Tag Archives: Tides

Full Moon and the Tide

 Picture this: A crab scuttles into a damp rock crevice.
Snails chug along rock faces, secretings mucus along the way.
Barnacles, glued in place, retreat into their protective shells.
An aggregation of anemone’s grab little pebbles with their tentacles. Hugging them close. All in an attempt to retain moisture and avoid desiccation — these critters all call the intertidal zone their home.
In other words, they are all reliant on the ocean’s tides: the daily rise and fall of the sea’s surface.
These organisms have all developed unique adaptations to help them deal with air exposure for several hours in a given day. Lucky for them, tides are predictable. In simple terms, tides are predicted by our understanding of the lunar cycle. The gravitational pull between the sun and the moon, and consequently its affect on the ocean, is dependent on positioning. When the moon is full, the orientation of the sun, the earth, and the moon look like this:
Moon tides
They are aligned with one another. This is when gravitational pull is at its strongest and causes the oceans to bulge. Right after a full moon the difference in height between a consecutive high and low tide, called a tidal range, is at its greatest. Another phrase for this effect is called a spring tide.
moon tides 1

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!


How the Moon and Sun Impact our Tides

Tides1Even though the sun is about 27 million times larger than the moon, at the end of the day the moon will always have a greater impact on our tides than the sun. So why is this the case? The sun may be significantly larger however it’s a lot farther away from Earth (about 390 times farther) than the moon is from Earth. Essentially this means that the sun’s impact on tides is about half that of the moon!

As the moon and the suns gravitational pull comes into play tidal bulges begin to form on opposite sides of the Earth due to gravity and inertia. Both a lunar and a solar tidal bulge will form. As the moon rotates around Earth and Earth rotates around the sun the angles of these tidal bulges change. These change in tidal bulge angles directly affect our tides.


The most extreme tides occur when the moon, Earth, and the sun are aligned with one another. These extreme tides are referred to as Spring Tides – this is when we will have very high high tides and very low low tides. More moderate tides occur when the moon, Earth, and sun are aligned in a 90 degree angle. These moderate tides are referred to as Neap Tides.

Screen Shot 2016-05-26 at 2.03.56 PM

Written By: Alex Feltes

Ocean Tides 101

Ocean tides are created by combining the gravitational pull of the moon and the sun, combined with the rotation of the earth. The moon’s gravitational pull is stronger than the suns, which makes it the most important factor in creating tides. The sun’s gravitational force on the earth is only 46 percent that of the moon. If the Earth were a perfect sphere without large continents, all areas on the planet would experience two similar high and low tides every day. The large continents on the planet block the westward passage of the tidal swells as the Earth rotates. This causes different patterns and cycles such as semidiurnal and mixed semidiurnal tidal cycles.

The west coast of North America experiences a mixed semidiurnal tide in which there are two high and two low tides daily and the heights differ between each two high tides and two low tides. Semidiurnal tidal cycles have two high and two low tides but are approximately the same size in height. Many areas on the east coast of North America experience this tidal cycle.

High Tide

High Tide

Low Tide

Low Tide

Neap tides are when the Moon is at 90 degree angles with the Earth and the Sun, the Sun and Moon interfere with each other in producing tidal bulges and tides are generally weaker. Spring tides are when Moon and the Sun are in parallel with the Earth such as during a new moon or full moon and creating a much greater gravitational force. This type of tide does not only occur every spring but rather called a spring tide because its springs further than a neap tide.

Local weather systems can influence a tidal cycle as well with local wind that can move water away from coastlines, amplifying low tides. The shape of bays and estuaries can magnify the intensity of tides. The Bay of Fundy in Novoa Scotia has the largest tidal difference of about 45 feet assisted by the funnel shaped bay that can alter the tidal magnitude.

Happy Pi Day! 3/14/15 at 9:26:53 a.m.

We may not teach a course on geometry at CIMI, but that doesn’t mean we can’t appreciate the importance of pi (π). Pi is a mathematical constant that represents the ratio of a circle’s circumference to its diameter. Ancient Egyptians and Babylonians were the first to approximate the number, calculating it to within one percent of its true value. It is an irrational number, meaning it cannot be expressed as a simple fraction and exists as an infinite series of numbers that will never end. When rounded up, the number comes to approximately 3.14. Thus, March 14th is Pi Day.

Why does a marine science camp care about Pi? Pi has all kinds of everyday applications. Think of all the round or rounded things that exist in this world: wheels, gears, eyes, rainbows, round rays. Engineers use pi to build machines. Architects use pi to create their blueprints. Geneticists use pi to understand the structure of DNA. The Earth itself is a sphere, so when an oceanographer measures the movement of the tides or the length of waves in the sea, they need to use pi in their calculations. So go celebrate pi today. Ride a Ferris wheel, eat a slice of apple pie, watch Life of Pi and get inspired by that beautiful scene with the bioluminescence and the whale all over again. Take a moment to watch the sunset and think about how big and beautiful and round it is, then wait for the moon to rise and look at that too. From all of us at CIMI, we wish you a very happy Pi Day.

Written by: Megan Petkovic


We would like to thank you for visiting our blog. Catalina Island Marine Institute is a hands-on marine science program with an emphasis on ocean exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and ocean happenings. This blog has been created by our staff who have at least a Bachelors Degree usually in marine science or related subjects. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science and ocean information. Feel free to leave comments, questions, or share our blog with others. Please visit www.cimi.org for additional information. Happy Reading!