7 Vivid Facts About Sea Slugs

These “butterflies of the ocean” are beautiful, deadly, and strange.


Bernard Picton, Wikimedia Commons // CC BY-SA 4.0

The bizarre, beautiful sea slugs called nudibranchs can be found in marine environments all over the world. Like orchids, nudibranchs vary widely in color and arrangement. Some sport the typical slug shape; others look like bottle brushes, internal organs, or Christmas ornaments.


Sylke Rohrlach, Wikimedia Commons // CC BY-SA 2.0

Nudibranch expert Karen Cheney calls the slugs the “butterflies of the ocean,” both for their Technicolor appearance and their intense toxicity. Like the bright wings of butterflies, nudibranchs’ loud coloration is a warning sign to potential predators that the slugs are not worth the pain. Still, only a few species present much of a threat to humans. Anyone who grabs the blue dragon (Glaucus atlanticus), pictured above, will end up with a handful of regret. 


Jerry Kirkhart, Wikimedia Commons // CC BY 2.0

In an O. Henry-style twist, a nudibranch will never see its own magnificence. Unlike the peepers of their terrestrial cousins, the eyes of sea slugs are extremely primitive and likely only detect light and dark. Nudibranchs do most of their navigating by scent, which they take in through the feather-like rhinophores on their heads.


Karen N. Pelletreau et al., Wikimedia Commons // CC BY 4.0

Some nudibranch species have evolved the plant-like ability to photosynthesize, or live off sunlight. The Elysia chlorotica shown here swipes photosynthesizing cells and genes from the algae it eats. When there’s no algae to be found, the slug can run entirely on solar power. 


Leonard Clifford, Wikimedia Commons // CC BY 2.0

Like most snails and slugs, nudibranchs are hermaphroditic, which really lets them make the most of each mating encounter. Two slugs line up facing in opposite directions, then plug their penises into each other, giving and receiving sperm at the same time.


Bernard Picton, Wikimedia Commons // CC BY-SA 4.0

Nudibranch lifespans vary by species, but none live to be more than a year old.


Crawl_Ray, Flickr // CC BY-ND 2.0

The “sea bunny” nudibranch Jorunna parva took the Internet by storm last summer, and it’s easy to see why.

Whale Sharks Can Live for More Than a Century, Study Finds

Some whale sharks alive today have been swimming around since the Gilded Age. The animals—the largest fish in the ocean—can live as long as 130 years, according to a new study in the journal Marine and Freshwater Research. To give you an idea of how long that is, in 1888, Grover Cleveland was finishing up his first presidential term, Thomas Edison had just started selling his first light bulbs, and the U.S. only had 38 states.

To determine whale sharks' longevity, researchers from the Nova Southeastern University in Florida and the Maldives Whale Shark Research Program tracked male sharks around South Ari Atoll in the Maldives over the course of 10 years, calculating their sizes as they came back to the area over and over again. The scientists identified sharks that returned to the atoll every few years by their distinctive spot patterns, estimating their body lengths with lasers, tape, and visually to try to get the most accurate idea of their sizes.

Using these measurements and data on whale shark growth patterns, the researchers were able to determine that male whale sharks tend to reach maturity around 25 years old and live until they’re about 130 years old. During those decades, they reach an average length of 61.7 feet—about as long as a bowling lane.

While whale sharks are known as gentle giants, they’re difficult to study, and scientists still don’t know a ton about them. They’re considered endangered, making any information we can gather about them important. And this is the first time scientists have been able to accurately measure live, swimming whale sharks.

“Up to now, such aging and growth research has required obtaining vertebrae from dead whale sharks and counting growth rings, analogous to counting tree rings, to determine age,” first author Cameron Perry said in a press statement. ”Our work shows that we can obtain age and growth information without relying on dead sharks captured in fisheries. That is a big deal.”

Though whale sharks appear to be quite long-lived, their lifespan is short compared to the Greenland shark's—in 2016, researchers reported they may live for 400 years. 

Animal Welfare Groups Are Building a Database of Every Cat in Washington, D.C.

There are a lot of cats in Washington, D.C. They live in parks, backyards, side streets, and people's homes. Exactly how many there are is the question a new conservation project wants to answer. DC Cat Count, a collaboration between Humane Rescue Alliance, the Humane Society, PetSmart Charities, and the Smithsonian Conservation Biology Institute, aims to tally every cat in the city—even house pets, The New York Times reports.

Cities tend to support thriving feral cat populations, and that's a problem for animal conservationists. If a feline is born and grows up without human contact, it will never be a suitable house cat. The only options animal control officials have are to euthanize strays or trap and sterilize them, and release them back where they were found. If neither action is taken, it's the smaller animals that belong in the wild who suffer. Cats are invasive predators, and each year they kill billions of birds in the U.S. alone.

Before animal welfare experts and wildlife scientists can tackle this problem, they need to understand how big it is. Over the next three years, DC Cat Count will use various methods to track D.C.'s cats and build a feline database for the city. Sixty outdoor camera traps will capture images of passing cats, relying on infrared technology to sense them most of the time.

Citizens are being asked to help as well. An app is currently being developed that will allow users to snap photos of any cats they see, including their own pets. The team also plans to study the different ways these cats interact with their environments, like how much time pets spend indoors versus outdoors, for example. The initiative has a $1.5 million budget to spend on collecting data.

By the end of the project, the team hopes to have the tools both conservationists and animal welfare groups need to better control the local cat population.

Lisa LaFontaine, president and CEO of the Humane Rescue Alliance, said in a statement, “The reality is that those in the fields of welfare, ecology, conservation, and sheltering have a common long-term goal of fewer free-roaming cats on the landscape. This joint effort will provide scientific management programs to help achieve that goal, locally and nationally."

[h/t The New York Times]


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