Discovering the tidal ecosystem of Saint Martin’s
A journey into the biodiversity treasure trove
Back in 2013, my classmates and I went on a study tour to the Saint Martin's Island. There, on a winter night, a little far from the shore, we noticed a set of torch beams. Upon reaching the source of the light, I was waiting to be fascinated with the tidal ecosystem for life.
The lights were of fishermen operating as beach seines. Thanks to the celestial moon and neap tide, the hauling fishing baskets were crammed.
Many species, mostly unknown to me back then, were shimmering under torches of varying shapes, sizes, colours and patterns. It was for the first time that I had seen that many shades of silver.
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Years after my visit to the island, it now faces an existential threat, following which experts have stepped forward with conservation strategies. Yet the experience of wonderment thrives on the biodiversity of Saint Martin's island – there is yet more to explore; the wildlife living within her waters are far more bewildering than speculated.
You just need to know where to look for a rarity!
The island of our shallow bay
On the Northeastern flank of the bay, Saintt Martin's Island (between 20°34'N and 20°39'N) is the only sedimentary continental island of the country.
Administratively, the island is a Union Parishad, which is divisible into five physiographic localities. The surface area of the island ranges from 5 to 8 square-kilometres – subject to the tidal level. Staged on the continental shelf, the island is rimmed by shallow water averaging around 10m, the shelf itself platforms the island to a maximum depth of 15-40m.
Rock, Crannies, Pool … and Tide
A prominent rocky platform fringes, the island spans from the supratidal to the subtidal – on the intertidal zone. The boulder bed has a width of 100m to 400m. Coral communities of a nonreefal origin dominated by scleractinian species are present in the subtidal zone of the island, beginning from the lower rocky intertidal to offshore zones. The dune system of the island is widespread and well-developed starting along the shoreline.
Crawlers and burrowers
When the tide is gone, to the naked eye, the dead coral rock of the island will appear barren and void of life. But, if you look closely, the rocks and the crevices present are teeming with life, observing your every move – crabs crawling inside, calcified barnacles and feather duster closing in, only to be reopened as you step aside.
The adjacent wet sand system and small pool race equally in terms of richness. Looking for crabs, you might get dazzled by bright flashes of colours – yellow, blue, and at times red. These are sergeantfish and damselfish seeking refuge till the next high tide. Even the sand will start moving as you look closer. Several worm-like fish – blenny and goby gesturing, foraging and jousting cause the sand to shift.
On the low tide, if you inspect through the magnifying glasses of Holmes, you may notice the burrows of mantis shrimps and bobbits or a blobby sea-cucumber waiting patiently for the next tide.
Disappearing, but noticed?
Delving deeper into the sub-tidal zone of the island, one will see that the corals are gone, so are its denizens. True, the whole island is in grave threat; yet there is a lot to be discovered. Still many small and diminutive species are seen taking shelter in the last remaining patches of gorgonian sea fans and submerged crannies.
The coral distribution around the island becomes extremely patchy, bleached and dead in past ranges. At the same time, just a year back, 11 new coral species were documented for the first time in Bangladesh.
New records on the food-stalls
With an oceanic island comes sea-food. Moreover, freshly caught fish and shellfish are delicacies. But, salivate gently! Take a snap before ordering it from the display. According to ichthyologists, of around 50 species documented from the island, more than 15 – including fishes, lobsters and crabs – were collected from beach-stalls.
A trove for sure
The tidal shelves of Saint Martin's Island are alive, busy and bustling, and it applies for our entire maritime boundary.
With the entire 710km of coastline, total of 118,813 square kilometre of territorial sea and 200nm of Exclusive Economic Zone and the Swatch of No Ground, the heterogonous and exclusive subtropical marine habitats of Bangladesh are unexpectedly modest.
We have a rough estimate of 450 marine fishes, around 110 marine crustaceans, similar meagre number of other invertebrates. Considering the island, the last compilation on marine fishes was done a decade back yielding around 240 species. However, there is no systematic survey on the invertebrates.
The potentials of biodiversity within the maritime habitats of Bangladesh is undoubtedly of higher dimension.
To perceive them all is to save them well
Bangladesh has now entered into the era of Blue Economy. To thrive on what the concept of Blue Economy offers, the best utilisations of maritime resources have to be realised.
That in turn would offer economic growth, improved livelihood, better job opportunities and sustainable ocean ecosystem health. Systematic and scientific explorations of the island water are needed.
Leave no stone unturned in search of life. Life will surprise you with new discoveries. To quote Dr Ian Malcolm from Jurassic Park, "Life cannot be contained." A close inspection will reveal heartbeats everywhere; caring will come instinctively.
New range records for Bangladesh observed at Saint Martin's from 2017-2019
