Scientists, conservationists, and fishermen alike are increasingly worried about how sea creatures will fare as the oceans warm. While there is clear evidence that higher temperatures are placing a lot of stress on mature marine animals, the effect of heat on their larvae – microscopic plankton drifting along in the water column – has not yet received sufficient scientific attention.
Now, a team of researchers led by the University of California, Santa Barbara has investigated the effect of elevated temperatures on Kellet’s whelk larvae, a common Southern California sea snail that is becoming an important target for an emerging local fishery.
“While young Kellet’s whelks are able to withstand a wider range of warmer temperatures than we expected, marine heatwaves remain a threat, especially as baseline temperatures rise,” said lead author Xochitl Clare, a doctoral student in Marine Biology at UC Santa Barbara.
The Kellet’s whelk is a predatory scavenger living in the rocky and sandy bottoms of kelp forests. This species – which is extremely abundant in the Santa Barbara Channel – develops in four stages over the course of their first month of life. The scientists focused on the last two of these stages: the veligers, which are still inside their egg capsules, and the free-swimming hatchlings.
To investigate the effects of high temperature on these larvae, the researchers placed test-tubes of velingers and hatchlings in a heat block for a one-hour trial, and measured mortality rates and developmental abnormalities. The heat block created a temperature gradient ranging from an ambient channel temperature of 15°C (50°F) on the left to temperatures up to 37°C (98.6°F) on the right.
The experiment revealed that mortality was similar between the two life stages, with half of the animals dying at about 34° C (93° F). By contrast, the hatchlings appeared to be more susceptible to defects caused by the heat than veligers, with half of the hatchlings exhibiting abnormal development or behavior at 27.6°C, versus 24.9°C for veligers (81.7°F versus 76.8°F).
In the near past, ocean water reached temperatures high enough to disrupt larval whelk development during “the Blob,” a massive marine heatwave in the northeastern Pacific which lasted from 2013 to 2016. “While we may not experience a 33°C ocean, we may see conditions where the larvae are not able to swim, where they’re not able to feed,” Clare explained. Thus, although the whelks may be able to survive such temperatures, many of them will not make it to their next stage of life.
“All in all, the whelks are proving to be super hardy in their early stages in comparison to other fished invertebrates in Santa Barbara, such as early stage abalone and squid. But as ocean warming continues to threaten our local seafood, it is critical that we understand which species will be resilient and remain ‘on the menu,’” she concluded.
The study is published in the Journal of Shellfish Research.
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