Hot limpets go south, stay cool

Spencer D.S. Virgin and David R. Schiel

This is a plain language summary of a Functional Ecology research article which can be found here.

            In 2016 a 7.8 Mw earthquake lifted 130 km of coastline along the South Island of New Zealand by up to 6m. This was bad news for most intertidal species. Fortunately, limpets recovered quickly but then had to cope with increased thermal stress in the newly configured intertidal zone. Limpets are mostly high and dry during low tides and are therefore well-adapted to withstand such conditions. However, in the summers that followed, extreme temperatures exceeding 40^oC were occasionally recorded. This may be a harbinger of the more frequent and intense heat events that are expected due to climate change. Because limpets are already living near their maximum thermal limits, their choice is to adapt to rising thermal stress or die. This paper shows how limpets adapt to changing levels of thermal stress throughout a year.

Cool limpets that are wired. Here heart-rate sensors attached to the tops and temperature probes underneath their shells

Two researchers moving boulders on the incoming tide using prybars and leverage from a bedrock outcrop

            During winter, when microalgae (the preferred food of limpets) is plentiful because of low thermal stress, limpets were evenly distributed throughout the high intertidal zone. But in summer, when air temperatures at low tide were high and food was patchy, limpets moved to shaded locations on the south sides of boulders where it was cooler, often by more than 10^oC. This reduced stress was evident physiologically. Limpets on cooler south facing surfaces had much lower heart rates than those on other surfaces of intertidal boulders (Fig 1). When these large (≥ 0.5 m³) boulders were turned experimentally (Fig 2), limpets moved back to the cooler side. It was surprising to find that heat shock protein responses, the go-to for most gastropods under heat stress, were not a major factor in their survival, as the limpets maintained similar levels year-round, regardless of location. Shade-seeking behaviour buffers limpets against extreme heat events, which may explain why there were no recorded mass-mortalities of limpets during times of extreme heat that negatively affected most other species at mid and high tidal elevations. Limpets can look forward to a sunny future spent in the shade.