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Friday, April 19, 2019

Sea Creatures Part 2 – Animals of the Pelagic


In Shark Station, most of the novel takes place deep beneath the waves, but there is a small portion that takes place near the surface. Due to many of the creatures encountered at the surface already being highlighted in previous blog posts (humpback whales, sperm whales, bottlenose dolphins, etc.), there will be only two animals highlighted in this post. In a way, it is poignant because the pelagic zone is so void compared to the continental shelf and coral reef regions of the sea. Regardless, I hope you enjoy learning about these two sea creatures.  

Mola mola

Flickr user: Ilse Reijs and Jan-Noud Hutten  https://www.flickr.com/photos/39891373@N07/ [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]

The silvery gray-colored ocean sunfish (Mola mola) is a unique creature of the sea. The most distinct feature is perhaps their shape. They have a flattened oval shape that contrasts with most fish species. Instead of a typical caudal fin, they have a truncated caudal fin fused to the body called a clavus that acts as a rudder to help them steer through the water(1). Elongated dorsal and anal fins are primarily used for locomotion. Their mouth is formed from two hard teeth plates that resemble a beak(2). All of these features lead to their nickname “swimming head”(1). Although their coloration is a silver to grayish-white color, they sometimes have gray spots on the posterior half of their body. Living for 8-10 years, they can grow to 2,268 kg (5,000lbs) and be up to 3m (10ft) long and 4.3 (14ft) tall(1)(3).

Distributed worldwide in temperate and tropical oceans, the ocean sunfish is often seen near the surface, but has also been recorded diving to depths and traveling long distances. It is thought that they dive deep to avoid predators. Predators of the ocean sunfish are killer whales, sea lions, and sharks(2). Ocean sunfish themselves prey upon algae, brittle stars, crustaceans, fish, jellyfish, squid, and zooplankton(1)(2). They have a mucous lining in their digestive tract to protect them from being stung by the jellyfish they eat(2).

Ocean sunfish are oviparous (meaning that they hatch from eggs). From larva to adult, they will grow 60 million times larger than the size in which they began(2). Mola molas have high fecundity. The females can produce up to 300 million eggs each breeding season; more than any other known vertebrate currently alive today. While the sunfish is still a larva, they have a tail and caudal fin, but eventually, in their second larval stage the tail absorbs and all the spines disappear. As juvenile ocean sunfish begin to grow, they can average up to almost 0.82kg (1.8lbs) a day in growth(4).

As for threats to their existence, humans in parts of Asia eat ocean sunfish and they are used in Chinese medicine(4). According to the IUCN red list, they are listed as vulnerable and their population is decreasing(3). Major threats besides human consumption are bycatch from drift nets and plastic debris such as plastic bags that they mistake for jellyfish(1).

An interesting fact about the ocean sunfish is that it’s the largest bony fish on the planet(1). They are related to pufferfish, but only exhibit spines during the second half of their larval stage(2).

Portuguese Man o’War

Rhalah [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]

Image courtesy of Islands in the Sea 2002, NOAA/OER. [Public domain]

The Portuguese man o’war (Physalia physalis) are closely related to jellyfish, but they are not a jellyfish. Instead, it is a siphonophore, which is a colony of individuals working as one(5). The siphonophore colony is made up of identical individuals that are known as zooids or clones(6). They have four separate polyps. The floating part at the top is called the pneumatophore. It is typically 30cm (12in) long and around 12.7cm (5in) wide. The tentacles are the largest part of the polyps. On average, they are 9.1m (30ft) in length but can grow as long as 50m (165ft) long with nematocysts filled with venom everywhere on the tentacles. The third polyp is the gastrozooids, which are the digestive organisms. The last one is the polyp that functions as the reproductive organ(5).

Unable to move on their own, they drift on the currents or the wind in the pelagic zone. If a threat of surface predation occurs, they can deflate their bubble on the top and submerge for a time(5). The float at the top (pneumatophore) can be a variety of colors such as blue, pink, or violet. The Portuguese man o’war is named as such due to the float resembling old-style Portuguese warships. Like warships, they will often float together, sometimes in groups of 1,000 or more. They feed on small fish and crustaceans(6). To feed, they use their feeding tentacles to stun prey and pull them up into their simple digestive tract. Due to their highly venomous nature, their only predators are sea turtles like loggerheads and the ocean sunfish (Mola mola)(7).

As for conservation, the Portuguese man o' war hasn’t been evaluated by the IUCN yet. Their populations could be thriving or declining, but as of now, scientists still do not know. Although their sting is known to be excruciatingly painful, rarely does it kill a human(1). However, if a  Portuguese man o' war does wash on shore, it can still sting you, even if its been there for weeks(2)!

I know this was the shortest creature feature yet but I hope you enjoyed it as much as the others. In two weeks, there will be another sea creature blog post—the last for Shark Station. Until then, you can check out the first sea creature feature for this novel if you missed it by clicking here. As always, if you have any questions or comments, you can leave them here on my blog or email me at elizataye@gmail.com. I always love hearing from my readers!


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