A common garden experiment on capelin (Mallotus villosus) early life history stages to examine use of beach and deep-water spawning habitats

Capelin (Mallotus villosus) in coastal Newfoundland are known to spawn on beaches but deep-water (demersal) spawning sites in close proximity (< 4 km) have recently been documented. Environmental features differ dramatically between the two spawning habitats, creating divergent selection pressures on early life history stages. We test for evidence of local adaptation or facultative spawning using a common garden experiment (CGE) design. Artificially fertilized eggs from two beach sites and one demersal site were incubated across a temperature gradient: 4 °C (cold; representative of demersal sites), 7 °C (medium) and 12 °C (warm; representative of beach sites). Reaction norms did not differ between beach and demersal sites, providing support that capelin are facultative spawners. Irrespective of the habitat adults were collected in, temperatures from 4 to 7 °C produced larvae with a higher probability of survival due to higher hatching success, length at hatch and nutritional reserves. The ability to behaviourally adjust spawning habitat based on prevailing temperature may be critical to maximize recruitment and minimize population-level impacts of climate change on this key forage fish.

► We use a common garden experiment design to examine use of two spawning habitats.
► Artificially fertilized eggs were incubated at 4, 7 and 12 °C.
► No evidence of adaptation to thermal conditions in early life history stages
► High quality eggs and larvae are produced at 4–7 °C.