Seas and oceans cover approximately 70% of our planet, yet much more attention has been historically and is being still devoted to terrestrial ecosystems as well as to their invertebrate and vertebrate inhabitants, Homo sapiens sapiens ahead of all, within an endlessly and increasingly "anthropocentric and anthropomorphic" world. Eight billion people currently live on Earth, with the most recent forecasts bringing such figure close to eleven billions by the year 2100. This will likely pave the way to future pandemics, following the dramatic one caused by the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), the viral pathogen responsible for CoronaVirus Disease-2019 (CoViD-19), which has officially killed almost 7 million people and which most likely originated from a natural spillover event of an animal (Rinolophus spp. bat) betacoronavirus into mankind.
Everything is reciprocally connected, this is the first lesson the SARS-CoV-2 pandemic has taught us, which means that what happens on land (currently inhabited by 8 billion people, let's keep this firmly in mind!) will unavoidably affect, sooner or later, the "health" of our marine and ocean ecosystems. This applies, just to make a couple of remarkable examples, to the growing, man-made chemical and plastic debris pollution of planetary seas and oceans, with a relevant portion of the latter being attributable to face masks and gloves protecting us from acquiring SARS-CoV-2 and other respiratory pathogens. Within this complex and alarming scenario, the unprecedented "ecological footprint" impressed by mankind on Mother Earth fully justifies the definition of Anthropocene, which has been coined for our epoch, with climate change and global warming representing the most striking and dramatic effects of our human impact. This is faithfully mirrored by the rising sea levels and temperatures, with marine mammals and fish - their prey - progressively moving to northern latitudes alongside a number of infectious pathogens carried by them.
Many of the agents naturally infecting aquatic mammals are characterized by a "terrestrial" life cycle, with this implying they are known to primarily infect vertebrate species living on land, before getting transferred into the marine environment by extreme weather phenomena such as heavy rains and floods, which are increasingly observed nowadays. This obviously and unavoidably makes "biological terrestrial life" progressively more and more connected to "biological sea life" and, as a consequence, "diseases and pathology of marine mammals" increasingly connected to "diseases and pathology of terrestrial mammals", including humans, who may also acquire in turn zoonotic infections from pinnipeds and cetaceans.
The aforementioned concepts and views can be very clearly and efficiently summarized with the words written by Pope Francis to Ivan Duque Marquez, the President of the Republic of Colombia, on the occasion of the World Environment Day (June 05, 2020): "We cannot pretend to live healthy in a sick world!". (G. Di Guardo, letter to the editor of the British Medical Journal 2022; 379)