A bit on how this is measured - interesting.

The Morphoedaphic Index--Use, Abuse, and
Fundamental Concepts
R. A. RYDER

Transactions of the American Fisheries Society 111 : 154-164 ,1982

Fundamental Concept of MEI

The MEI was developed originally to meet three major objectives(:1 ) to determine empirical relationships of fish yield with abiotic factors; (2) to provide fisheries managers with an easily applied technique for first approximation of annual fish yield; (3) to provide a fundamental conceptual base for the global synthesis
of production processes in aquatic systems. The fundamental concept implicit in all morphoedaphic expressions is that energy and matter
placed in an aquatic system from external sources are channeled, cascaded , dissipated, or retained in the system because of its morphology. These two inputs regulated and constrained by the basin shape produce both a yield of fishes and other biotic outputs such as production of plants and invertebrates. Fish yield in this paper is considered to be harvest, and presumed to be a substantial predictable proportion of total internal production (turnover
rates)in intensive fisheries , energy from the sun, dispersed as heat and light ,affects rates of autotrophic production and other biological processes within aquatic communities. Matter, most relevantly nutrients and oxygen, is either allochthonous or emanates from within the lake basin. The morph or shape of the basin not only
channels energy and matter in predictable patterns, but also tends to dilute or dissipate them and consequently is a sink for both nutrients
and energy (Ryder 1978). Energy and matter inputs are inexorably linked because energy is required for nutrient transportation in both the abiotic and biotic sectors of an ecosystem.