so would this be right?
fungi--> seaweed--> sea snail--> herring--> shark
No, the proposed food chain is not accurate. In a marine food chain, the general flow of energy is from producers (such as phytoplankton or seaweed) to consumers (such as small fish) to predators (such as larger fish or sharks). Keep in mind that there are various pathways in a food web, and not all organisms follow a linear chain. However, a more accurate example in a marine ecosystem could be:
Phytoplankton/seaweed --> Small Zooplankton --> Small Fish (e.g., herring) --> Large Fish (e.g., tuna) --> Apex Predators (e.g., sharks).