Hang on Tight: Association with Algae During Egg Development Limits Invasiveness in Haloa japonica

Abstract

Characterizing population demography and habitat selection is one of the key factors in predicting invasion outcomes. Native cephalaspidean Haminoea vesicula and introduced Haloa japonica on San Juan Island, WA are distinct in their egg-laying substratum preference. The former is indiscriminate in substratum use whereas the latter almost exclusively oviposits on macrophytes and algae. We investigated whether occurrence of macroalgae or macrophytes is essential to the development of cephalaspidean eggs. We reciprocally transplanted native 2 Haminoea vesicula and introduced Haloa japonica from their respective habitats in False Bay and Argyle Lagoon on San Juan Island, WA, and replicated reciprocal rearing in the lab. Our field surveys and transplant experiments indicate that oviposition on filamentous algae leads to higher rates of egg development in H. japonica. This strong algal association could constrain adult habitat selection to sites with high macroalgal/macrophyte availability, controlling the invasive potential of H. japonica. Such sites may not be optimal for H. vesicula for oviposition, even in the absence of H. japonica, as H. vesicula egg masses ruptured pre-hatching when reared in reciprocal conditions in the lab. Our field survey also revealed a third species of cephalaspidean occurring in these well-studied nature preserves—Haminoea virescens—and enabled comparative analyses of their egg mass biology.