UVB Effects on Aquatic Biota

UVB

Effects on Aquatic Biota

Ultraviolet radiation (UVR) accounts for about 7% of the radiation emitted by the sun.

The Solar radiation spectrum contains ultraviolet radiation which is broken down into ultraviolet C (UVC, 100-280 nm) 60%, ultraviolet B (UVB, 280-315 nm) 12%, and ultraviolet A (UVA, 315-400 nm) 28% ultraviolet radiation. As the most energetic UVC wavelengths are absorbed by stratospheric ozone in the upper atmosphere, UVB is the highest energy-level radiation able to reach the surface of the earth. UVA radiation travels through the atmosphere without significant reduction, and it is the least harmful of the UV wavelengths to living organisms.

"UVB radiation at current levels is harmful to aquatic organisms and can reduce the productivity of aquatic ecosystems, which is considered a significant alteration (Bancroft et al. 2007, Hader et al. 2007).  It has also been suggested that increased UVB changes the food web structure and function by the differential UV sensitivities of the phytoplankton species, the major aquatic biomass producers. At the cellular level, exposure to UVR impairs the survival of the bacterioplankton and DNA damage has been detected at depths down to 5 m in tropical coastal waters. UVB affects the motility, protein biosynthesis, nitrogen fixation, and survival of cyanobacteria, as well as the photosynthesis of flowering aquatic plants. UVB constitutes a significant stressor for macroalgae even without ozone depletion, affecting photosynthesis, morphology, and growth rates (Hader et al. 2007)"

Ultraviolet B Radiation Induced Alterations in Immune Function of Fish                               University of Jyvaskyla

The level of UVB penetration is largely determined by the DOC (Dissolved Organic Carbon) level of the water and only secondarily by POC (Particulate Organic Carbon) or chlorophyll a. This is evidenced by the facts that in the open ocean, UVB can penetrate over 15 m., but in a humic lake this penetration may be limited to only a few centimeters.

As a part of Solar radiation, UVB is also influenced by elevation, latitude and season (See maps below)

  

 

Plankton

Recent studies show that DOC mainly reduces UV-B radiation while POC mainly decreases the UV-A radiation in the water column. The optical effects of zooplankton and phytoplankton on UV reduction in freshwater ecosystems are usually low, but bacterioplankton plays a major role (cf. Zepp, et al.2). While DOC is only slowly degraded in the water column, it is readily fragmented by solar UV to smaller subunits, which are consumed by bacterioplankton. This increases the UV transparency of the water column where the resulting deeper UV-B penetration affects bacteria and other organisms. In principal, this is basically how a pond UV clarifier functions and although they may improve the water clarity by adversely affecting phytoplankton, they also exacerbate and hasten the penetration depth of solar UVB.

In addition, photobleaching increases UV transparency. Increasing temperatures associated with global climate change are generally expected to decrease DOC concentrations and thus increase the penetration of UV-B radiation into the water.

Plankton can be subdivided, based on physiological or taxonomic criteria into major groups of bacterioplankton, phytoplankton (including cyanobacteria and eukaryotes) and zooplankton. In aquatic ecology, size (on a logarithmic scale) is used as a subdivision criterion: femtoplankton (0.02–0.2 micron), picoplankton (0.2–2 micron), nanoplankton (2–20 micron), microplankton (20–200 micron) and macroplankton (200–2000 micron). Even though the smallest organisms contribute a significant share to aquatic biomass productivity, these taxa have not yet been studied extensively in terms of UV sensitivity.

Protective and mitigating strategies of cyanobacteria include mat or crust formation, vertical migration of individuals within the mat, or self shading due to changes in morphology as observed in Arthrospira platensis. In microbial mats the surface layer often serves as a protector for the organisms underneath.

Some phytoplankton taxa including dinoflagellates and diatoms produce toxic substances, such as neurotoxins and domoic acid, and are a severe threat to animals and humans when they form blooms. These organisms have a low sensitivity to solar UV radiation and escape damage of their photosynthetic apparatus by switching to heterotrophic growth.

Zooplankton includes unicellular and multicellular life forms and can be classified in several size classes as mentioned previously. It is also comprised of larval forms of fish, crustaceans, echinoderms, molluscs and other phyla.

Zooplankton community structure in freshwater ecosystems is controlled by multiple factors, including DOC content and distribution throughout the water column, which regulates UV penetration.

An example of how zooplankton is affected by solar UVB is its effect on Daphnia Survival and production of F1 (first generation offspring) were significantly lower in the UVB exposed parental generation  F1 exposure to UVB significantly decreased F1 survival and reproduction. Reproduction was lowest in UVB exposed F1 animals whose parents were also exposed to UVB. Adverse effects of UVB on offspring production may be magnified in successive generations suggesting that any short-term experiments could underestimate the impact of increased UVB exposure on populations.

                               Amphibians

Among other factors, solar UV-B radiation has been variously implicated as a possible contributing factor involved in malformation and mortality, especially during the embryonic development.

                                          Fish

Visual predators, including most fish, are necessarily exposed to damaging levels of solar UV radiation. Skin and ocular components can be damaged by UV, but large differences are found between different species. It is known that Carp (Cyprinus carpio) is more sensitive to UVB than Rainbow Trout (Oncorhynchus mykiss).

The skin of fish is particularly vulnerable to the intense radiation because it lacks a keratinized outer layer and has dividing cells in all layers of the epidermis. Mucus is an important factor maintaining the protective function of the skin, and artificial UVB has been seen to decrease the number of mucus-secreting goblet cells in exposed fish.

UVB exposure makes a fish more susceptible to pathogens, and radiation induced lesions (' summer lesion syndrome') in the skin are often accompanied by secondary fungal and mycobacterial infections. In one study Mosquito fish (Gambusia holbrooki), was wxposedto a factorial design of low and high UVB levels and low (18C) and high (25C) temperatures. The combination of high UVB and high temperature interacted synergistically to suppress metabolism and exacerbate infection intensity by the fish pathogen whitespot (Ichtyhophthirius multifiliis).

The eggs and larvae of many fish are sensitive to UVB exposure. In fish larvae a 3 day exposure to UVB increased the water content of blood plasma by over 20%. This increase is often exhibited as edema.

Fish spawning depth strongly correlates with UV exposure with fish seeking those spawning areas where UVB in minimized.

Overall, UVB exposure-

   -delays healing in fish.

   -damaging (lethal) to fish embryos and larvae, suppresses growth.

   -educes physiological stress

   -causes oxidative stress

Conclusion

Given the rapid changes in the thermal environment globally, the

interaction between UVB and temperatures on energy use and disease resistance

could pose significant problems for aquatic animal health in the context

of both pre-existing and emerging diseases.

-

The Nitrogen Cycle - The Paradigm Shifts

In an earlier posted article, Archaea The not-so-new-kids-on-the-block, we briefly discussed the emergence of certain species of the Domain Archaea as the prime ammonia oxidizing organisms in both terrestrial and aquatic environments world-wide.
Over the past several years there has been increasing evidence that a similar altering of perceived role dominance is extant in Nitrite oxidation.
Some bacterial and archaeal species defy replication under lab condition and have also defied easy identification by past known means. The bacterium Nitrospira is one such micro-organism. Only recently has a method been developed allowing for somewhat better identification. As a result, what has been discovered has changed the paradigm not only as relates to Nitrite oxidation but also, to a point, Ammonia oxidation.
Enough evidence has been amassed to date to confirm that in many aquatic environments Nitrospira is the dominant Nitrite oxidizing specie instead of Nitrobacter. This is most noticeable in waters that have an elevated Ammonia level. These elevated Ammonia levels inhibit the Nitrite oxidizing process in Nitrobacter but has no effect on the efficiency of Nitrospira. This means in an aquatic habitat where the Nitrogen cycle is not established or balanced Nitrospira will likely be the dominant Nitrite oxidizer with Nitrobacter increasing in numbers only when Ammonia levels have been reduced. This does not mean that Nitrospira’s role becomes diminished. Nitrospira has the almost unique ability to also convert Urea into Ammonia. It forms a quasi-symbiotic relationship with Nitrosomonas and, it is suspected, Archaea, supplying Ammonia in ezchange for Nitrite. So even in an established well-balanced aquatic habitat the Nitrite oxidizing duties are at least shared by Nitrobacter and Nitrospira.
In addition, Nitrospira remain active in anoxic conditions.
No longer are certain processes relegated exclusively to certain micro-organisms, but rather new organisms have emerged as the dominant players that are capable of performing multiple processes in the Nitrogen cycle.
The paradigm continues to shift.

Archaea--Update

In 1977, while Dr. Carl Woese and his colleagues at the University of Illinois were using a then new process of DNA sequencing for studying relationships between bacteria, it was discovered that there were two distinctly different groups. Those “bacteria” that lived at high temperatures (extremophiles) or produced methane formed a group quite different genetically from the usual bacteria. Because of this vast genentic difference in makeup, Dr. Woese proposed that a new domain of life be added…Archaea.

The scientific community was understandable shocked by this proposal and for several years balked at accepting such a major revision in century old thinking. Further research subsequently validated Dr. Woese’s proposal and in 1990 the existing three domains of life (Bacteria, Archaea, Prokaryote) were created.

Initially thought to exist only in extreme environments, those devoid of oxygen and whose temperatures were near or above the boiling point of water, microbiologists soon realized that Archaea are a large and diverse group of organisms that are ubiquitous to all environments-terrestrial and aquatic and significant contributors to the global carbon and nitrogen cycles. It is the role of Archaea in the nitrogen cycle (specifically aquatic) that is of interest and the focus of this document.

Since the acceptance of Archaea as a separate Domain of life, research has been both intensive and massive, delving into all aspects of this life form. Much of this research has been on the role of Archaea in the Nitrogen Cycle with the results of this research simultaneously upending some long held beliefs and yet clarifying other processes.

For Pondkeepers, maintaining the equilibrium of the Nitrogen cycle is of the first order of importance. To be able to do so requires a certain level of knowledge of how the involved biological processes work. Most Pondkeepers know that Ammonia is oxidized by Nitrosomonas bacteria et.al. to Nitrite which is oxidized by Nitrobacter bacteria et.al. to Nitrate which is assimilated by algae and plants or reduced to Nitrogen gas by other bacteria. Archaea do nothing to change this, but supplement the process, providing, shall we say, more efficiency in the initial Ammonia oxidation stage.

AOA (Ammonia Oxidizing Archaea) and AOB (Ammonia Oxidizing Bacteria) both occupy important niches in the Nitrogen cycle. In Oligotrophic (low nutrient) waters, AOA are the predominant organisms and in Eutrophic (high nutrient) waters AOB dominate.

In the world’s oceans, AOA are now known to be the primary oxidizers of Ammonia, replacing AOB which for decades were believed to have performed this function. The same has been found true in many freshwater lakes and even in some soils. So what does this mean to a Pondkeeper?

Although no true research has been undertaken targeting ponds specifically, there have been two (2) papers^1,2 (2011 and 2014) addressing the roles of AOA and AOB in aquaria. Additionally,  a Master’s thesis³ on this subject was also written in 2014. The results of these three (3) documents can logically be applied to garden ponds as both (ponds and aquaria) are closed systems.

What was revealed in all of these research documents was that in established and balanced aquaria, AOA were not only the dominant, but in some cases, the only oxidizer present. This is not to imply that AOB have lost their status as being an integral part of a pond’s Nitrogen cycle, but that their role of importance is limited to establishing the initial balance in a new pond when Ammonia levels are high.

This begs the question: Does this really change anything?

The simple answer is…No. It does, however, because of some unusual characteristics of AOA, offer a different perspective on the Nitrogen cycle process.

For instance, it has been shown that AOA are fully capable of Ammonia oxidation in suboxic (low oxygen) conditions. They have been isolated from the sludge at various Waste Water Treatment Plants which were almost devoid of Oxygen. How Archaea are able to do this is still being researched.

It has also been suggested by some, denied by others, that AOA are still able to function at temperature approaching freezing. If proven true it could make a difference to Pondkeepers in higher Latitudes.

As yet, Archaea have only been found that convert Ammonia. None have been found that oxidize Nitrite. Considering the fact that research into this amazing organism is really in its infancy, future surprising discoveries can certainly not be ruled out.

For certain, with the newly acquired knowledge of AOA and Anamox (a subject for another discussion), a new paradigm is required for the Nitrogen Cycle.

References:

1. Temporal and Spatial Stability of Ammonia-Oxidizing Archaea and Bacteria in   Aquarium Biofilters

     Samik Bagchi1.¤, Siegfried E. Vlaeminck1., Laura A. Sauder2, Mariela Mosquera1,

Josh D. Neufeld2, Nico Boon1

2.  Aquarium nitrification revisited: thaumarchaeota are the dominant ammonia oxidizers in freshwater aquarium biofilters

     Laura A. Sauder, Katja Engel, Jennifer C. Stearns¤, Andre P. Masella, Richard Pawliszyn, Josh D. Neufeld

3. Ecology of Ammonia-oxidizing Archaea and Bacteria in Freshwater Biofilters

     Natasha Alexandria Szabolcs