What Matters?

At some point the only reason we really care about threats such as acidification, plastics, toxins or over-harvesting is either a) a direct threat to the health of our own species (humans), or b) the loss of biodiversity. Bio diversity is about both the abundance of individuals and richness of species on the planet. It is about both raw quantity of life, and the number of types. This is what makes a monoculture of exotic marine seaweed (e.g. Caulerpa taxifolia) in the Mediterranean, dramatically less important and valuable than a healthy coral reef. The reef may have less actual mass of life, but it is far richer in specific types of life...and therefore DNA. While we may not like to see marine debris in the water per se, it really matters if it either harms us, or diminishes life on earth.

An important new project is pulling together a global network of research teams to assess marine life at all levels and locations. This Global Ocean Census is an unprecedented resource for marine conservation.

The Threats

Marine life is under intense pressure on multiple fronts. These run the range of direct harvesting and killing to weakening effects that increase susceptibility to other threats. Most common on the list are:

1. Over-harvesting- this is about decades, or centuries of catch beyond any sustainable rate. Marine life is harvested, numbers decrease and may in some cases collapse in the same manner that caused the extinction of the Passenger Pigeon in North America. This is especially difficult in the sea as we rarely have anywhere near the population data or transparency to know where things stand.
2. Habitat destruction- often tied to the above, the physical deterioration of ocean habitats has a major and long lasting effect on the ability of the sea to support life. Trawl lines dragging like field plows, silting, land reclamation, sea wall construction, dynamite fishing- even ship wrecks in certain cases can dramatically undermine the ability to support life.
3. Bio-pollution- this is principally about invasive species or long-term shifts in the ecosystem that make it extremely difficult for native species to survive. A great example is the explosion of long-spined sea urchins  (Diadema) in the Canary Islands. Likely arriving as stowaways in ship ballast, these urchins have exploded in local waters- literally consuming the once rich and productive algae community. We now see scoured lava rock amidst thousands of urchins and very few fish.
4. Acidification is a direct threat to all marine life that builds carbonate shells- lobsters, clams, most plankton, coral... The higher pH frustrates formation of these calcium shells and therefore slows the growth of the animals.
5. Temperature rises- Ocean temperature rises through either natural phenomenon like El Nino or climate change can knock out major chunks of local biodiversity. Ocean water changes have always occurred- its the sudden nature that is a problem here
6. Pollution is a broad ranging threat that includes physical harm like an Albatross swallowing discarded toothbrushes, or a sea turtle in a net...all the way down to long term persistent chemicals. Toxin pollution is particularly disturbing and dangerous because it can be so hard to detect and understand. Rarely is this a simple case of "fish dying"... it can just as easily be a long-term reduction in fish health, smaller size, or reduced breeding success. While we are shocked about oil spills in the Gulf, few people understand how our own heavy doses of pharmaceuticals passing into local waters create perhaps much more serious threats to marine life.

These threats do not exist in isolation, but strongly interact- mostly in ways that we understand very poorly. A population of giant bluefin tuna that has been over harvested to 5% of its natural level (threat 1), that is swimming across seafloor subject to bottom trawling that looks like an Iowa farm field (threat 2), and is also carrying a high load of synthetic toxins is in a very, very bad place. Any one of these threats is a severe risk, together the odds of full extinction build. On top of this, natural disturbances and variation in the environment, e.g. El Nino, a volcano, or a disease outbreak...now become extinction threats. All natural populations oscillate in size- get small enough and they will inevitably bounce across the "zero" line and go extinct. Stress, on top of stress, on top of stress applied to small populations is a recipe for collapse.

Where we stand

Understanding the loss of biodiversity on land is tough enough. In the ocean our understanding of populations and even the number of species is weak. The less we know, the easier it is to delay action or make poor choices. Jeremy Jackson (see link below) has done important work putting together a rough picture of where we stand. The results are not good. Here a few indications:

1. Large whales -95%
2. Sirenia (manatees, Stellar Sea cows, dugongs) - 90%
3. Sea birds -57%
4. Sea Turtles -87%
5. Oysters -91%
6. Atlantic Cod -96%
7. Oceanic White Tip shark -99%
8. Live coral cover (Caribbean) 80-93%

We have also lost entire species, many of them large charismatic animals. Just a few (last year reported)

1. Caribbean Monk seal (1952- picture below)
2. Chinese River Dolphin (2006)
3. North Atlantic Gray Whale (18th century)
4. Stellar Sea Cow (18th century)
5. Great Auk (19th century)

Our own limited visibility or historical perspective to these losses strongly limits the extent to which people feel compelled to act. In some cases, its simply hard to miss something you either never knew existed, or have virtually no reference marks to. This problem of "shifting baselines" makes it hard for us to understand what we have lost. My perception of the Florida Keys is really only valid to the 1980's. I may therefore see some loss of large branching corals, fish and turtles. I cannot, however fully appreciate the complete disappearance of sawfish, giant mantas, crocodiles...or the fun of diving with lots of really big sharks  :) This typically makes talking to old maritime people really depressing.

Most marine conservationists are becoming increasingly concerned that we are headed for a major collapse of ocean biodiversity. This will will not only diminish our practical ocean resource, but greatly risk life on earth. We cannot imagine a collapse of life on 71% of the Earth's surface not affecting all life on land- including us.

Here are just a few good overall articles and links that get to the core of the issue

Scripps Institution of Oceanography: Historical Photographs vividly reset the baseline, reminding us of what we have lost

National Academy of Sciences: Ecological Extinction in a Brave New Ocean