Impacts of artificial light at night on the early life history of two ecosystem engineers

Abstract

Sessile marine invertebrates play a vital role as ecosystem engineers and in benthic-pelagic coupling. Most benthic fauna develop through larval stages and the importance of natural light cycles for larval biology and ecology is long-established. Natural light-dark cycles regulate two of the largest ocean-scale processes that are fundamental to larvae's life cycle: the timing of broadcast spawning for successful fertilization and diel vertical migration for foraging and predator avoidance. Given the reliance on light and the ecological role of larvae, surprisingly little is known about the impacts of artificial light at night (ALAN) on the early life history of habitat-forming species. We quantified ALAN impacts on larval performance (survival, growth, development) of two cosmopolitan ecosystem engineers in temperate marine ecosystems, the mussel Mytilus edulis and the barnacle Austrominius modestus. Higher ALAN irradiance reduced survival in both species (57% and 13%, respectively). ALAN effects on development and growth were small overall, and different between species, time-points and parentage. Our results show that ALAN adversely affects larval survival and reiterates the importance of paternal influence on offspring performance. ALAN impacts on the early life stages of ecosystem engineering species have implications not only for population viability but also the ecological communities that these species support. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Keywords: development; growth; larvae ecology; light pollution; supply-side ecology; survival.

Figure 1.

Example of larvae size measurements taken in ImageJ software. Carapace length (a), width (b), and area (c) measurements for Austrominius modestus cyprid. Maximum shell length measured parallel to the hinge line on day 60 for Mytilus edulis (d). The black dots inside the larvae are the eyes. Image credit: Fraser Brough.

Figure 2.

(a) Influence of irradiance on survival of the barnacle Austronimius modestus survival nauplii and cyprid per 100 animals. (b) Influence of irradiance and parent on the average developmental time of barnacle larvae from nauplii to cyprid. (c) Relationship between of the average developmental time and survival of barnacle from different parents. The figures show the raw data (dots are jittered, darker areas represent overlapping data points), predicted relationships (solid lines) and 95% prediction intervals (dotted lines). Note that barnacle data are displayed as survival to allow better comparison between species. Image credit: Harms [40].

Figure 3.

Influence of irradiance on (a) the survival of blue mussel Mytilus edulis larvae per 10 000 animals (from fertilization until Day 60) and (b) the length of mussel larvae (measured in µm) on Day 9. The figure shows the raw data (dots are jittered, darker areas represent overlapping data points), predicted relationships (solid lines) and 95% prediction intervals (dotted lines). Image credit: Fraser Brough.