Indexes
ecosystem health index
Generally speaking, an index in the field of biology is a method to represent results in a simple and conceptual way. Especially in Ecology indexes are used to describe the complex condition of a systen or habitat in an informative manner. Often bioindicators are used as a tool to gather informations and measurements, from which the index will be calculated. This implies that an index is based on relations or aggreates of these measurements. For instance the Shannon-Wiener Index is a mathematical index which describes community diversity depending on abundance and frequency of species \citep{Ellis2015}.
The probably most commonly used index in the assessment of marine ecosystem health is the Ocean Health Index. This index is a score from 1 to 100, indicating the state of the investigated marine ecosystem, whereby the score 1 expresses the worst condition and 100 implies an ideal healthy ecosystem, established on the concept of ecosystem health. The calculation of this number is based on ten goals, describing an ideal human-integrated marine system by divinding the score into different sub-sections. These departments include coastal protection, tourism and recreation, livelihoods, economies, iconic species, lasting special places, clean waters, habitats and species which desctibe biodiversity, mariculture and fisheries, and artisanal fishing opportunity. The sub-sections have an individual score themself and the conjuction of the goal score leads to the overall score. The Ocean Health Index provides informations about regional marine sites as well as an annual score of the gloabl ocean health \citep{Halpern2012}.
Indexes repesent scientific results in a simple, numerical way and thereby give an generall overview of the assessment results. This gives the method of indexes the abilty to display a rather complex investigation in an clear way. Due to that indicators seem to be useful as a baseline which indicate a focus and can be realated to in further studies. At the same time this simple approach can also be too facile or vacuous since it only gives a number as outcome. Without looking at the evaluation how this number was constructed or an explanation which are the causes for this outcome, one might not understand the excact statement and validity of the index, especially if it is a highly complex index. Therefore the communicabilty, especially to laypeople, which represent the broader audience, is decreasing in value or remains rather trivial. Combing the index with a further method such as mapping could benefit the communicability. Indexes being a mathematical contruct of various variables are fairly sensitive and reactive to changes, due to the fact that a change of number of one variable directly effects the calculation. However the effectivesness of the index remains dependant on the individual index. The Ocean Health Index, which has already been mentioned earlier in the paper is a quite comprehensive index to illustrate ocean health. But this broad spectrum of evaluation also gives the possibilty of lack of data, hence the measureabilty as well as the sensitivity of the index declines.