are there any environmental issues here?
Yes, floodplain sediments.
Mediterranean Sea
Based on a broad variety of methods, e.g. historical documents, analysis of trade relations, floodplain sediments, pollen, tree-ring and further archaeometric analyses and population studies, 
what is homarus gammarus? It is a species of clawed lobster. where can you find these creatures? The eastern Atlantic Ocean, Mediterranean Sea and parts of the Black Sea. can humans consume it? Yes. in what forms is it available for consumption? Fresh, frozen, canned or powdered. what is the significance of the second sea that you mentioned in the middle ages? The Byzantines and Arabs controlled vast portions of this sea during their reigns and the Norsemen used it to trade during their time.
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Mediterranean Sea [SEP] Environmental issues
For 4,000 years, human activity has transformed most parts of Mediterranean Europe, and the "humanisation of the landscape" overlapped with the appearance of the present Mediterranean climate. The image of a simplistic, environmental determinist notion of a Mediterranean paradise on Earth in antiquity, which was destroyed by later civilisations, dates back to at least the 18th century and was for centuries fashionable in archaeological and historical circles. Based on a broad variety of methods, e.g. historical documents, analysis of trade relations, floodplain sediments, pollen, tree-ring and further archaeometric analyses and population studies, Alfred Thomas Grove's and Oliver Rackham's work on "The Nature of Mediterranean Europe" challenges this common wisdom of a Mediterranean Europe as a "Lost Eden", a formerly fertile and forested region, that had been progressively degraded and desertified by human mismanagement.