Which of the following is the best example of a food chain in a marine ecosystem?
a.
algae → phytoplankton → shark → crab
b.
phytoplankton → krill → herring → mackerel → shark
c.
orca whale → seals → algae → salmon
d.
phytoplankton → mussels → otters → tuna fish → octopus

B.

Phytoplankton → krill → herring → mackerel → shark

Explanation:

Just like on land, there are food chains in sea life as well. Marine ecosystems are composed of marine plants and animals. They survive based on what kind of food chain they are the part of. Some fishes eat plants whereas some fishes eat other sea animals. There s similar competition for survival observed underwater as it is observed above water i.e. on land.

The best example of marine food chain can be seen through  

Phytoplankton → krill → herring → mackerel → shark.

i think it's severe storms but i might be wrong