An important part of any ecosystem is the presence of producers. They create organic substances from inorganic ones under the influence of sunlight. At great depths, sunlight almost does not penetrate and therefore there are much fewer producers there, respectively, there is less food and consumers too. Oxygen at great depths is just as little, and it is necessary for all living things, Therefore, there are more ecosystems in the coastal part, at a shallow depth, than in the main body of water.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.