Yes, it refers to their coverage. How much people they are able to reach.

yes it does refer to how many people it covers, reaches or influences through journals or / and publications.

Coverage and cobertura are "falsos amigos" here. "Coverage" is the wrong word. It can correspond to "cobertura" in relation to academic journals; it can refer to their inclusion in databases such as Scopus or Web of Science, for example: you can talk about a journal having good coverage if it is widely indexed. "Coverage" can also refer to the range of subjects a journal covers (on which it publishes articles). But here it refers to something else.

John has indicated the sense of "cobertura" here: in this context it means, basically, how widely these journals circulate; it refers to their effectiveness in terms of "divulgación". It's being used in this sense (the following is not about academic journals but the meaning is the same):

"Las revistas ganaron un 6,7% de cobertura en noviembre
De acuerdo con el informe ARI 360º, presentado por la asociación de revistas, el pasado mes de noviembre los títulos asociados a ARI generaron más de 135 millones de contactos (audiencia impresa, digital y social), lo que supone un incremento del 6,7% respecto al mes de agosto"
http://www.marketingnews.es/medios/noticia/1095578028405/rev...

It's measured by the number of reader contacts through all media. This is not called coverage in English, but reach:

"Journal metrics——Impact, Speed and Reach
[...]
Reach
Our journals have global authorship and readership. Journal Insights provides graphics indicating: The number of downloads at the country level over the last five full years available. The number of primary corresponding authors at the country level over the last five full years available."
https://www.journals.elsevier.com/international-journal-of-a...

"Bioscientifica collaborates with leading biomedical societies to publish and develop journals that have high impact, a wide reach and a healthy financial return."
https://www.bioscientifica.com/publishing

"Modelo de optimización de cobertura y calidad.
Modèle d'optimisation de couverture et qualité.
Model of optimization of reach and quality."
https://journals.openedition.org/polis/4955

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Note added at 4 hrs (2019-06-14 04:55:33 GMT)
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(Actually, other answerers have correctly interpreted "cobertura": how many people a journal reaches; they've just used the wrong word in English.)

Could be an option. 'Scope' in the sense of reach, as well as the subject areas covered.
"As an author, your choice of journal is most frequently based on reaching the readership which can make the best use of the information in your paper. And for the reasons given above, the scope of the journal will be a primary determinant in your choice of a journal."

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Note added at 15 hrs (2019-06-14 16:02:05 GMT)
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NB: In the sample sentence I cited above, "scope of the journal" seems to refer to the readership reached rather than just the content covered.