [we could produce as many as 500 succession schemes for the Cross River swamp alone!] • Adopting the theory of succession made mangrove studies a tedious descriptive and subjective project • We held the conviction that mangrove species zones were not stages in a succession development towards the stable or climax forest. Each species zone was actually a stable mangrove community.

36. Fig. 3.3: Succession Schemes for Lagoon and Estuarine Mangroves (after Jackson 1964)

37. 3.3. The Dynamic Equilibrium concept: (Borrowed from practitioners in the sub-discipline of geomorphology) • If it is admitted that the climax vegetation or steady state vegetation is based on the relationship of the vegetation to environmental factors ranging from climate to soil, slope and etc., then there could be many climaxes or steady state vegetation (depending on the intensities of the relationship of these environmental factors to the vegetation). • The implication here is that a single vegetation community at any time is therefore the climax and steady state vegetation irrespective of the structure of that vegetation. [i.e. whether the vegetation looks mature or young, tall or stunted], for as long as it has a relationship to any of the environmental factors. • If the environmental conditions change, the resulting vegetation is the climax under the new set of conditions. • Therefore the vegetation is in a state of Dynamic Equilibrium with the environment because it is constantly adjusting to any emerging condition. • In the case of mangroves, we theoretically established that the species are in a state of dynamic equilibrium with the ever changing swamp landscape. • We were therefore able to explore and seek understanding of the distribution and spatial patterns in mangroves using methods which were hitherto not applied to the mangrove ecosystem • The dynamic equilibrium concept permitted reciprocal analyses of mangrove - environment interrelationships using regression techniques, statistical curve fitting procedures and other high powered data distortion techniques e.g. canonical correlation, principal component analyses, detrending and polar axes ordination (Ukpong 1992a, 1992c, 1994a, 1995a, 1995b, 1995d, 1995f, 1999d)

38. 3.3. Gradient Analysis • We also sought boldly to reveal the fundamental spatial patterns exhibited by mangrove vegetation in relation to (a) Environmental factors e.g. soil, (b) Species population structure and composition, and (c) Characteristics of communities. The method of gradient analysis was made popular by Robert H. Whittaker, an American, along the obvious moisture gradient of the pine forests of the Great Smokey Mountains of the USA[see Whittaker,1967]. We borrowed from him. • In that classical study,Whittaker (1967) differentiated the methods of gradient analysis into two. We also did the same. (a)Direct gradient analysis • In this analysis, vegetation was related with some environmental data by arranging species on a scale of values on the environmental factors. In some cases the environmental factors were assumed as given. • We carried out several direct gradient analyses in the mangroves of SE Nigeria which demonstrated clearly that there were overlap in species population peaks and that there were gradations between species zones. (Ukpong 1991, 1998a, 1998b, 1999f, 2000a, 2000b)

39. Fig. 3.4:

40. Direct gradient analysis (Contd.) • We were able to assess and generate practical predictive models of the stability of the swamp landscape in relationship to the species occurrence, abundance and population modes. • Our modest contribution to the understanding of the behaviour of mangrove species as influenced by the complex of environmental factors was acknowledged. Direct gradient analysis provided an insight to ecological group classification of mangrove species. • A thesis titled: Gradient Analysis in Mangrove Swamp Forests was published in 2000 on the results of these analyses.[see Ukpong, Imoh E(2000)Tropical Ecology,.41, 25-32

41. 3.5. Derivation of Ecological Species groups: • In mangrove swamps, an ecological group would consist of species that show similar relationships to important site factors, e.g. salinity and nutrient factors or gradients. • The species of an ecological group should therefore be closely similar in their life forms. and should display closely coinciding modes along specific environmental gradients • Ecological species group classification in relationship to important site factors therefore enabled us to establish the relationships among species, for e.g., - Why some mangrove species tend to occur in mixed stands rather than mono-dominant stands - Why some species show dominance over others in the mixed stands - Which species show dominance at the ecotones and why they are ecologically more important at the mangrove-high forest boundaries - Which species have the widest ecological amplitudes[ occurring everywhere in the swamp on all habitats] • Which species occur at the highest values of the site factor and are always mono-dominant [where other species cannot compete] (Ukpong 1991, 1998b, 2000d).

42. Fig. 3.5 a: Ecological Groups of Species on Salinity Gradient

43. Fig. 3.5 b: Ecological Groups of Species on Salinity Gradient

44. Fig. 3.5 c: Ecological Groups of Species on Salinity Gradient

45. Indirect gradient analysis • In this analysis, the vegetation is grouped according to some attributes of the vegetation itself. Then the environmental factors common to each group are identified (Ukpong 1992a, 1995b, 1999d) • It involves ordination of vegetation or species characteristics along two or more axes of variation in theoretical hyperspace • Several abstract mangrove communities [presumably determined by some yet unknown environmental factors] were classified in the hyperspace.

46. Fig. 3.6: Ordination of Mangrove stands in hyperspace

47. (b) Indirect gradient analysis Contd. • When we analysed the abstract mangrove communities using field data, the communities were observed to be significantly different from each other in terms of species density, dominance and the corresponding soil and environmental properties • Indirect gradient analysis by means of ordination proved to be an effective tool for summarizing and linking together both the vegetation and environmental sub-systems in mangrove swamps [see Ukpong, I. E. (1995) An ordination study of mangrove swamp communities in West Africa, Vegetatio 116, 147-159]

48. 4.0 NATURAL AND ECONOMIC BENEFITS OF MANGROVE SWAMPS Mangroves occupy low-energy marine environments and therefore can be quite firmly rooted in mud. To some extent, mangroves provide significant value as buffer against shoreline erosion, storm surge and tsunamis. However, the capacity of mangroves to ameliorate high wave energy events is limited and their long term impact on rates of coastal erosion is also limited. It is common to see many mangroves stands falling into the water channels as result of active erosion at the banks while new trees are appearing on other areas where there is sediment accretion. Mangroves contribute to improved water quality by filtering and assimilating pollutants and stabilizing bottom sediments. Although there are no endemic species in the mangroves, yet mangroves are known for their diverse pelagic fish communities, including some narrowly distributed species, abundant avifanna and the presence of some rare mammals and turtles. The mangroves provide habitat to the threatened West African Manatee (Trichechus senegalensis) and the soft-skinned turtle (Trionyx triunguis) and the pygmy hippo (Hexaprotodon liberiencisis heslopi), the near endemic sclater’s monkey (Ceriopithecus sclateri) etc. Coastal mangroves are also important for large concentarations of birds that use the area during migration (see Hughes 1992 and Jones, 1994).

49. NATURAL AND ECONOMIC BENEFITS OF MANGROVE SWAMPS Contd. • Since estuarine mangrove swamps are constantly replenished with nutrients transported by freshwater runoff, and flushed by ebb and low tides, they support a bursting population of bacteria, decomposers and filter feeders. The ecosystem sustains billions of worms, protozoa, barnacles, oysters and other invertebrates. • Thus the swamps function as nurseries for shrimp and exporters of organic matter to the adjacent coastal food chains. For e.g. the Niger Delta provides spawning/nursery areas for the fisheries in the Gulf of Guinea. There is a high diversity in the pelagic fish community with 48 species in 38 families (Ajao 1993). • The leaves of Nypa palm are used for the making of thatch-shingles for roofing (which lasts for 3-5 years), hats, mats, raincoats, brooms, floats for fish nets, fishing poles and ropes. • The young seeds of nypa when coated with sugar can be eaten as sweetmeats. The mature seed, which are very tough and not edible, can be converted by grinding into animal feed. The mature seeds can be used as vegetable ivoryand for buttons. • Mangrove wood particularly Lumnitzeria spp is used for carving furniture due to its durability. Wooden toys are made out of Excoecaria wood. • Sonneratia leaves and fruits are used for the preparation of vegetable dishes while Rhizophora leaves are used to cook with fish to acidify the meat. • Avicennia spp is highly prefered as fuelwood.

50. NATURAL AND ECONOMIC BENEFITS OF MANGROVE SWAMPS Contd. • The scraped skin of Bruguiera seedlings is applied to stop bleeding while Avicennia bark is used to treat skin parasites. Tea brewed from Acanthus leaves is used as pain killer. • Nypa sap can be used to make sugar, vinegar, alcohol and other beverages. With a sucrose content of 14-17%, nypa sap compares favorably with other crops such as sugar cane and sugar beet. (In Malaysia nypa estates yields up to 15,638 litres/hectare/year of 95% alcohol. Sugar cane, in comparison yields only 3,350 to 6,700 litres/hectare year). The advantages of alcohol/sugar production from nypa are many but the processes are intricate. With availability of other palms e.g. Raphia and Elaeis in Nigeria and also sugar cane, nypa utilization for alcohol/sugar production in this hostile environment can only be viewed as a potential. • Mangrove wood is used in the construction industry at various places e.g. poles and scaffolding.