Read Online Spirals in Time: The Secret Life and Curious Afterlife of Seashells by Helen Scales - Free Book Online Page B
Authors: Helen Scales
Tags: science, History, Non-Fiction, Nature, Life Sciences, Social History, Marine Biology, Seashells
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intricate shape and noticing details that other people miss. In his book A Natural History of Shells , he writes about how his hands have allowed him to explore the way shells from different places vary in appearance: the geography of shape.
He describes how the shells he finds on tropical shores are radically different from those on Dutch beaches. For starters, they are much more carefully made. Individuals from the same species of tropical mollusc will make shells that are identical copies of each other. They stick closely to a set of hidden rules, imposed perhaps by the presence of so many predators and competitors. Slightly wonky shells just won’t cut it in the race for survival in these crowded, species-rich waters; they might not be strong enough, or well protected enough from attack. In cooler and deeper waters, where life in many ways is more relaxed and less extreme, molluscs can get away with being less finicky about their shells. On the whole, away from the tropics, molluscs are built relatively sloppily.
Vermeij also writes in his book about another key moment in his life, when a big idea hit him. He spent the summer of 1970 in the western Pacific Ocean, on the island of Guam, on a field trip with his friend Lucius G. Eldredge. On one particular day they were searching for shells in the falling tide at Togcha Bay on the windy side of the island when Eldredge (known as Lu) handed Vermeij the shell of a Money Cowrie with its top sliced clean off. Lu made an offhand remark that he often saw crabs cutting open cowries in his aquarium tanks.
Until then, Vermeij hadn’t paid much attention to the fact that he often found masses of broken shell pieces on tropical beaches and he suddenly got to thinking about predation. He realised that tropical seashells have a really hard time with so many predators trying their best to crack, smash, peel open and drill into them. He began to wonder how their shells have evolved to ward off these attacks, and soon realised there are many reasons why shape matters.
An obvious way a mollusc can avoid getting eaten is by making a very big, thick shell, but that comes at the cost of having to make and then drag around a massive, heavy lump. A more economical way to make a shell more difficult to handle and swallow is to give it a covering of spines and bumps. Realising this, Vermeij finally understood why Mrs Colberg’s Floridian shells, and so many other tropical species, have fancy ornaments. In the crowded tropics, molluscs are doing their best to survive. As they grow, they can add embellishments to their shells; prongs can be added at regular intervals, or they can form a dense tangle like the quills of a porcupine. Spondylus , for example, the thorny oysters, are industrious spine-makers, expertly producing new ones and fixing any that have broken at a rate of a few millimetres every day.
Vermeij also figured that the pleats and corrugations on many tropical shells are a cost-effective way of creating a strong body armour that’s difficult to break into while keeping the weight down. Thickening and flaring out theaperture of shells is another way of deterring predators, as in the Malaysian microsnails with their trumpet-shaped mouths.
Shape can also help shells to hide. Sleekly shaped molluscs can slip silently through the water without sending out telltale ripples that predators detect; being more hydrodynamic also allows for a quicker getaway. We can surmise that parts of Raup’s imaginary museum may remain empty of real shells simply because they are not streamlined enough.
For shells that live in sandy, muddy places, shape can mean the difference between resting on top and sinking in. Epifaunal species are ones that have adapted to a life of lying on the surface of the seabed; their shells are often wide and flat, acting like snow shoes. They include species like the Big Ear Radix, a gastropod that lives in lakes across Europe; throughout their lives they continually
He describes how the shells he finds on tropical shores are radically different from those on Dutch beaches. For starters, they are much more carefully made. Individuals from the same species of tropical mollusc will make shells that are identical copies of each other. They stick closely to a set of hidden rules, imposed perhaps by the presence of so many predators and competitors. Slightly wonky shells just won’t cut it in the race for survival in these crowded, species-rich waters; they might not be strong enough, or well protected enough from attack. In cooler and deeper waters, where life in many ways is more relaxed and less extreme, molluscs can get away with being less finicky about their shells. On the whole, away from the tropics, molluscs are built relatively sloppily.
Vermeij also writes in his book about another key moment in his life, when a big idea hit him. He spent the summer of 1970 in the western Pacific Ocean, on the island of Guam, on a field trip with his friend Lucius G. Eldredge. On one particular day they were searching for shells in the falling tide at Togcha Bay on the windy side of the island when Eldredge (known as Lu) handed Vermeij the shell of a Money Cowrie with its top sliced clean off. Lu made an offhand remark that he often saw crabs cutting open cowries in his aquarium tanks.
Until then, Vermeij hadn’t paid much attention to the fact that he often found masses of broken shell pieces on tropical beaches and he suddenly got to thinking about predation. He realised that tropical seashells have a really hard time with so many predators trying their best to crack, smash, peel open and drill into them. He began to wonder how their shells have evolved to ward off these attacks, and soon realised there are many reasons why shape matters.
An obvious way a mollusc can avoid getting eaten is by making a very big, thick shell, but that comes at the cost of having to make and then drag around a massive, heavy lump. A more economical way to make a shell more difficult to handle and swallow is to give it a covering of spines and bumps. Realising this, Vermeij finally understood why Mrs Colberg’s Floridian shells, and so many other tropical species, have fancy ornaments. In the crowded tropics, molluscs are doing their best to survive. As they grow, they can add embellishments to their shells; prongs can be added at regular intervals, or they can form a dense tangle like the quills of a porcupine. Spondylus , for example, the thorny oysters, are industrious spine-makers, expertly producing new ones and fixing any that have broken at a rate of a few millimetres every day.
Vermeij also figured that the pleats and corrugations on many tropical shells are a cost-effective way of creating a strong body armour that’s difficult to break into while keeping the weight down. Thickening and flaring out theaperture of shells is another way of deterring predators, as in the Malaysian microsnails with their trumpet-shaped mouths.
Shape can also help shells to hide. Sleekly shaped molluscs can slip silently through the water without sending out telltale ripples that predators detect; being more hydrodynamic also allows for a quicker getaway. We can surmise that parts of Raup’s imaginary museum may remain empty of real shells simply because they are not streamlined enough.
For shells that live in sandy, muddy places, shape can mean the difference between resting on top and sinking in. Epifaunal species are ones that have adapted to a life of lying on the surface of the seabed; their shells are often wide and flat, acting like snow shoes. They include species like the Big Ear Radix, a gastropod that lives in lakes across Europe; throughout their lives they continually
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