In the 1860s, when the Bohemian glassblower Leopold Blaschka began sculpting models of underwater creatures, the Industrial Revolution, population growth and climate change had yet to take their toll on marine biodiversity. Over three decades, using techniques that still baffle experts, Leopold and his son, Rudolf, handmade about 10,000 marine sculptures, each one rendered in minute detail: impossibly delicate anemones, livid orange cuttlefish – creatures at once alien and unnervingly lifelike.

In a world before scuba diving, underwater photography or ocean life surveys, the Blaschkas’ models proved an invaluable educational resource, with universities worldwide purchasing collections of glass specimens. One of the largest, with 570 models, belongs to Cornell University in the US, where until recently it was all but forgotten, stowed in a warehouse in a state of disrepair. As a young professor in the 1990s, Dr Drew Harvell began cataloguing the collection, discovering a “time capsule” of 19th-century marine biology. “There’s value in the entire collection,” she says. “It’s what you could see 150 years ago, frozen in time.”

Facebook Twitter Pinterest A tube worm (Riftia pachyptila). Photograph: 2014 Gary Hodges Photography

Harvell’s 25-year love affair with the Blaschka models has led her from Italy to Indonesia, resulting in her book, A Sea of Glass. Part natural history, part memoir, it recounts her attempt to assess the glass creatures in the collection and determine, as she puts it, “which of those are still present in our oceans, and how abundant they are”. The Blaschkas worked largely from real specimens, shipped live and packed in algae from a laboratory in Naples, so Harvell focused much of her search in that corner of the Mediterranean. “Those were amazing dives,” she says, “seeing the slugs, anemones, jellyfish – all these exact Blaschka matches.”

The outlook for other species, however, is bleak. Many of the Blaschka invertebrates have declined and some, especially deep-water species of octopus and squid, may even be extinct. Equally troubling is the state of several Mediterranean corals and sponges that have suffered “massive mortality” from climate change-related warming and acidification. “Corallium rubrum, Balanophyllia europaea, Asteroides calycularis” says Harvell, listing species under threat. When asked to repeat the Latin she apologises: “They’re like my friends, I just rattle off their names.”

Aside from being a scientific study, A Sea of Glass is also an artistic monograph; an appreciation of the unique “gestalt” created by the Blaschkas. “No one on the planet can produce glass like that today,” says Harvell, “and it wasn’t just the glass, it was the living animals they cared so much about capturing.” She compares the Blaschkas to the great ornithological artist John James Audubon, with the important difference that the glass models retain their scientific function today. “I use them in my teaching”, she says. “My students could never see this range of live invertebrates”.

Facebook Twitter Pinterest Left: the mauve stinger jellyfish (Pelagia noctiluca), photographed by Drew Harvell. Right, its glass counterpart. Photograph: Museum D’Histoire Naturelle Geneva

Harvell seems to channel the devotion that motivated the Blaschkas, describing with particular passion the glass octopus vulgaris in the Cornell collection, carefully restored from its shattered former state. “Masterpieces of art can translate nature for us,” she says. “There’s something about the way it passes through human hands; they’re bringing this magic undersea world to life.”

A Sea of Glass by Drew Harvell is published by University of California Press (£22.95).