When thinking of extreme environments in the ocean you may picture the dead sea or hydrothermal vents.
It may be hard to imagine, but the shoreline created by tides is actually one of the most challenging places for an animal to live. In this week’s Deep Sea Diary post, we will delve into the amazing area of the ocean known as the intertidal zone, and discuss some of the aquatic animals that call this area home.
The intertidal zone is the area of the shore water reaches during high tides, but during low tide it is left exposed.
Canada is home to the largest tidal flux in the world – the east coast is home to the Bay of Fundy, which experiences tidal cycles with highs of over 16 meters (52 feet), about the height of a five-story building! These tidal cycles create a complex and dynamic environment with large fluctuations in many environmental factors. At high tide, the environmental conditions are relatively stable and constant as animals are covered by seawater. At low tide, however, the area becomes more of a terrestrial habitat and animals experience large fluctuations in temperature, salinity and oxygen level. Plus, during low tide, these species are exposed to predators and the threat of drying conditions!
Let’s explore some of the animals commonly found in the intertidal zone on our Canadian coasts, and how they survive in this extreme environment.
Limpets are small marine snails that inhabit the area known as the spray zone.
This area is mostly terrestrial and only becomes covered with seawater at very high tides. The spray zone, however, is frequently exposed to splashing waves and wind-blown spray. Limpets use a muscular foot to attach themselves to rocks so they don’t get knocked around and they have a strong shell to protect their body from the constant wave shock. They can even raise and lower their shell to help them control the temperature of their body. Limpets use their strong teeth to scrap algae off of rocks. This doesn’t sound very interesting until you learn that limpet teeth are the strongest natural material currently on record, six times stronger than spider silk!
In the high intertidal zone you will find an abundance of crustaceans.
Not the crustaceans you may commonly think of, like lobster and crab. Instead, barnacles (yes, they’re crustaceans too!) inhabit this area. Larval barnacles get batted around the intertidal zone until they find a suitable place to call home. They glue themselves to that location and stay there forever, constructing a hard shell around their body. The shell not only protects them from predators, it also allows them to keep reserves of water to use during low tide. You may also see barnacles living on other animals such as whales and turtles, don’t be alarmed though, they are harmless and just filter feed on plankton in the water!
Sea urchins and sea stars are also animals common to the intertidal community, often inhabiting the mid intertidal zone.
Urchins and sea stars move using hundreds of small suckers, called tube feet. They have a complex system of water canals inside their body and they control the movement of their feet by squeezing water in and out of them. During low tides urchins, sea stars and sea cucumbers often become trapped in small pools of water and remain there until high tide. This is when they are vulnerable to terrestrial predators and it becomes a fight for survival! Urchins use sharp spines that protrude from their body to wound predators, some species also have venomous stinging spines they can use as an additional weapon. When attacked, sea stars will actually drop off their arm to escape and regrow it later. Sea cucumbers will take that strategy to another level and eviscerate (or “puke up”) their whole gut to distract and confuse predators!
Another resident often seen in these tide pools is the sculpin. These small fish are quite extraordinary! Tide pools often experience times of very low oxygen which would normally make survival quite hard. Sculpins however have adapted to extract oxygen directly from the air, using their skin to breathe! Their body also has no scales and instead they defend themselves using sharp spines on their head and gill covers. Many species of sculpin can also change the shade of their skin to camouflage with their surroundings and avoid predators.
This is just a small taste of some of the amazing inhabitants of the intertidal zone. You can find many more in the Canadian Waters gallery at Ripley’s Aquarium of Canada. Swim on by to see these animals in action and learn even more about the ocean.