On land, most biomass is in trees.

In the oceans, it's mostly in arthropods and fish! (Bacteria aside, that is...)

Biomass distribution of Earth estimates: https://www.pnas.org/doi/10.1073/pnas.1711842115

Trees outweigh everything else, and:

A worldwide census of the total number of trees (32), as well as a comparison of actual and potential plant biomass (17), has suggested that the total plant biomass (and, by proxy, the total biomass on Earth) has declined approximately twofold relative to its value before the start of human civilization. The total biomass of crops cultivated by humans is estimated at ≈10 Gt C, which accounts for only ≈2% of the extant total plant biomass (17).

Humans haven't yet put such a dent into fish biomass, but we're getting there.