TOPICS

Antarctica: Increase in ultraviolet radiation: How much does it affect southern marine life?

Antarctica: Increase in ultraviolet radiation: How much does it affect southern marine life?


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

By By Santiago G. de la Vega

The arrival of the spring season implies for most Antarctic organisms the beginning of a new stage in their reproduction and growth cycles. On the other hand, the ozone concentration has decreased to half its normal values ​​since the last 20 springs.

The arrival of the spring season implies for most Antarctic organisms the beginning of a new stage in their reproduction and growth cycles.

On the other hand, a few kilometers away - in the upper atmosphere - the ozone concentration decreases at that station to half of its normal values. At least that is how it has been happening for the last 20 springs, according to continuous records that are being taken.

What does the existence of the so-called "ozone hole" imply for Antarctic marine life?
Well, basically, the increase in ultraviolet radiation it receives.
But what are ultraviolet rays?
The spectrum of ultraviolet rays extends between 200 nm to 400 nm and is divided into (the shorter the wavelength, the higher the energy):
- UV-C, 200-280 nm
- UV-B, 280-320 nm
- UV-A, 320-400 nm

Photosynthetically active radiation (from .400 to 750 nm) and UV-A are not filtered by the ozone layer, and consequently are independent of its variation.
UV-B is the one that is entering with the most intensity through the "hole in the ozone layer". Upon reaching the sea and as it passes through the water column, this radiation is absorbed and dispersed, especially by dissolved and particulate substances.
The layer of water that filters up to 90% of the solar radiation of 310 nm (UV-B) varies in thickness from about 20 m in the clearest oceans of the world, to a few centimeters in lakes with turbid waters and rivers .

Some comparative data of the depth in meters at which 90% of the UV-B has filtered compared to that which enters the water column:
Sea of ​​Zargazos (Caribbean) 19.8 m
Bellingshausen Sea (Antarctica) 9.0 m
Mouth of the Orinoco River (Venezuela) 0.11 m

A peculiarity in Antarctic waters is that the seasonal changes in radiation are very large. After the winter darkness, a gradual increase in light begins. Under these conditions, the time required for photoadaptation to UV is a critical factor in tolerance for many living things, especially small unicellular ones.

UV-B is known to have lethal and mutagenic effects on various aquatic organisms. DNA (deoxyribonucleic acid, constituent of genetic material) is the first to be damaged, and side effects include absorption by RNA (ribonucleic acid), proteins, pigments, etc.

After at least 20 years of increase in ultraviolet radiation, the unicellular species that in a few days produce new generations would have begun to be selected, favoring the more tolerant ones.
In more complex living things, with cycles of one year or longer, the effects would be felt in the longer term.

Organisms that live under rocks, that live below the layer of penetration of light or nocturnal habits, would be less directly affected.
Among organisms exposed to radiation, their size, shape, or outer covering can serve more or less as a protective barrier. Age, sex, and "health" also determine different effects.

Among the defensive systems, three cellular mechanisms have been identified that act in the repair of DNA damage.

Mycosporins are substances that absorb ultraviolet radiation and are assumed to provide protection against UV-B; adaptation with analogy to the protection of our skin by melanin.
These compounds have been recorded in groups such as dinoflagellates, red algae, stars, sea squirts, zoanthids, some bivalves, and even a few fish. Animals would obtain mycosporins by ingesting algae that produce them or by their presence in symbiotic organisms.

What is known about the effects of increased UV-B on groups of marine life?
Well, it depends on who we are talking about. Let's see some advances in knowledge about important groups.

Bacteria

The food web of bacteria is the main pathway for organic carbon through aquatic ecosystems. This recycling of nutrients has evolved over millions of years, with complex relationships between dissolved organic material, bacteria, flagellates, and phytoplankton.

UV-B influences all these "levels" but with so many variables at stake and unknowns to be revealed, it is considered that it is not possible to make accurate predictions about how the microbial food web is affected.

Due to their short generational cycles, bacteria should adapt quickly to changes in the environment, and they precisely have different defenses.
Thus, for example, there are UV-induced DNA repair mechanisms or the elaboration of UV-absorbing compounds, although many studies are lacking.
On the other hand, bacteria do not depend on light to obtain the organic substrates that nourish them and UV-B can affect their viability only up to 10 meters deep in Antarctic waters.
Algal cells, on the other hand, only grow to the depth of penetration of solar radiation necessary for photosynthesis. Consequently, on a broad scale, the risks of bacteria declining their activity would not be as great as for phytoplankton.

In addition, the reduction of bacterial activity has an important indirect effect on the abundance of phytoplankton: by lowering the rate of remineralization of inorganic nutrients, there are fewer nutrients available for the photosynthesis of algae.

Microalgae

Field and laboratory experiences have estimated a decrease in the primary production of microalgae of between 6% and 15% in surface waters of the southern ocean (1992) due to UV-B effects.

The different sensitivity to ultraviotela of about 20 species of diatoms has been determined. In general, when exposed to low UV-B radiation, an increase in their growth was observed, since DNA synthesis would be stimulated.

Already with high radiation, cells stop dividing although they continue to grow and photosynthesize. The smallest cells - with a large exposed surface in relation to their volume - would be the most damaged.

As in the southern seas they would make the greatest contribution to primary production, the effect of UV can imply great ecological changes. For example, it has been suggested that larger cells could become dominant.

The diatom Corethron cryophilum, abundant in Antarctic phytoplankton, is, among the species studied, the most resistant to UV.

Phytoplankton and ice algae exhibit different UV-B absorbances, and mycosporins are known in ice algae communities. But there is still much to know. According to recent studies, UV-A causes a greater decline in photosynthetic rates of phytoplankton than UV-B.

Macroalgae

Little is known about the effects of UV on macroalgal communities, some of which are highly exposed to radiation, such as those that grow in the intertidal zone.

Responses to the effect of UV-B are also unknown when stress due to lack of nutrients, desiccation or high pressure of herbivores is added.

Species with a simple structure, such as filamentous algae, would be more susceptible to damage than those with a more complex thallus, such as laminar algae. It is necessary to know the specific mechanisms of repair or protection in this group.
Seven mycosporins have been identified in Antarctic macroalgae. They are more abundant in red algae, also recorded in brown algae, and less frequent in green algae.

The stress caused by ultraviolet rays can also cause indirect effects. For example, preliminary results with the alga Dictyota dichotoma indicated that UV exposures reduce the concentration of its defensive chemicals and make it more "palatable" to predators.

Invertebrates

Over 50 species of Antarctic invertebrates in which the existence of mycosporins was analyzed, they were detected in 90% of them.
Limpets (Nacella cocna) are one of the organisms that appear in the ice-free intertidal zone, since the beginning of spring.
In the life cycle, their larvae released into the water column are exposed to the highest levels of radiation. It is possible that UV-B has an influence on their mortality, as must also be the case for embryos and larvae of many invertebrates.

Already in the adult stage, the shell provides protection against rays, while the mycosporins were found in variable concentrations depending on the tissues, being high in the ovaries.
Furthermore, in the most exposed limpets in the intertidal zone, higher concentrations of mycosporins were found than in limpets always covered by water.

It has been suggested that it is important to know the influence of the UV increase on the productivity of "key" organisms such as krill, although this variable is very difficult to determine for these organisms.

Birds

Bird feathers are very good protection against UV rays, especially while birds are nesting. The chicks obtain shelter with the protection of the body of their parents.
Although the high reflection of ice and snow, would determine that Antarctic birds are more exposed to have problems in corneas due to UV effects in relation to birds from more temperate areas.
But the greatest potential damage to the members of the winged world would be in relation to dietary changes arising from alterations in phytoplankton.

Mammals

Antarctic marine mammals have a good protective barrier in their skin and pigmentation.
Seals receive higher UV radiation from reflection on snow and ice, and to a lesser extent on land and water.
This radiation can damage the cornea, although they have good tolerance to radiation. There is evidence that the ocular perception of UV-B influences the regulation of neuroendocrine physiology in mammals, although it is not known whether this effect occurs in Antarctica.
In any case, the negative effects of UV-B on the dynamics of their food chain can be harmful to them.
What are those changes? One among many answers to be determined.

* Santiago G. de la Vega
Lic. In Biological Sciences
www.contactosilvestre.com.ar


Video: The 1975 ft. Greta Thunberg - The 1975 Music Video (July 2022).


Comments:

  1. Fezuru

    Absolutely agrees with you. In this something is I think that it is the excellent idea.

  2. Berdy

    young fellow

  3. Sahran

    What words ... Great, a remarkable phrase



Write a message