Wild Vault

Twilight Zone: A Tale Between Two Tides

When the tide heads out, the shallow watery plains come alive with many surprises

Text, photos and videos by: Samuel John

In the Andaman archipelago, Havelock Island is one of the most popular beach destinations for Indian tourists. Visitors come here for the promise of white sandy beaches, clear blue waters, and stunning underwater pictures. While travel agents, hotels, and dive shops influence how one may experience the marine environment of Havelock, the role of tides remains largely unknown to most visitors. This became evident to us when confused tourists landed on the shoreline close to our home on Beach no.5 and wondered where the beach had gone. Every six hours and fifteen minutes or so, the sea oscillates between fully submerging and fully exposing the spaces where it meets land. In some places, like the intertidal area (the area subject to tides), this shift is dramatic with the rise and fall in sea levels ranging up to two metres. This story subtly sneaks past the physics and phases of the moon to give you a glimpse of the transformation of life in this twilight zone.

(Left) A bed of sargassum engulfs a rock at low tide with an air-breathing slug (Onchidiidae) navigating the algae. (Right) Sargassum rises into towers of green during high tide and gives shelter to a school of juvenile fish.

The Rise and Fall of Sargassum
Sargassum, are marine algae that first became well known in the 15th century through their trysts with curious Portuguese sailors. The sailors who regularly encountered these algae drifting through the open ocean fondly named it after sargaço (Halimium lasianthum), a shrub native to their homeland. In a section of the Atlantic Ocean that would come to be named after the algae (the Sargasso Sea), vast swathes of sargassum float on the surface of the open ocean. Gas-filled spheres, called pneumatocysts, give these floating wanderers the buoyancy they need. However, the sargassum patches outside our home seemed less inclined to travel and have comfortably anchored themselves to rocks and boulders. As the high tide engulfs these rocks with about two metres of water, the sargassum springs to life. Irregular columns of green sway hauntingly in the blue waters as young fish take shelter in their forest-like presence. When the tide recedes to its lowest point, the algae rests gently on the rocks. Its job as a cradle for life does not end with the departure of the water. Look closely enough at low tide, and life begins to emerge — from shy crabs peeking curiously to air-breathing slugs that patiently feed around the algal patch.

Stylocheilus striatus in a mating aggregation. Sea hares like these are hermaphrodites (having both male and female reproductive organs). They form long mating chains, where an individual plays the role of a male to the individual in front of it, and the role of a female to the sea hare behind it!

As a person who spends most of his time on land looking at spiders and other tiny creatures, I carry my obsession for the minuscule into the water. Marine slugs do just as well as spiders in making you question everything you thought you knew about the world. Plakobranchus ocellatus, a slug that regularly keeps us company on our swims at high tide, belongs to the superorder Sacoglossa, or as the Internet fondly calls them, “solar-powered slugs”. When these slugs feed on marine algae, they retain chloroplasts from the algae and store them for up to 10 months (kleptoplasty). As these preserved chloroplasts photosynthesise, they supply the resourceful slug with nutrition! The gastropods of Havelock have also been kind enough to grace us with spectacular appearances at low tide. On a morning stroll in February 2020, we encountered a phenomenally massive aggregation of the sea hares (Stylocheilus striatus). With millions of slugs forming smaller clusters around us, the intertidal zone was briefly reserved for love amidst this mass mating aggregation.

(Top) An octopus searches the intertidal zone for small crustaceans. The goby, a symbiotic partner of the burrowing shrimp, promptly quells the threat. (Above) A snowflake moray eel (Echidna nebulosa) searches the intertidal zone at high tide for its next meal. While moray eels are mostly known to be ambush predators, the intertidal zone presents some spectacular surprises.

Prolific Predators
On our nature walks with friends and guests through the intertidal zone, there is an eight-limbed hunter that consistently solicits exclamations of “Where? I don’t see it!” followed by a “Whoa!”. The intertidal zone provides an excellent hunting ground for various octopuses, from young reef octopuses to smaller species like the algae octopus. These tactful predators glide around intertidal pools looking for small crustaceans. They regularly envelope small rocks or clumps of algae to spook unsuspecting crabs straight into their hungry embrace. Watching curious octopuses explore holes in the intertidal ground is an edge-of-the-seat thriller. Some holes in the ground present the octopus with its next meal, while others introduce it to a goby who does not appreciate having its home prodded.

Another league of hunters that roams these shallow watery plains are small moray eels like the snowflake moray eel. Much like the octopuses, eels can be seen searching clumps of algae, rock crevices, shallow corals, and holes in the ground for small crustaceans and fish. Unlike the limbed strategy of the octopus, eels tend to have a more head-on approach (on account of having no limbs). These eels use their paddle tails to move in mesmerising zig-zag paths (imagine a snake floating through a fluid) and regularly dip their heads in and out of crevices looking for their next meal. While most eels are ambush predators that hide in rocks and crevices, the eels we regularly met on our intertidal walks seemed to prefer this active approach of securing a meal.

A secluded stretch of the coast on Havelock Island bears signs of human presence with hundreds of fishing nets caught in the mangroves. The fine net hanging in front has the remains of an unfortunate crab.

A secluded stretch of the coast on Havelock Island bears signs of human presence with hundreds of fishing nets caught in the mangroves. The fine net hanging in front has the remains of an unfortunate crab.

Untouched Paradise
This story offers only a glimpse of the incredible processes and transformations of life where land meets the sea. An entire world of wonder awaits anybody willing to spend time staring into even a single tide pool. From the adorably fuzzy presence of hairy crabs to the nervous stares of blennies, the intertidal zone is an unending source of surprises. While advances in travel and technology allow us to reach “untouched paradises” and make it back in time for a Monday morning meeting, it is essential to consider how we interact with destinations that are home to a vast diversity of life. If we want to enrich our travel experiences meaningfully, we need to spend a little time learning about our destinations’ natural habitats and inhabitants. More importantly, it will sow the seeds of empathy for unfamiliar forms of life — both elements that often inspire environmentally conscious travel decisions. At the very least, we will know where the beach went.

Samuel John
Samuel John

is an ex-corporate zombie who found the answers to life, the universe, and everything, on a spider's web. He can be seen at times playing the blues for his eight-legged audiences.

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