Marine Iguana Expert
El Niño Changes Summer Trend to Thick
Crystal blue waves roll onto the white velvet beach, one after another like kids in line at an ice cream truck. The clear sky is filled with the sounds of tropical birds and stretches on for miles, interrupted only by rocky outcroppings of other islands. To most people, this sounds like a summer vacation, or a Sandals ad for a vacation they wish they could take. That is, until the scene is completed. Sea lion pups lay emaciated in sweltering sun while fur seal skeletons ornament the rocky shoreline. The wind carries the stench of death across the remote island as one malnourished sea lion pup prods at its mother’s underside, yelping in protest. Her milk production has ceased in the past days as a means to reduce energy expenditure. Now she lies idly on her stomach. Her skin is stretched tight over protruding bones and one fin is flopped into the sky as if flagging for help. She is dead. The pup continues to whine and nuzzle at her underside. Natural selection strikes again.
Natural selection is the increased survival and reproduction of some organisms due to favorable genetic traits highlighted by competition (1). In many places by the equator, competition is heightened during El Niño summers. The summer months are always thought of as being vibrant and bustling with life. Many humans and animals alike thrive in the warmer months from May to September. However, during El Niño years, the Galapagos Islands show a different story. El Niño is a climate cycle that occurs about every five to seven years due to a shift of warm waters from the Pacific Ocean to the coast of South America. This shift increases rainfall and humidity in South America and can last from a few months up to a year or longer (1).
In the Galapagos, this warm current takes the place of the cool and nutrient rich Humboldt Current, making it hard for marine organisms to survive. Most researchers agree that El Niño begins to replace the currents along the coast of Ecuador and Peru in December; however, the true effects of El Niño take months to augment, which often leave the summer months April-September as the most altered (1). Travel Blogger Dena Haines reiterates what many scientists believe1 when she says that, “The effects of El Niño are seen most drastically along the equator because
the warm water along with it’s warm moist air patterns are not pushed out,” (2). This means that the Galapagos Islands and Ecuador experience the most severe weather patterns arising from El Nino. Though the rainfall helps land flora and fauna thrive, the warm waters are stripped of nutrients essential to marine life survival. Due to this, marine life suffers greatly during El Niño Years (1). The predators of these marine species, like the sea lions and fur seals, also suffer greatly due to decreased food supply. This decrease in food supply has lead to an increase in competition among individuals (3). Increased competition eventually then lead to natural selection which resulted in the relative survival of the more fit sea lion (3).
The most recent extreme occurrence of El Niño took place from 1982 to 1983. Before this, the years 1976-1978 also showed extreme effects. Extreme El Nino events nearly back to back had devastating effects on marine life and marine predators, specifically the Otariidae, the family of mammals to which sea lions and fur seals belong. During the time period 1977-2001 the population of Galapagos sea lions fell almost 65%3 and the Galapagos fur seal population fell about 80% (4). El Niño is thought to be the cause of these fatalities.
The current year (2015-2016) is an El Niño year. It has been deemed relatively weak in comparison to past years and is even expected to change to a La Niña year (La Niña years have the opposite effects of El Niño years the predominant circulation being cold water and dry land conditions). This year is also the first year that I experienced all the effects of El Nino firsthand. In a recent trip to the Galapagos Islands, I enjoyed the benefits of El Niño while snorkeling. The water was warmer than most showers at Cornell! However, I also experienced the sweltering humidity brought on by El Niño. On Bartolome Island, I was overcome by this heat and fell victim to natural selection…almost.
I remember standing on the rocky shore of Bartolome watching the early morning sun inch higher above the horizon and listening as our guide explained El Niño. The air around our intimate group was stagnant and thick with overbearing moisture. Waves of heat washed over my body as I struggled to tear off my cotton button-down drenched in sweat. My vision became blurred and white washed as my companions lowered me to the rocky ground. Stay awake, stay awake, I urged myself as they asked me questions. Their offers of water and food echoed in my head but
all I could suffice was a shake of my head. Consuming anything would only hinder my concentration on staying awake. Minutes crawled by and finally, color returned to my vision and shapes became people, people still standing. My companions had naturally favored traits that allowed them to withstand the heat while I did not.
According to the comparative population decimations, it appears as though the Galapagos sea lions are most like my colleagues in this manner, they survived better than the Galapagos fur seal (me in this example) during El Niño years. This relative survival is due to natural selection. Natural selection is the higher survival of an organism due to a genetic trait. Thus there is some trait that sea lions possess and fur seals lack that allowed sea lions to maintain a higher survival rate during El Nino events. However, after experiencing the humidity of a “weak” El Niño year, it is hard for me to imagine how any members of Otariidae survive extreme El Niño years at all. It does not take a supermodel to confidently conclude that both Galapagos sea lions and fur seals have more blubber than I. Further, seal lions have more blubber than fur seals because of their increased dive depth and frequency. So why did a lower percent of the sea lion population fall victim to El Niño than the fur seal? Perhaps the answer lies within the diet disparities of the two species.
During the El Nino year 1982-1983, scientists conducted a study comparing the diets of both the Galapagos sea lion and the Galapagos fur seals. This study found that the sea lion consumed 24 different species of fish while the Galapagos fur seal consumed 26.5. A later study in 2011, revealed that the diet of the fur seal had changed slightly to include a few different species of squid. The Galapagos sea lion however, did not follow this trend and still was found to only eat fish (6). This selective introduction of squid to the only the fur seal diet may be an adaptation as a result of high food competition. The decrease in marine life during El Niño may have forced the fur seal to further expand its diet in order to survive. With this in mind, the logical question now becomes: how did the sea lion manage to have less diversity in its diet, larger proportion of blubber, and comparatively still out-survive the fur seal in the heightened competition of El Niño? The exact answer is still ambiguous. However, since El Niño results in warm water at only the ocean’s surface, so it makes sense that the diving depth of each Otariidae is another large factor.
Due to their relatively large size and abundance of blubber, Galapagos sea lions were found to dive deeper and spend more time diving than the smaller Galapagos fur seals (6). This appears to be advantageous in El Niño years because even though the surface temperature of the water increases and many organisms die due to lack of nutrients, the underlying water stays at a cool temperature (allowing for benthic marine
animals to survive). Since sea lions are able to survive at these cold temperatures and dive to deeper depths to find food, El Niño affects them relatively less when compared to the fur seal that is less adapted to benthic (the ecological zone at the lowest level of the ocean) diet as well as unable to dive as deep in search for food. Thus, an apparent disadvantage in the warm El Niño years (blubber) proves to be a favorable trait for the survival of the Galapagos sea lion.
This trait was selected as favorable by natural selection. In a time of high competition with the effects of the El Niño year, it was advantageous for Otariidae to have more blubber in order to find food. This resulted in the relatively higher survival rate of Galapagos sea lions over Galapagos fur seals. Perhaps if we were to revisit the shores of the Galapagos and look a little more closely, we would recognize the disproportionate number of fur seal skeletons to deceased sea lions. Just maybe, we would also see that two yards from the deceased mother sea lion hailing the heavens, there was larger sea lion in the same pose. She also props her fin up to thermoregulate, but she is larger. She is alive.
1. Staff, By Live Science. "What Is El Niño?" LiveScience. TechMedia Network, 20 Aug. 2015. Web. 26 Apr. 2016.
2. Haines, Dena. "What Is El Niño? How Does It Affect the Galapagos Islands? | Red Mangrove Galapagos Lodges: All Inclusive Adventure." Red Mangrove Galapagos Lodges: All Inclusive Adventure. N.p., 26 June 2012. Web. 26 Apr. 2016.
3. Trillmich, F. 2015. Arctocephalus galapagoensis. The IUCN Red List of Threatened Species 2015
4. Trillmich, F. 2015. Zalophus wollebaeki. The IUCN Red List of Threatened Species 2015
5. Trillmich, F. and Limberger, D. (1985) Drastic Effects of El Niño on Galapagos Pinnipeds. Oecologia 67.1 19–22.
6. Páez-Rosas, David Diego, Juan José Aurioles-Gamboa, and Daniel M. Palacios Alava. "Stable Isotopes Indicate Differing Foraging Strategies in Two Sympatric Otariids of the Galapagos Islands." Get It! Cornell. Elsevier, 1 Aug. 2012. Web. 29 Feb. 2016.