Tag Archives: Adaptation

The Intertidal Zone and their Mighty Animals

Most people are familiar with the concept of tide pools; shallow puddles of water that form along flat rocky coastlines and are exposed when tides are low. However, you may not be aware of the daily drama that takes place in this area called the Intertidal Zone where animals must be well adapted to living both in and out of water.

First lets talk tides. Tides are variations in the levels of water along a coastline that are caused by the gravity of the sun and the moon. There are two types of tides, spring and neap. Spring tides occur when the sun and moon are in line with the earth and take place during full and new moons. These tides are responsible for very large variations in the tides where you get dramatic changes in high and low tides. Neap tides occur when the sun and moon are a ninety-degree angle from each other and occur in very small variations in the tides, much less dramatic than spring tides. Each beach has a different tide type called diurnal, semi-diurnal, and mixed tides. Diurnal means that there are is just one high tide and one low tide in that region. Semi-diurnal means that there can be multiple highs and lows in one day that are about the same height, this is what we have on Catalina Island! Finally, Mixed tides are multiple highs and lows that differ in their heights.

Now on to the drama. All these variations in tides make life in the intertidal zone a little hectic to say the least. There are 4 parts to the intertidal zone and we are going to start off with the one with the easiest living, the low intertidal zone. This region is only exposed during the lowest of spring tides so it is submerged the vast majority of the time. The low intertidal zone teems with diversity and abundance of animals due to its protection from larger predators because of wave action, tons of food from an endless algae buffet that thrives from ample sunlight, and lack of worry from drying out or desiccation. Lots of algae is present in this zone as well as fish, sea hares, sea stars, crabs, abalone, eels, octopus, snails, and slugs. This area is like the VIP section of the intertidal zone.

intertidal zone

Next, we have the mid intertidal zone. Here life starts to get a little harder as it is equally submerged and exposed during the daily cycles of tides. Diversity and abundance of life starts to drop slightly as animals must deal with spending more time out of water and increased waves crashing all over there sensitive bodies. Anemones have suction cups and very soft bodies to resist waves ripping them off, mussels have byssal threads that allow them to grab onto rocks, and sea stars have tube feet to hold on tight. Most animals here are filter feeders and use tentacles and other appendages to grab food from the constant flow of new nutrient rich water. Animals like anemones, sea urchins, barnacles, and sea stars, limpets, and snails along with some algae dominate the club level seats of the intertidal.

The high intertidal is where things really get interesting. This region only gets water during the high tides of every daily cycle. Animals are even less diverse and abundant when you get here because of the lack of water and higher temperatures. Shelled animals are the kings as they are able to close their shells to retain water like barnacles and mussels. Snails do well as they secrete mucous to keep their bodies moist. Anemones will pull back their tentacles and cover their bodies with rocks for the same purpose. But this is nothing compared to the next zone.

Finally, the spray zone is the area where it is only exposed to the water during storms and from the spray of waves crashing on the rocks. Here the animals have to deal with incredibly salty environments from evaporation, desiccation from the complete lack of water, and high temperatures from increased sun exposure. Only the hardiest of animals can live here and the diversity and abundance is almost zero. This area can only be described as the nosebleeds of the intertidal zone.

intertidal zone 1

The intertidal zone is an amazing place filled with some incredible adaptations to help animals survive from drastic changes in temperature, water availability, and wave action. As you go from the spray zone to the low intertidal zone there is an increase in diversity and abundance. So next time you’re at the beach whether it be on vacation, near your home, or at CIMI give some respect to our tide pool residents and enjoy seeing their cool adaptations!


Ground Squirrel vs. Rattlesnake: Evolutionary Arms Race

Evolutionary arms race is a term used to describe escalating adaptations and counter-adaptations between certain predators and preys. When one evolves an adaptation to better defend or attack, it is countered by an even more effective adaptation that cancels out that initial adaptation. This back and forth continues on and on and on and on…

squirrel rattlesnake

An example of an arms race between a crab and its prey, a snail.

Here on Catalina, where resources are scant and evolution moves quickly, we have our very own evolutionary arms race that has intensified. The battle is between the ground squirrel and the rattlesnake, with the ground squirrel in the ‘Prey’ corner and the rattlesnake in the ‘Predator’ corner.

squirrel, rattlesnake

A Catalina Island rattlesnake basks in the sun, contemplating how to defeat its nemesis, the ground squirrel.

Our battle starts off with the rattlesnakes’ initial strike…. Due to the isolation of the island, the rattlesnakes here have evolved intensified venom to more easily subdue their prey. In response, however, the adult squirrels have gained the ability to neutralize venom. So, in turn, the snakes began to then target only juvenile squirrels who have not yet developed strong enough resistance. But the squirrels had something remarkable up their sleeve…. The ground squirrel began to use the snake’s amazing infrared vision against it! Usually the snake can sense heat to more easily find these juvenile squirrels. Using this to their advantage, the squirrels began to throw dirt at the snakes’ eyes and shake their tails high above their body, producing heat and making themselves seem much larger and more intimidating! Adult squirrels have also been known to eat snake skin and lick their offspring to mask their scent!

Squirrel Rattlesnake

A ground squirrel contemplates its place in the universe, and how to ultimately defeat its arch enemy, the rattlesnake.

Time will only tell where this amazing evolutionary battle continues to go and who comes out on top!


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