The tiny little piece of rocks is quite interesting, they do not have any distinct shape, but their bright colors and rough texture create a marine-like scene in the tank. Fishes love to flutter around in the water, hide behind those pebbles and play with them. These shades are not only a treat to our eyes but also attractfish towards them. Adding the fish tank wood or aquarium gravel for plants serves a great aesthetic purpose.
What else are they used for?
Nature has created everything for multiple uses gravels; gravels not only serve for decoration purposes but also are used for water filtration of the tank; the rough surface of the gravel filters and catches tiny dirt particles in water and fixes them upon their surface; they also act as a hiding place for little fishes. The gravels are a substrate for bottom dwellers to search for food bits left from the larger fishes. It is also a spawning site for eggs.
Here is how it is used for plants
Marine plants require a medium to bind their roots; unlike terrestrial plants, marine plants are top to bottom in water. Therefore, a hard surface is required to stop them from drifting away, hence these gravels. The rough texture of gravel creates friction between roots and water, and this is how it holds the plants in their position.
Like every aquarium part, these gravels should also be cleaned and changed from time to time to maintain a healthy environment. Otherwise, excess fungal growth makes the water oxygen scarce, and fishes start to die. Keeping in mind, these simple ideas can make aquariums enjoyable.