Furthering a former post of the impacts of artificial light on intertidal organisms, today’s featured study centres its discussion on the impact of Ecological Light Pollution (ELP) on the strictly nocturnal adult O. tuberculata, a talitrid amphipod which is dominant specie in the upper intertidal zone of exposed sandy beaches of central and southern Chile. 

Figure 1.  Orchestoidae tuberculata

ELP, similar to ALAN (mentioned in earlier posts) refers to artificial light that affects natural light and dark patterns of organisms in the ecosystem. The presence of artificial light is once again significant to sandy beach invertebrates. Similar to intertidal fishes, most amphipods display circadian rhythms as well, searching for food in the night while staying buried under intertidal sediments in the day. Thus, increased light pollution would have implications for their activity patterns and growth.

Formerly, a survey conducted by Giaconni (2006) had found abundant populations of this species in all but one sandy beach system which, coincidentally, was the only one exposed to ELP. This study furthers this observation by experimentally assessing the influence of ELP on the locomotor activity and feeding ecology of adult O. tuberculata. Here’s what they found:

1. Changes to Circadian Rhythm 

Amphipods exposed to ELP was found to be active in a decrease proportion of the night (Figure. 2). However, by the seventh day of ELP exposure, abnormality of circadian rhythm was observed. Amphipods started to show indication of a reversal of night and day activity patterns. This observation is new to former studies which only detected an extended activity period in ELP-exposed nocturnal amphipods. 

2. Stunted Growth

Impact on amphipod growth is also observed as a result of exposure to ELP. In particular, those exposed to artificial light experienced only a third of the growth experienced by those under natural conditions (Figure. 3).

This is consistent with the decreased consumption rates observed where consumption of ELP-exposed amphipods vis-a-vis control amphipods was halved (Figure. 4). Furthermore, no differences in absorption efficiency were found (Figure. 5). This lack of physiological response observed means that amphipods do not have a natural mechanism to compensate for decreased food availability with increased absorption efficiency.

However, since amphipods are free to migrate from one habitat to another in a natural setting, findings derived from laboratory experiments have to be read with caution to avoid extrapolation of its results.

Talitridae crustacean amphipods, as one the dominant organisms (in biomass and abundance) in temperate sandy beaches, have a significant role in its ecosystem. With its responses to ELP, prolonged exposure to artificial light is bound to be felt along the food chain. Fortunately, in some studies, the effects of light exposure are suggested to decrease significantly with distance from the light source. Hence, we can be hopeful that with proper usage and arrangement of artificial light fixtures, light pollution can be managed without imposing significant harm to the marine ecosystem and its organisms. 

Till next time!

Trudie

References:

• Biodiversidad Chile. (2012, April 9). Orchestoidea tuberculata Nicolet, 1849 [Photograph]. Flicker. https://live.staticflickr.com/2663/5826706113_593fc8e65a_b.jpg
• Giaconni, C. (2006). Efecto de la contaminacion lumínica sobre la abundancia, riqueza y comportamiento de la macroinfauna de playas arenosas de la IV Region. Centro de Egresados de Ingeniería en Recursos Naturales Renovables, Memorias y Publicaciones, Universidad de Chile.
• Jelassi, R., Ayari, A., Nasri-Ammar, K. (2014). Effect of light intensity on the locomotor activity rhythm of Orchestia montagui and Orchestia gammarellus from the supralittoral zone of Bizerte lagoon (North of Tunisia). Biol. Rhythm Res. 45 (5), 817e829.
• Luarte, T., Bonta, C. C., Silva-Rodriguez, E. A., Quijón, P. A., Miranda, C., Farias, A. A., & Duarte, C. (2016). Light pollution reduces activity, food consumption and growth rates in a sandy beach invertebrate. Environmental Pollution, 218, 1147-1153.