More Ocean Weirdness
Thursday, December 5, 2024
More Ocean Weirdness
[NB from CynthiaW: This is from 2021. It came to mind because of discussion of other sea animals Tuesday.]
Today’s special animal friend is Americoliva sayana (or Oliva sayana), a large, predatory sea snail that lives in the Lettered Olive Shell, the State Shell of South Carolina. It is a member of the Olividae family; all these mollusks produce a smooth, elongated oval shell. A. sayana lives in the intertidal sand flats on shores near inlets. They are found on the coast of the United States from North Carolina to Texas and along the Gulf coast of Mexico. Garden City Beach, South Carolina, is a typical location (and a very relaxed vacation destination).
A. sayana’s cylindrical shell can reach over 3 inches in length and has thick, dense walls. The snail is one of the fastest sand-burrowers, zapping beneath the surface when the waves withdraw. These snails are voracious carnivores, capturing small crustaceans and bivalves – clams, especially the small coquinas – and dragging them beneath the sand to tear them apart and consume them.
You may be able to see in the videos that part of the snail’s body, the mantle, covers the shell while the snail is alive. This is why most olive shells found on the beach have such a smooth, shiny surface: they are not exposed to friction from sand and other debris. Olive snails produce a chemical, similar to murex secretions, which can be used in dyes.
Female olive snails lay eggs on the sand in transparent capsules, about 20 to 50 at a time. The eggs hatch in about a week as a type of planktonic larvae called “veligers.” This is a life stage for many mollusks. Veligers have a shell covering some of their organs and a “velum” that extends out of the shell. The velum is covered with cilia (small hairs) and is used for propulsion and to capture food particles. The larva eventually develops a foot and settles to the sea floor, where it undergoes metamorphosis into its adult snail stage and begins killing, eating, and growing.
Websites devoted to salt-water aquariums warn fish fanciers to avoid introducing olive snails to their aquariums. They are very dangerous to other animals and can latch onto a fish and kill it.
During my vacation, I also found shells of the Atlantic Auger, Terebra dislocata. These drill-bit-shaped shells are made by carnivorous, sand-dwelling snails which use a venomous barb to stun their prey, mainly marine worms. There are over 400 species of Terebridae in the world's oceans.
Finally, I found a Moon Snail, Polinices duplicatus, still alive in its shell. Moon snails, family Naticidae, have a powerful proboscis, which they use to drill through the shell of crustacean prey and eat the soft tissue. I put it back in the water!
All these mollusks are prey for shore birds, larger mollusks (including their own species), fish, and crabs. The ocean is a scary place!
Today’s special animal friend is the Cheetah, Acinonyx jubatus. Our tour has moved along to Chobe National Park in Botswana. The oldest national park in Botswana, it is also the most biologically diverse. It is famous for a lion population that eats elephants. We’re going to try to avoid them while concentrating on the cheetah. But first, an overview of the park:
https://www.youtube.com/watch?v=YY8joJlz1pU
There are four subspecies of cheetahs. Here in southern Africa, we have A. jubatus jubatus, the “nominate subspecies,” of which there are over 4,000 individuals in Angola, Botswana, Mozambique, Namibia, South Africa, and Zambia. Northeast and Northwest African cheetahs number in the hundreds, while a population of fewer than 50 Asiatic cheetahs lives in Iran.
https://www.youtube.com/watch?v=cq9-Nh7FzEU
The world’s fastest land animal – up to 65 mph for short distances – cheetahs are built like a greyhound, with long, thin legs, a small head, and a large chest. Their spines are unusually flexible, and their hip and shoulder joints extend further than most quadrupeds’. A large male can be about three feet high at the shoulder and weigh up to 150 lbs. (A leopard is a similar size, though differently proportioned, while lions are two to three times heavier.) Cheetahs’ claws retract only a little, unlike other cats’. This helps with traction when they accelerate and then stop.
https://www.youtube.com/watch?v=lGhTCPzMHvY
Cheetahs are active during the day when they share habitat with other large, feline predators. If they are the only big cat around, they are more likely to hunt at night, especially when there is bright moonlight. They usually eat smaller ungulates such as Dorcas gazelles, impala, and duiker, rarely pursuing prey weighing over 90 lbs. The cheetah usually bites a prey animal’s throat, holding on for up to 5 minutes to strangle the animal. Their hunting success is pretty good, over 40% for the smallest prey animals.
https://www.youtube.com/watch?v=dlj4Jw8omIc
Cheetah society includes groups of male siblings called coalitions. These bros will stake out a territory as a group, defend it from other males, and sometimes hunt cooperatively. The coalitions do not have to be biological relatives. Orphaned males raised in captivity can be paired with a non-relative and released; the two will maintain the attachment for life.
Females are solitary except when living with their young cubs or, occasionally, an adult daughter. Their home ranges often overlap the territories of several groups of males. Female fertility seems to be correlated with exposure to males and their scent markings, and it is more common when prey and water are abundant. A female will mate with several males during estrus. Gestation is about three months, and up to 8, but usually 3 or 4, cubs are born.
https://www.youtube.com/watch?v=OfZ7Ekn56sU
Cheetahs are rated as Vulnerable by IUCN. They are legally protected throughout their range. They are threatened by habitat loss, illegal hunting, and declining prey populations.
Good morning, everyone. Happy Thor's Day!