Artificial isopod burrows provide a refuge from desiccation for intertidal crustaceans

Abstract

The novel habitats created by ecosystem engineers can serve as key refuges for other species, particularly in stressful intertidal habitats. However, the specific benefits these habitats provide and why other species use them are less understood. The introduced burrowing isopod Sphaeroma quoianum is a widespread intertidal ecosystem engineer in Northeast Pacific estuaries. Numerous species inhabit its burrows during low tide suggesting burrows may confer benefits to their occupants. We tested if burrows created by S. quoianum provide a refuge for intertidal invertebrates using lab and field desiccation experiments that compared a) survival of three common estuarine taxa (S. quoianum, Gnorimosphaeroma noblei, and gammarid amphipods) and b) microclimate (humidity, temperature) inside and outside of artificial isopod burrows in wood and sandstone substrata. In the lab, invertebrates survived 2–3 times longer inside of burrows than outside of burrows under aerial exposure. In the high intertidal, the probability of survival in burrows was 6.5 times greater for S. quoianum after four days and 12.7 times greater for G. noblei after two days, compared to isopods on the surface. In contrast, in the mid-intertidal, G. noblei was 1.75 times more likely to survive in burrows, whereas S. quoianum survival did not differ between burrows and the surface. Burrows were also substantially more humid than surfaces, but temperature did not differ consistently. Our results show that even small microhabitats like isopod burrows provide a refuge from desiccation for intertidal invertebrates and may help explain their use by other estuarine intertidal species.