Seawalls: Allowing humans to build closer to water, but altering processes along shorelines.

By Abby Tinari, SRC intern

Participating in the Shark Research and Conservation Program’s Urban Shark Project, I have spent a decent amount of time on the water throughout downtown Miami. In this time, I have noticed the concrete shoreline that shapes Miami’s shores. Of course, there are sandy beaches, but much of the barrier between land and water is a hardened seawall. It made sense, considering 20 feet from the seawall is a high-rise building, that needs the support and the seawall provides. This realization, at how much humans have changed and destroyed the coastlines, intrigued me. I then started to wonder how has shoreline hardening and urbanization effected the marine environment?
Coastal cities around the world are hardening their coasts. As the desire to be along the water increases there is a higher pressure to create structures that support buildings. These hard structures replace the natural shoreline, creating a barrier between land and water. Depending on the area and the infrastructural need, a variety of structures can be used. An alternative to natural shorelines, including seawalls, are used to provide stability for sediment and infrastructure built upon the sediment through erosion prevention (Gittman, Scyphers, Smith, Neylan, & Grabowski, 2016). Seawalls are also used as protection from wave energy and storm surges. Seawalls allow humans to complete their desire of living along the coast when they otherwise would have to move inland when the land erodes away. If designed properly, they can be used to prevent sea level rise in a low lying area. The vertical nature of seawalls occupy considerably less space than other shoreline armoring structures, making it an ideal structure in cities and areas where space is limited. Seawalls can last over 30 years in saline environments if designed and maintained properly.

Example of engineered-shore structures: seawall (Gittman et al., 2016)

Example of engineered-shore structures: seawall (Gittman et al., 2016)

Although seawalls are important coastal structures they produce adverse effects on the coastal environment. Removing the natural shoreline disturbs and changes longshore currents, wreaking havoc on properties and the shoreline farther along the current. Seawalls remove areas where erosion and deposition would otherwise take place. The sediment in water is deposited somewhere else, altering sediment transport and causing sediment starvation. Sediment starvation usually occurs at the end of a seawall where water velocity speeds up, eroding sediment. Because there is a lack of sediment transferred along the wall the sediment eroded at the end does not have anything to replace it, creating a “starved” area. Erosion still occurs around seawalls, just not along the shoreline. It is prevalent at the base in front of the wall and can weaken the structure due to the change in forces acting on the wall (Figure 2). Concrete does not absorb and reflect energy as a beach or rocky shoreline would. Much of the wave energy is reflected, creating potential boating hazards. These are just the physical process seawalls change.

Erosion occurring at the base of the seawall. Scour erodes sediment that leads to an unstable structure and possible collapse. (ctmirror.org)

Erosion occurring at the base of the seawall. Scour erodes sediment that leads to an unstable structure and possible collapse. (ctmirror.org)

How are seawalls affecting organisms that were once present in urban environments? Are they changing biodiversity? One obvious effect seawalls have is they remove natural habitat, reducing the amount of shoreline conducive for organisms. Plants and animals are unable to travel between terrestrial and marine environments reducing the connectivity between the two communities. In the past, as sea level rises, ecosystems have been able to adjust, slowly moving inland. With a concrete barrier, inland migration is extremely difficult, if not impossible for plants and animals. This could lead to a loss of nursery and foraging grounds for birds and fish (Bulleri & Chapman, 2010). These vertical structures reduce the size of the intertidal zone, crowding intertidal species into smaller areas. This zone is the bridge for energy exchange between marine and terrestrial environments (Sobocinski, Cordell, & Simenstad, 2010). Abundances and assemblages of organisms are changing due to the difference in substrate. The lack of crevices and protection from predators and wave energy reduce the likelihood of larval survival (Bulleri & Chapman, 2010). Many of the species sea walls directly affect are sessile, meaning they are immobile. If larvae are not able to survive on the seawall then adults will not be able to either. The lack of native organisms has the potential for exotic species to flourish. In certain situations seawalls do benefit the marine community. Seawalls in Sydney Harbor, Australia provide shading, which has led to an increase in species diversity (Bulleri & Chapman, 2010). Bulleri and Gittman through literature searches found that seawalls do significantly decrease the biodiversity of abundance of species when compared to natural shorelines.
Seawalls are essential to coastal urban infrastructure, but how can we reduce the impact they have on the ecosystem while still having the same structural benefit? In areas where space is available living seawalls can be an excellent alternative. Living seawalls are typically layered or terraced. Each layer provides habitat for different organisms. These work bridge the connectivity gap between terrestrial and marine environments. Fake mangrove panels are a new alternative for South Florida’s sea walls. The panels are concrete but mimic red mangroves, an important habitat for many of South Florida’s marine organisms. University of Kansas assistant professor, Keith Van de Reit, designed these panels which, so far, are proving to be successful in creating habitat for organisms. Riprap, while not providing the same strength as a sea wall can increase the biological activity of the structure. If the stability cannot be compromised, walls such as one in Sydney Harbor (Figure 3), can be useful to mimic a rocky tidal pool environment. The openings in the walls are placed so they are flooded at high tides but retain water at low tides. This provides an environment for rocky tidal species, a marine environment common in Sydney.

(a) Intertidal 'rock-pools' constructed in the vertical dace of a seawall in Sydney Harbor (Australia). These features of habitat were introduced to seawalls to mitigate efforts of loss or degradation of rocky platforms on intertidal biodiversity. (b) Details of a rock-pool retaining water during low tide. (Bulleri & Chapman, 2010)

(a) Intertidal ‘rock-pools’ constructed in the vertical dace of a seawall in Sydney Harbor (Australia). These features of habitat were introduced to seawalls to mitigate efforts of loss or degradation of rocky platforms on intertidal biodiversity. (b) Details of a rock-pool retaining water during low tide. (Bulleri & Chapman, 2010)

Although there are some studies on the biological impact of seawalls, more research needs to be done, especially with the rising coastal population. Other alternatives, like the mangrove panels, should be researched. A healthier and more ecologically connected water way helps human in numerous ways. It would increase water quality and create habitat. It would also provide for more tourism and an economic benefit for cities.

Works Cited
Bulleri, F., & Chapman, M. G. (2010). The introduction of coastal infrastructure as a driver of change in marine environments. Journal of Applied Ecology, 47(1), 26-35. doi:10.1111/j.1365-2664.2009.01751.x
Gittman, R. K., Scyphers, S. B., Smith, C. S., Neylan, I. P., & Grabowski, J. H. (2016). Ecological Consequences of Shoreline Hardening: A Meta-Analysis. Bioscience, 66(9), 763-773. doi:10.1093/biosci/biw091
Sobocinski, K. L., Cordell, J. R., & Simenstad, C. A. (2010). Effects of Shoreline Modifications on Supratidal Macroinvertebrate Fauna on Puget Sound, Washington Beaches. Estuaries and Coasts, 33(3), 699-711. doi:10.1007/s12237-009-9262-9
Spiegel, Jan Ellen. “Connecticut’s Trouble with Seawalls.” The CT Mirror. N.p., 17 Feb. 2014. Web. 24 Mar. 2017

A Study of Microplastics in San Francisco Bay

By Lauren Kitayama, SRC intern

Introduction

Microplastics (defined as being < 5mm in size) are small enough to be ingested by filter feeders and planktonic organisms. Studies have shown that the average seafood consumer could be ingesting 11,000 pieces of microplastic annually (Cauwenberghe & Janssen, 2014). The human health impacts are not well understood, but preliminary research suggests that the particles themselves may not be able to pass through the intestinal wall. However, additives and toxins including chemicals that are known carcinogens and hormone disruptors are still a cause for concern (Galloway, 2015) Microplastics come as pre-production beads (often called nurdles), exfoliating beads in personal car products, microfibers that come from washing synthetic clothes, and the breakdown of larger plastics already in the ocean.

Plastic from facial scrub next to a dime. Photo credit: Dave Graff. Source: plasticaware.org

Plastic from facial scrub next to a dime. Photo credit: Dave Graff. Source: plasticaware.org

Average measurements of 700,000 microplastic particles/ km2 (range: 15,000-2,000,000 particles/km2) makes the waters of San Francisco Bay the most microplastic polluted body of water sampled in North America.

Microplastics in San Francisco Bay

In 2016, researchers sampled eight wastewater treatment facilities that discharged into the San Francisco Bay. These facilities represent about 60% of wastewater discharged into the Bay. They voluntarily allowed researchers to sample their final effluent (the water that would be directly released). The rate of microplastic discharge from the wastewater treatments plants was 0.086 particles per liter, which equates to about 90 million particles a day. There was no difference among discharge rates between facilities that had secondary or tertiary treatment suggesting that waste water treatment plants are ineffectual at capturing and removing microplastics from waste water. Fibers were the most common type of microplastic found.

Samples were collected once from each wastewater facility during peak flow by passing the wastewater through 0.355 mm and 0.125mm sieves for 2 hours. They were then cleaned, and organic material was dissolved. Plastic particles were visually identified, and classified as one of five categories: fragment, pellet, fiber, film or foam.

Microplastics were also sampled at 9 sites inside the bay using a Manta Trawl and standard protocols. These surveys occurred at rising tides. Samples were cleaned, all organic material removed and visually classified just like the wastewater samples. All surface samples contained plastic ranging from 15,000 to 2,000,000 particles/ km2. On average, density was higher in SF Bay, than the Great Lakes, Chesapeake Bay and Salish Sea.

Estimated abundance of microplastic particles in surface water at nine sites in San Francisco Bay. Circles are located at trawl midpoints. (Sutten et al, 2016).

Estimated abundance of microplastic particles in surface water at nine sites in San Francisco Bay. Circles are located at trawl midpoints. (Sutten et al, 2016).

High concentrations of microplastic pollution in the San Francisco Bay could be due to a high urban population surrounding a small, closed body of water. However this does not necessarily explain why densities would be higher in San Francisco Bay than in other urban surrounded bodies of water. Possible explanations include water conservation measures taken by the state during a severe drought that concentrates plastic. Other pollution pathways such as runoff and fragmentation may also play a large role. This study was an initial snapshot of microplastic pollution in SF Bay. Its findings indicate the need for more in-depth studies to look at the possible effect of tidal flux, 24-hour water use differences and impacts of storm water runoff. It also makes clear the need to better understand the implications of exposure to wildlife and humans. (Sutton et al, 2016).

The Bigger Picture on Little Plastics

Microplastics are becoming increasingly recognized as a threat to ocean and human health. Global release of primary microplastics is estimated to be 1.5 Mtons/year (Boucher & Friot, 2017). Microbeads in personal care products are often considered to be a large source of these microplastics. In fact in 2015 US passed the Microbead-Free Waters Act, banning the manufacturing and sales of products with microbeads with the intent of decreasing microplastic pollution in the countries waterways (2015). Canada, Ireland, the UK and the Netherlands have similar national legislation. But recent reports show that these exfoliating microbeads represent a small portion of microplastics pollution (2%). Whereas microfibers, released during the laundering of synthetic materials represents 35% of microplastics (Boucher & Friot, 2017).

Breakdown of primary microplastic loss into the ocean. (Boucher & Friot, 2017).

Breakdown of primary microplastic loss into the ocean. (Boucher & Friot, 2017).

Companies like Patagonia have begun recognizing this threat to the planet, and are investing in solutions like a laundry bag that captures microfibers before they get blown out of the drier vent (O’Connor, 2017).

Work Cited

Sutton et al (2016). Microplastic contamination in the San Francisco Bay, California, USA. Marine Pollution Bulletin 109: 230-235. http://dx.doi.org/10.1016/j.marpolbul.2016.05.077

Microbead-Free Waters Act. (2015). 21 U.S.C. 331. https://www.gpo.gov/fdsys/pkg/BILLS-114hr1321enr/pdf/BILLS-114hr1321enr.pdf

O’Connor, M. (2017). Microfibers are polluting our food chain. This laundry bag can stop that. The Guardian. https://www.theguardian.com/sustainable-business/2017/feb/12/seafood-microfiber-pollution-patagonia-guppy-friend

Cauwenberghe, L. and Janssen, C. (2014). Microplastics in bivalves cultured for human consumption. Environmental Pollution 193: 65-70. http://dx.doi.org/10.1016/j.envpol.2014.06.010

Boucher, J. and Friot D. (2017). Primary Microplastics in the Oceans: A Global Evaluation of Sources. Gland, Switzerland: IUCN. 43pp. https://portals.iucn.org/library/sites/library/files/documents/2017-002.pdf

Galloway, T. (2015). Micro- and Nano-plastics and Human Health. Marine Anthropogenic Litter pp 343-366. http://link.springer.com/chapter/10.1007/978-3-319-16510-3_13

Plastic debris contamination in the Acoupa weakfish (Cynoscion acoupa) in a tropical estuary

By Elana Rusnak, SRC intern

The Acoupa weakfish (Cynoscion acoupa) is an economically important fish that lives along the tropical east coast of the American continents. They tend to live in estuary systems—calm, brackish water habitats—as juveniles and sub-adults, and then move to saltier areas as they age. Tropical estuaries are one of the most productive ecosystems on Earth, and they provide shelter, food, and developmental grounds for many species of fishes and invertebrates. Unfortunately, since estuaries are more sheltered environments, plastic debris tends to accumulate and be ingested by the many species that make the estuary their home.   A study by Ferreira et al. in 2016 explored the feeding habits of all life stages of the Acoupa weakfish in the Goiana Estuary in Brazil, and described the plastic debris contamination of the area and how it affects these economically important fish.

In this study, the fish were subdivided into three study groups: juvenile, sub-adult, and adult. They were observed and captured in the upper, middle, and lower parts of the Goiana Estuary, with the lower part being the saltiest. About 470 juveniles, 25 sub-adults, and 33 adults were used in this study. The stomach contents of each fish were removed and examined to determine the ratio of plastic debris to their natural diet (fish, crustaceans, worms, seaweed, plant fragments). The researchers found that in almost every fish, the majority of the stomach contents consisted of plastic debris, followed by crustaceans and fish (64.4% of juveniles, 50% of sub-adults, and 100% of adults were contaminated with plastic). Multicolored plastics were also found in the digestive tract, and a few specimens had nothing in the stomach other than plastic debris.

Plastic debris inside a penaeid shrimp, a primary food source for adult Acoupa weakfish (Ferreira et al., 2016)

Plastic debris inside a penaeid shrimp, a primary food source for adult Acoupa weakfish (Ferreira et al., 2016)

 

Zoomed in image of red plastic debris inside the digestive tract of an Acoupa weakfish specimen (Ferreira et al., 2016)

Zoomed in image of red plastic debris inside the digestive tract of an Acoupa weakfish specimen (Ferreira et al., 2016)

 

So what does this all mean?

First, the Goiana Estuary waters are polluted with plastic debris at densities comparable to half the density of the fish larvae that reside in it (Lima et al., 2015). This indicates that this estuary system is very polluted. Moreover, the Acoupa weakfish isn’t the only organism ingesting all this plastic. The direct ingestion of plastic debris might primarily occur during the early stages of the Acoupa weakfish, whereas sub-adults and adults ingest debris through the trophic food chain (their prey ingests the plastic, then it is left behind in the adult fish’s stomach). This occurs through a process called biotransferrence. The presence of plastic in the digestive system is also problematic, as it can lead to digestive injuries and induce starvation. Since the Acoupa weakfish is a top predator in their estuarine habitat, they are more susceptible to food web disturbances.

This fish is not only a primary food source for the locals in the area, but it is also commercially fished. If they are filled with plastic, they are not getting the nutrition they need to become large, healthy fish. Without this growth, both the locals and the commercial industry will suffer. This study really showed the large-scale change that needs to begin now with regards to reducing plastic waste and keeping our environment clean and healthy.

Works cited

Ferreira, G.V.B., Barletta, M., Lima, A.R.A., Dantas, D.V., Justino, A.D.S., Costa, M.F. 2016. Plastic debris contamination in the ife cycle of Acoupa weakfish (Cynoscion acoupa) in a tropical estuary. ICES Journal of Marine Science 73: 2695-2707.

Lima, A. R. A., Barletta, M., and Costa, M. F. 2015. Seasonal distribu- tion and interactions between plankton and microplastics in a tropical estuary. Estuarine, Coastal and Shelf Science, 161: 93–107.

Making a run for it: escaped farmed Atlantic salmon integrating with wild populations

By Robbie Roemer, SRC master’s student

Atlantic salmon (Salmo salar) as their name implies, are primarily found in northern Atlantic waters and are classified as androminous (living in the sea, and returning to freshwater to spawn). Known to be a popular recreational sport fish, this largest species found in the genus Salmo is prized for its table fare and thus, faces heavy commercial fishing pressure. This species is particularly sensitive to habitat alteration and human influence (Staurnes et al. 1995; Kroglund et al. 2007) and coupled with the high commercial demand, has seen significant historical declines over the last half century. These declines have led to substantial increases in aquaculture farming techniques where salmon are raised in pens on the very same waters utilized by native, wild populations to spawn. Breeding and farming programs have greatly altered the genetic makeup of Atlantic salmon as commercial enterprises target specific characteristics such as: larger total size, faster growth rates, efficient food utilization, and meat quality. But what happens to the inevitable large quantity of farm “escapees”?

Atlantic salmon are popular sport fish in Norway and beyond [Image by Vetle Kjærstad]

Atlantic salmon are popular sport fish in Norway and beyond [Image by Vetle Kjærstad]

A recent study by Diserud Karlsson and others investigated and quantified genetic introgression (genetic mixing or “hybridization”) of escaped farmed to wild Atlantic salmon. Extracting genetic material from either scales or fin clips, and using several specific genetic markers representative of both wild and farm raised individuals; the team was able to quantify genetic introgression in 147 salmon rivers in Norway. A study of this magnitude was able to account for and represent three quarters of the total wild spawning population in the entire country. What the team found was an average level of genetic introgression of 6.4%, within a total range of 0.0% to as high as 42.2%. Moreover, significant genetic introgression had occurred in 51 separate wild salmon populations, with significant genetic introgression also occurring in 77 of 147 sampled rivers.

So why is the genetic introgression or “mixing “of farmed salmon to wild salmon ecologically important? The main concerns by the authors regarding genetics are the loss of genetic variation within a population, the loss of genetic variation between populations, and the loss of overall animal ecological fitness. It has long been shown that farmed salmon have much lower genetic variation compared to their wild counterparts ((Mjølnerød et al. 1997; Skaala et al. 2004, 2005; Karlsson et al. 2010). In addition, substantial loss of ecological fitness has been documented in farm-raised salmon. If wild to farmed genetic introgression continues at this rate, it is feared wild salmon populations will too lose genetic attributes, all of which are critical in sustaining healthy, disease-free, wild salmon populations.

Map of Norway showing rivers with farmed genetic introgression (Karlsson et al. 2016).

Map of Norway showing rivers with farmed genetic introgression (Karlsson et al. 2016).

This research has real-world applications, as many hydropower companies that alter the natural state of rivers, and reduce natural productivity of native salmon compensate this “offset” by releasing farm raised fish into the river system. In the western United States, native cutthroat trout are facing a similar threat, as genetic introgression with rainbow trout is occurring at a rapid rate. It has been proposed to list the few remaining genetically “pure” populations of cutthroat trout under the Endangered Species Act (ESA). Similar proposals have been made to Atlantic salmon, even going so far as to list farm-raised salmon a different species, and treating farm raised “escapees” as an exotic species, to help deter genetic hybridization and introgression with wild populations.

One positive finding within the study was the lowest genetic introgression rates were located within Norwegian nationally protected lands (National Salmon Rivers and National Salmon Fjords), thereby demonstrating the ecological importance of preserved lands to wildlife populations. Indeed, there is no clear, sound solution to this problem, especially as the numbers of salmon farms are increasing globally. However, it is clear that at the present time, near-zero limits are the only viable solution to protect the genetic integrity of wild Atlantic salmon populations.

Works Cited

Karlsson, S., Diserud, O.H., Fiske, P. and Hindar, K., 2016. Widespread genetic introgression of escaped farmed Atlantic salmon in wild salmon populations. ICES Journal of Marine Science: Journal du Conseil73(10), pp.2488-2498.

Kroglund, F., Rosseland, B.O., Teien, H.C., Salbu, B., Kristensen, T. and Finstad, B., 2007. Water quality limits for Atlantic salmon (Salmo salar L.) exposed to short term reductions in pH and increased aluminum simulating episodes. Hydrology and Earth System Sciences Discussions4(5), pp.3317-3355.

Staurnes, M., Kroglund, F. and Rosseland, B.O., 1995. Water quality requirement of Atlantic salmon (Salmo salar) in water undergoing acidification or liming in Norway. Water, Air, & Soil Pollution85(2), pp.347-352.

Caribbean Spiny Lobster Fishery Is Underpinned by Trophic Subsidies from Chemosynthetic Primary Production

By Molly Rickles, SRC intern

Caribbean spiny lobsters are a very commercially important species that brings in millions of dollars in revenue annually. The lobsters are especially important to the Bahamas, which has a large fishery. Recently, artificial reefs were created for the lobsters in areas where they are usually fished. This made it easier for the present study from Higgs and colleagues to take place, which analyzed the Caribbean spiny lobster diet. The main purpose of the study was to show that a significant portion of the lobster’s diet is from chemosynthetic primary production in the form of lucinid clams, which are found on artificial reefs. (Figure 1).

Figure 1: This image shows that the Caribbean spiny lobster trade is very lucrative, especially in the Bahamas. It also shows the food web and how the lobsters obtain their food from chemiosynthetic primary production. The lobsters consume the clams, which obtain nutrients from sulfate that was fixed by sulfate fixing bacteria from detritus. (Higgs, N. D., Newton, J., & Attrill, M. J. (2016). Caribbean Spiny Lobster Fishery Is Underpinned by Trophic Subsidies from Chemosynthetic Primary Production. Current Biology, 26(24), 3393-3398. doi:10.1016/j.cub.2016.10.034)

Figure 1: This image shows that the Caribbean spiny lobster trade is very lucrative, especially in the Bahamas. It also shows the food web and how the lobsters obtain their food from chemiosynthetic primary production. The lobsters consume the clams, which obtain nutrients from sulfate that was fixed by sulfate fixing bacteria from detritus. (Higgs, N. D., Newton, J., & Attrill, M. J. (2016). Caribbean Spiny Lobster Fishery Is Underpinned by Trophic Subsidies from Chemosynthetic Primary Production. Current Biology, 26(24), 3393-3398. doi:10.1016/j.cub.2016.10.034)

Researchers sampled 160 lobsters from both natural and artificial reefs. Tissue samples were collected from the tail muscle of the lobsters and dietary tissue samples required the whole lobster. (Figure 2) To study the lobster’s diet, scientists used stable isotope analysis to organize the lobster’s diets into five main food groups. Through this approach, it was found that the phototrophic group, or autotrophs, made up the majority of the lobster’s diet. These results show that chemosynthetic primary productivity plays an important role in commercial fisheries since the lobsters are mainly dependent on phototrophic productivity for food. The results also show that 1/5 of the lobster’s diet is from the chemosynthetic primary productivity of lucinid clams, which are found on artificial reefs in the lobster’s habitat. The clam’s productivity is from the chemoautotroph organisms that live symbiotically with them. In addition to studying the diet, the researchers compared the diets of lobsters living on natural reefs against lobsters that lived on artificial reefs. It was found that lobsters living on natural reefs have higher values of chemosynthetic productivity in their diets. This is mainly due to the fact that natural reefs have denser sea grass, which allows for higher chemosynthetic productivity.

Figure 2: This figure shows how the study was carried out. The top picture is of an artificial lobster shelter, which is where the lobsters used in this study normally were found. Image B is the carapace of a lobster used in the study. Image C is of a lobster dactylus, the last appendage of the lobster’s thorax. Image D shows lucinid clams, which the lobsters mainly feed on. (Higgs, N. D., Newton, J., & Attrill, M. J. (2016). Caribbean Spiny Lobster Fishery Is Underpinned by Trophic Subsidies from Chemosynthetic Primary Production. Current Biology, 26(24), 3393-3398. doi:10.1016/j.cub.2016.10.034)

Figure 2: This figure shows how the study was carried out. The top picture is of an artificial lobster shelter, which is where the lobsters used in this study normally were found. Image B is the carapace of a lobster used in the study. Image C is of a lobster dactylus, the last appendage of the lobster’s thorax. Image D shows lucinid clams, which the lobsters mainly feed on. (Higgs, N. D., Newton, J., & Attrill, M. J. (2016). Caribbean Spiny Lobster Fishery Is Underpinned by Trophic Subsidies from Chemosynthetic Primary Production. Current Biology, 26(24), 3393-3398. doi:10.1016/j.cub.2016.10.034)

This study is important because it was the first to determine the diet of the Caribbean spiny lobster. Since this species is heavily fished, this study showed the importance of spiny lobster management to maintain its population. It is also important to maintain chemosynthetic production on the artificial reefs to maintain a food source for the lobsters. This study also outlined the importance of the spiny lobster in marine ecosystems, since it was shown that the lobsters play an important role in transferring chemosynthetically fixed carbon from deep sediment to the organisms in the ecosystem. Since lobsters are both economically and ecologically important species, it is vital to protect and manage their population so that they can continue to contribute to the human diet and marine ecosystem.

Works cited

Higgs, N. D., Newton, J., & Attrill, M. J. (2016). Caribbean Spiny Lobster Fishery Is Underpinned by Trophic Subsidies from Chemosynthetic Primary Production. Current Biology, 26(24), 3393-3398. doi:10.1016/j.cub.2016.10.034

Sneaky Predators

By Arina Favilla, SRC intern

“Everything you see exists together in a delicate balance, ” Mufasa wisely tells Simba in The Lion King right before a pouncing lesson. This is true of any ecosystem on the planet—the sun provides energy for plants to grow, plants are grazed on by herbivores, who are eaten by consumers, who are prey to other predators. Any prey-predator imbalance can have cascading effects on the entire ecosystem, particularly when invasive predators are especially sneaky predators, beating Simba in the element of surprise.

The element of surprise is difficult to accomplish in the aquatic environment because there are several cues (smell, sight, vibrations) that warn prey of a nearby predator and illicit a fast-start response, allowing them to get as far away as quickly as possible. It is debated whether this fast-start response is an autonomic response, similar to a knee-jerk reflex, or whether an individual can optimize their escape response in accordance to the threat.

Image of the red lionfish (Pterois volitans) displaying its characteristic fins and venomous spines. (From Wikimedia Commons)

Image of the red lionfish (Pterois volitans) displaying its characteristic fins and venomous spines. (From Wikimedia Commons)

McCormick and Allan (2016) investigated the red lionfish’s (Pterois volitans) success as a predator by determining the response of prey. The red lionfish, native to the Pacific Ocean, is a threatening invasive species in the Caribbean because of their success as predators easily devouring 8-10% of their body weight each day. They quickly decimate reef fish populations and destroy the delicate balance of a reef ecosystem. Moreover, recent research suggests lionfish are successful, sneaky predators by avoiding associative learning, a survival mechanism that allows prey to associate cues with dangerous predators leading to effective fast-start responses and successful escapes.

The study compared the response of whitetail damselfish to two predators, the red lionfish and the common rockcod, as well as a non-predator fish, the three-lined butterflyfish. First, the damselfish were conditioned to associate potential risk with the sight and odor of the two predator species coupled with chemical alarm cues. Previous studies have shown tropical fish species, including damselfish, can quickly learn to associate cues of a predator as a threat. Damselfish were then exposed to olfactory cues (seawater from the predator or non-predator tank) and/or visual cues (predator or non-predator tank placed adjacent to the damselfish tank) before being startled by a stimulus (release of a metal weight at the water’s surface) to provoke the fast-start response.

Comparison of the different aspects of the damselfish’s fast-start response when forewarned through chemical (white), visual (light grey), or a combination of cues (dark grey) of either one of two predators (red lionfish or rockcod), a non-predator (butterflyfish), or controls. The optimal fast-start response would have a short response latency time, high average response speed and maximum speed, and large distance travelled. Damselfish exposed to controls had the lowest response while those exposed to the rockcod had the highest response. Both the butterflyfish and lionfish elicited similar intermediate responses. (McCormick and Allan 2016)

Comparison of the different aspects of the damselfish’s fast-start response when forewarned through chemical (white), visual (light grey), or a combination of cues (dark grey) of either one of two predators (red lionfish or rockcod), a non-predator (butterflyfish), or controls. The optimal fast-start response would have a short response latency time, high average response speed and maximum speed, and large distance travelled. Damselfish exposed to controls had the lowest response while those exposed to the rockcod had the highest response. Both the butterflyfish and lionfish elicited similar intermediate responses. (McCormick and Allan 2016)

McCormick and Allan (2016) found that the damselfish had greater fast-start responses when forewarned about the predatory rockcod through olfactory or visual cues, but showed similar ineffective fast-start responses—slow to react and slower speeds—when exposed to the cues for the lionfish as well as the non-predator butterflyfish and controls (Figure 2). In other words, the damselfish misidentify the lionfish as a non-predator, reducing its chance of escape if attacked. These results suggest that lionfish are capable of circumventing associative learning, leading to higher success rates in attacking prey. The findings of this study begin to explain the success of lionfish as predators, but further studies are required to better understand the mechanisms lionfish use to avoid forewarning of prey.

Works cited

McCormick, M. I. and B. J. M. Allan. 2016. Lionfish misidentification circumvents an optimized escape response by prey. Conservation Physiology 4:1–9.