An Ecological Stronghold : Mangroves of The Pambala-Chillaw Lagoon

A lagoon is a shallow body of water that is partly or completely separated from the sea by obstacles like sand barriers, coral reefs, barrier islands or mangrove belts. Lagoons can be a huge biodiversity hotspot that includes various floral and faunal species. Some of them are mangroves, seagrasses, algae, planktons, fishes, crustateans, molluscs, birds and other fauna like plychaetes and crocodles. As a island country consisting of 14 coastal districts, Sri Lanka provides home for a plenty of lagoons- ex: Chillaw lagoon, Negombo lagoon, Batticolo lagoon, Koggala lagoon, Rekawa lagoon and etc…

Out of all the flora and fauna found in the lagoon areas in Sri Lanka, mangroves pay a vital role as an economically and ecologically important flora. Mangroves provide ecological services such as stabilization of lagoon systems, providing nursery and breeding grounds for fish, support avifauna and wildlife, enhancement of water quality, nutrient cycling and most importantly carbon storage and climate change mitigation. Therefore mangroves being the ecological backbone of Sri Lanka’s lagoon ecosystems themselves explains why it must be widely discussed about the diversity, distribution and prevailing threats to mangroves.

Figure 1. Map of Pambala-Chillaw Lagoon

The Pambala-Chillaw lagoon complex represents one of the most biologically diverse mangrove ecosystems in Sri Lanka, supporting a rich assemblage of flora and fauna within a relatively smaller geographical area nearly about 1300 hectares.

As per every other lagoon Pambala Chillaw lagoon also receives fresh water through external freshwater inlets. Karabalan oya and Deduru oya are the main freshwater inlets. Seasonal rainwater runoff from the surrounding catchment and multiple inland channels like Marambettiya Ela, Pol Ela and Dutch Cannal also contributes regularly to the lagoon, specially during the Northeast monsoon. The average annual rainfall is so far recorded as 1000 – 1300 mm. These interconnections via various inputs and outputs maintains the ecosystem linkages.

The structural complexity of this ecosystem contain several main interacting components. Mangroves of the area has a better distribution along the salinity gradient that extend from the lagoon shore towards the inland. Species like Rhizophora sp. dominates the shoreline whereas Aviccinea sp. ,Brugeria sp., lies towards the inland. Another fact that increases the structural complexity of the lagoon system is that both high salinity tolerant and low salinity tolerant mangroves lie in the same lagoon- Ex: Aviccenia offcianalis, Soneratia caseolaris grow in low salinity whereas Aviccinea marina, Soneratia alba grow in high salinity level. Mangove associates like Acanthus ilicifolius, Acrosticum aureum, Derris scandens and etc…grow along with these true mangrove species. The dense rootmass of the mangroves in the shoreline provides breeding grounds for juvenile fish. Fish species like Chanos chanos, Lates calcifier and Mugil spp. Interactively grow in mangrove boundary lines. Various crab species- ex: Scylla serata, Uca sp.,Sesarma sp., prawn species -ex: Penaes sp, molluscus like ,oysters, clams and cockels and other benthic animals like mudskippers successfully survive in this ecosystem. While this aquatic creatures establish their habitats here birds like little egret(Egretta grazetta), Gray heron(Andrea cinera),common sandpiper(Actitis hypoleucos) and reptiles and amphibians like water monitor ( Varanus salvator),estutuorine crocodiles (Crocodylus poorosus), Skipper frog (Euphlyctics cyanophlyctis)also shelters here. Mamals like fruit bats (Pteropus sp.) can also be seen.

The main environmental factors that keep changing this ecosystem are salinity which varies in a range of 0-40 ppt,tides,rate of sediment accumulation and rainfall. The Pambala – Chilaw lagoon is a good example for a lagoon that posses ecological stability .This ecosystem haven’t experienced large changes in its characterstics over a short time and it is capable of returning to its equilibrium state after pertubation. The rainy season that occurs from April-May and Octomber – December which is twice a year and tide inundation everyday on the months May and November flushes fresh water providing high dynamism.This causes changes in salinity levels and sedimentation .

Owing to its high structural complexity, dynamic environmental stability and well developed ecological linkages the Pambala – Chillaw lagoon supports a highly diverse and resilient mangrove ecosystem.

Despite this ecological richness, the mangroves face growing pressures from human activities and environmental changes, which threaten to disrupt the delicate balance that sustains the lagoon’s unique biodiversity. The oil spill from the fishing boats, unsustainable aquaculture practices like over fishing, salterns, agricultural waste that gets added to the lagoon through the fresh water runoff from the surrounding catchment literally destroys the aquatic habitats. A vast mangrove destruction was occurred in 1885 and relavent time due to the commencement of shrimp farming practices. Unplanned tourism activities, clearing of mangrove forests for construction, and improper waste disposal basically destroy the floral resources in mangrove marginal regions. Migration of alien and invasive species through natural water channels can be identified as a potential challenge, too.

Figure 2 pictures of the mangroves in Pambala-Chillaw Lagoon

Pollution control, recognizing forests reserves, introducing sustainable fishing techniques, control of aquaculture, awareness and community participation in conservation efforts , policy implemention, monitoring, reasearch and promoting ecotourism can be various conservation .statergies where most of them is currently being carried out in mangrove marginal regions together with the support of Lanka Mangrove Museum and Learning Center. LMM & LC is an extention of the mangrove conservation efforts which was initially carried out in the name Small Fisheries Federation. Small fisheries federation carried out various replantation programs in various different sites which have enormously contributed to the present distribution and richness of the mangrove forests in the area. From 1994 different projects were carried out with funding of different agencies. They are,

1994-UNDP
1996-Netherland Embassy
1998-Ministry of Environment

By championing conservation of the Pambala-Chillaw mangroves, the Lanka Mangrove Museum and Learning Center safegaurds a unique ecosystem that is essential for biodiversity, coastal protection, and ecological balance.