Sargasso Sea

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Introduction

Deep within the Atlantic Ocean, near the Bermuda Triangle, lies a sea shrouded with mystery named the Sargasso Sea. Uncannily calm, the Sargasso Sea was believed to be the demise of sailors. With little wind, ships lay stagnant for days in this “sea of lost ships”, leading to historical accounts of crews going into the sea, but never coming out. Eventually these accounts were mutated into urban legends of whole ships disappearing or broken down vessels roaming this sea manned by skeleton ghost crews and all.(The Sargasso Sea) Realistically speaking though, the Sargasso Sea was believed to be first found by Christopher Columbus and his crew. They named this sea after the seaweed dominating the sea’s surface named Sargassum. They named the sea “Sargaco”, which means grape because Sargassum looks like grapes. (Gladnick, 2008)

Description of Niche

U.S. Fish and Wildlife Service.

Where located?

More precisely, the Sargasso Sea is located in the middle of North Atlantic Ocean bounding the Great Antilles on the south, the Gulf stream on the west, and Bermuda on the north.(Teal & Teal, 1975) These currents move around the Sargasso sea in a clockwise orientation. Having a latitude between 20N and 35 N and a longitude between 30W and 70W, the Sargasso Sea is comparable to the United states in size.( Teal & Teal, 1975) Both this great size and the location of the Sargasso Sea have great implications on its physical conditions.

Physical Conditions?

What are the conditions in your niche? Temperature, pressure, pH, moisture, etc. Because it is not bounded by coastline and is surrounded by strong currents, the Sargasso Sea is considered an isolated, oligotrophic (little to sustain life) area. The surrounding currents provide a strong physical boundary separating the Sargasso sea from the more nutrient-rich waters of the North America shelf. The northern region contains warm water known as eighteen-degree water that moves outwards along the surface of the sea, allowing it to maintain that temperature year round whereas coastal waters with the same latitudes freeze in the winter. With increasing depth, water temperature declines and pressure builds up restricting much life (Teal & Teal, 1975) Also, the water in the Sargasso Sea is said to be salty and warm, maintaining a salinity around 36% and euphotic zone temperature up to 22°C. For these reasons, even though there are several species of plankton and massive amounts of seaweed floating on the water surface, the Sargasso Sea is still not nutritious enough to attract large communities of fishes. These factors of low wind, low nutrients, and high salinity help to justify why the Sargasso Sea is considered a desert of oceans with little sign of life.

As mentioned before, little nutrients are detected in the Sargasso Sea. One conformation of this belief is Phosphorous amounts. With dissolved inorganic phosphate (DIP) concentrations of 0.2 to 1.0 nanomolar on surface water, there are signs of a relatively severe phosphorus depletion in the Atlantic. This depletion can be attributed to the high ratio of DNN (dissolved nitrate plus nitrite) to DIP (dissolved inorganic phosphate). This high nutrient source N:P ratio causes available P to be depleted before N by algal growth after upward nutrient injections into the euphotic zone through advection or diffusion.( Wu et al., 2000)

Another type of nutrient found in the Sargasso Sea are slicks, natural fat and oil buildup. Not only do these nutrients contribute to the sea’s overall calm glasslike surface, bacteria can collect and grow on these leveled surfaces. They contain abundant useable organic materials; and, once the bacteria dies, the bacteria yields even more oil to these slicks. Unfortunately, one slick area does not last long and tends to fade away gradually due to various chemical and bacterial activities.(Teal & Teal, 1975)

How Research Began

To understand what is known about the Sargasso Sea, one needs to understand why we wanted to know more about it in the first place. Although most scientists thought that this expanse of sea contained no sustainable life, observations showed that oxygen and other elements were being consumed at a higher rate than theories and models could account for. This led scientists to think there must be some nutrient source fueling the blooms of phytoplankton in the Sargasso Sea.( Carlowicz, 2006, LiveScience) This discovery, in turn, led to the discovery of eddies.

Eddies and Their Influence on the Sargasso Sea

Even with such a hostile environment, there exists vast phytoplankton bloom and higher oxygen consumption rate than predicted in the surface euphotic area. The vast amount of organisms in the Sargasso Sea documented in Venter et. al is shocking in comparison to the lack of “nitrate, phosphate, trace metals, and other nutrients” present (Carlowicz, 2006). This suggests that there is internal water mixing and continually pumping up of rich nutrients from deeper water layers. This swirling water system is called eddies. (LiveScience) Eddies are episodic underwater current systems that pump nutrients up from the ocean floor. They form from “differences in ocean temperature and salinity that give water different densities. Like oil and water, water masses of different densities tend to keep separate, rather than mix. ” What causes eddies to spin and therefore mix during the summertime is the Earth’s natural rotation, also known as the Coriolis force. (Carlowicz, 2006) This brings necessary food to the phytoplankton and other microbes. Specifically, during the winter, the incoming cold water forms a “subtropical mode,” that allows phytoplankton to multiply due to increase nutrients resulting in an increase in other organisms such as zooplankton that ultimately feed the entire environmental niche. (Venter et al., 2004, LiveScience) This also fuels sargassum growth and without this, organisms living within the sargassum would not be able to survive (“Sargasso Sea Without a Coastline”). Therefore eddies, often called “the oasis of the ocean”, can be essential to many microbes living in the Sargasso Sea. (LiveScience)

Who lives there?

Many types of brown algae, particularly from the genus Sargassum, live throughout the world’s tropical oceans. Sargassum natans and Sargassum fluitans are found predominantly in the surface of Western North Atlantic (Coston-Clements et al., 1991).

Cyanobacteria that attach to surface of another organism, specifically Dichoothrix and Oscillatoria, contribute largely to the overall production and fixation of nitrogen within the Sargassum ( Coston-Clements et al., 1991).

Gentle inward surface current are created by evaporation of the water in the center of the sea. The evaporation is faster here than the surrounding waters, and it helps keep the floating patches of Sargassum, or gulf weed, from scattering. Small fishes and larvae find easy hiding places on the tangled branches of the Sargassum. Because of the large surface area of Sargassum, it’s ideal for the colonization of sedentary animals. Therefore, the Sargassum community acts as “living net,” filtering out unnecessary particles from living organisms, and providing nutrients for larger animals in the food chain (Genthe, 1998).

Although most of the life is microscopic, humpback whales, dolphins, swordfish, and sea turtles all journey far to the beautiful blue Sargasso Sea. Interestingly, this is where the humpbacks songs were first recorded (Genthe, 1998).

The sea’s food chain in which all existing animals rely on for survival, starts with the surface plants acquiring energy and sunlight. The plant tissues grow, containing various synthesized chemicals that animals can consume and pass along as they are eaten themselves. However, the process of vertical migration is very gradual and slow in the sea. Vertical migration is the downward transport of assorted animal species who have consumed other animals or phytoplankton and will be eaten themselves by the lower-dwelling animals; this process occurs in order to obtain food and gain energy. This food chain allows the sea’s animals to coexist and depend upon one another for food and energy gain (Teal & Teal, 1975).

Which microbes are present?

You may refer to organisms by genus or by genus and species, depending upon how detailed the your information might be. If there is already a microbewiki page describing that organism, make a link to it.

Non-Microbes: Plants and Animals

Pelagic sargassum supports a diverse community of marine organisms including micro and macro epiphytes, fungi, more than one hundred species of invertebrates, over one hundred species of fishes, and four species of sea turtles.(Coston-Clements et al., 1991)

Among the diverse organisms living within the Sargasso Sea include sea turtles and eels. After a sea turtle hatches, it goes into the sea and migrates to an area with favorable conditions. The turtles generally spend 2-4 years here then migrate back to the North American coast. (AH) During their first year of life, turtles associate themselves with Sargassum rafts, mats of brown algae, about 7 million tons of which can be found in the Sargasso Sea.(AG) Though different species of sea turtles aquire different diets as they grow older, Sargassum provides food and shelter for the sea turtles which is desperately needed during their early years. (AG) To get to the Sargasso Sea, turtles use earth’s magnetic field as guidance. This is extremely important because although the Sargasso Sea and the rest of the North Atlantic gyre have a favorable environment for the sea turtles to grow in, going north of the gyre to lower temperatures could be detrimental to the turtle’s survival. (AH)

Unlike sea turtles, who migrate to the Sargasso Sea as juveniles, for eels the Sargasso Sea is a place to spawn. Two major species of eels are found here, the European eels Anguilla anguilla and the American eels Anguilla rostrata. (AE) Eels have a variety of diets based on age and species. For instance, American eels will eat large invertebrates as adults and phytoplankton as babies. After birth, the eels head toward Europe or North America and come back later in life to lay their own eggs. AF Sadly, there seems to be a decline in eel recruitment which scientists believe to be linked to climate changes in the Sargasso Sea.(AD)

Do the microbes that are present interact with each other?

Describe any negative (competition) or positive (symbiosis) behavior

Do the microbes change their environment?

Do they alter pH, attach to surfaces, secrete anything, etc. etc.

Do the microbes carry out any metabolism that affects their environment?

Do they ferment sugars to produce acid, break down large molecules, fix nitrogen, etc. etc.

Current Research

Genetic Analysis: A new way to explore microbial ecology and to discover new species from environmental sample collections

Scientists now believe that genetic material may originate outside its environment and that the physical processes of the Earth or carrier organisms (for example, birds) are their means of travel. A study has recently critically analyzed the Baas-Becking hypothesis, stating that everything is everywhere and the environment selects. This study on comparitive metagenomics takes two very different environmental sequencing projects, the first from Minnesota farm soil and the second from the Sargasso Sea microbes, and compares the sequencing projects to find molecular evidence of a transfer of microbes over distant environments. The theory behind this is that genetic material can be anywhere and doesn’t necessarily mean it will survive in a new environment but, it can still contribute its genome. To determine this, they measured three distinct characteristics, guanine/cytosine (GC) content, oligomer frequency patterns (OFPs), and lastly protein similarity between translated open reading frames in both data sets (Hooper et al., 2008).

Later on, by applying shot-gun sequencing and phylogenetic comparison on uncultured microbes collected from ocean samples, the scientists discovered several previously unknown species that don’t grow in laboratory condition. For example, in 2007, Not et al., showed the discovery of Picoplanktonic protists. By 18s rRNA analysis of different water columns in Sargasso Sea, species in Kingdom Chromalveolata and Rhizaria are found to be the prodominent protista. Among Chromalveolata, Stramenopiles, which exist only in surface euphotic area, and Alveolata, which are discovered from surface to deep sea area, are dominant species. Many of which contain choloroplast; thus living as autotrophs carrying out photosynthesis. Radiolaria is the major species found in Kingdom Rhizaria, they live mainly from 500m thermocline to 3000m deep sea and are heterotrophic zooplanktons. They may be important to ocean biogeochemical cycling and carbon transport (Ghedin & Claverie, 2005). (please refer to microbewiki for details in these species)

Not et al., utilized the similar method, genome sequence analysis and phylogenetic comparison analysis to unveil the existence of Mimivirus relatives in Sargasso Sea, a DNA virus of 0.1 to 0.8 microns in size. They are evolutionarily closer to Mimivirus and exist in large abundance in the collected water samples. The discovery is published in 2005 and further research is needed (Not et al., 2007).

Metabolic and Proteome Analysis – “SAR11 Bacteria and the State of the Ocean”

Dr. Stephen Giovanni and his cohorts have done extensive research on the SAR clade of bacteria. Of special interest to them is the Pelagibacter ubique organism. Currently they are trying to use P.ubique for a few different research interests. First, they are trying to predict the different organic carbon sources used by P.ubique. They are doing this through a method of metabolic reconstruction. Second, they are using mass spectrometry to understand P.ubique’s regulatory responses in regards to environmental factors. By doing this, it will give the researchers insight to the proteomic state of the organism. With this they can then use P.ubique as a proxy to report the biological state of the specific system they are in. Last, a long-term goal is to be able to model the metabolic processes of P.ubique. It is an ideal candidate because it is one of the smallest and simplest known cells. With this information, it could be possible to integrate and optimize metabolic processes to be more efficient during low nutrient periods (Monterey Bay Aquarium Research Institute).

Unique Geological Feature: Floating Plastic

Frequently discovered throughout the western regions of the Sargasso Sea are unusual amounts of broken plastic fragments afloat on the water surfaces, roughly 3500 per square kilometer. Since these plastic fragments have become apart of the sea, various groups of hydroids and diatoms are often found on them. There are concerns regarding the ever increasing plastic production along with its improper disposal methods, which can disrupt ocean life and harm animals that may ingest plasticizers such as polychlorinated biphenyls (PCB’s) (Carpenter & Smith, 1972). Researchers inspecting the Sargasso discovered on average, about 8,000 to 10,000 of floating plastic pieces per square mile (Murphy, 1986). In addition, the Sargasso Sea consists of many plastic fragments due to its slow circulation (Greenpeace International) and its northern region includes one main, circularly moving gyre in which waste and plastic pieces flows to and accumulates (Watson, 2006).

Unique Biological Feature: Antioxidant Activity

It has been found that the seaweed of the genus Sargassum yields a methanol extract with potent antioxidant and antimicrobial properties. When compared with Ampicillin, it shows a more pronounced bactericidal effect on gram-positive and gram-negative bacteria. Scientists were able to evaluate these properties against three different species of bacteria, namely, Staphylococcus aureus, Bacillus subtilis, and Eschericia coli – the last being among the most common cause of food poisoning. For this reason, it has been suggested that the methanol extract of Sargassum sp. should be utilized as a cheap and plentiful natural source of food with the benefits of having antimicrobial and antioxidant properties. Nonetheless, more studies are required due the fact that the precise mechanism of how it works against bacteria is not well understood as well as possible allergic reactions. (Patra et al., 2008).

Conclusion

Conclusion To sum it all up, the culmination of data that has arisen in the past decade after the initial study by Venter et al. has shed light into the oceans unexplored biodiversity. The study of the Sargasso Sea has brought more questions to the table that researchers are tackling currently. Questions such as: “What else in the ocean don’t we know about? Are there many more genes in marine organisms than we ever imagined? Have we missed the major players in the ocean’s energy cycles? “ have scientists baffled at the possibilities(Ruder et al., 2008).

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by [Sherry Pablo, Hugo Frazao, Patricia Tu, Asa Gardner, Cam Nguyen, Shanice Wang], students of Rachel Larsen