When We Mess Up, Can Microbes Still Fix the Problem?

Humans greatly impact, and often harm, the environment by emitting greenhouse gases, destroying habitats, and by polluting the area, especially. Oil spills are a deadly and costly way that humans pollute the water ways. They are also quite notable, consider the Exxon Valdez spill near Alaska or the Deepwater Horizon spill in the Gulf of Mexico. Thankfully, nature is often able to fix our mistakes. Microbes play a huge role in degrading oceanic oil spills. However, microbes in the arctic seem to face particular challenges that are not experienced in warmer environments.

An article in Science Daily presents the challenges for oil-eating microbes in the Arctic. These difficulties are due to six things: low temperatures, sea ice, low nutrient content, particle formation, prolonged sunlight in the summer months, and potential lack of microbial adaptations.

Low temperatures cause the oil to become more viscous and thicker. This means it is harder for the oil to disperse into small droplets that can be consumed by a wide area of microbes. Sea ice inhibits wave formation and impact. This decreased power also makes it harder for the oil to disperse into small droplets. Few nutrients in the water cause decreased activity of the oil-consuming microbes, and high particle formation and concentrations allow the oil to clump and settle to the floor where microbial productivity is decreased. Furthermore, 24 hour arctic summer sunlight may make the oil more toxic to marine life, although it could make the oil easier to process as well; the answer is still unclear. Finally, lack of exposure to oil spills may promote microbes without the adaptations to digest and process oil. However, further research is required to determine this with certainty.

This article brings to light the importance of being cautious when handling harmful pollutants. Although microbes can help clean up the oil, they may not work efficiently in arctic environments causing the death of thousands of marine organisms. The effectiveness of microbes is important especially because mechanical removal of oil can only remove 15 to 25 percent of the oil. Therefore, it is crucial that people are careful with their actions and encourage research in microbial life in the oceans because microbes, although small, play a huge impact on the health of marine environments. 

Aarhus University. "Oil-eating microbes are challenged in the Arctic." ScienceDaily. ScienceDaily, 20 February 2018. .

How one species uses hydro-thermal vents to incubate their young

In 1977 near the Galapagos islands scientists first observed that hydro-thermal vents helped create a thriving deep-sea habitat. For the first-time creatures such as crabs, snails, and bivalves were seen using this rich source of nutrients in an otherwise barren place to thrive. Almost 40 years later in 2015, scientists took the ROV (remotely operated vehicle) Hercules down to the observe these vent systems and the variety of life that lived within them they noticed something unusual. What appeared to be egg capsules both old, and currently in use were crowding the vents.

      They observed that these capsules were located very close to the vents and that there was an abundance of old egg capsules which showed that this

process had been going on for quite some time. After collecting samples of the egg cases for DNA resting and taking careful measurements of the cases the species was determined to be Bathyraja spinosissim, which is a species of Deep Sea Skate, a relative of the shark. These creatures have one of the longest incubation periods of almost any creature in the animal kingdom, which seemed to make sense as to why they would choose to lay their eggs here to incubate.

Figure 1. Deep Sea Skate Bathyraja spinosissim, also known as the Pacific White Skate

The heat given off from the hydrothermal vents seemed to help speed up the incubation period for the skates. Other animals in this genera, such as   B. parmifera which resides in the Bearing Sea, and has an incubation period of almost 1290 days at 4.4 degrees Celsius. So, if the Pacific White Skate has a time frame for development much like its relative, then with the water being at an average temperature of 2.76 degrees Celsius, the estimated incubation period would be around 1500 days.

          Studies have shows that there is a positive correlation for water temperature and incubation period, so with that being a main factor contributing to the hatch rates of the skates then it would make sense that they would lay their eggs near the vents where the water would be warmer and incubation time would be cut down.

          Not only was the water temperature an ideal place for the skates to lay their eggs, the environment also has an ample food supply and ideal shelter. The vents have a wide variety of creatures living there as well, so when the young hatch they can be sure they will not starve. The vents plumes of black smoke also help provide coverage for the young skates against any potential predators giving them a small advantage at the start of their lives, so temperature may not be the only influential factor to skates when they choose where to lay their eggs.

Figure 2. Skates egg capsules 

This study has helped marine biologists to get a better understanding as to the behavior of the skates and given them ideas on how to help conservation efforts to raise the sates population. With this study being the first time that skates’ eggs have been found in extremely high density it has given conservationists ideas to what they should look into when creating reserves for skates to breed, lay eggs, and thrive in creating a more positive outlook for this species survival.

       

Click here for a short video showing the ROV's trip to the egg incubation site


References:

https://news.nationalgeographic.com/2018/02/Pacific-white-skate-eggs-hydrothermal-vents-animals/

https://www.nature.com/articles/s41598-018-20046-4

http://www.newsonia.com/reader/report/deep-sea-skates-use-hydrothermal-vents-as-egg-incubators/

Images and video from :https://www.nature.com/articles/s41598-018-20046-4
                      http://www.newsonia.com/reader/report/deep-sea-skates-use-hydrothermal-vents-as-egg-incubators/

Combined effects of microplastics and chemical contaminants on the organ toxicity of zebrafish

In todays day an age plastic pollution in the oceans is common. Because of this researchers are studying the effects of this plastic on fish. Plastic really only gets broken up into smaller and smaller pieces. This is what is referred to as micro plastics. Micro plastics are a global concern.

Ingested micro plastics have been shown to effect the way other contaminants are sorbed by fish. To test this idea this study used four groups of zebra fish with different feeding protocols. Group A was a control, Group B had feed supplemented by micro plastics, Group C had feed supplemented with micro plastics with a mix of PCBS, BFRs, PFCs and methyl-mercury, Group D had feed supplemented with the contaminants only. This study was conducted for three weeks. After completion, the fish are dissected, and the liver, intestines, brain and  muscular tissue were examined.

FIGURE 1: A cross-section of the fish liver. You can observe the different amounts vacuolization. 

The results of the study were interesting. Group B which was the feeding group with microplastics didn't show a significant amount of change in gene expression. Group D (which was the feeding group that had food supplemented with chemical contaminants) showed a significant amount of difference in gene expression. The fish that were in Group C (which was the group with plastic and contaminants) showed the highest amount of difference in gene expression. These genes are known as biomarkers and there changes can be troublesome. This data can be observed in Figure 2.

FIGURE 2. Differential gene expression of three genes in fish livers.  

The most prominent effects of the treatments were detected in the livers at the microscopic and molecular levels. The results of the study show that while micro plastics are harmful, they are even more harmful in the presence of contaminants. The micro plastics were found to have a magnifying effect on the harmfulness of the contaminants  

Citation: Rainieri, S., Conlledo, N., Barranco, A., Larsen, B. K., & Granby, K. (2018). Combined effects of microplastics and chemical contaminants on the organ toxicity of zebrafish (Danio rerio). Environmental Research, 162135-143. doi:10.1016/j.envres.2017.12.019

Lionfish Invasion and How Fishing May Help

Easily recognized by their bright colors and long spines, lionfish have become a hot topic of discussion in recent years. When speaking about lionfish, two particular species are often the focus: Pterois volitans (red lionfish) and Pterois miles (devil firefish). These closely related species are similar in appearance; both species have large fan-like and dotted fins, but P. miles has fewer dorsal- and anal-fin rays. Their spines are long and venomous, marked with bright orange, maroon, brown, and cream stripes. A sting from a lionfish can last for days and may cause extreme pain, difficulty breathing, and in some cases paralysis.

Pterois volitans, a.k.a. Red Lionfish

P. volitans is native to the southern Pacific while P. miles is native to the Indian ocean, with the two species intersecting near Sumatra. Despite the differences in their native ranges, both species have been found along the North American Atlantic coast in recent years (particularly along Mexico). Due to their popularity as an aquarium fish in North America, it is thought that they may have been introduced to the Atlantic through release by previous owners. As carnivorous fish that thrive in tropical waters, these two species have become invasive and threaten native marine life. Slow-moving hunters, lionfish are typically nocturnal but Atlantic populations seem to have increased diurnal activity. In many Atlantic coral reefs P. volitans and P. miles have become the top predators, using their large fins to ambush and corner prey. Invasive lionfish out-compete native fish and there are concerns that they may harm populations of ecologically important species such as parrotfish. In addition to their lack of natural predators in the Atlantic, lionfish can also reproduce year-round with females releasing approximately 2 million eggs per year. As the Atlantic populations continue to grow, their range expands further along the coast.

Fortunately, lionfish do have one potential predator – humans! While venomous, lionfish are not poisonous; removing the spines makes the fish completely safe to eat. While caution must be taken when handling the fish and removing the spines, if properly prepared the result is well-worth the effort. A popular meal in its native ranges, lionfish are known for excellent taste and populations could potentially be kept in check through fishing. Eating invasive lionfish provides relief to native over-fished species by removing competitive stress, giving over-fished populations a chance to recover. Lionfish is described as being a white flaky fish, similar to halibut in texture and slightly buttery. While beautiful to look at, lionfish also make a beautiful addition to the dinner table and are even growing in popularity to the point of being found at some restaurants. Hopefully, increasing awareness may bring the lionfish invasion under control and prevent P. volitans and P. miles from spreading further.

Deep-fried lionfish nuggets

Schofield, P.J., J.A. Morris, Jr, J.N. Langston, and P.L. Fuller, 2018, Pterois volitans/miles: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/factsheet.aspx?speciesid=963, Revision Date: 2/7/2018, Peer Review Date: 4/1/2016

U.S. Department of Commerce, National Oceanic and Atmospheric Administration. “What Is a Lionfish?” NOAA's National Ocean Service, 28 July 2016, oceanservice.noaa.gov/facts/lionfish-facts.html.

Harrel, Scott. “Eating Lionfish.” Lionfish Hunting, 2014. https://lionfish.co/eating-lionfish/

Variability in Estuary Habitat Use by American Alligators—But What About Shark Encounters?

An estuarine habitat is very important for a lot of species due to freshwater and marine conditions, ecological reasons recreational reasons, and commercial importance. Salinity levels fluctuate, the tides go through cycles, and there is input from upstream freshwater flows. All of these factors determine the density population of the American Alligator within the estuary. Other factors that contribute are reproductive cycles and temperature.

 

Figure 1: An American Alligator eating a shark.

Alligator mississippiensis¸ or the American Alligator, is a primarily freshwater species. It is spatially and temporally heterogeneous largely due to a salinity gradient that fluctuates. This species hangs around the estuary near the Atlantic Ocean in Southern Florida. The density of alligators in the downstream zone was lower than that of the midstream zone during the dry season when salinity increases due to reduced precipitation. Conversely, the density of the large size alligators was higher in the downstream zone than in the midstream zone because of the wet season, probably due to a decrease in salinity concentration. The authors’ results indicated high adaptability of alligators to the fluctuating habitat conditions. Use of estuaries by alligators is likely driven in part by physiology and by reproductive cycles, and their results supported the alligators’ opportunistic use of estuary habitat and ontogenetic niche shifts.

The American Alligator is an intriguing candidate for this study. The researchers were curious to the drive of alligators to and from the estuary. They found that typically the only alligators present in the estuary were of the larger class size because of their smaller surface area to volume ratio whereas the small class has a higher surface area to volume ratio. Alligators have a limited osmoregulatory capability in saline environments. Alligator nests were not found in moderate-high salinity areas, which suggests that salinity has a strong effect on the nesting sites of alligators. Therefore, altered salinity by changes in freshwater flows into estuaries likely affects the location of alligators, hence why they travel upstream during droughts and travel downstream during the wet season. The researchers used a long-term monitoring program to determine trends in relative density of alligators in the Shark River estuary.

 

Figure 2: An American Alligator eating what presumably looks like a large fish or a small shark.

Large alligators may make more frequent excursions to the downstream zone during the wet season because of lower salinity and higher temperature. As a mobile top predator, the alligator transfers energy and nutrients by their movement and foraging activities across ecosystems. In this study, the alligator connects freshwater, estuary, and near-marine zones by their movement and foraging. During the dry season, it is noted that the adult male alligators spend twice as much of their time in an upstream zone. The larger alligators are more tolerant to salinity concentration differences. Because of their tolerance, they have more foraging options, especially in the Shark River.

Recent surveys indicate the declining density of alligators in multiple wetland compartments in southern Florida, even up to a 99% decline in the southern Everglades. Historically, population counts were higher, but recently, due to human and nature involvement (droughts), the density has decreased. Human development has disturbed these estuaries and the many life forms that call these places home. There are efforts to improve the conditions in the southern estuaries to more natural patterns. If restoration is achieved, it is expected that alligator density will increase and that more medium and small class size alligators will be observed as salinity becomes more favorable, whereas in this study mostly large sized alligators will observed.

Typically all class size alligators consume estuary/marine species including mud crabs, horseshoe crabs, blue crabs, grass shrimp, and fish, but juvenile alligators consumed less frequently than larger alligators. Large-sized alligators do travel downstream into the estuaries where other predators are present. Alligators will eat anything that typically fits into their mouths which begs the question, what if there is a competing predator. With this in mind, do alligators come across sharks and what happens?

It is reported that alligators and sharks do come into contact, and the outcome is interesting regarding encounters of sharks with alligators and then again with crocodiles. “Alligators are opportunistic” and surely they wouldn’t pass up a “big chunk of protein that’s swimming by.” There is evidence of alligators eating lemon, nurse, and bonnethead sharks, as well as an Atlantic stingray. “Gators will eat almost anything that will fit in their mouths” says a researcher at the Northwestern State University of Louisiana, though the researcher points out that he has never found shark remains in the stomach of an alligator. This may be due to the highly acidic stomachs of the alligators, which could dissolve the cartilaginous skeletons of sharks with little trace. The literature was searched for crocodile encounters, and the conclusion was quite the opposite. The crocodile, more often than not, was the prey in many cases—great white sharks preying on American crocodiles in Columbia and tiger sharks eating estuarine crocodiles in Australia.  

Check out this short 1 minute video on the shark/alligator ancient rivalry

References

Fujisaki, I., Hart, K., Cherkiss, M., Mazzotti, F., Beauchamp, J., Jeffrey, B., & Brandt, L. (2016). Spatial and Temporal Variability in Estuary Habitat Use by American Alligators. Estuaries & Coasts, 39(5), 1561-1569. Doi:10.1007/s12237-016-0084-2

https://www.newscientist.com/article/2148317-alligators-versus-sharks-who-wins-this-ultimate-showdown/

Biological Destruction of Coral Reefs

Biological destruction of coral reefs is something that is incredibly important to consider. The major agents of this kind of destruction can be divided into grazers, etchers, and borers. Grazers are animals such as echinoderms and a wide variety of fish. These organisms graze on live or dead coral substrates, encrusting coralline algae, tufted or filamentous algae which grows on hard reef substrates. They do this action in order to search for food or to produce a cavity in which to give them protection against predators or wave action (Hutchings 1986).  A picture of an example of this is seen below in Figure 1: 

Figure 1. "Fish in Coral Reef". 

Etching is done by bacteria, fungi, and algae. Etching is a means of penetrating coral substrates. It has also been shown that bacteria may be involved in the breakdown of limestone surfaces. More work is needed to document the destructive role of bacteria in the field as well as calcite (Hutchings 1986). An example is seen below in Figure 2: 

Figure 2. "Fungi on Coral Reef".

Borers bore holes into plant material and corals. Sponges are a huge culprit of this. The importance of sponges in the processes of erosion, sediment production, and calcium carbonate dissolution was not realized until the late 1960’s. Most of the evidence of this was found in Bermuda by a scientist names Rutzler in 1974. Bivalve molluscs are also perpetrators of this action. They bore into rock, coral, and shell and this action is well developed within the three families of bivalves. They use mechanical means of penetration into rock. Sipunculans are endolithic animals which are found in many reef areas. They bore into live and dead coral but also limestones in both intertidal and subtidal zones. Studies of this organism’s boring strategy in the Caribbean, specifically in Belize. Two scientists, Rice and MacIntyre did these studies in the Caribbean and they discovered that six of eight recorded species were borers in coral substrate (Hutchings 1986). An example is shown below: 

 Figure 3. "Sponge on Coral Reef".

The impact of bioerosion is extremely complex and hard to determine fully for scientists. Corals are one of the richest and diverse marine ecosystems known to man.  Bioerosion is responsible for the creation of a large number of reef habitats. Each reef habitat is characterized by its own community. Bioerosion, when paired with physical erosion, is responsible for the creation of newly available substrates which is caused by weakened coral colonies becoming dislodged during storms. Small scale disturbances have been important in maintaining the species diversity of coral reefs. Though bioerosion may sound like a negative thing, the activities of many bioeroders actually encourage and help facilitate reef growth (Hutchings 1986).

Every group discussed above attributed to the rates of bioerosion. There are some limitations in some measurements dealing with these organisms. There is also some variability in rates of bioerosion both over time and space. Bioerosion is a major factor which influences reef morphology. Through the few quantitative estimates of rates, it spears that bioerosion is a major component of the total erosional modification of reefs. When this is paired with the chemical and physical erosion, this facilitates the formation of characteristic reef structures. These structures include boulder tracts, eroded reef flats, and sediments. Bioerosion also may be very important in maintaining the high diversity of coral reefs which can be seen mostly on protected leeward reefs. Bioerosion is a very important source determining the shape and form of coral reefs, although it is a very neglected one. This is a topic that will hopefully be taken into more comprehensive studies in the future.

Research Paper Source: 

Hutchings, P. 1986. Biological Destruction of Coral Reefs. Coral Reefs. 4, 4:239-252. https://www.researchgate.net/publication/226779075_Biological_destruction_of_coral_reefs_a_review-Coral_Reefs4_239-252_Berlin

Picture Sources: 

"Fish in Coral Reef." Bing, Microsoft, Images. 13 February 2018. 

"Fungi on Coral Reef." Bing, Microsoft, Images. 13 February 2018. 

"Sponge on Coral Reef." Bing, Microsoft, Images. 13 February 2018. 

Skeletal Muscle Atrophy in Polar Bears

Figure 1: Example of polar bear with Atrophy

Seasonal declines in food availability causes many animals to reduce their physical activity and use their tissue storage for energy and function. This decline in activity brings a decrease in skeletal muscle loading and neural activation. These factors potentially cause skeletal muscle atrophy that is characterized by loss of muscle mass and strength. Catabolism of tissue caused by fasting is also a cause of muscle atrophy in animals.

Across the Arctic tundra, polar bears (Ursus maritimus) experience food deprivation and changes in physical activity over seasonal changes. Pregnant female bears hibernate, give birth, and nurse in maternal dens from November until March.  Other bears such as males and non-pregnant females are still active during these months, however, their hunting ability is decreased due to seals not being active on the ice during winter months. Once offspring are grown, mothers and their cubs emerge onto the ice and become highly active from April through July.

Figure 2: Mother bear surfacing from hibernation with cubs

Due to annual ice melts that peak during August through October, polar bears are forced to fast once more. In one of the 19 sub-populations in the Southern Beaufort Sea (SBS) area, nearly 70 percent of individuals follow the retreating sea ice as it recedes north beyond the continental shelf waters, while 30 percent  of the animals come to the shore. The bears that follow the sea ice that retreats beyond the continental shelf waters become food deprived. Seal food sources follow the ice retreat while terrestrial prey that is rich in nutrients becomes scare.

This study examined the nutritional status and physical activity of polar bears in the SBS after winter food deprivation and during summer fasting. Predictions tested were that bears on the sea ice over the continental shelf during the months of April through May are recovering from atrophy induced by reduction in activity and food deprivation. The second prediction was that bears that are on-shore in August demonstrate no atrophy because of high activity and excessive eating. Third, they predicted that polar bears on-shore in October exhibit little to moderate atrophy due to competing influence of reduced activity and feeding from washed up whales. The last predication tested was that bears on sea ice over deep water in October show moderate to substantial atrophy from reduced activity and fasting over the summer months.

Table 1: Idealized timeline of polar bear cycles in SBS

Samples included bear's bicep femoris muscle that was collected during each season. Captures of bears were done between Barrow, Alaska and the USA-Canada border both on the shoreline and offshore on coastal sea ice. Figure 1 below shows the study area with (A) being the Beaufort Sea Region boxed, (B) being the Beaufort sea region of the Alaskan coasts and distribution of the sea ice (white) in May of 2009. The picture (C) shows the same area with sea ice as of August 2009. The circles represent locations of 31 polar bears over the previous week.

Figure 3: Mapping of polar bears in SBS region

Atrophy was most pronounced during the spring months of April through May as a result of food deprivation during the previous winter. The bear's muscles exhibited reduced protein concentration, increased water content, and lower kinase mRNA. These polar bears increased their feeding and activity in the spring when seals became more readily available to them. This increase in feeding initiated a period of muscle recovery.

During the following ice melt of late summer, nearly 30 percent of the SBS polar bears abanded retreating ice for the land dwelling animals. In August, the shore bears exhibited no muscle atrophy. This indicated that the bears had fully recovered from food deprivation in the winter. These individuals were found to eat whale carcasses during October, and they had retained good muscle condition because of this. In contrast, nearly 70 percent of SBS bears follow the ice north in the late summer. This takes bears to an area of deep water and less prey. These bears fast, and by October, they exhibited muscle protein loss and rapid changes of myosin because of their reduced activity.

In summary, these findings indicate that unlike other bears during winter hibernation, polar bears without food in summer cannot escape muscle atrophy. Prolonged summer fasting resulting from climate change-induced ice loss creates an increased risk of greater atrophy and reduced abilities to hunt and travel.

Whiteman, J.P., Harlow, H. J., Durner, G.M., Regehr, E. V., Rourke, B.C., Robles, M., ... Ben-David, M. (2017). Polar bears experience skeletal muscle atrophy in response to food deprivation and reduced activity in winter and summer. Conservation Physiology, 5(1), cox049. http://doi.org/10.1093/conphys/cox049   https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5550809/#cox049C64

Sea Star Wasting Disease in Southwest Alaska

Sea stars, a keystone species and alpha predator in the oceans circle of life, are in danger. There have been large mortality events in sea star populations in the past, and it seems it may be happening again. The sea stars' food, mussels, multiply without being eaten, changing the habitat if sea stars were to leave. This danger to the sea stars is called Sea Star Wasting Disease (SSWD), and it is an epidemic. It is very difficult, if not impossible, to filter out of water. The disease is viral, not being filtered by a 0.22 µm filter. At least 20 species of sea stars are affected by the disease, and high mortality has been experienced in the United States west coast. Several locations in southeast Alaska, Western Prince William Sound, and Kachemak Bay have experienced the disease. Stars often lose arms when infected and die within a few days of exhibiting symptoms. 

Figure 2: Sites that were surveyed in Prince William Sound (1) and National Parks that border the Northern Gulf of Alaska (1), Kachemak Bay (2), and the Western Aleutian Islands (3).

The National Park Service, U.S. Geological Survey, UAF, NOAA, and GulfWatch Alaska began looking for the disease together in 2014, in southcentral Alaska. Researchers searched for the disease both in long-term monitoring sites and outside the boundaries of the long-term monitoring, in the Western Aleutian Islands.

Figure 3: GulfWatch Alaska long-term monitoring sites. Kenai Fjords NP surveyed in 2014, Prince William Sound surveyed in 2015

Nine of 1,588 sea stars across 30 sites were found to be infected with SSWD in 2014. All nine were found in Kenai Fjords National Park. In 2015, 69 of 2,016 observed sea stars had the disease. Almost all were found in Kachemak Bay. In Prince William Sound, 2 of 884 had the disease, also in 2015. Only 2 sea stars were found exhibiting the disease in the Western Aleutian Islands. Even with the small prevalence increase in 2015, diseased star occurrence is still low compared to the lower 48 and southeast Alaska. More information is needed to determine why Kachemak Bay harbored the most sea stars exhibiting the disease.

https://www.nps.gov/articles/sea-star-wasting-disease.htm

And for another blog post on this disease, you can visit this page. 

Flatfish Facts and Indirect Development

Fish like flounders and halibuts are pretty unique, they have both eyes on one side of their body. This allows them to lay flat on the ocean floor and hunt. The interesting thing about this is that these fish aren’t hatched out like this. When first hatched, larval flat fish swim just like any other fish. The eyes of these fish are on either side of their bodies. It isn’t until they undergo metamorphism that the eyes migrate to one side and the fish starts to hang out on the bottom.

For a long time, flatfish seemed to be an exception to evolution. Creationists often used this to “disprove” evolution. This is because no one could find transitional fossils. For a while it seemed that flat fish swam like normal fish and one day they just decided to switch. This changed when someone reexamined previously discovered fossils. Through CT scans it was discovered that these fossils were indeed related to flatfish.

As it turns out flat fish are actually wired to swim flat even when they are just larvae. Fish are able to keep their sense of direction and keep upright by utilizing two organs, their inner ears and their eyes. If their eyes don’t work, they just use their ears. However, flat fish larvae don’t do this. Flat fish have inner ears that are wired for the fish to lay flat, but their eyes are actively keeping them upright. When placed in a pitch black aquarium they are unable to keep upright. They flutter around and swim awkwardly. The video documenting this behavior can be seen by clicking here.  

The reason behind this flatfish behavior is that it prevents the larvae from competing with the adults. If larvae flatfish were on the bottom they would also stand the chance of being consumed by adults. By swimming throughout the water column like a normal fish they are able to better hunt zooplankton.

Source: http://www.pbs.org/wgbh/nova/next/evolution/flatfish-evolution/