I am concerned about comments on a few websites and in the press over the last year. Most disheartening is a EU memo entitled “Questions and Answers on Destructive Fishing Practices”
When scientists talk about vulnerable marine habitats in the context of the deep sea, they are referring to structures such as cold-water corals, hydrothermal vents, sea mounts or deep sea sponge beds. Not a great deal is known about such structures, but two things are already clear from the research that has been conducted to date: 1. that they function as concentrators of biodiversity in what are otherwise relatively barren and featureless expanses of sea bed…
And to justify the lack of blanket ban on bottom trawling
Biodiversity in the deep seas is not evenly distributed, but is concentrated in a number of specific areas, which tend to be those where vulnerable marine ecosystems are found.
When we discuss deep-sea habitats, we can loosely characterize them into a few broad groups hydrothermal vents, methane seeps, coral or sponge groves, whale falls, hard-substrate (i.e. rock), and soft-bottom (i.e. mud). Seamounts can contain any of the previous habitats. A majority, over 95%, of the deep sea is soft bottom. In the mid-19th century, Edward Forbes proposed that the deep ocean was void of life, the azoic hypothesis. A mere 25 years later this was overturned and we now know the soft-bottom deep sea is species rich. In the 1960’s, Sanders (you can download the paper from JSTOR) demonstrated that deep-sea diversity was greater than shelf and coastal in soft-bottom communities. This lead Grassle (1991, also available from JSTOR) to lead an article with the following statement in large bold print “The ocean bottom supports communities that may be diverse as those of any habitat on Earth.” Thus, the muddy deep-sea floor contains a wealth of species and to characterize it as barren or a desert is a travesty.
The muddy seafloor is probably not charismatic to most of the public as it is relatively flat to the human eye. But closer inspection yields a habitat pot-marked with tube-building animals, mounds created by burrowing organisms, and depressions caused by other organisms plowing the bottom in search of food. The seafloor is only featureless to the unobservant.
I understand why methane seeps, coral/sponge fields, and hydrothermal vents capture the public’s interest. The organisms are colorful, large, and dense. It is the later that I want to address more fully. All these environments possess more biomass per unit area than the background muddy seafloor. To restate, vents, seeps, and coral/sponge fields have more grams of life (carbon) per meter squared. As such they are more visually obvious. However, it has never been quantitatively shown that any of these environments possess more species than the muddy seafloor per unit area. Indeed, it is unlikely to be the case as both seep and vents are dominated by one to two species.
Perhaps it’s best to frame the issue in more familiar terms and environments. Sequoia National Park is composed of dense assemblages of high biomass (large size) sequoia trees. They are easily recognizable and were quickly protected in the late 1800’s, probably one of the Unites States’ first protected areas. They are worth protecting but equating sequoia groves with high plant biodiversity is a jump, as on the forest floor there is relatively little else growing. Compare this to similar size area of tall-grass prairie much lower in biomass but likely to possess many more species. This lack of “charisma” may in part be the reason that most prairies did not receive protection until the 1990’s.
As a society we need to think beyond what is trendy and charismatic (whales, dolphins, coral reefs) and conserve what is meaningful. All of the deep-sea floor deserves and requires protection regardless of habitat. Indeed, the most “boring” habitats may be the most important, harboring the greatest diversity. The deep sea is our last chance to protect an environment in a near pristine state, historically buffered from anthropogenic influences.
