Snook in Extreme Environments

By Delaney Reynolds, SRC Intern

Earth’s climate is warming, and rising temperatures are impacting animal species and their habitats in alarming ways. Since 1970, temperatures have increased approximately 0.17°C (0.3°F) per decade (Dahlman, 2017). Such changes threaten animals’ ability to adapt to increased heat and induced stress. In the article, “Can animal habitat use patterns influence their vulnerability to extreme climate events? An estuarine sportfish case study,” researchers observed how migration patterns impacted species’ vulnerability to extreme climate events (ECEs), episodes of uncommon climactic periods in which ecosystem structure is transformed beyond what is characteristically normal (Smith, 2011).

Figure 1: Juvenile Snook

A Juvenile Common Snook caught in the Everglades National Park. Image Source:

The State of Florida enjoys mild lows of 65-41°F during its winter season. Extreme cold fronts, however, occur approximately once every 10 years and can result in colder, more fatal environmental systems. During extreme cold fronts, South Florida’s Everglades National Park often experiences dramatic declines in sportfish populations and, thus, is the experimental ground used to study Snook and climate vulnerability. In 2010, for example, the Park faced one of its most severe cold fronts in a century and saw imperative tropical fisheries decrease 80%.

One of the Park’s residents, the Common Snook, has been useful in studying climate vulnerability because, “the abundance of adult Snook, the most sought after gamefish in the area, decreased by over 90% following the passage of this event” (Boucek, 2017). Once water temperature drops below 60°F, the Snook begin to struggle and become particularly vulnerable.

Looking at Everglades estuaries, Common Snook are observed in various cold-temperature regions. Snook often reside in rivers and for this reason three distinctive areas of the Everglades’ Shark River estuary were studied: the upstream, bay, and downstream zones. The downstream zone consists of the most Snook predators, but also the most Snook prey, and so Snook population and productivity is relatively higher compared to the upstream and bay zones. Passive acoustic telemetry computed Snook distribution patterns predicted for 2012 to 2016 during ECE periods. The researchers found that downstream zones were found to be the warmest, causing little effect on Snook populations, and upstream zones the coldest, killing most tropical fish. When a cold spell is detected in high vulnerability communities, most fish species migrate to areas of higher resistance, ensuring a higher survival rate. When it came to dispersing among less vulnerable habitats, Snook did not portray migration tendencies when detecting ECEs. Another study during the 2010 ECE found that most Everglades Snook showed the same behavior and did not move long distances, but rather made short journeys to areas that would function as a refuge from less severe, but more frequent ECEs (Stevens, 2016).

Figure 2: Snook Habitat Resistance, Animal Distribution, Detection and Response

This figure demonstrates animal distribution in high and low resistance environments, the shaded shapes, as well as their response to ECEs. As shown on the right, when a cold spell is detected in low vulnerability communities, fish will migrate to areas of higher resistance (shown in bright green) and return to their original habitat once it has passed, ensuring a higher rate of survival among the population. Image Source: Can animal habitat use patterns influence their vulnerability to extreme climate events? An estuarine sportfish case study.

Snook face higher risk of population degradation when they are unable to immigrate to congenial territories, yet their populations did not face large casualties due to the ECEs because they tend to typically dwell in the warmer downstream zone. By staying in warm water areas, the Common Snook helps us better understand how species respond to a change in their habitats’ climate. As ECEs become more common and severe it will be vital to continue to monitor fisheries so as to learn how our warming climate impacts species and their habitats.

Works Cited

Boucek, R. E., Heithaus, M. R., Santos, R., Stevens, P., & Rehage, J. S. (2017, April 7). Can animal habitat use patterns influence their vulnerability to extreme climate events? An estuarine sportfish case study. Retrieved from file:///C:/Users/derey/Downloads/boucek%20et%20al%202017b.pdf

Dahlman, L. (2017, September 11). Climate Change: Global Temperature. Retrieved October 22, 2017, from

Smith, M. D. (2011, April 15). An ecological perspective on extreme climatic events: a synthetic definition and framework to guide future research. Retrieved from

The effects of elevated temperature and ocean acidification on the metabolic pathways of notothenioid fish

By Abby Tinari, SRC intern

Notothenioid fish are typically found in the deep, cold waters of the Southern Ocean. Three species of fish native to the Ross Sea were studied to see how they may react to warmer and more acidic oceans.

Figure 1

(a) Pagothenia borchgrevunki (, (b) Trematomus newnesi (, (c) Trematomus bernacchii (Wikimedia Commons), (d) Ross Sea Location (Wikimedia Commons)


To measure the effects of temperature on the fish, individuals were randomly selected and placed in one of the four experimental treatment tanks. The experimental tanks consisted of a control treatment, a low temperature and high pCO2, high temperature and low pCO2, and high temperature and high pCO2 to test the individual and overall effects of temperature and pCO2 on the three-fish species. pCO2 is the partial pressure of carbon dioxide in the water. Each fish had an acclimation period that lasted anywhere from 7 to 56 days. Measurements of fish condition and growth were recorded over the course of the experiment. A few tests were performed to analyze enzymatic changes in the liver, white muscle tissue, and gills. One of the tests, the citrate synthase activity test measured how well the fish can release stored energy.


T. bernacchii, the emerald codfish, was the only fish to display any significant impact from the treatments. The growth and condition declined significantly due to temperature but slowed as the acclimation period increased. The group of fish with the faster acclimation period had the largest decline of condition and growth, especially those that also had the multi-stress (high temperature and high <em>p</em>CO2) treatment. The temperature also influenced the Emerald Codfish’s oxygen consumption and metabolic rate. The high <em>p</em>CO2 tank had a small increase in metabolic rate. There were significant increases in citrate synthase activity, the first of which occurred after 7 days in the multi-stress treatment in the gills. By the 28-day acclimation, all treatments had significantly increased in both the liver and the gills.

The bald notothen, P. borchgrevinki, metabolic rates were significantly affected by temperature in the shorter acclimation periods. Interestingly, the oxygen consumption rates decreased in the high temperature treatments over time. Time and temperature were the main drivers in the citrate synthase activity increase in the gill tissues.

Metabolic rates in T. newnesi differed significantly between the acclimation groups with temperature as the main effect. No significant difference between pCO2 and temperature was present. There was however, an increased oxygen consumption rate after the 7 and 28-day acclimation period. The T. newnesi showed the least sensitivity to the treatments. The changes in Citrate synthase activity were not statistically significant.

Figure 2

Citrate synthase enzyme activity (±SE) of Trematomus bernacchii gill (A) and liver tissues (B), Pagothenia borchgrevinki gill (C) and liver tissues (D) and Trematomus newnesi gill (E) and liver tissues (F) acclimated at 7, 28 and 42 or 56 days to a control treatment (low temperature + low pCO2; black bars), low temperature + high pCO2 (white bars), high temperature + low pCO2 (dark gray bars) and high temperature + high pCO2 (light gray bars with cross hatches). Groups not connected by the same letter are significantly different from each other. (Enzor et al. 2017)


This group of fish, the Notothenioid fish are critical to the Ross Sea food web. The three-species studied are consumed by seals, penguins, and other top predators. Studies like this one help to predict population responses for not only the Notothenioidei suborder but also other species which depend on these individuals for food.

Temperature had a greater adverse effect on the energy demands for two of the studied species. The fish may be able to acclimate to the higher temperatures, but only to an extent. Higher temperatures may mean a decreased ability to efficiently ingest food leading to decreased growth and other detrimental effects as seen in the Emerald codfish.

It should be noted that the long-term implications of the temperature and pCO2 on growth should be cautiously interpreted due to the small sample size and lack of growth even in the control samples.


Enzor LA, Hunter EM, Place SP (2017) The effects of elevated temperature and ocean acidification on the metabolic pathways of notothenioid fish. Conserv Physiol 5(1): cox019; oi:10.1093/conphys/cox019

Atypical and Estuarine Habitat of the Maroni River Mouth Altering Green Turtle Behavior in French Guiana

By Casey Dresbach, SRC intern

Green Sea Turtle, Chelonia mydas. (Your Shot National Geographic, 2013)

Green Sea Turtle, Chelonia mydas.
(Your Shot National Geographic, 2013)


In this experiment, satellite telemetry was used to assess the behavioral adjustments of twenty-six adult female green turtles. Sixteen Argos-linked Fastloc GPS tags were deployed on green turtles from February to June 2012 on both sides of the Maroni River: Awale-Yalimpo and in the Galibi Nature Reserve in Suriname. At the same time, ten other females in the Amana Nature Reserve were equipped with Conductivity-Temperature-Depth-Fluorometer Satellite Relayed Data Loggers, which provided the locations of the turtles via Argos data, and recorded profiles of the dive depth, time at depth, dive duration and post-dive surface interval, and oceanographic data in the form of vertical temperature and salinity profiles taken during the rising phase of these turtles’ dives as seen in Figures 1 and 2. The intent of tagging was to analyze three entities: home range, diving behavior, and environmental conditions.

Figure 1. Extreme temperatures recorded in-situ by the Argos-Linked Fastloc GPS tags on green turtles Chelonia mydas of 2012.) (Chambault, et al.)

Figure 1. Extreme temperatures recorded in-situ by the Argos-Linked Fastloc GPS tags on green turtles Chelonia mydas of 2012. (Chambault, et al.)

Temperature-salinity diagram for the green turtles tagged with a CTD-SRDL tag in 2014. (Chambault, et al.)

Temperature-salinity diagram for the green turtles tagged with a CTD-SRDL tag in 2014. (Chambault, et al.)

In relation to home range, the findings show that Chelonia mydas stayed close to both the shore and their nesting beach, exhibiting limited movement. By staying close to shore, the turtles are likely to save energy for oviposition, the act of laying their eggs. Regarding diving behavior, dive data showed that individual female green turtles were spending extended periods at the surface. This may be related to their highly diurnal resting activity, where they are active during the day. The data also shows that these turtles went for short and shallow dives. One of the reasons for this suggests basking at the surface, which can be beneficial for thermoregulation, especially in these warmer waters. Also, this behavior permits the avoidance of aggressive males or potential predators, delay of algal or fungal infestations, and also an enhancement of immune response. Additionally, spending time at the surface is associated with both their lungs’ positive buoyancies (being denser than water surrounding it) as well as foraging activity. In terms of finding food, a green turtle’s preferred choice of sustenance is seagrass. However, the waters of the French Guiana provide an extreme environment for these turtles, where large river outputs generate very warm water (~27 to 29° C) and highly variable salinities (1.2 to 35.5 psu), as shown in Figures 1 and 2. In these waters, the high river outflow lead to low levels of irradiance, probably resulting in the lack of seagrass. The turtles of the French Guiana have adapted to this consequence by seeking alternate food sources and also relying on stored body fat for energy, defining the population as capital breeders. Adaptations are often compromises; each organism must do many different things to compensate for their surroundings (Reece, Urry, Cain, Wasserman, & Minorsky, 2014). We humans owe much of our versatility to our flexible limbs, but they are also prone to sprains, torn ligaments, and dislocations. Hence, structural reinforcement has been compromised for agility. These turtles are compromising their preferred food choice because it is unavailable. Their available alternatives include those befitting the water’s turbid environment such as: crustaceans, polychaete worms, and cnidarians. Jellyfish are fairly abundant on the French Guiana continental shelf, and these female turtles are adapting an appetite for an alternative source of nutrition to enable survival.

This study provides the first data to describe the inter-nesting events, habitat use, dispersal and diving behavior of green sea turtles. The findings show this population of Chelonia mydas has adapted many behaviors in response to the deviant and estuarine habitat of the Maroni river mouth. This is the first study to track this specific population of green turtles during their inter-nesting season. Satellite tracking made it possible to locate and quantify the habitat used by Chelonia mydas during their inter-nesting seasons. Their survival is at risk, both with increasing climate change and the life-threatening illegal fishing along the Guiana coast. By evaluating their home range, it makes it possible to obtain a reliable visual of areas where these turtles nest, to thus identify hotspots that need protection. The endangered species is particularly vulnerable during their inter-nesting periods, especially in the atypical environment they are residing in. Further research should be done to evaluate the interactions between green turtles and fisheries to ultimately seek permission to delineate a Marine Protected Area.

Works cited

Chambault, P., Thoisy, B. d., Kelle, L., Berzins, R., Bonola, M., Delvaux, H., et al. (2016). Inter-nesting behavioural adjustments of green turtles to an estuarine havitat in French Guiana. Marine Ecology Progress Series , 555: 235-248 .

Dunand, A. (2013, October 15). Your Shot National Geographic .

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., & Minorsky, P. V. (2014). Campbell Biology . Boston: Pearson.