Dispersants: A Modern Method For Cleaning Up Oil Spills: Advantages and Disadvantages

By Nicole Suren, SRC intern

In 2010, the Deepwater Horizon oil rig in the depths of the Gulf of Mexico exploded, causing the release of approximately 500 thousand tons of crude oil into the ocean in the second largest oil spill in global history, commonly known as the BP oil spill (Fingas, 2013). This spurred constant media coverage of the spill itself, as well as the cleanup. Oil spill cleanup generally includes several main steps: first the spill is contained using booms, then oil is absorbed on a large scale and skimmed off the ocean surface using boats and large amounts of absorbent materials (often more booms), and finally materials called sorbents are added to the water to remove trace amounts of oil not visible to the naked eye. What was unique about the cleanup of the Deepwater Horizon spill was the incredibly high amount of compounds called dispersants used before and during the official cleanup. Dispersion is when fine droplets of oil are transferred into the water column by wave action or turbulence (Fingas, 2013), removing oil from large slicks at the surface and allowing it to diffuse into deeper parts of the ocean. Dispersants are compounds usually sprayed on oil slicks that promote the formation of small droplets of oil, making dispersion much easier when waves stir up the oil. BP’s heavy use of dispersants was very controversial because dispersants had never been used on such a large scale before. Scientists were uncertain about two main things: 1) the effectiveness of dispersion as a cleanup method, and 2) the potential toxicity of dispersants on their own and/or mixed with oil. Since 2010, a significant amount of progress has been made in determining the effectiveness and toxicity of dispersants.

An airplane spraying dispersants over an oil slick in the Gulf of Mexico (Source: Wikimedia Commons)

An airplane spraying dispersants over an oil slick in the Gulf of Mexico (Source: Wikimedia Commons)

The petroleum industry is confident that dispersants are helpful in cleaning up oil spills (Schrope, 2013). Independent scientists, however, have not found data on the subject to be quite as conclusive. The effectiveness of dispersants depends on a variety of factors, including the type of oil, wave energy, and the amount of dispersant added. Dispersants are never 100% effective, meaning they never cause 100% of the oil from an oil slick to disperse, and even after the initial dispersal has occurred oil can often resurface within a day or so to reform the slick (Fingas, 2013). A study funded by Exxon Mobil describes a very optimistic outlook on the effectiveness of dispersants, saying that oil degrades faster when dispersed than when on shore (degradation by bacteria can occur within a matter of weeks when dispersed, according to the study) and that despite the fact that the dispersants have been shown to remove close to 50% of the oil from an oil slick in EPA-approved lab tests, they remove closer to 95% of oil in large wave tank experiments, leading Exxon’s scientists to believe that EPA estimations of effectiveness greatly underestimate effectiveness in the field (Prince, 2015). Biodegradation is a term that describes the degradation of a material by bacteria, and it is an important concept in relation to the effectiveness of dispersants. Petroleum companies argue that the increased surface area of the oil provided by dispersants allows bacteria greater access to the oil, and therefore biodegradation can occur more quickly (Prince, 2015). However, this assessment does not take into account other materials like tar that are not so easily degraded by bacteria or dispersed. Furthermore, each species of bacteria that can use oil as a food source “can utilize only a few related compounds at most, [so] broad-spectrum degradation does not occur.” (Fingas, 2013) Since degradation is not complete, dispersed oil can then be sequestered at the bottom of the ocean in association with marine snow (organic materials that rain down to the deepest parts of the ocean from the surface). In the presence of dispersants, the amount of marine snow increases dramatically and includes droplets of oil, creating an oily sludge along the ocean floor that is not being degraded by bacteria (Justine S. van Eeenennaam, 2016).

An oil slick untreated by dispersants being cleaned up by skimmer boats. The oil appears very dark and dense from the surface. (Source: Wikimedia Commons)

An oil slick untreated by dispersants being cleaned up by skimmer boats. The oil appears very dark and dense from the surface. (Source: Wikimedia Commons)

An oil slick treated by dispersants. The color of the oil slick appears much lighter from the surface, as a lighter or coffee-colored oil slick is typical of the appearance of dispersed oil. Shown here May 6, 2010, is an aerial view of the Deepwater Horizon oil spill off the coast of Mobile, Ala., taken from a U.S. Coast Guard HC-144 Ocean Sentry aircraft. (U.S. Navy photo by Mass Communication Specialist 1st Class Michael B. Watkins/Released)

An oil slick treated by dispersants. The color of the oil slick appears much lighter from the surface, as a lighter or coffee-colored oil slick is typical of the appearance of dispersed oil. May 6, 2010, is an aerial view of the Deepwater Horizon oil spill off the coast of Mobile, Ala., taken from a U.S. Coast Guard HC-144 Ocean Sentry aircraft. (U.S. Navy photo by Mass Communication Specialist 1st Class Michael B. Watkins/Released)

Not only is this sludge problematic because it is stopping the biodegradation of the oil touted by Exxon’s study, but it is toxic to the organisms that become buried below it (Justine S. van Eeenennaam, 2016). Toxicity of dispersants is a major concern, and several studies have shown that dispersants can compound a toxic situation created by the initial oil spill. First, increased biodegradation is promoted as an ideal solution for oil cleanup facilitated by dispersants, but “the aquatic toxicity of the biodegradation products is sometimes greater than that of the parent compounds,” (Fingas, 2013) so while the dispersants themselves are less toxic than oils by a magnitude of ten (Fingas, 2013), (Prince, 2015), they facilitate the production of more toxic compounds. The Exxon study also claims that dispersants show neither androgen nor estrogen receptor activity (Prince, 2015), meaning that they do not have any effect on regular endocrine function of organisms that consume or come in contact with them. While this is true for the dispersants used in the Deepwater Horizon spill, it is certainly not true for all dispersants (Richard S. Judson, 2010). Many dispersants have also been shown to be lethal to cells in culture, suggesting that they are toxic to larger animals as well (Richard S. Judson, 2010), and they can persist in the water column for years, rather than break down quickly as predicted (Helen K. White, 2014). In short, dispersants are not innocuous tools for cleanup, but have significant environmental effects that cannot be ignored.

The main benefit of dispersants is that their use can prevent large slicks of oil from contaminating coastal ecosystems and adversely affecting sensitive species like sea birds. However, “the use of dispersants remains a trade-off between toxicity to aquatic life and saving birds and shoreline species.” (Fingas, 2013) No matter what, introducing oil to an ecosystem will adversely affect that ecosystem. Because biodegradation is a questionably effective method of oil removal from marine ecosystems, the use of dispersants is essentially humans choosing which ecosystems should be more or less adversely affected, and since we see and interact with coastal ecosystems far more than deep ocean systems it is no surprise that dispersants are used to protect coastlines. However, the ecological impact of degrading deep water ecosystems should not be underestimated, and the effect of dispersants should be monitored long-term to determine whether they should be used again.

Works cited

Fingas, M. (2013). The Basics of Oil Spill Cleanup (3 ed.): CRC Press.

Helen K. White, S. L. L., Sarah J. Harrison, David M. Findley, Yina Liu, Elizabeth B. Kujawinski. (2014). Long-Term Persistance of Dispersants following the Deepwater Horizon Oil Spill. Environmental Science and Technology Letters, 1(7), 295-299.

Justine S. van Eeenennaam, Y. W., Katja C.F. Grolle, Edwin M. Foekema, AlberTinka J. Murk. (2016). Oil spill dispersants induce formation of marine snow by phytoplankton-associated bacteria. Elsevier, 104, 294-302.

Prince, R. C. (2015). Oil Spill Dispersants: Boon or Bane? Environmental Science and Technology, 49(11), 6376-6384.

Richard S. Judson, M. T. M., David M. Reif, Keith A. Houck, Thomas B. Knudsen, Daniel M. Rotroff, Menghand Xia, Srilatha Sakamuru, Ruili Huang, Paul Shinn, Christopher P. Austin, Robert J. Kavlock, David J. Dix. (2010). Analysis of Eight Oil Spill Dispersants Using Rapid, In Vitro Tests for Endocrine and Other Biological Activity. Environmental Science and Technology, 44(15), 5979-5985.

Schrope, M. (2013). Researchers debate oil-spill remedy: oil industry maintains that dispersants should be part of routine response to deep-water blowouts. Nature, 461.

How the geographic range characteristics of a species can affect its conservation

By Elana Rusnak, SRC intern

For many of us scientists, our end goal is conservation of our target species. But what does this mean, and how do we reach these goals? Unfortunately, the answer to this question is not cookie-cutter and requires the input of multiple factors that are not so easily or frequently studied.

At the largest scale, the two broad measurements of geographic range can either provide too much or too little area to be taken into account with regards to protecting a certain species: the extent of occurrence (EOO) and the area of occupancy (AOO). The area of occupancy is all the local area in which a species has been recorded, but only accounts for those localized areas. It may not take into consideration the other hospitable habitat in which individuals simply haven’t been recorded yet. The extent of occurrence is generally larger; as it encompasses all of the area a species could possibly live in, including the space between the recorded individuals (Gaston, 1991). The debate between area of occupancy and extent of occurrence may yield different results, which could cause complications especially with policymakers. While it may seem ideal to cover as much habitat as possible in order to protect a species, it is expensive and requires a lot of enforcement, therefore making it difficult for policymakers to go only on extent of occurrence, since it might include habitat in which the species does not ever reside. However, it also might include area in which a species is migrating, but only during a small part of the year. Why would they want to spend valuable resources to protect an area that does not need to be protected? For example, the White Ibis has year-round populations along the coast of the southern United States and Mexico, as well as a population in northern South America. They are migratory birds, and spend part of the year more inland in the United States, yet it is only a few months of the year (The Cornell Lab of Ornithology, n.d.). If these birds were to become endangered, it is likely that there would be conflicts in determining how much of the yearly range should be protected and why.

The area of occupancy of the White Ibis (Eudocimus albus) (http://geocat.kew.org/editor)

The area of occupancy of the White Ibis (Eudocimus albus) (http://geocat.kew.org/editor)

The extent of occurrence of the White Ibis (Endocimus albus) (http://geocat.kew.org/editor)

The extent of occurrence of the White Ibis (Endocimus albus) (http://geocat.kew.org/editor)

Another factor determining the geographic range is it’s shape. The shape of the geographic range generally constrained from the North and South, or from the East and West. North-South constraints are frequently controlled by the macroclimate (ex. temperature and precipitation), whereas East-West constraints are controlled by topography and availability of suitable habitat (Brown et al., 1996).

Habitat controlled by macroclimate, creating North-South constraints

Habitat controlled by macroclimate, creating North-South constraints

Habitat controlled by topography, creating East-West constraints

Habitat controlled by topography, creating East-West constraints

A problem in present times stems from climate change, which may alter the range shape due to rising temperatures. If a northern bird’s climate suddenly becomes too warm to endure, they may move north in order to compensate. If they were protected in their original habitat, however, the protected area may not cover their new habitat, which may result in population losses. A study done by Møller et al. in 2002 indicates just that: rapid climate changes are associated with dramatic population loss of migratory birds in the Northern Hemisphere. This can be a difficult situation for policymakers, especially if the population is both moving and declining at rapid rates.

Brown et al. further describes the issues of range size and boundary by commenting on the fact that the range edge is never defined. The internal populations of a geographic range tend to be steadier, with larger, constant populations. However, the outer edges of the range are mercurial, which makes it very difficult to determine. This brings us back to the extent of occurrence vs. area of occupancy issue. While individuals are seen at the borders of ranges, or in an excluded area, it does not necessarily mean that they are within the “geographic range” of their species. Since the edges change constantly, policymakers generally need to decide if they want to protect the bulk of the population, or the entire area that they cover.

At the smallest of scales, genetics also plays a role in conservation. While species can change and evolve into different species over very long periods of time, the genetic analysis tools we have today can show that what we thought was one species is actually two. For example, the California newt (Taricha torosa) was divided into two species in 2007. The newts living on the coast keep their Latin name, while the separate species living in the sierra has been named Taricha sierrae. (Kutcha, 2007). Modern speciation events like this can also have an effect on policy. If both species are endangered, policymakers would need to protect both species instead of just the one beforehand, which leads to more money spent and another proposal to be passed.

It is no wonder, now, that policymakers take so long to get a species protected. The factors discussed above are only a few of the considerations they must take into account in order to pass a proposal supporting protecting part of, or the entire geographic range of a species. With all that being said, every bit of science contributing to conservation is important science, which is why we do it.

Literature cited

Brown, J. H., Stevens, G. C., & Kaufman, D. M. (1996). The geographic range: size, shape, boundaries, and internal structure. Annual review of ecology and systematics, 27(1), 597-623.
Gaston, K. J. (1991). How large is a species’ geographic range?. Oikos, 434-438.
Møller, A. P., Rubolini, D., & Lehikoinen, E. (2008). Populations of migratory bird species that did not show a phenological response to climate change are declining. Proceedings of the National Academy of Sciences, 105(42), 16195-16200.
Shawn R. Kuchta (2007). “Contact zones and species limits: hybridization between lineages of the California Newt, Taricha torosa, in the southern Sierra Nevada”. Herpetologica. The Herpetologists’ League. 63 (3): 332–350. doi:10.1655/0018-0831(2007)63[332:CZASLH]2.0.CO;2.
The Cornell Lab of Ornithology. (n.d.). White Ibis. Retrieved March 25, 2017, from https://www.allaboutbirds.org/guide/White_Ibis/id

Threats facing South Florida’s coral reefs and possible solutions

By Molly Rickles, SRC intern

Coral reefs are dynamic ecosystems that harbor a quarter of all marine species while only occupying 0.2% of the world’s oceans (Chen, 2015). Coral Reefs are critical to the ocean’s health because of their biodiversity and complex ecosystems. However, climate change and anthropogenic disturbances has had a profound effect on coral reefs worldwide, with many reefs losing over 50% of their coral cover in the last 40 years (Baker, 2014). This is due largely to coral bleaching, a stress response induced by higher temperatures and excess nutrients. Bleaching is episodic, and the most severe events are coupled ocean-atmosphere events (CITE). Increased sea surface temperature causes coral cover to decrease when the temperature is higher than 26.85 degrees Celsius (Chen, 2015). Coral bleaching causes an increase in coral diseases as well as loss of habitat for many marine species. This eventually leads to a decrease in coral cover, which can disrupt the marine ecosystem and negatively impact the environment.

This map shows the location of South Florida’s reef system, which travels all the way down into the Florida Keys. The second image shows Dry Tortugas National Park, TNER is Tortugas North Ecological Reserve, TSER is Tortugas South Ecological Reserve, TBO is Tortugas Bank Open and DRTO is Dry Tortugas National Park. (Ault, 2013)

This map shows the location of South Florida’s reef system, which travels all the way down into the Florida Keys. The second image shows Dry Tortugas National Park, TNER is Tortugas North Ecological Reserve, TSER is Tortugas South Ecological Reserve, TBO is Tortugas Bank Open and DRTO is Dry Tortugas National Park. (Ault, 2013)

In addition to coral reefs being ecologically important, they are also economically important. Reefs generate $29.8 billion in global net benefit per year (Chen, 2015). Climate change has caused a decrease in ecotourism, resulting in a decrease in profits from coral reefs. It is estimated that the lost value in terms of global coral reef value could range from $3.95-23.78 billion annually (Chen, 2015). In order for many coastal areas to retain this profit from the reefs, corals must be protected from the harmful effects of climate change.

Florida’s coral reefs are particularly vulnerable to the effects of climate change, due to the high population concentration around the coast and the large amount of pollution in coastal waters. Since 1960, Florida’s population has increased by 379% (Ault, 2013). In addition, Southeast Florida is the 8th most densely populated area in the US (Futch, 2011). Increased population leads to increased pollution and runoff, which can be harmful to reef systems. In addition, large infrastructure projects, pipe systems, and beach nourishment can contribute to stresses on corals, all which occur in Florida. The Florida reef system supports the tourism and fishing industries, making it commercially valuable. Without the reef system, Florida would lose two of its largest income generating industries. It is necessary to implant policies that will protect Florida’s reefs from future destruction in order to support the tourism industry as well as to protect the ecosystem.

Another threat facing South Florida’s reefs is from sewage and waste runoff. Due to an increased population, the increased amount of sewage produced is something that the septic systems are not always prepared for. This leads to excess runoff. Water, sponge and coral samples were collected off of the Southeast Florida reef tract and noroviruses were detected in 31% of samples (Futch, 2011). Runoff is particularly dangerous because of wildlife contamination, which has already been observed, but also because excess nutrients in the water cause lead to algal blooms, which can then cause coral bleaching events (Futch, 2011).

This image show various types of corals as they were placed on reefs in South Florida to test the ability of the reef to recruit new corals to add to its growth. (Woesik, 2014)

This image show various types of corals as they were placed on reefs in South Florida to test the ability of the reef to recruit new corals to add to its growth. (Woesik, 2014)

Through the use of monitoring systems all throughout South Florida and the Florida Keys, it has been determined that there has been a 44% decline in coral cover since 1996. This shows that there is a dire need to protect Florida’s reef systems. There are various strategies that have been tested to see what works to preserve coral reefs. Often times, management policies are most successful in dealing with marine ecosystems, since they are generally difficult to directly monitor. One such strategy is the use of a marine protected area (MPA). Marine protected areas are generally very successful, and reefs in MPA’s normally show an increase in size, adult abundance and occupancy rates among reef fish (Ault, 2013). This strategy is especially important in Florida because of the large fishing industry. Intensive fishing has diminished top trophic levels, which affects the entire ecosystem’s balance (Ault, 2013). With the main goal of protecting coral reefs, MPA’s also make the entire ecosystem healthier and prevent unsustainable fishing. Environmental policies that limit the number of fish taken from a reef or limit the boating activity in a certain area are very effective at limiting the human disturbances on coral reefs, and can help marine ecosystems recover from anthropogenic disturbances.

In addition, coral recruitment has been used to regrow portions of bleached reefs. This was done in the Florida Keys and Dry Tortugas National Park. However, the results were not promising. Because of already present stressors such as pollution and warm temperatures, most of the corals did not survive once they were deployed on the reef. These results indicate that coral reefs have slow recovery times after bleaching events or environmental stressors (Woesik, 2014).

Coral reefs are vital to the health of the oceans. Without them, many marine species would be critically threatened. It is necessary to protect the reefs that are alive now to ensure their survival in the future. By implementing management policies, it is possible to protect the reefs from further anthropogenic disturbances, and allow them to recover from already-present stressors. If the health of coral reefs in South Florida increase, then Florida will not only benefit economically, but ecologically with improved marine ecosystems.

Works Cited

Ault, J. S., Smith, S. G., Bohnsack, J. A., Luo, J., Zurcher, N., Mcclellan, D. B., . . . Causey, B. (2013). Assessing coral reef fish population and community changes in response to marine reserves in the Dry Tortugas, Florida, USA. Fisheries Research, 144, 28-37. doi:10.1016/j.fishres.2012.10.007

Futch, J. C., Griffin, D. W., Banks, K., & Lipp, E. K. (2011). Evaluation of sewage source and fate on southeast Florida coastal reefs. Marine Pollution Bulletin, 62(11), 2308-2316. doi:10.1016/j.marpolbul.2011.08.046

Woesik, R. V., Scott, W. J., & Aronson, R. B. (2014). Lost opportunities: Coral recruitment does not translate to reef recovery in the Florida Keys. Marine Pollution Bulletin, 88(1-2), 110-117. doi:10.1016/j.marpolbul.2014.09.017

Chen, P., Chen, C., Chu, L., & Mccarl, B. (2015). Evaluating the economic damage of climate change on global coral reefs. Global Environmental Change, 30, 12-20. doi:10.1016/j.gloenvcha.2014.10.011

Baker, A. C., Glynn, P. W., & Riegl, B. (2008). Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook. Estuarine, Coastal and Shelf Science, 80(4), 435-471. doi:10.1016/j.ecss.2008.09.003

 

My, What Big Teeth You Have!

By Jennifer Simms, SRC outreach intern

The word “shark” conjures up many pictures in ones’ mind. Images range from majestic swimmers in a deep, blue ocean to the lethal rows of teeth easily seen protruding when a shark swims. These teeth serve multiple purposes for both the shark and scientist alike. Scientists study the morphology of teeth, mostly in mammals, to understand how the shape of teeth provides function/purpose to an animal. Most morphological teeth studies have been conducted on the extant (living) mammals and the ancient (well preserved fossilized tooth record). And the tooth can be considered the “fork and knife” for the shark, however, not all teeth are created equal.

In 2010, Lisa Whitenack and Philip J. Motta conducted a study on both living and fossilized species of shark to unlock clues about the variability of teeth shape, structure and function. The authors pointed out that a majority of previous studies have looked at musculature and jaw movement. Whitenack and Motta focused on several goals through the paper focusing on force, cutting performance, and diet. Although the article provided insight into tooth morphology, its focus was on the results found in living sharks.

To address their goals, the authors investigated three general categories of extant teeth from ten species of sharks; 1) tearing-type, 2) cutting-type and 3) cutting–clutching-type. Through a series of tests, they compared teeth morphology and function (functional categories mentioned above) on a variety of soft and hard body prey items, such as fish (soft body) and crustaceans (hard body). Tooth performance was tested by puncture and unidirectional draw. Puncture occurs when a tooth enters at a 90 degree angle to the prey item such as during biting. Unidirectional draw assumes the tooth has already entered the prey, and involves lateral movement through tissue and may occur, for instance, during head shaking.

The results showed differences in puncturing success that occurred among a variety of prey items, indicating that not all ‘soft’ prey items are alike. In some cases, broader triangular teeth (Tooth F, H, and C shown in the chart below) were less effective at puncturing prey than narrow-cusped teeth as shown in the image below (Tooth I, A, and J). Overall, all teeth shapes were able to puncture prey, but not all teeth were designed for tearing flesh in a unidirectional draw or for holding prey in the cutting/clutching role.

Does this mean that scientists can “read” shark teeth and generally determine the function of their teeth? Yes! Here are some examples of sharks that fall into one of the three teeth groups mentioned above, tearing, cutting, cutting-clutching. The Bull, White, and Blue shark all have triangular shaped teeth with serrated edges. This shaped was proven in the article to be less effective at puncturing prey. Instead, the serrated edges of the tooth are like a steak knife and the shark to tear chunks for flesh as outlined in the unidirectional draw. On the other hand, teeth that are narrow and pointy are used for holding prey, such as slippery fish, in the mouth. Sharks with this teeth design are Lemon, Shortfin Mako, and Blacktip shark.

Perhaps now, the word “shark” will inspire the reader to take a closer look at shark teeth design, whether they are observed as fossils on the beach, seen on TV, or view in person in the wild. Practice “reading” shark teeth by using the image below and determine if the shark tooth is designed for cutting and tearing large pieces from prey or is the tooth created to hold prey, such as a whole fish, in the mouth. Those rows and rows of teeth, or fork and knife, are not created equal.

Works Cited

Whitenack, Lisa B., and Philip J. Motta. “Performance of Shark Teeth during Puncture and Draw: Implications for the Mechanics of Cutting.” Biological Journal of the Linnean Society 100.2 (2010): 271-86. Web.

A challenge for a better future: Bringing life back to dead zones

By Arina Favilla, SRC intern

The diversity of life in the ocean, from shallow reefs to deep-sea canyons, is evidence that marine species can successfully adapt to a variety of environments, including low oxygen conditions. For example, in certain places in the world, natural coastal upwelling of nutrients leads to high productivity, which depletes the dissolved oxygen in the water. In these oxygen minimum zones, the benthic fauna have adapted to extremely low levels of dissolved oxygen (0.1 ml of O2/liter) (Diaz et al. 2008). But, what happens when the environment changes drastically in a short period of time? Can the animals adapt fast enough to survive?

Conceptual graph of how ecosystem energy dynamics change due to changes in oxygen levels. In normal ranges (normoxia), 25-75% of energy is transferred from the benthos to higher-level organisms. As hypoxic conditions emerge, an increased amount of energy is transferred to higher-level organisms. However, the ecosystem cannot support this if hypoxia persists and eventually, microbes process most of the energy as hydrogen sulfide, which further enhances anoxic conditions (Diaz et al. 2008).

Conceptual graph of how ecosystem energy dynamics change due to changes in oxygen levels. In normal ranges (normoxia), 25-75% of energy is transferred from the benthos to higher-level organisms. As hypoxic conditions emerge, an increased amount of energy is transferred to higher-level organisms. However, the ecosystem cannot support this if hypoxia persists and eventually, microbes process most of the energy as hydrogen sulfide, which further enhances anoxic conditions (Diaz et al. 2008).

In the case of hypoxic dead zones, the answer is usually no. When hypoxic conditions (i.e. low dissolved oxygen) emerge quickly due to unnatural causes, dead zones will likely result. The low oxygen conditions can no longer support life, causing mass mortality and drastic changes in community structure (Diaz et al. 2008). Not only do hypoxic zones cause mortality of benthic fauna, but it also propagates its effects to upper trophic levels, including important commercial species (Vaquer-Sunyer et al. 2008) (Figure 1).

A major culprit contributing to the increase in hypoxic zones worldwide is eutrophication. Eutrophication occurs when river runoff brings excessive amounts of nutrients, such as nitrogen and phosphorous from agriculture fertilizers, into the ocean causing increased primary productivity, such as phytoplankton blooms. When organic matter builds up in the ecosystem faster than it can be decomposed, hypoxic conditions develop. If the physical dynamics of the area promote stratification so that the upper oxygenated water in contact with air does not mix with the bottom water, the region will be especially prone to hypoxia (Diaz 2001).

The locations of hypoxic systems match the global human footprint, which is expressed as a normalized percentage, particularly for the Northern Hemisphere where more information is available (Diaz et al. 2008).

The locations of hypoxic systems match the global human footprint, which is expressed as a normalized percentage, particularly for the Northern Hemisphere where more information is available (Diaz et al. 2008).

Hypoxic zones tend to be around coastal population centers, where the human footprint is greater (Figure 2). The number of dead zones has doubled each decade since the 1960s, now reaching over 400 zones that cover a combined area of 245,000 km2—an area as large as Oregon (Diaz et al. 2008). This is because increased population and living standards have led to agricultural and industrial needs that depend on fertilizers and/or produce other nutrients in the process (Diaz 2001).

While each hypoxic zone is unique in regards to its persistence (e.g. seasonal, periodic, or persistent) and other ambient and physical conditions, a lot can be learned from the successes and failures of one region. Declining oxygen concentrations has been observed in the Black Sea starting in the 1940s and 1950s due to the expansion of agriculture and industry, particularly in the Danube watershed (Diaz et al. 2008, Rabotyagov et al. 2014). The Black Sea hypoxic zone is part of only 8% of dead zones that experience severe, persistent hypoxia and the zone has increased from 3,500 km2 in 1973 to 40,000 km2 in the late 1980s, making it at one point the second largest hypoxic region (Rabotyagov et al. 2014, Diaz et al. 2016). This led to severe problems for the commercial bottom fisheries where only 6 of the 26 highly valued fish species were able to continue to support a fishery (Diaz 2001). It became clear that an intervention was needed—which is exactly what they did. In the early 1990s, the economies bordering the Black Sea agreed to reduce fertilizer use, and by 1995, the hypoxic zone had practically vanished (Rabotyagov et al. 2014). This case exemplifies the effects of excessive nutrients and subsequently reduced nutrient influxes on hypoxic conditions.

Eutrophication is projected to continue to increase, and climate change is expected to further exacerbate the spreading of hypoxic zones through a multitude of pathways. Models predict that climate change may increase stratification and warming, change rainfall patterns, and enhance freshwater river discharge and nutrient flux from agriculture into coastal regions (Diaz et al. 2008, further reading Altieri et al. 2014). Therefore, actions should be taken to limit the expansion of these dead zones. While it is unrealistic to reach nutrient levels of preindustrial times, more regions should attempt to reduce their nutrient inputs in hopes of seeing positive effects similar to that of the Black Sea (Diaz et al. 2008). More importantly, different states and countries must collaborate on the effort—if areas near the coast reduce their nutrient inputs while areas upstream of a river continue to contribute their same nutrient loads, the efforts of the coastal communities would be futile. The importance and sensitivity of this environmental issue is highlighted in the following quote: “There is no other [environmental] variable of such ecological importance to coastal marine ecosystems that has changed so drastically over such a short time as [dissolved oxygen]” (Diaz et al. 2008).

Just as you and I need oxygen to survive, marine organisms require sufficient amounts of dissolved oxygen in the ocean to live. Imagine hiking up to an altitude where it becomes difficult to breathe because the air is “thinner” (i.e. the partial pressure of oxygen is reduced), and feeling the symptoms of altitude sickness, which include those similar to a hangover, but never being able to come back down and recover. When marine populations are starved of oxygen, not only do they suffer, but the entire ecosystem also feels the effects, including us humans who depend on marine resources for food and much more. Therefore, finding a way to bring life back to dead zones and prevent new ones from forming is crucial to preserve our oceans.

 

Works cited

Altieri, A. H., & Gedan, K. B. 2014. Climate change and dead zones. Global Change Biology 21: 1395-1406.

Diaz, R. J. 2001. Overview of Hypoxia around the World. Journal of Environment Quality 30: 275.

Diaz, R. J., & Rosenberg, R. 2008. Spreading Dead Zones and Consequences for Marine Ecosystems. Science 321: 926-929.

Diaz, R., & Rosenberg, R. 2016. Threats To Coastal Ocean Sustainability: Current Status And Future Trends In Dead Zones. International Seminars on Nuclear War and Planetary Emergencies 48th Session. 

Rabotyagov, S. S., Kling, C. L., Gassman, P. W., Rabalais, N. N., & Turner, R. E. 2014. The Economics of Dead Zones: Causes, Impacts, Policy Challenges, and a Model of the Gulf of Mexico Hypoxic Zone. Review of Environmental Economics and Policy 8: 58-79.

Vaquer-Sunyer, R., & Duarte, C. M. 2008. Thresholds of hypoxia for marine biodiversity. Proceedings of the National Academy of Sciences 105: 15452-15457.

Effects of Climate Change on the invasive Lionfish: Pterois volitans and Pterois miles

By Patricia Albano, SRC intern

Across the globe, marine environments face anthropogenic stressors that threaten their continued survival. Throughout the world’s oceans, a colorful variety of marine communities exist, each with their own native flora and fauna and unique interspecific and intraspecific interactions. When the balance of these ecosystems is altered, negative ecological impacts can follow. The introduction of invasive species into marine communities in which they do not belong can have significant and long-lasting effects on the health, balance, and abundance of native species in the environment (Carlton, 2000). A well-known culprit, the Indo-Pacific lionfish, Pterois volitans or Pterois miles, has invaded the Western Atlantic ocean where it voraciously preys upon native species and reproduces in abundance. Via the reports of various divers, researchers, and fishing operations, it has been determined that the lionfish distribution along the east coast of North America may span from the Florida Keys to Cape Hatteras, North Carolina and include water depths up to 100m (Whitfield et al., 2002). For such invasive species to thrive in non-native ecosystems, several environmental factors come into play, one of the most notable being climate change. It has already been noted that increasing global ocean temperatures can predictably influence the growth and reproduction of marine fish and invertebrates (Brown et al., 2004). Consequently, increased growth and reproduction rates can directly impact population increases. For native species, this would be less of a concern; however, with the destructive influence that invasive species propose, it has become an epidemic. All of this considered, it can be concluded that climate change likely propagates invasions rather than halting them, especially in the case of lionfish (Côté and Green, 2012).

Indo-Pacific Lionfish: Pterois volitans. Popular in the aquarium trade for their superfluous body shape and coloration, Indo-Pacific lionfish pose a threat to invaded areas due to their voracious appetite and extreme reproductive capacity.  Image source: Wikimedia Commons

Indo-Pacific Lionfish: Pterois volitans. Popular in the aquarium trade for their superfluous body shape and coloration, Indo-Pacific lionfish pose a threat to invaded areas due to their voracious appetite and extreme reproductive capacity. Image source: Wikimedia Commons

After being introduced into coastal Florida waters in the 1980s through the aquarium trade, the Indo-Pacific lionfish has taken over the entire Caribbean basin and much of the Western Atlantic, infiltrating coral reefs, seagrass beds, and mangrove communities. It is predicted that lionfish life-history and behavior are intrinsically temperature-dependent based on observations of their reproduction and diet (Côté and Green, 2012). In a study concerning the effects of warming temperature on lionfish pelagic larval duration and dispersal and predation rate, it was found that increased temperatures set the perfect stage for an invasion to thrive. Due to their generalist diet, ability to expand their introduced range, and high fecundity, lionfish will continue to remain a threat in the Western Atlantic (Côté and Green, 2012). Increased temperature was predicted to drive the present imbalance between prey consumption and production rates, resulting in the lionfish having the upper hand in the ordeal. As oceans continue to warm, the lionfish will be able to expand its range to areas that are currently too cold for their inhabitation, specifically as the 10°C isotherm expands north and south in both of the hemispheres (Morris and Whitfield, 2009; Côté and Green, 2012). Finally, lionfish spend less time in the pelagic larval stage with increased ocean temperature, leading to growth of populations as temperatures continue to rise (Côté and Green, 2012).

Temperature anomaly of average global sea surface temperature from 1880-2015.  This increased warming trend is predicted to continue and proceed to facilitate the lionfish invasion into regions further north and south of the equator. Figure source: United States Environmental Protection Agency (https://www.epa.gov/climate-indicators/climate-change-indicators-sea-surface-temperature)

Temperature anomaly of average global sea surface temperature from 1880-2015. This increased warming trend is predicted to continue and proceed to facilitate the lionfish invasion into regions further north and south of the equator. Figure source: United States Environmental Protection Agency (https://www.epa.gov/climate-indicators/climate-change-indicators-sea-surface-temperature)

According to the National Ocean and Atmospheric Administration (NOAA), average global sea surface temperature has risen at an average rate of 0.13°F per decade since 1901 (Figure 1). Although this may seem like an insignificant increase, at this rate, global average sea surface temperature is predicted to hover around a 1°F anomaly from historical average by the year 2020, and steadily increase from there. With these elevated sea water temperatures, lionfish will continue to capitalize on climate change if this pattern is not halted. For the time being, one of the only limiting factors that the lionfish invasion faces is the fish’s intolerance to minimum water temperatures of some of its extended ranges away from the equator during the winter time (Kimball et al., 2004). However, this temperature anomaly pattern could facilitate expansion of the depth and latitude range of these invaders. In a study conducted on thermal tolerance and potential distribution of lionfish, it was found that the mean chronic lethal temperature for lionfish was 10°C and mean temperature for them to cease feeding was 16.1°C (Kimball et al., 2004). The average temperature for Florida waters during the winter time is 22°C and about 10°C at the northern limit that lionfish range, Cape Hatteras. These average water temperatures and this study show that as water temperatures continue to increase, the range of lionfish will continue to expand.

Overall, it can be deduced that climate change proposes a large threat to marine communities, especially where invasive species are concerned. As temperatures continue to rise above the norm, lionfish will extend their invasion further along the Western Atlantic.

Works Cited

Brown JH, Gillooly JF, Allen AP, Savage VM, West GB, 2004. Toward a metabolic theory of ecology. Ecology 85: 1771–1789.

Carlton JT, 2000. Global change and biological invasions in the oceans. In: Mooney A, Hobbs RJ ed. Invasive Species in a Changing World. Covelo, Calif ornia: Island Press, 31–53.

Côté IM, Green SJ (2012) Potential effects of climate change on a marine invasion: The importance of current context. Curr Zool 58:1–8

Kimball ME, Miller JM, Whitfield PE, Hare JA (2004) Thermal tolerance and potential distribution of invasive lionfish (Pterois volitans/miles complex) on the east coast of the United States. Marine Ecology Progress Series 283:269–278

Morris JAJ, Whitfield PE, 2009. Biology, ecology, control and management of the invasive I ndo-Pacific lionfish: An updated integrated assessment. NOA A Technical Memorandum NOS NCCOS 99.

Whitfield PE, Gardner T, Vives SP, Gilligan MR, Courtenay WR, Jr., Ray GC, Hare JA (2002) Biological invasion of the Indo-Pacific lionfish Pterois volitans along the Atlantic coast of North America. Mar Ecol Prog Ser 235:289–297