Jennifer Gray and Robert Chandler open our eyes to the abundance of creatures and plants that have made one of the harshest habitats in Bermuda their home.
To the untrained eye, Bermuda’s rocky coastline is rugged, uninviting and somewhat barren. But look more closely, and you will see West Indian topshells, nerites, corals, crabs and plants that have adapted to withstand some of nature’s toughest challenges.
The stretch of south shore from Devonshire Bay to Ariel Sands is one of the best examples of rocky coastal intertidal habitat. Environmentalist, Jennifer Gray, and geologist, Robert Chandler took The Bermudian on a tour of this dynamic environment, sharing a lifetime of experience, knowledge and anecdotes. The intertidal zone is the area between ocean and land, Gray begins, and “it’s absolutely remarkable just how much life there is.”
To survive here, this life has to be tough and adapt, and that’s what makes it interesting: “You can get hurricanes and crashing waves. You can have calm, boiling-hot days. You have to have really tough shells to protect from pounding waves. You have to have strong hold fasts or muscles to grip onto the rocks.”
It’s not just the physical adaptations that help creatures survive down here. There are behavioural adaptations too, such as those of the Sally Lightfoot crabs: “They have little claws that hang on tight, and these crabs dash down between waves to grab things and then dash back up again. They’re so fast.” When a storm comes, they hide in the many niches and crevices. “When you start to look inside them, that’s where everybody hides,” Gray explains. “Most of the time, they’re hiding during the scorching sun at low tide and then they come out at high tide or at night, when it’s cooler.” There are also physiological adaptations which allow the animal to cope with extreme salinity and heat.
There are four intertidal zones, which can be defined by the creatures that live in them. These are the lower intertidal, middle intertidal, upper intertidal and the splash zone, which is furthest away from the water. Closest to the water requires the strongest “hold fasts.” Covering this area are algae, bits of coral and chitons, nicknamed “suck rocks” by St David’s Islanders. Chiton’s are easily identified by their eight plates and, as their nickname would suggest, are very difficult to remove from the rock. If you do manage to do so, they curl up into a ball to protect their soft tissue.
The most abundant creatures in this intertidal zone are West Indian topshells, which were reintroduced by Dr David Wingate and renowned diver Teddy Tucker in 1982 after being eaten into extinction in the post-settlement decades. In and around the tidal pools we also see nerites, zoanthids, sea anemones, glass shrimp and a baby cow polly – formal name, sergeant major. And, with a feat of vision strength that only the very well-trained eye could achieve, Chandler carefully extracts the egg case of a mollusc. “All the pieces of sediment and sand are glued together by its mucus and then the eggs are inside it,” explains Gray. Zoanthids, which look a bit like Cheerios, are a coral relative, and nerites are sea snails, the most fascinating of which is the bleeding tooth nerite because of the red colouration on the tooth-like features on the underside of its shell. While Gray is happy to pick up the occasional shelled creature to reveal the operculum, which acts as a trap door to protect from storms, predators and nosy humans; the radula, which scrapes off the algae they feast on; and, in the case of the West Indian topshell, the milky fluid they release when they’re disturbed, injured or mating, she always puts them back exactly where she found them.
Alone in another tidal pool, we spot a beaugregory, which is a type of damselfish. These are very territorial and aggressive towards anything that comes near them. Gray puts her hand in to demonstrate and the fish heads straight for it: “He’s not afraid of me. That’s probably his grazing plot,” she explains. “That’s where they lay eggs and he’s not going to let anybody get near it if he can help it.” While this beaugregory is fully grown, many juvenile fish rely on the tide pools for survival including angelfish, parrotfish and jewel fish. Also visible in this tide pool is Siderastrea or star coral. “It will survive in this tide pool because this is in the mid-lateral zone, which means,” she says, “when the tide comes up, it gets flooded with fresh water.” Chandler explains, “Siderastrea transports sand particles very efficiently away, so it can grow in environments that are often quite sandy, and it will stand up during high tide and storms in particular. The brain corals are not quite as efficient.” Adds Gray, “It’s an adaptation of the species to survive this type of environment. Any other coral would have bleached by now in the heat.”
Together they continue to point out masses of different creatures as we move further away from the ocean: Thousands of little worm snails that have attached to the limestone, a sea anemone, which Chandler calls a Bartholomea, scorch muscles, and in the splash zone are beaded periwinkles, “prickly winkles” and zebra periwinkles. “This is a beaded periwinkle,” explains Chandler. “The bumps are slightly softer and it’s more white in colour. They would feed mostly when it rains or splash makes the rocks wet. It makes it easier for them to graze on the algae.” The “prickly winkles” are slightly smaller, and zebra periwinkles, as the name suggests, have dark stripes. It isn’t just the creatures that define the different intertidal zones. The colour of the algae they feed on also varies. In the wettest zone, the algae are a rich brown red, in the middle they’re green with some red, and then further back, they’re blue-green algae, also known as cyanobacteria.
As we leave Devonshire Bay and head towards Ariel Sands, Gray and Chandler point out that it isn’t just creatures that have adapted to this harsh environment. The plants, trees and grasses have too, including sea ox-eye, buttonwood, bay grape, seashore rush and sheathed paspalum. We are also treated to a flowering night-blooming cereus, which only comes out at night and lasts for a day. This rocky coastline is also littered with evidence of vegetation and soils from ancient time periods hundreds of thousands of years ago, including what Chandler describes as “tree stumps in rock formation,” which, he says, “would have been a palm of some sort” and would have grown in soil that would have covered this area. “What happens is, sea levels lowered, beaches developed and sand drifted back towards the shore creating a very rapid burial of those trees.”
Along the coastline, where the water is deeper, large parrotfish swim up to shore. This area is also a popular spot for common octopi, which feed on the snails. One of the most entertaining species we see, however, is blennies and not just because of their names—tide pool blenny and hairy blenny. They also jump seaward, from pool to pool. Chandler explains: “They’re in a rock pool. They feel it’s getting too warm maybe, if they’re stranded at the high tide. They can actually have a mind map of the next rock pool and how far away it is. They’re under the water, they have to figure out the velocity to get up out of the water and make it to the next pool.” These leaping fish also have round fins that form suction cups, so if it gets too wavy, they use them to grip.
If you look carefully beneath the rocks and in the pools’ crevices, there are three species of sea urchin to be found. The rock urchin, the pencil urchin and the Tripneustes. “You can eat the gonads,” declares Chandler of the latter. While the Sally Lightfoot crab is difficult to spot because of its speedy movements, bits and pieces left by herons litter the area. Occasionally, we come across a leg or a claw, which crabs can drop in a process called autotomy, allowing them to escape from predators. Once they have outgrown their shell, they moult, leaving a complete exoskeleton for us to find. “He literally went backwards out of that hole,” says Gray, pointing to the part of the shell the crab exited from. “He will withdraw all his body parts, and climb out the back.” She knows the crab was male because the “plastron” on the underside of the shell is pointed. The female’s is more rounded to carry the eggs. A new shell then gradually hardens, during which time the crab is particularly vulnerable to birds or fish.
This area of the south shore holds many happy memories for Gray who would bring her children down regularly when they were young. Since this time, the landscape has changed very little, but the life has varied. There are many more West Indian topshells, but far fewer fish. West Indian topshells are a protected species, which has helped them to thrive, and Gray strongly believes that such protections need to be extended. “If we want the ecosystem to stay intact, habitats should be protected, not the individual species,” she says. The rocky shoreline, for example, and everything in it.
