First of all, what are the levels of the ocean?
I believe they're talking about the three levels of the ocean based on how much sunlight they receive. There are three levels:
Euphotic - receives the most amount of sunlight possible, enough for photosynthesis to occur.
Dysphotic - still receives a little amount of sunlight, but photosynthesis does not occur at this level.
Aphotic - the last level. It is pitch dark, which means no sunlight manages to reach this area.
Note: If you have trouble remembering these, look at the morphology of the words. The prefix "eu-" means "well" (sunlight penetrates). The prefix "dy-" means "bad" (sunlight penetrates but not as good). The prefix "a-" means "no" (no sunlight penetrates).
Producers, consumers and decomposers:
Like in any food-chain, we have the producers, which are plants and microscopic organisms that do photosynthesis; we have consumers, which feed on plants or on other consumers; and we also have decomposers, which feed on consumer/producer remaining.
Procedure:
Choose one of the ocean levels (I recommend choosing the euphotic level since you can work on microorganisms that do photosynthesis, which is easier since there are many exceptions in regarding the algae energy collection) and study the producers, consumers and decomposers that it contains.
Recommendations:
I recommend you doing a software presentation rather than a video because it can be easier and simpler. All you have to do is explain the different types of organisms (producer, consumer and decomposer) and get images of them. I also recommend you do your own food web - be careful. When making your food web, make sure you choose animals that live in the same sea/ocean, otherwise, it might look weird. Give simple explanations to the food chains and the relationship between organisms.
When talking about adaptation, be clear with your words. Let's say you start talking about a swordfish. Explain some key characteristics and explain how they suit its environment, predation, etc.
When talking about the ocean environment, just be clear and detailed. Everything should be fine that way.
Hope it helped,
BioTeacher101