Seasonal variability of emerging invertebrate assemblages in a sheltered soft-bottom sublittoral habitat

- Emerging invertebrate assemblages showed strong seasonal variation.
- The pattern of variation paralleled to that reported for pelagic assemblages.
- A thorough understanding of benthic biota dynamics should consider emergent fauna.

In the Humboldt Current upwelling ecosystem of northern Chile, seasonal variation in the assemblage structure of pelagic invertebrates is strongly coupled with seasonal oscillations in upwelling intensity, however, benthic assemblages apparently show no clear responses to seasonal changes in the environment. Herein, we assess seasonal variability in the structure of the emerging assemblage (i.e., invertebrates that migrate nocturnally from the seabed to the water column, returning to the seabed during the day). This assemblage uses both the pelagic and benthic habitats daily, and thus offers an interesting group to study in order to assess their response to seasonal variability. We carried out replicated sampling during the austral autumn, winter, and spring of 2012 and the summer of 2013 in the subtidal zone of Bolsico (northern of Chile), using traps specifically designed to capture emerging benthic invertebrates, at 7 m depth in a sheltered soft-bottom habitat. We observed clear seasonal effects, with total abundance increasing during spring and a cyclical pattern in assemblage structure of the emerging benthos. Three main patterns characterized seasonal changes in species abundance; peaks of abundances during autumn (e.g. amphipods Eudevenopus gracilipes and Liljeborgia sp.), summer (e.g. amphipods Aora typica and Microphoxus sp.) and spring (e.g. copepods Tigriopus sp. and Corycaeus sp.). Strong seasonal patterns in emerging invertebrates closely resembled the pattern observed in the pelagic fauna.