if biomass of producer is lower than that of the consumer in aquatic ecosystem how can it sustain itself?
Answers
Answer:
As in every ecosystem, it's secondary predators. Those are large carnivorous or omnivorous animals that feed actively on almost every other life form. They are regulators of animal numbers and are crucial to the “health” of ecosystem. In different aquatic environments those are different animals. Let's take a look at them.
Seas and oceans are the most diverse of all aquatic ecosystems. Their secondary predators are sharks, orcas, dolphins, sea lions and some large fish (eg tuna). On reefs those are usually rays or different forms of sea eels. In the depths of the ocean there are anglerfish and near the seashore those can also be some birds (comodors, albatrosses, puffins, penguins etc.)
Lakes and ponds have a lot of biodiversity, but obvious lack of really big predators. The only one falling to that category is crocodile and similar animals (alligators, caymans and gavials). Other very specialized predators are big fish (such as catfish or pike). But probably the biggest threat comes from the dry land in form of birds (herons, storks) and mammals such as otter.
Rivers have very similar secondary predators as lakes, but I have to mention that in Amazon a group of small fish can make quite a good first-grade predator. Of course, those are piranhas.
All these animals have greater size than the rest of the biocenosis, but their number is way smaller. You see, one orca gives one young every two or korw years, but one herring gives more than 5000 young (counting only surviving eggs). Thus, the number of herrings in the ocean is way greater than orcas because of their fas reproduction. This way, herrings become food for orcas, but because of their great number they also preserve the species. Orcas don't need many infants since they don't have natural predators that could harm their species.