Under The Sea Cake With Ocean Decorations

I baked this under the sea cake for a family birthday, and it quickly became the centerpiece of the table. The colors alone made everyone stop and stare before even tasting it.

Layer after layer, the cake looked like rolling waves, and the decorations brought it to life—tiny shells, coral branches, and little fondant fish swimming along the frosting.

It felt as if the ocean had been captured in sugar and butter. The process of building it was exciting from start to finish.

Mixing the different shades of blue buttercream felt like painting, each layer blending into the next until the cake had a soft, wavy texture.

Adding the decorations was like placing treasures around a reef—every shell and piece of coral had its own spot, making the whole cake feel alive.

This cake isn’t just about flavor, though the sponge is soft, buttery, and moist with just the right balance of sweetness.

It’s also about the joy of creating something that surprises people the moment they see it.

Children’s eyes widen at the little fish swimming through frosting waves, while adults admire the careful detail and color work. It’s playful, artistic, and delicious all at once.

If you enjoy baking that feels creative and celebratory, this under the sea cake will give you exactly that—a centerpiece dessert that looks stunning and tastes just as good as it looks. It’s a cake meant to be remembered long after the plates are empty.

Table of Contents

Under The Sea Cake Recipe

Ingredients

For The Cake

2 ½ cups all-purpose flour
2 ½ tsp baking powder
½ tsp baking soda
½ tsp salt
1 cup unsalted butter, softened
1 ¾ cups granulated sugar
4 large eggs, room temperature
2 tsp pure vanilla extract
1 cup whole milk, room temperature
½ cup sour cream, room temperature

For The Buttercream Frosting

1 ½ cups unsalted butter, softened
6 cups powdered sugar, sifted
3–4 tbsp whole milk
2 tsp vanilla extract
Blue gel food coloring (light blue, teal, navy)
Green gel food coloring (for seaweed details)

For Decoration

Fondant in pastel shades (peach, coral, ivory, blue, yellow, pink)
Gel food colors to tint fondant if needed
Cornstarch for dusting while rolling fondant
Small edible sugar pearls
Piping gel (optional for attaching details)

Instructions

Preheat oven to 350°F (175°C). Grease and line three 8-inch round cake pans with parchment paper.
In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, beat butter and sugar until pale and fluffy, about 3–4 minutes. Add eggs one at a time, beating well after each. Mix in vanilla extract.
Alternate adding the dry ingredients and the milk with sour cream, starting and ending with dry ingredients. Mix until just combined, do not overmix.
Divide batter evenly among the prepared pans. Bake for 25–30 minutes or until a toothpick inserted in the center comes out clean. Allow cakes to cool for 10 minutes in pans before transferring to wire racks to cool completely.
For the frosting, beat butter until creamy. Gradually add powdered sugar, then milk and vanilla, and whip until smooth and fluffy. Divide into separate bowls and tint with different shades of blue and teal.
Place the first cake layer on a serving board and spread frosting evenly on top. Repeat with remaining layers. Apply a crumb coat over the entire cake and chill for 30 minutes.
Using an offset spatula, apply tinted frosting in waves around the cake, blending light blue at the top, teal in the middle, and navy at the bottom for an ocean effect. Gently swirl the spatula to create textured wave patterns.
Roll out fondant in different colors and shape seashells, coral branches, fish, seaweed strips, and ocean creatures. Use small cutters or sculpt by hand. Allow decorations to dry slightly for firmness.
Place fondant decorations on the cake, arranging coral and seashells on top, fish on the sides, and seaweed at the base. Attach with a small dab of frosting or piping gel.
Add edible pearls to resemble bubbles rising through the water.
Refrigerate the cake for 30 minutes to set the decorations before serving.

How Can I Make The Cake Layers Even?

Uneven cake layers can make decorating difficult, but with a few small tricks you can get a neat finish.

First, always use a kitchen scale to divide the batter equally among pans so that each layer bakes at the same height.

Second, bake the cakes at the same temperature on the middle rack so they rise evenly.

If the tops still dome slightly, wait until they are fully cooled and then use a serrated knife to gently trim them flat.

Leveling gives a steady base and makes the finished cake look tall and polished.

How Do I Get Smooth Buttercream Waves?

Creating waves on the cake isn’t about perfection, it’s about movement. Once your crumb coat is set, use an offset spatula to apply tinted frosting in small swoops.

Use the right consistency: Buttercream should be creamy and spreadable, not stiff or runny.
Layer the colors gradually: Start from the top with light blue, then teal, and finish with dark navy at the bottom.
Blend softly: Overlap each shade slightly while smoothing to mimic the gentle flow of ocean water.
Add texture: Move your spatula in short, curved strokes to form wave-like ridges.

This technique makes the cake look artistic and natural, even if you’re not experienced with decorating.

How Can I Shape Fondant Decorations Easily?

Fondant details bring the whole design to life. To make the process enjoyable and less overwhelming, break it down into steps.

Work with small pieces: Roll out only what you need so fondant doesn’t dry out too quickly.
Use simple tools: A small knife, cutters, or even household items like a straw can help shape seashells and coral.
Dust lightly with cornstarch: This prevents sticking while rolling or shaping.
Let them firm up: Leave shaped pieces at room temperature for 30 minutes so they hold their shape when placed on the cake.

These details may look delicate, but they are easier to create than they seem once you get the hang of it.

Can I Make The Cake Ahead Of Time?

Yes, preparing ahead makes the decorating process smoother and less stressful. Bake the sponge layers one or two days earlier, let them cool completely, and wrap them tightly in plastic wrap before storing them at room temperature.

The buttercream can also be prepared a day in advance and kept in an airtight container in the refrigerator. Before using, bring it back to room temperature and whip it briefly to restore creaminess.

Decorations made from fondant can be shaped several days before, as they actually benefit from drying slightly before being placed on the cake.

How Do I Store Under The Sea Cake?

Storage depends on how soon you plan to serve it, as the cake stays fresh for a good amount of time if handled properly.

Short-term storage: Keep the decorated cake in the refrigerator for up to 3 days. Place it in a cake box or loosely cover it with plastic wrap to avoid absorbing odors.
Room temperature storage: If the weather is cool and not humid, the cake can sit at room temperature for about 24 hours without spoiling.
Freezing the cake: Undecorated cake layers freeze very well. Wrap them in plastic wrap followed by aluminum foil and store for up to 2 months. Thaw overnight in the refrigerator before decorating.
Fondant decorations: Store separately in a dry box at room temperature. Avoid the fridge, as moisture may soften and damage them.

Proper storage helps retain the taste and structure, so your cake looks as good as when it was first made.

How Do I Keep The Cake Moist?

Dry cake can spoil the experience, but a few careful steps ensure that your sponge stays soft.

Do not overbake: Remove cakes from the oven as soon as a toothpick inserted comes out clean.
Seal the layers quickly: Once cooled, wrap them right away to lock in moisture.
Use a simple syrup if needed: Brushing each layer with a light sugar syrup before frosting can add extra moisture, especially if you plan to serve the cake a day later.

These little practices guarantee a tender and moist sponge that pairs beautifully with the creamy frosting.

What Occasions Are Best For This Cake?

An under the sea cake isn’t limited to birthdays, though it shines at children’s celebrations. It can also be prepared for baby showers, summer parties, or any event with a marine or beach theme. Its colorful design makes it a centerpiece dessert that naturally becomes part of the decoration.