Bottom Trawling: Deforestation of the Ocean

        The diversity and density of species on the ocean floor is being threatened more than ever and humans are to blame. The use of bottom trawls on the ocean floor effectively clears out large areas of the ocean floor in a matter of minutes. The species I have covered in my previous blogs: sea stars, sand dollars and squids are all currently being harmed by these over fishing methods. They are not the only animals harmed by bottom trawling, pretty much any species whose niche lies at the ocean floor is in danger. Probably the worst thing about bottom trawling is that many of the aquatic life captured are not kept, but they are thrown back with damages beyond repair. To understand its impact we first must understand how bottom trawling works and what is actually used for.

   

Lophelia pertusa reef reduced to almost nothing after being trawled. Images courtesy of Fisheries and Oceans Canada/Peches et Oceans Canada

         Bottom trawls are made up of large nets that are weighed down by heavy weights that can way up to several tons. The net is kept open with small buoys above the weights, this creates an opening at one end of the net while the back is also weighted down and closed. The trawl is then dragged by a fisherman’s boat with the open end facing the boat. The boat drags the open end around the sea floor picking up everything, even things fishermen are uninterested like corals. Fisherman mostly use bottom trawls to catch shrimp, cod, sole and flounder but destroy the ocean floors ecosystem in the process. Just to drive the point home let us reiterate the destructiveness of bottom trawling. ( A detailed look on what a bottom trawl is)

 

 BY PRODUCT:

 

Source: Brian Skerry, ocean soul

        

 Bottom trawling is a very unselective mean of fishing, taking many fish other than the desired fish. The bycatch, fish caught by mistake, of bottom trawls is about 90% of the trawl. Bottom trawling also digs into the ocean floor breaking loose sediment and mud that spreads like clouds over the surface of the ocean, which inhibits the absorption of light by the aquatic life that need it. This spread of mud that follows bottom trawling can be seen from satellite images by scientists. There is good news on this subject though and that is that there is action being taken against it. The studies by marine biologists have led to restrictions against the destructive fishing. The United Nations General assembly has started to put an end to trawling in  sea areas that covers 45% of the earth, while South Pacific nations put an end to trawling in a large portion of sea. Still, bottom trawling is still very serious today with the fragile state are oceans system is in. With recent oil spills, the increased acidification of sea water and the ice caps melting our marine life is enough danger as is. We need to put an end to bottom trawling if we want to save our marine life. (Source on effects of bottom trawling)

Sand Dollars: Not Just Shells

                 The very popular shells you may look for on the beach, known as sand dollars, are actually the shells of living creatures. That’s right, sand dollars are not just pretty shells for tourists to shell hunt for but they are living invertebrates. When sand dollars are alive they are actually very colorful creatures whose color can range from gray to dark purple. Sand dollars are very abundant suspension feeders of the ocean floor and are evolutionary equipped to be very efficient at it. First, sand dollars have tiny spine like pincers to capture plankton floating by called pedicellariae. The now captured food in the pedicellariae needs to be transported to the mouth or madreporite. To accomplish this task sand dollars have cilia along their spines, not to be confused with a vertebrate spine, which lead right to the madreporite. These cilia, which are like tiny moving hairs, direct the food along the food grooves on the oral side of the organism to the madreporite where food can be digested. Sand dollars even position themselves to increase their ability of filter feeding. When sand dollars are in calm waters they “standup” by burying a portion of their shell under the sand and allowing the unburied portion to stand up right. If the currents are too high the sand dollar will lay flat or even bury itself to reduce the risk of being taken away by the current. Smaller sand dollars will even ingest sand to act as a weight belt for further stability in rougher waters. Sand dollars are capable of movement from tiny tube like feet that protrude from the ambulacra, the radial areas on the oral side of the shell. So sand dollars are living organisms but whats their importance to their ecosystem? Well, sand dollars are very dense in population on the sea bed, even though they lack species diversity. Sense they are so dense in population they are high contributors in the predation of tiny planktons and crustaceans which some feed on the algae on the sea bed. In short, they keep the populations of these tiny organisms in check. Even more important though is that they are a very large food source for fish and crabs. Fish and crabs are able to crush the shell of the sand dollars and eat the actual organism. Sand dollars are much easier prey than their close relative the sea urchin which are equipped with sharp protruding spikey spines to defend itself, so naturally sand dollars are a better choice. So it’s important to know that the shells we so happily collect were ecologically valuable organisms when they were alive, but that doesn’t mean you shouldn’t collect the shell for a keepsake! 

(Source and further reading on sand dollars)

(Second source)
(Follybeach.com)

Study on the effects of climate change to the sand dollars population

Sea Star Wasting Syndrome: The Mystery Killer

           The balance of the Pacific and Atlantic Oceans ecosystems along the coast might soon be tilted in an unknown direction due to a new threat, which is killing off thousands of its starfish, known as Sea Star Wasting Syndrome. Sea Star Wasting Syndrome is the new marine disease so devastating it has an estimated mortality rate on infected starfish of ninety-five percent and it already affects over twenty species on the U.S. coasts. This horrific disease causes starfish to lose entire limbs in a matter of days leading to their inevitable death. The symptoms are well known by marine biologists, but the actual pathogen causing the disease is not. High mortality rates of sea stars are significant to the entire ecosystem of the species since they are a keystone predator of many crustaceans and Mollusca. First let us look at the symptoms of Sea Star Wasting Syndrome to grasp an understanding of its severity.

  Courtesy USCS Long Marine Lab

           

             Marine biologists, studying sea stars with the disease, describe the main symptom of the syndrome to be, sea stars tearing themselves apart which is a good interpretation of the disease in a nutshell. The disease first causes white lesions in the ectoderm of the sea star on the body or a single limb, the initial lesion may then spread to other areas of the organism. The sea stars tissue begins to deteriorate around these lesions. Finally, the sea star begins to fall apart around the lesions due to the surrounding deterioration of tissue. The fragmentation is what leads the sea star to death, but the actual pathogen causing the disease is still a mystery.Source 1

            The first documentation of sea star syndrome was in the summer of 2013 and the exact pathogen causing the disease has not been found yet. Scientists have come to the assumption that: recent increase in temperatures are aiding the pathogens infection rate by putting sea stars under abnormal stress. This assumption is based off the fact that most of the first infected species were in the warmest of water, like intertidal zones. Now scientists have spotted signs of infection in colder waters and swift currents in areas such as the Washington’s San Juan Island. San Juan Island has only recently experienced the infection do to the rise in temperatures of its waters during the summer, the islands are usually cooler than the adjacent continent. This assumption that warm waters is aiding to the rise of the infection seems to be fairly correct but, the actual pathogen is still a mystery. Scientists believe that the pathogen is a bacteria or virus but do not know which, even though the first documentation was over a year ago. Source 2

  Credit: Melissa Miner

           

             Sea Stars are keystone species to many oceanic ecosystems, meaning it has a tremendous effect on the ecosystem relative to the size of its population. Keystone species, such as many sea star species, have a critical role in maintaining balance in their ecosystem. Sea stars are keystone predator that feed on Mollusca and crustaceans, and since there are many different types of Mollusca and crustaceans for sea stars to feed on there was a high abundance in sea stars. Now that sea stars are becoming less common, some species in California and Florida are on the verge of extinction, there are many more of these Mollusca and crustaceans. Scientists are skeptical on just how the ecosystem will change, but my prediction is that there will be an increase of grazing like organisms like snails, which are easy prey for sea stars, and subsequently a decrease in algae. I believe that the overpopulation of these grazers will lead to a decrease in oxygen levels in the ocean and increase carbon dioxide levels. What this means exactly I am not very sure, but hopefully a solution can be found (or a mutation to arise) to reset the balance in the effected ecosystems. 

Further Study:

Sea Star infection finds way into museum 

A map to show areas of infestation