Tsunami-driven rafting: Transoceanic species dispersal and implications for marine biogeography

By Grant Voirol, SRC intern

On March 11, 2011, the Tohoku coast of Honshu, Japan was struck by a tsunami reaching heights of 125 feet. The tsunami caused widespread destruction along the coast, casting boats, docks, and other objects into the western Pacific Ocean. Many of these items were homes for marine communities or were soon colonized, turning these floating debris into life support rafts traveling across the Pacific. Circulating through the ocean, these rafts eventually began to make landfall on the western coast of North America and Hawaii (Figure 1). In the five years following the arrival of the first transoceanic rafts in 2012, scientists conducted a massive scale collection of biodiversity levels supported by each of piece of debris found along the coasts of Alaska, British Columbia, Washington, Oregon, California, and Hawaii.

[Figure 1.] Major ocean currents in Northern Pacific Ocean showing the path of that marine debris took following the 2011 tsunami.
(Source: Carlton et al. 2017)

In order to sample the widest range possible, a large-scale coordination took place between the scientists conducting the study and local, state, and federal officials, as well as volunteer beach clean up groups to collect and photograph samples. In total, 634 pieces of Japanese debris were assessed for animal diversity. Scientists found 289 different species of animals on the debris, mostly consisting of invertebrates such as mollusks, crustaceans, worms, and other fouling organisms.  Researchers even found fish native to coastal Japan living in the innards of fishing vessels (Figure 2). Fishing vessels and other larger debris such as docks were able to support much more diverse communities of organisms, while smaller debris such as crates or beams might only support few or one species. Additionally, multiple generations of the same species were found, indicating that these transoceanic rafts are suitable for reproduction to take place.

[Figure 2.] Examples of organisms found by researchers. (A) Dock found with high species richness, (B) Fishing vessel fouled with barnacles, (C) Japanese barred knifejaw fish found in a large fishing vessel, (D) wood beam bored by shipworms, (E) buoy with a single limpet, (F) buoy covered by bryozoans.
(Source: Carlton et al. 2017)

What this study shows is that man-made marine debris is a highly effective way to introduce nonnative species to coastal environments. While still present, very few rafts were composed mainly of natural materials such as wood. Mainly these rafts were consisted of metal, plastics, and fiberglass. These materials can survive for much longer periods in the ocean and therefore represent new ways for species to spread their geographic range. Additionally, the way that transoceanic rafts work increases their chances of spreading organisms from far off ecosystems. Firstly, they move slowly which lets the organisms that are along for the ride acclimatize to their new environment. Secondly, rafts can support large networks of reproducing organisms as opposed to planktonic juvenile organisms that need to grow to reproductive size. Finally, these rafts have an incredibly large geographic range, being able to make landfall at any point along the coast. Previous dispersal methods such as transport by ballast water confine nonnative organisms to harbors. What this means is that as we increase our use of non-biodegradable materials in coastal cities that can be swept away be storm, we are increasing the chances of species dispersal with consequences that we cannot fully predict.


Carlton, J.T., Chapman, J.W., Geller, J.B., Miller, J.A., Carlton, D.A., McCuller, M.I., Treneman, N.C., Steves, B.P., Ruiz, G.M. “Tsunami-Driven Rafting: Transoceanic Species Dispersal and Implications for Marine Biogeography.” Science 357.6358 (2017): 1402–1406.

Declining oxygen in the global ocean and coastal waters: A summary

By Abby Tinari, SRC intern

Oxygen is not only important for life on Earth, but it also regulates major nutrient and carbon cycles globally. All the past major extinction events have been associated with oxygen-deficient oceans and warm climates. Over the last 50 years, the anoxic (no oxygen) volume of the ocean has quadrupled, and hypoxic (low oxygen) zones have increased by the size of the European Union (Figure 1). In the summary below, Breitburg et al 2018 describe the causes (Global warming and nutrient enrichment), good and bad effects and responses (effects of ocean deoxygenation & biological responses and Biogeochemistry), current predictions and models (predicting oxygen decline), and some solutions that are available (reducing deoxygenation and its negative effects).

Figure 1 Breitburg et al 2018

 Global warming

Warming waters reduce oxygens ability to dissolve into water. This decrease in solubility contributes ~15% of the total oxygen loss. Metabolic rates also influence the total oxygen loss. Higher metabolic rates, which are caused by warmer temperatures, require organisms to consume more oxygen, leading to higher CO2 production, and more acidic waters. More acidic waters harms and decreases organism’s ability to efficiently use dissolved oxygen. The other 85% of total oxygen loss comes from the reduction of ventilation, the transport of oxygen into the interior of the ocean, and the supply of nutrients that control organic matter production. The low oxygen predicted with global warming may have a human benefit for a time, winds are expected to be strengthened and in turn increase upwelling along coasts. The increase in upwelling may see an increase in commercially popular marine organisms. But upwelling brings hypoxic water to the surface, adding to the deoxygenation problem. Just like in the open ocean, water stratification and a decrease oxygen solubility are expected to increase in coastal waters but at a faster rate.

Nutrient enrichment of coastal waters

Nutrient loads entering coastal waters have increased by 43% from 1970 to 2000 with the increase in human population and agricultural production. The excess nutrients (Nitrogen and Phosphorus) cause eutrophication. Eutrophication encourages algae growth and ultimately causes a decrease in oxygen through excess decomposition (which consumes oxygen). Low vertical exchange and long retention times further exacerbate the hypoxic conditions in coastal waters.

Effects of ocean deoxygenation & biological responses

Effects of low oxygen will occur in organisms in a variety of ways, as they have a wide range of oxygen tolerances. Life processes in aerobic organisms from genes to entire ecosystems depend on oxygen. Different exposures to low oxygen levels can reduce survival and slow growth, impair reproduction, induce genetic changes in future generations, and alter immune responses. Organisms that depend on oxygen gradients to migrate may be constrained, effecting not only those organisms, but also their predators. Alternatively, organisms that can tolerate hypoxic waters may better avoid predators and expand their ranges. Mobile organisms, such as fish and invertebrates are expected to shift poleward and to deeper waters with ocean warming.

Figure 2 Breitburg et al 2018


Since many nutrient-cycling processes are dependent on oxygen, small changes in local low oxygen areas can influence productivity, nutrient (N, P, Fe and many others) budgets and trace metal distributions on global scales. Many of the by-products of low oxygen levels are toxic or greenhouse gases, i.e. hydrogen sulfide, nitrous oxide, cyanobacterial blooms etc.

Predicting oxygen decline

Reliable numerical models to predict different scenarios on the effects of climate change and eutrophication in waters around the world are the basis of marine ecosystem management. The models agree on the amount of oxygen lost by the end of the century (a few percent) which could have substantial effects on abiotic and biotic systems. But where the low oxygen zones will be located is under debate, limiting our ability to predict and create management plans for these areas. These complicated models need to predict a multitude of factors from human population growth rates to the timing and intensity of precipitation and warming and 3-D water movement and quality models to the effects of education and income on sanitation and animal protein use. All aspects of life need to be integrated into the models to predict the effects.

Figure 3 Breitburg et al 2018

Reducing deoxygenation and its negative effects

Efforts need to be made on local, national, and global scales to limit declines, restore, and support the resilience of ecosystems that have dealt with unusual levels of oxygen. Many of the solutions to deoxygenation can substantially benefit society, i.e. improved sanitation can reduce nutrient loads in waters and help increase human health.  Some of the solutions will take time, i.e. oxygen demand from sediment can take decades to decrease, but other methods such as nutrient reduction in the Chesapeake Bay have already produced results not seen since 1984. To create an ecologically and economically effective plan, a combination of methods must be used and stakeholders from all parts of society (scientist, government, industry and the public) must be involved.

Works Cited

Breitburg, D., L. A. Levin, A. Oschlies, M. Grégoire, F. P. Chavez, D. J. Conley, V. Garçon, D. Gilbert, D. Gutiérrez and K. Isensee (2018). “Declining oxygen in the global ocean and coastal waters.” Science 359(6371): eaam7240.

Expanding fisheries management and marine conservation across borders

By Mitchell Rider, SRC master’s student

In 2006, the U.S. Congress reformed the Magnuson-Stevens Fishery Conservation and Management Act (MSA) – an act that directs marine fisheries management – by amending the High Seas Driftnet Fishing Moratorium Protection Act. This new amendment directed Secretary of Commerce to recognize foreign nations identified as participating in the bycatch of protected living marine resources (PLMRs) by including them in a biennial report presented to Congress. The responsibility of identifying participating foreign nations was delegated to NOAA Fisheries. The procedure for identification was delineated as follows: Once participation in bycatch is confirmed, NOAA must consult with the participating nation to inform them about the MRA, define the requirements of meeting positive certification, offer help in meeting that certification, and outline the consequences of receiving negative certification. Positive certification is met when a management plan to regulate bycatch is implemented and yields results comparable to that of the U.S. Negative certification is received when the participating nation fails to do so, and this is met with U.S. sanctions.

Image of a loggerhead turtle escaping a net equipped with a turtle excluder device (TED). [By NOAA – http://www.nmfs.noaa.gov/pr/images/turtles/loggerhead_ted-noaa.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=24936235]

Mexico was the first nation to be recognized for PLMR bycatch and was recognized specifically for the bycatch of an internationally shared PLMR, the North Pacific loggerhead turtle in 2013. In their paper, Senko et al. (2017) illustrates the effects of identifying Mexico for bycatch of the North Pacific loggerhead turtle and potential recommendations for improving management and its implementation.

Loggerheads nest along the coast of Japan, but perform developmental migrations taking them into the North Pacific basin where a proportion of the population recruits into the Gulf of Ulloa along the Pacific coast of Baja California Sur. It is in this location off the coast of Mexico loggerheads are subjected to high rates of bycatch by bottom-set nets targeting commercially important species like halibut. Mexico was identified after the concurrent discovery of >1,000 beached loggerhead carcasses and 88 loggerheads captured in bottom-set nets.

Upon identification, Mexico initially denied the bycatch of loggerheads even though they had agreed to reduce bycatch rates. At this point, the Mexican government disregarded its collaboration with the U.S. to test turtle friendly fishing gear, and instead proposed a plan to establish a protected area for the loggerhead within the Gulf of Ulloa. In response, the U.S. decided, as a compromise, to grant Mexico more time to establish this protected area. Instead, Mexico utilized this time to establish a partial fishing reserve. Since Mexico did not comply with U.S. regulation standards, the U.S. gave Mexico a negative certification. Almost a year later, Mexico established new loggerhead bycatch control measures, which ultimately lead the U.S. to grant a positive certification.

A map of Mexico where the Baja California Sur (BCS) is shaded in with green.[CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=63837]

From this case, Senko et al. proposed policy recommendations to improve the processes of identification and consultation of the new amendment. Because of the Gulf of Ulloa closure and the trade sanctions, thousands of fishermen did not receive an income for one summer. Therefore, the U.S. should consider the potential socioeconomic and political effects that result from these threatened trade sanctions. In addition, there should be a universal form of reporting bycatch data from each country so fewer countries that do report their data are not as dissected as ones that do not do this. Finally, the authors suggested NOAA Fisheries be provided with more resources to create better collaborative relationship with the identified nation. In this case, a better relationship with Mexico may have prevented them from denying allegations initially, thus delaying the process of management implication. If these recommendations are implemented into the identification and consultations processes, the U.S. could avoid creating socioeconomic and political hardships.

Works cited

Senko, J., L. D. Jenkins, and S. H. Peckham. 2017. At loggerheads over international bycatch: Initial effects of a unilaterally imposed bycatch reduction policy. Marine Policy 76:200-209.

Adaptation or Extinction: the Necessity of Fish Reproductive Acclimation in the Face of Climate Change

By Trish Albano, SRC intern

In an ever-changing marine environment, organisms must respond to their surroundings in order to remain reproductively successful.  However, with the current rate of climate change predicted to raise sea surface temperatures by approximately 3°C by the year 2100 (Collins et al., 2013), species are faced with a choice: shift geographic range or gradually adapt to changes cross-generationally.  In fishes, reproductive regulation and temperature are innately intertwined.  Changes in environmental temperature have the ability to impact the hypothalamo-pituitary-gonadal (HPG) axis in the reproductive system of many species of fish.  This gland controls the regulation of reproductive hormones necessary for reproductive success following a temperature cue.  In a study at James Cook University in Australia, researchers aimed to evaluate if there was a difference in gene expression in adult spiny chromis damselfish (A. polyacanthus) (Image 1) that had different reproductive capabilities as a result of developmental and transgenerational exposure to increased temperature (Veilleux, Donelson, & Munday, 2018).

Image 1. Study species: spiny chromis damselfish (A. Polyanthus). Species of damselfish from the West Pacific (Source: Wikimedia Commons)

Overall, this study’s goal was to assess the potential for reproductive plasticity in the face of increased temperatures. In order to assess if damselfish had partially acclimated reproductive capability, the researchers evaluated gene expression in the fish using a step-wise transgenerational temperature treatment (Donelson et al., 2016) (Figure 1).  It was hypothesized that the expression of reproductive genes would be down-regulated in damselfish who were exposed to the same high temperature levels as their parents.  However, it was also hypothesized that the expression of genes in the step-wise temperature treatment (parents exposed to +1.5°C, offspring exposed to +3.0°C) would be similar to that of the control group (no temperature increase) due to partial acclimation of the reproductive system in response to elevated temperature.

Figure 1. Experimental design of the study showing the control group (no transgenerational temperature increase), developmental (+3.0 degrees C in offspring), step-wise (+1.5 degrees C in parent, + 3.0 degrees C in offspring) and transgenerational (+3.0 degrees C in parent and offspring). Duration of the experiment is shown in the gray bars on the left. (Source: Veilleux, Donelson, & Munday, 2018).

After completing the experiment, it was found that the step-wise treatment group had a comparable proportion of pairs that reproduced to the control group.  On the other hand, pairs that were exposed to an immediate +3.0°C temperature increase (transgenerational and developmental) had fewer and no pairs reproducing successfully.  The results of this experiment support the researcher’s hypothesis that partial reproductive acclimation to elevated temperatures would lead to more reproductive success.  If climate change trends continue to result in increasing environmental temperature, maintaining reproductive success is key to marine species taking the adaptation approach versus changing geographic range.

Works cited 

Collins M, Knutti R, Arblaster J, Dufresne JL, Fichefet T, Friedlingstein P, Gao X, Gutowski WJ, Johns T, Krinner G, et al. (2013) Long-term climate change: projections, commitments and irreversibility. In Stocker TF, Qin D, Plattner GK, Tignor M, Allen SK, Boschung J, et al, eds. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, United Kingdom and New York.


Donelson JM, Wong M, Booth DJ, Munday PL (2016) Transgenerational plasticity of reproduction depends on rate of warming across gen- erations. Evol Appl 9: 1072–1081.

Veilleux HD, Donelson JM, Munday PL (2018) Reproductive gene expression in a coral reef fish exposed to increasing temperature across generations. Conserv Physiol 6(1): cox077; doi:10.1093/conphys/cox077.


Narwhals Display Perplexing Escape Responses to Human-Induced Stress

By Olivia Schuitema, SRC intern

Narwhals (Monodon monoceros) are Arctic marine mammals that have traditionally been relatively isolated from anthropogenic contact, making them particularly vulnerable to disturbance (Williams, 2017). The lack of ecological interference also makes narwhals adequate study organisms regarding anthropogenic effects. With larger declines in Arctic sea ice, narwhals have been increasingly exposed to predation, human hunting and seismic exploration (Williams, 2017). For example, seismic surveys in the Arctic aim to pinpoint fossil fuel reserves and in the process release high-energy noise that can affect marine mammal migration and behavior (Jørgensen, 2013). Scientists aimed to gauge the stress responses of release after entanglement or stranding by monitoring the behavior and the cardiovascular and energetic responses of narwhals inhabiting East Greenland (Williams, 2017).

Figure 1: Study area in eastern Greenland with GPS tracks for five instrumented narwhals, Williams, 2017

When exposed to stressful conditions, animals tend to respond in one of two ways: 1) “fight or flight” reaction; stay to fight the threat or flee from the threat, or 2) freeze reaction; extreme decrease in heart rate. Mammals who flee their situation show signs of tachycardia (elevated heart rate) and increased rates of respiration (Williams, 2017). Conversely, mammals that “freeze” tend to show signs of bradycardia (slowed heart rate) and slowed behavior. These two escape systems stem back to two different anatomical positions in the mammalian brain, making fleeing and freezing simultaneously very unlikely.

Scientists placed electrocardiograph-accelerometer-depth monitors on five narwhals immediately released from entanglement and stranding (Williams, 2017). These devices were attached via suction cup for varying amounts of time (0.4-3 days) and measured heart rate, speed, and depth of the escaping narwhals. The studied organisms showed a paradoxical response upon release; a fleeing response with high stroke frequencies immediately followed by heightened bradycardia (“cardiac freeze”), a freezing response (Williams, 2017). Data also showed that the longer it took to release the entangled narwhals, the more likely they were to undergo cardiac freeze (Williams, 2017). These results show the negative effects of human-induced stress, but also highlight the inconsistencies of marine mammal responses to such stress.

Figure 2: Narwhal with ECG-ACC recorder (Electrocardiograph-accelerometer-depth monitor) on dorsal side of the body, Williams, 2017

The profound melting of sea ice due to climate change has opened up the Arctic to a variety of stressors including human influence. Arctic predators such as killer whales have increased access to Arctic prey items like narwhals (Breed, 2017). More research must be conducted in order to further explore the effects of anthropogenic stress on marine mammals like the narwhal in the Arctic. This example showcases the connection between rise in global temperature and melting sea ice due to climate change. “Climate change” can be a broad and sometimes obscure topic, but as seen by the paradoxical narwhal escape responses, the effects of this phenomena can extend to very specific organisms.

Works Cited

Breed, G., Matthews, C., Marcoux, M., Higdon, J., Leblanc, B., Petersen, S., . . . Ferguson, S. (2017). Sustained disruption of narwhal habitat use and behavior in the presence of Arctic killer whales. Proceedings of the National Academy of Sciences of the United States of America, 114(10), 2628-2633.

Heide-Jørgensen, Hansen, Westdal, Reeves, & Mosbech. (2013). Narwhals and seismic exploration: Is seismic noise increasing the risk of ice entrapments? Biological Conservation, 158, 50-54.

Williams, Terrie M., Blackwell, Susanna B., Richter, Beau, Sinding, Mikkel-Holger S., & Heide-Jorgensen, Mads Peter. (2017). Paradoxical escape responses by narwhals (Monodon monoceros). Science, 358(6368), 1328.

Could Eating Smaller Meals Sometimes Benefit Predators More Than Eating Larger Meals?

By Jessica Daly, SRC intern

Sometimes, predators have the ability to choose what size prey to consume when feeding, but little is known about how this decision is made. Several previous research experiments have examined the relationship between prey size and “predator gape size,” or how long it takes to chase, capture, and consume the food. It has been hypothesized that predators may select their prey in part because of possible effects of prey size on digestion and metabolism, but evidence is required to support this.

Metabolism is the rate at which food is broken down into energy. Aerobic scope (AS) is the difference between an animal’s resting and maximum aerobic metabolism, and tells how well the animal can take in oxygen and provide energy to its cells. The specific dynamic action (SDA) measures how much energy is needed to digest and break down food, and is part of the AS. While eating bigger prey will provide more energy to a predator, bigger meals take more energy to metabolize and absorb than smaller meals. If the animal uses a lot of energy breaking down food, that means that it will have less energy to do things like fight or escape from a predator. Because of this, it was hypothesized that it might actually benefit the predator to intentionally choose smaller prey.

A barramundi, the predatory fish which was used as the model organism for this experiment. [Thorne, Nick. 14 July 2006. https://commons.wikimedia.org/wiki/File:Barramundi.jpg ]

This idea was tested with the predator fish barramundi, which usually eats large amounts of food at once. Twenty-four juvenile fish were fed different amounts of food, somewhere between 0.6 and 3.4% of their body mass, for two minutes. They were then transferred to individual respirometry chambers for 42 hours. Information gathered from the chambers allowed the scientists to calculate the metabolic rate and SDA for each fish. They were then transferred to a tank for a three-minute “chase” exercise, to simulate a predator attack. After the three minutes, the fish were returned to the respirometers to calculate the aerobic metabolic rate, SDA, and SA after exercise. The growth rates of the fish were also calculated over a period of seven weeks.

Graphs depicting the relationship between growth rate (top) and growth efficiency (bottom) vs. food intake. Each barramundi is a data point. [Norin and Clark. https://miami.app.box.com/s/wjo39y4nm2ibw8eicf22fz4pgfgy9vhv/file/263749479008]

The study found that the fish who were fed larger meals had less excess energy, and higher growth rates came at the cost of a decreased AS. This means that after eating a larger meal, the fish spent so much energy metabolizing it that there was less energy left over afterwards. Less energy stores means that a fish can’t swim as fast or as long, and is more likely to be caught and eaten by a predator. The evidence from this experiment suggests that the increased risk of predation outweighs the benefits of the larger size that come with eating large meals. It would likely be beneficial for the barramundi to choose its prey size based on its environment. For example, if the fish were in a relatively safe and isolated area, it might be better to consume more food, whereas in a high-traffic area with high predator abundance, it would be more beneficial to eat less.

Works cited:  

Norin T, Clark TD. 2017. Fish face a trade-off between ‘eating big’ for growth efficiency and ‘eating small’ to retain aerobic capacity. Biol. Lett. 13: 20170298. http://dx.doi.org/10.1098/rsbl.2017.0298