Luck was against these young cockles, which were likely washed up on to the beach during a storm and did not survive the cold air temperatures during low tide.
Observation by Brandon Thynes:
I went to collect water samples for Phytoplankton IDing for SEATOR and Petersburg Indian Association at Sandy Beach Park. The weather had just changed from around 5 degrees F for the week to around 30 degrees F on Friday The 17th. There wasn't a storm swell that week. I saw 2 sand dunes with young cockles scattered, exposed and some of them were open. I just got back from checking to see if they were there at low tide and they were not. I have seen larger cockles sitting on the ground but never this many little one at one time.
Shared via email with Erica Lujan
Mandy Lindeburg, Fisheries Research Biologist with the National Oceanic and Atmospheric Association (NOAA), writes:
Cockles (Nuttall cockle, Clinocardium nuttallii) in southeastern Alaska, and in general, inhabit the low intertidal to depths of 30 m in small cobble to sandy substrates. They are shallow burrowers near the surface due to a short siphon (12mm or 0.5 in) for filter feeding. In contrast, a razor clam can go down to 3 feet! Often adult cockles can be found just lying on the surface, likely using their very agile "foot" to thrash around and escape common predators like sea stars and dungeness crabs. Inhabiting areas near the surface also increases the risk of exposure to the elements especially for their young called "spat" that settle out in the intertidal and shallow subtidal.
In this case, timing is everything and the odds were stacked against them: an Arctic blast of single digit temperatures, gale force winds with -20 F wind chill, and minus tides. These spat were likely pushed up the beach in the storms and exposed to lethal air temperatures during very low tides. As they succumb to the cold temperatures their adductor muscle weakens and they can no longer keep their shells closed, further solidifying their demise. So, their gaping appearance is often symptomatic of this scenario. Similar scenes of young cockle mortalities have been seen in the Juneau area along with sea stars that were caught in this recent lethal cold temperature event. On a positive note, these spat are providing critical winter calories for other marine invertebrates, seabirds, and sea ducks.
Comments from LEO Editors:
The temperature chart below shows daily temperatures in Petersburg dropping below the average low temperature for mid-January.
