Lost in the Pa­cific Man­grove For­est Mi­cro­bio­mes

by Me­chas Zam­brano

Fig­ure 1. Anadara tu­ber­cu­losa. Source: Mi­reya Os­o­rio. Fron­tispiece: Man­grove For­est. Source: Me­chas Zam­brano

One of the perks of be­ing a mi­cro­bi­ol­o­gist is par­tic­i­pat­ing in ex­pe­di­tions at re­mote lo­ca­tions to col­lect sam­ples for our projects. My most re­cent ex­cur­sion was to the south­ern Pa­cific coast of Colom­bia, a far-off re­gion re­plete with man­grove forests. The pur­pose was to ob­tain sam­ples of the bi­valve Anadara tu­ber­cu­losa, lo­cally known as pi­angua, to study its genome and as­so­ci­ated mi­cro­biome. I went there with my col­leagues Mireya Os­o­rio and Di­ana Tru­jillo from Uni­ver­si­dad de los An­des, Bo­gotá, Colom­bia. Our experi­ence was a very brief yet eye-open­ing im­mer­sion into a lifestyle of min­i­mal con­ve­niences in a set­ting sur­rounded by na­ture both ma­jes­tic and fierce.

Fig­ure 2. The Chocó Bio­geo­graph­i­cal Re­gion. Source

The Pa­cific coast of Colom­bia is part of the Chocó biogeo­graphical re­gion, unique in our planet in terms of ecosys­tems, species rich­ness, and en­demism, un­known to most and trea­sured by sci­en­tists and con­ser­va­tion­ists. The Chocó oc­cu­pies about 187,400 square kilo­me­ters and ex­tends along the Pa­cific Coast from Panamá to Ecuador (map). The bi­o­log­i­cal unique­ness of this re­gion stems from a combina­tion of geo­lo­gi­cal and cli­matic fac­tors that sep­a­rated this coastal strip of land from other ecosys­tems in the conti­nent. Tec­tonic move­ments that brought to­gether North and South Ame­rica con­nected these large masses of land, form­ing the isth­mus of Panama that led to the mi­gra­tion of species known as the Great Amer­i­can Bi­otic In­ter­change. The for­ma­tion of the An­des Moun­tain range in South Ame­rica served to pro­gres­sively iso­late this coastal re­gion from other con­ti­nen­tal habi­tats. The sep­a­ra­tion of the Pa­cific and At­lantic oceans al­tered cur­rents and trans­formed the Chocó re­gion into one of high hu­mid­ity and pre­cip­i­ta­tion with a va­ri­ety of ecosys­tems that range from moun­tains and rain­forests to rivers, swamps, and man­groves. Over the mil­lennia and thanks to processes of evo­lu­tion and adap­ta­tion, this re­gion along the north­ern Pa­cific coast of South Ameri­ca be­came rich in plant and an­i­mals and home to myr­iad en­demic species, mak­ing it a one of the most bio­di­verse ar­eas on the planet. In Colom­bia alone the Chocó re­gion har­bors most of the country's reg­is­tered species, in­clud­ing many en­demic plants and birds. With an­nual pre­cip­i­ta­tion rang­ing be­tween 3 and 12 me­ters, this is one of the raini­est re­gions in the world, cre­at­ing con­di­tions that make hu­man habi­ta­tion ex­tremely dif­fi­cult. To­day, the Chocó is still largely in­ac­ces­si­ble and sparsely pop­u­lated. The few hu­mans that brave this en­vi­ron­ment live in di­verse mul­ti­eth­nic com­mu­ni­ties and have carved out a unique lifestyle in these harsh sur­round­ings.

Fig­ure 3. A vil­lage along the Is­cuandé River. The school is in the dis­tance (blue walls). Source: Me­chas Zam­brano

Our jour­ney took us by air from Bo­gotá to the city of Guapi, from where we em­barked on a 1.5 hour-long mo­tor­boat ri­de along an in­tri­cate net­work of river deltas un­til we reach­­ed a small com­mu­nity of wooden houses built on stilts at the mouth of the Is­cuandé River. The rivers in this area, among which are the Guapi and Is­cuandé Rivers, dis­charge large amounts of wa­ter and sed­i­ments that shape and give the area its unique fea­tures and ma­jes­tic land­scape. Man­grove trees flour­ish at the wa­ter-land bound­ary formed by the daily ebb of tides and river cur­rents.

Man­grove species are found world­wide in saline or brack­ish wa­ters of trop­i­cal and sub­trop­i­cal re­gions and are unique in their adap­ta­tions to salin­ity and low oxy­gen and their ca­pac­ity to with­stand fre­quent tidal flood­ing. Once viewed as swampy waste­lands, man­grove ecosys­tems are now known to pro­vide an es­sen­tial habi­tat for di­verse species that work to­gether to main­tain these coastal zones healthy and vi­brant. Man­grove trees trap se­diment and pol­lu­tants, sta­bi­lize shore­lines and pro­tect them against ero­sion from the ocean. They are home to many species, from bac­te­ria to bar­na­cles and al­gae, and are the breed­ing ground for crabs, shrimp and fish. By pro­vid­ing an es­sen­tial habi­tat for thou­sands of species, man­grove forests are cru­cial for main­tain­ing a pro­duc­tive food chain in coastal zones.

Fig­ure 4. Man­grove trees. Source: Me­chas Zam­brano

Col­lect­ing pi­anguas is not an easy task. It is car­ried out mostly by women ex­pe­ri­enced in find­ing these small clam-like mol­lusks bur­rowed in the mud. Equipped with small buck­ets, gloves, boots, and pro­tec­tion from mos­qui­tos and the sun, the women dig up pi­anguas amid the en­tan­gled man­grove roots that hover el­e­gantly over the mud left be­hind as the ocean wa­ter re­cedes dur­ing low tide. Lack­ing the proper knowl­edge or at­tire to par­tic­i­pate, I am rele­gated to ob­serv­ing from the small mo­tor­boat, the lo­cal trans­porta­tion cur­rency. Iso­lated ge­o­graph­i­cally and by the ab­sence of com­mu­ni­ca­tion, I mar­vel at the dis­par­i­ties in lifestyles. The ad­vances and com­forts we take for granted dur­ing our daily rou­tines are ren­dered al­most mean­ing­less when faced with the dif­fi­culty of sub­sist­ing with the bare es­sen­tials.

So why are we col­lect­ing pi­anguas in this se­cluded cor­ner of the world? Man­grove-as­so­ci­ated mi­crobes are, not surpri­singly, an es­sen­tial part of these ecosys­tems. They con­tribute to the car­bon and ni­tro­gen biogeo­chemical cy­cles and are thus cru­cial for pro­duc­tiv­ity and the en­tire food web. Their role in car­bon turnover in sed­i­ments also makes them key to car­bon stor­age. How­ever, the ex­tent of the micro­bial func­tions un­der­ly­ing the di­verse ecosys­tem ser­vices pro­vided by man­grove forests are not yet fully un­der­stood.

Fig­ure 5. Women col­lect­ing pi­anguas. Source: Mireya Oso­rio

Which is the rea­son why a group of sci­en­tists re­cently launched the "Man­grove Mi­cro­biome Ini­tia­tive." This inter­national net­work pro­poses to work on the man­grove micro­biome with the ob­jec­tive of reach­ing a more com­plete un­derstanding of the mi­cro­bial func­tions and in­ter­ac­tions that con­tribute to a healthy ecosys­tem. They pri­or­i­tized re­search ar­eas, such as char­ac­ter­i­za­tion of the mi­cro­bio­mes and their bio­geo­chem­i­cal processes, to ob­tain a holis­tic view of these com­mu­ni­ties and their di­verse roles. This work, how­ever, needs to be done by co­or­di­nat­ing re­search ef­forts and us­ing stan­dard­ized meth­ods and ap­proaches that can en­able com­par­isons and val­i­da­tion across sites. The hope is to un­veil key mi­cro­bial processes that can aid ef­forts aimed at man­ag­ing and con­serv­ing these ecosys­tems.

The chal­lenge is how to trans­late this re­search into infor­mation that can be both ac­ces­si­ble and use­ful across cu­ltural and eco­nomic di­vides. Af­ter all, and as was made clear by the leader of the com­mu­nity we vis­ited, we are not re­ally work­ing on a "project," which equates with eco­nomic or ma­te­r­ial gain, but do­ing a "study," which trans­lates into not re­ally know­ing if or when the work will have an im­pact. And this is so true about so much of the work we do in mi­cro­bial ecol­ogy. But the hope that some­day it might do some good plus eye-open­ing ex­pe­ri­ences such as this visit to the Chocó keep us go­ing.

 

Me­chas (María Mer­cedes) Zam­brano is a mi­cro­bi­ol­o­gist and the Scien­tific Di­rec­tor of Cor­pogen In­sti­tute in Bo­gotá, Colom­bia.