I’ve had exams for the past two weeks, and they’ve completely consumed my time and my energy. Although I only had two exams, they were pretty heavy in content. One was on sharks, and the other on Extreme Marine Habitats. Extreme Marine Habitats has been a pretty interesting module, delving from life in the Polar regions and how ocean acidification is affecting organisms in Antarctica to deep sea corals and hydrothermal vents. I also had to write my own marine blogs which you can find here.
The ocean has some of the most fascinating biomes on earth, and some of the most extreme conditions to life. If you’ve watched Blue Planet 2 recently, then you’ll have seen lots of these extreme environments and the organisms that reside there. Since I’ve spent the last few months learning about them, I thought I’d share some of the science behind life at Hydrothermal vents.
Hydrothermal vents are full of weirdly wonderful creatures all adapted to life at unusual extremes. It was believed that an abundance of life could not exist at such depths due to lack of light, however in 1977 the East Pacific Rise, at Galapagos Rift was discovered by scientists using the DSRV ALVIN. Such a discovery led scientists all over the world to believe that if life could be found in such extreme conditions without light, then maybe life could definitely be found on other planets previously seen as inhospitable.
There are 5 main extreme factors that life at such depths has had to adapt to; Lack of light, Temperature, Hydrostatic pressure, Heavy metals and Sulphide toxicity.
Hydrothermal vents occur deep down in the depths of the ocean where light cant penetrate. This was initially believed to be a major factor in determining where life could be found, but life prevailed in abundance. One highly notable adaptation from an organism, comes from the shrimp Rimicaris exoculata, who have developed “Novel eyes”. These novel eyes, are actually photoreceptors and do not have image forming lenses. Instead they can sense the radiation given off by sulphide vents, being able to detect a 350°C 10cm wide vent from 2.3m distance. This aids survival of the shrimp as they have a chemosymbiotic relationship with sulphide-loving bacteria, and so must stay within high sulphide vent areas, to ensure they survive.
Temperature at Hydrothermal vents can range from 2ºC to 400ºC. This is due to fluctuations in the vent fluid and the ambient temperatures around the vents. However, exposure depends on distance from the vent, for example, feather duster worms and Galatheid crabs will be exposed more to ambient sea water. Organisms closer to the vents however need to be better adapted to fluctuating temperatures. Really high temperatures can cause a break in mitochondria, which results in lack of ATP production and eventually the cell stops functioning. So the organisms closest to the vent such as Riftia Pachyptila, Bythrograea thermydon and Paravinella grasslei have adapted to higher break temperatures. Other adaptations to temperature can be seen in Alvinella pompejana, opening when water comes up through venting tube and passes through a u-shaped tube of parchment or organic material, siphons water through, animals exposed to both hot thermal water and ambient seawater, as a thermal siphon. This allows the sulphide-loving bacteria that lives exosymbiotically with the worm, to gain what it needs, whilst also keeping the worm alive.
At the depths of the ocean there is an incredible amount of hydrostatic pressure. This pressure can affect an organism’s protein structure and function and membrane structure and function. To overcome this, organisms have adapted to cells with more lipid in their plasma membranes to maintain their structure. This is known as homeoviscous adaptation, as lipids are more compressible and can change fluidity at high pressures, which usually reduce fluidity.
Heavy metals also affect organisms at hydrothermal vent. Not quite the likes of Metallica and Iron Maiden, but compounds like copper and zinc, which are prevalent at vent sites. Metals in high dose can be toxic to organisms and poison them. To counteract poisoning, some organisms have developed proteins. These proteins are described as “Metallothien-like”, and work by binding to the metals. In some organisms such as Calyptogena Magnifica, these proteins bind and then get moved to the kidneys, where they form intracellular granules and eventually get excreted. In other organisms such as Alvinella pompejana they can be found in the digestive tract and epidermis. Some just don’t have these proteins at all and instead excrete a mucus to aid in detoxification, this can be seen in Paralvinella.
Metals aren’t the only toxic element that can be found to harm vent life. Infact the vents themselves are highly dangerous as they release sulphides which are poisonous to life. Sulphide can inhibit the production of ATP, which then leads to a reduction (or complete cease) of cell function. Vent organisms cant prevent the sulphide from passing over their epidermis or respiratory system, as many need the sulphide for their chemosymbionts, so instead- they oxidise it! By oxidising it they can turn it into a non-toxic product, and that’s what they do, its known as thiosulphate.
Perhaps the most interesting adaptation of all though is chemosynthesis. Due to the lack of light many organisms get their energy/food source from a chemosymbiotic relationship with bacteria. Studies have found over 250 different types of symbiont in the deep sea, which oxidise a range of elements from sulphur to methane. The symbiont lives within the hosts tissue, in exchange for giving the host energy through nutritional carbon and nitrogen. The host provides shelter, oxygen, carbon dioxide and sulphide necessary for the symbiont to metabolise. For some species like Riftia pachyptila, symbionts provide the only source of energy.
And there you have it, a brief little introduction to the main factors organisms at Hydrothermal vents (and cold seeps) have had to adapt to! Life at hydrothermal vents are somewhat perfectly adapted to such an unusual environment, however life there is still has one risk that no organism could ever really adapt to. The risk of the vent dying out.
Until next time,