can you please name a few of these organisms
Whales, sharks, and tuna live etc
Aquatic ecosystem
The oceanic zone is the vast open part of the ocean where animals such as whales, sharks, and tuna live. 
please tell me more about jaekelopterus It is a genus of predatory eurypterid, a group of extinct aquatic arthropods. is their species still alive? UNANSWERABLE where can they be found? It lived in non-marine aquatic environments. you mentioned that these were predators, what more can you tell me about them as predators? Fully grown "Jaekelopterus" would have been apex predators in their environments and likely preyed upon smaller arthropods (including resorting to cannibalism) and early vertebrates. you mean they ate each other, but what would be the benefit? UNANSWERABLE what harm can come by eating each other? It has been shown in some studies that the risk of encountering an infected victim increases when there is a higher cannibalism rate. do you know any other species that eats each other? Aquatic ecosystems please tell me more about this Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems.
wiki:5838395
Aquatic ecosystem [SEP] Marine
The benthic zone consists of substrates below water where many invertebrates live. The intertidal zone is the area between high and low tides; in this figure it is termed the littoral zone. Other near-shore (neritic) zones can include estuaries, salt marshes, coral reefs, lagoons and mangrove swamps. In the deep water, hydrothermal vents may occur where chemosynthetic sulfur bacteria form the base of the food web. Classes of organisms found in marine ecosystems include brown algae, dinoflagellates, corals, cephalopods, echinoderms, and sharks. Fishes caught in marine ecosystems are the biggest source of commercial foods obtained from wild populations.