The balmy waters of the Caribbean could turn into a deadly heat trap for countless tiny creatures. Authors of a new study conducted at the Smithsonian Tropical Research Institute (STRI) in Panama discovered that microscopic sea urchin eggs and larvae may suffer stunting or death when the water temperature spikes just a couple of degrees above normal, adding to the impact of climate change in already warm tropical oceans.
Sea urchins, pincushion-shaped relatives of the starfish, graze the sea floor from shallow coastal areas to deep ocean vents from pole to pole. Their young look nothing like them. Adults release millions of eggs and sperm into the water, which develop into pinprick-sized free-swimming larvae. Only a minute fraction will survive and metamorphose into adults. Scientists think the developmental stages from egg to larvae are extra sensitive to temperature changes, but very few studies compare the vulnerability of the offspring to that of the adults.
The balmy waters of the Caribbean could turn into a deadly heat trap for countless tiny creatures. Authors of a new study conducted at the Smithsonian Tropical Research Institute (STRI) in Panama discovered that microscopic sea urchin eggs and larvae may suffer stunting or death when the water temperature spikes just a couple of degrees above normal, adding to the impact of climate change in already warm tropical oceans.
Sea urchins, pincushion-shaped relatives of the starfish, graze the sea floor from shallow coastal areas to deep ocean vents from pole to pole. Their young look nothing like them. Adults release millions of eggs and sperm into the water, which develop into pinprick-sized free-swimming larvae. Only a minute fraction will survive and metamorphose into adults. Scientists think the developmental stages from egg to larvae are extra sensitive to temperature changes, but very few studies compare the vulnerability of the offspring to that of the adults.
"That's because they're tiny and generally inaccessible," said Rachel Collin, STRI staff scientist and lead author of the new study, published in Ecology and Evolution in July. She and coauthor Kit Yu Karen Chan, now at the Hong Kong University of Science and Technology, collected and studied sea urchins from the lagoons around Bocas del Toro, Panama, which normally experience temperatures around 27 to 29 degrees Celsius (C). They exposed adults and offspring in various developmental stages to two hours of acute heat stress by placing them in water baths with temperatures ranging from 28 to 36 degrees C.
Early stage larvae of one common species, the green sea urchin, Lytechinus variegatus, died at temperatures above 32 degrees C, while eggs and late stage larvae died closer to 34 degrees C. Adults survived up to almost 35 degrees C. Long-term exposure to temperatures above 30 degrees C reduced larval survival and growth, with all larvae dying when temperatures reached 32 degrees C.
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A microscopic photograph of a sea urchin from the plankton collection on the Seward Johnson II.
