Threat s t o Mangroves

Threat s t o Mangroves

Naturally resilient, mang ro ve fo rests have withsto o d severe sto rms and c hang ing tides fo r many millennia, but they are no w being devastated by mo dern enc ro ac hments. In the past, their surfac e area has been estimated at 170, 000 square kilo metre s. Sinc e 1980 this has been reduc ed by a third wo rldwide. An estimated 50 perc ent o f the mang ro ve fo rests that o nc e existed wo rldwide have been destro yed in rec ent

4 4 Mang ro ves – Func tio ns and Threats

Shrimp farming c an harm mang ro ves

Shrimps fo r sale o n a Marketplac e

Illeg al Waste Dumping

dec ades, so that mang ro ve fo rests are amo ng the mo st threatened habitats in the wo rld - even mo re threatened by destruc tio n than tro pic al rainfo rests. With the damag e to mang ro ves, tro pic al c o asts will lo se the habitat fo r diverse hig h- spec ialised spec ies, o f whic h pro bably o ne third still aren’t even sc ientific ally registered at present.

Enviro nmental stress c an kill larg e numbers o f mang ro ve trees. In additio n, the c harc o al and timber industries have also severely impac ted mang ro ve fo rests, as well as to urism and o ther c o astal develo pments. Wherever mang ro ve fo rests have been cleared, the yields o f co astal fisheries have drastically fallen. The reaso n is that many ec o no mic ally impo rtant fish spec ies use the mang ro ves fo r their repro duc tio n. The lo ss o f these refuges re mo ves a life- suppo rting reso urce, no t just fo r these fish po pulatio ns but also fo r the

c o astal po pulatio n. With the felling o f the fo rest, a natural pro tec tive belt is lo st. The g ravest threat to the wo rld’s re maining mang ro ves is the rapidly expanding shrimp aquac ulture industry.

Sinc e mang ro ve fo rests have been c lassified by many g o vernments and industries alike as useless swamps, it has made it easier to explo it mang ro ve fo rests as c heap and unpro tec ted so urc es o f land and water fo r shrimp farming . Tho usands o f hec tares have been c leared to make ro o m fo r artific ial shrimp po nds. The amo unt o f mang ro ve fo rest destruc tio n is alarming . Fo r instance, in Ec uado r and the Philippine s, the Shrimp Aquac ulture Industry has been respo nsible fo r defo resting 70 % o f mang ro ve fo rests in tho se reg io ns. The use o f an area fo r shrimp breeding is pro blematic bec ause after a maximum o f ten years’ use, shrimp po nds have to be abando ned due to c o ntaminatio n o f the po nd bo tto ms with c hemic als, o ver- fertilisatio n, pestic ides and antibio tic s. Refo restatio n is usually impo ssible fo r dec ades afterwards. That means that new areas have to be develo ped. In 1990 the pric e fo r o ne kilo g ram o f shrimps was abo ut ten do llars, ho wever due to mass farming - a six- fo ld inc rease in shrimp pro duc tio n in the last 25 years - the pric e beg an a severe dec line. The same amo unt o f shrimps c o sts o nly US$ 4. 70 to US$ 1. 60 at present. Onc e o ne hec tare o f mang ro ve fo rest o ffered liveliho o d fo r abo ut ten families - no wadays a 500 hec tare shrimp- farm pro vides o nly five jo bs. Glo bally, as muc h as 50 % perc ent o f mang ro ve destruc tio n in rec ent years has been due to c lear c utting fo r shrimp farms. Mang ro ve fo rests are in dang er o f disappearing fro m the c o asts in the next twenty years.

It has to be in o ur interest to do everything po ssible to preserve the mang ro ves ec o lo g ic al func tio ns. Eac h further destruc tio n o f mang ro ves fo r shrimp farms o r c o nstruc tio ns o r deg eneratio n bec ause o f waste

c o nc erns the who le wo rld c o mmunity and c an no lo ng er be accepted.

Global Nat ure Fund – EU Asia Pro Ec o IIB 4 5

M angrove D is M angrove D is M angrove D is M angrove D is M angrove D ist ribut ion t ribut ion t ribut ion t ribut ion t ribut ion

Text by Pro f. Jayamanne

Mang ro ve distributio n is limited by several fac to rs. Sinc e mang ro ves are tro pic al spec ies, they depend o n air and water temperature. The plants do no t to lerate freezing temperature s. They do no t c o pe with aridity and are therefo re mo re develo ped in c o astal areas that have hig h inputs o f rainfall. Ano ther impo rtant fac to r is the salinity o f the water in whic h mang ro ves are g ro wing . Mang ro ves c an g ro w in freshwater c o nditio ns but no rmally the c o mpetitio n with freshwater spec ies is to o hig h so that in areas with hig her salinity they are favo ured. Tidal fluc tuatio n plays ano ther impo rtant indirec t ro le fo r mang ro ve distributio n, bec ause they bring saltwater up estuaries ag ainst the o utflo w o f freshwater, transpo rt sediments, nutrients and c lean water into the mang ro ve habitat. Also impo rtant are the c o mbined energ y levels o f sediments and waves, as mang ro ves g ro w best in an enviro nment with a lo w wave energ y. Hig h waves limit the ac c umulatio n o f fine sediments.

Copi ng wi t h Rough Envi ronment al Condi t i ons and Reproduct i ve St rat egi es

In c o mpariso n to land plants, mang ro ves experienc e vario us pro blems bec ause they live in an enviro nment that is ‘physio lo g ic ally dry’ due to their pro ximity to sea o r salt water. To survive under these to ug h

c o nditio ns, mang ro ve plants have adapted to c o pe with this spec ial enviro nment. The main pro blems fac ed by the mang ro ves and their adaptatio ns: