since the appearance of terrestrial creatures so aquatic creatures is not important to exist

Actually, aquatic creatures are incredibly important to the existence and functioning of the planet's ecosystems, even if one might consider the existence of terrestrial creatures. Here's why:

1. Biodiversity: Aquatic creatures represent a significant proportion of Earth's biodiversity. The oceans, lakes, rivers, and other water bodies host millions of species, many of which are unique to their environments.

2. Oxygen Production: Aquatic organisms, particularly phytoplankton in the oceans, produce a large portion of the Earth's oxygen through photosynthesis, which is essential for the survival of all aerobic life forms.

3. Carbon Sink: Oceans act as a carbon sink, absorbing a significant amount of the carbon dioxide produced by various natural processes and human activities, helping to mitigate climate change.

4. Food Source: Aquatic creatures are a primary food source for many organisms, including humans. Fisheries are a critical part of the food supply and economy for many regions around the world.

5. Ecosystem Balance: Aquatic ecosystems play a vital role in maintaining ecological balance. They are home to complex food webs and contribute to nutrient cycles that influence both aquatic and terrestrial ecosystems.

6. Climate Regulation: Ocean currents help regulate global climate patterns by distributing heat around the planet. The absence of aquatic life could significantly alter these patterns.

7. Habitat and Niche Filling: Aquatic creatures fill unique ecological niches that terrestrial creatures cannot. They contribute to ecosystem services such as waste decomposition, disease control, and pollination (in the case of certain aquatic plants).

8. Medical Discoveries: Many medicines and medical treatments have been derived from aquatic organisms, such as antibiotics from marine bacteria and compounds that can treat cancer.

9. Cultural and Recreational Value: Aquatic environments provide recreational opportunities such as swimming, diving, and fishing, and they hold cultural and spiritual significance for many societies.

10. Indicators of Health: Aquatic creatures can serve as bioindicators of environmental health. Changes in their populations or behaviors can signal broader ecological problems.

In summary, while terrestrial creatures certainly have their own importance and ecological roles, aquatic creatures are equally vital to the health and balance of our planet. Both groups of organisms coexist and interdepend, contributing to the overall resilience and diversity of life on Earth.