can aquatic creatures completely be replaced terrestrial creatures

No, aquatic creatures cannot be completely replaced by terrestrial creatures due to the following reasons:

1. Different Habitat Requirements: Aquatic species have evolved specifically for life in water, with adaptations like gills for respiration, fins for movement, and streamlined bodies for efficient swimming. Terrestrial animals are adapted for land environments and cannot survive in water without developing specific adaptations.

2. Unique Ecological Roles: Aquatic creatures play unique roles in their ecosystems, such as serving as food sources, maintaining water quality through nutrient cycling, and supporting biodiversity. Terrestrial animals occupy different niches and would not be able to fulfill these aquatic roles without undergoing significant evolutionary changes.

3. Life Cycle Differences: Many aquatic species have life cycles that are entirely dependent on water. For example, fish reproduce by laying eggs in water, where the larvae develop. Terrestrial animals have different reproductive strategies that do not rely on an aquatic environment.

4. Biochemical Adaptations: Aquatic organisms often have biochemical adaptations to their environments, like osmoregulation to maintain salt balance in their bodies. Terrestrial organisms have different biochemical needs, and replacing aquatic species with terrestrial ones would disrupt these delicate balances.

5. Symbiotic Relationships: Aquatic species have developed intricate symbiotic relationships with other aquatic organisms, such as coral reefs and their associated species. Terrestrial animals lack these specialized relationships and cannot replicate them in water.

6. Environmental Impact: The presence of aquatic organisms contributes to the overall health and stability of aquatic ecosystems. Replacing these species with terrestrial ones would fundamentally alter the ecosystem dynamics, potentially leading to a decline in biodiversity and ecosystem functioning.

7. Evolutionary Distance: Aquatic and terrestrial species are separated by millions of years of evolution. While there are some transitional species that can survive in both environments (e.g., semi-aquatic animals), these are exceptions rather than norms. The vast majority of aquatic and terrestrial species are distinct and cannot simply replace each other.

Replacing aquatic creatures with terrestrial ones would not only be ecologically damaging but also biologically implausible due to the unique adaptations and roles that each group of organisms plays in their respective environments. Ecosystems are complex and interconnected, and the loss or replacement of one group of organisms would have cascading effects throughout the entire system.