In search of secret wildlife Part IV: The ocean depths

Octocoral. Image: NOAA

By |2021-10-13T11:16:13+00:00October 13th, 2021|Deep-sea mining, Fish, Fisheries, In search of secret wildlife, Marine, Oceans|Comments Off on In search of secret wildlife Part IV: The ocean depths

Continuing our ‘In search of secret wildlife’ series, Nina Seale dives into the mysteries surrounding marine ecology and conservation, exploring the dangers that mining and industrial fishing present when so little is known about the potential impact.

We know so little about our ocean, we can’t even guess the number of zeroes we need to measure marine life.

There are currently approximately 200,000 described marine species (about 11 per cent of all described species). But there could be more than 10 million.

However, we do know that the vast accumulation of life which has evolved and flourished in our ocean plays a very important role in how we experience life on land.

A mangrove forest of short stout trees with roots extending from the trunk down into turquoise seawater (the horizon is in the background).

Coastal forests such as mangroves provide important protection to terrestrial ecosystems from events such as tsunamis. Image: Jamie Patra CC BY-NC-ND 2.0

The role of ocean biodiversity

An example of the effect that losing marine life can have on land can be observed with seagrass meadows. When seagrass meadows are lost, it can affect temperature and sea level, as well as the frequency of storms and hurricanes. More broadly, when coastal ecosystems collapse, there are declines in local fish catch and water quality, as well as increased coastal flooding and harmful algal blooms. In the 2004 tsunami, areas buffered by coastal forests were less damaged than areas without.

But due to the difficulty of studying our planet’s marine diversity, we cannot boast that we understand all the complex relationships between marine life great and small, the seafloor, and the aquatic environment itself.

Sperm whales dive more than 6,000 feet in pursuit of prey and much about their ecology is still unknown, and yet commercial sperm whaling from the early 18th century is estimated to have reduced the global population by approximately 73 per cent. Image © iStock

Mysteries of the ocean

There are many examples of people exploiting ocean resources before understanding the consequences of their activities. One well-known cautionary tale is that of whaling, which has crippled many populations of whales around the world (the pre-whaling population of blue whales in the Southern Hemisphere was about 250,000, and there are now estimated to be fewer than 1,500). The decline in great whale numbers due to whaling is estimated to be at least 66 per cent and perhaps as high as 90 per cent.

So, we already came devastatingly close to losing our whales while having barely scratched the surface of understanding their ecological importance. A 2019 study published an estimate of the economic value of a great whale based on carbon capture, whale watching, and impact on the food chain, at more than USD 2 million.

The ecology of European eels has presented a zoological mystery for thousands of years. Image © iStock

A glass eel, the larval stage of the European eel. Image: Flickr/canopic CC BY-NC-ND 2.0

Another example is that of the European eel, which was once an abundant freshwater catch in many areas of Europe and northern Africa but is now a Critically Endangered species. The life history of these eels has proved a mystery for thousands of years (ancient Egyptians believed eels were produced by the sun warming the Nile). Even now as their mysterious origins are becoming known to science, the strangeness of their story is worthy of such a long mystery. It is a fascinating tale of metamorphosis and epic journeys floating thousands of miles between the Sargasso Sea on the Gulf Stream before transforming into finger-length, transparent miniature ‘glass eels’.

However, over the past 40 years, the number of glass eels arriving in Europe has fallen by 95 per cent. Due to the complexity of the eel life cycle and many more mysteries about their ecology we have not yet understood all the reasons for their decline, but it could be due to all manner of human-related activities such as climate change, dams, overfishing, and pesticides.

With even such a historically common species as the European e