With the rising awareness of light pollution, fish-y business has entered the debate. In particular, the business of intertidal fishes.  

Image 1. Intertidal Zone (Rocky Shoreline)

This study shows that intertidal fish (G. laevifrons) exposed to Artificial Light Pollution at Night (ALAN) experience two main changes — 1. interruption of circadian cycles and circatidal rhythms, and 2. increase in oxygen consumption. But first, let’s talk about what ALAN is. ALAN refers to the process of disruption in which artificial light alters the natural cycles of light and dark in ecosystems. 

1. Interruption of Circadian Cycles and Circatidal Rhythms

G. laevifrons exposed to ALAN was found to stop displaying natural circadian cycles and circatidal rhythms that were otherwise observed in other fishes under a natural 12 hour: 12 hour light-dark cycle. In the experiment, control G. laevifrons clearly displayed a single activity peak in accordance to tidal changes, however, this activity peak was altered or lost in those exposed to ALAN. Figure 1 illustrates this change showing the increases in activity of G. laevifrons exposed to ALAN throughout the day.

This increase in activity is studied in relation to its scototaxis behaviour, referring to the preferential movement of fishes to dark zones as opposed to bright ones under natural conditions. While bright, illuminated zones leave fishes vulnerable to visual predators, dark zones are associated with safety and hence preferentially visited. However, in the study fish exposed to ALAN showed an increased movement between the refuge (dark) and the light zones of the experimental setup. Such behaviour suggests that fishes modify their activity patterns in response to ALAN, which can potentially pose a risk to these intertidal fishes.

2.  Increase in Oxygen Consumption

Increase in oxygen consumption was also detected in fishes exposed to ALAN (Figure 2). This increased oxygen consumption was a likely consequence of increased fish activity under ALAN exposure mentioned above. Such demands might increase the metabolic cost of living which likely impacts fish weight in the long run. Hence, in addition to a greater physiological demand imposed on G. laevifrons, its overall energetic balance is also adversely impacted.

Together, long-term exposure to ALAN is likely to have severe implications on the long-term population sustainability of G. laevifrons and more broadly, intertidal fishes. However, besides the impact of excess light on fishes, it is also integral to note the magnitude of the problem. As of 2018, approximately 22% of coastal areas in the world are exposed to artificial light at night. This hints at the possible extent and severity of impact ALAN has on coastal marine ecosystems and if not, stresses the increasing risk of ALAN. 

Let’s remember to protect our fishy friends! You know how it goes — Fish are friends, not food!

 

Till next time, 

Trudie

References:

• National Geographic Society. (2019, September 3). Intertidal zone. https://www.nationalgeographic.org/encyclopedia/intertidal-zone/
• On the Edge: Living in The Intertidal Zone [Photograph]. (n.d.). Hō‘ike o Haleakalā Curriculum. https://www.hoikecurriculum.org/wp-content/uploads/2012/07/IMG_6541.jpg
• Pulgar, J., Zeballos, D., Vargas, J., Aldana, M., Manriquez, P. H., Manriquez, K., Quijón, P. A., Widdicombe, S., Anguita, C., Quintanilla, D., & Duarte, C. (2019). Endogenous cycles, activity patterns and energy expenditure of an intertidal fish is modified by artificial light pollution at night (ALAN). Environmental Pollution, 244, 361-366. https://doi.org/10.1016/j.envpol.2018.10.063
• Taywilsoncx. (n.d.). Fisharefriendsnotfood Findingnemo GIF [Gif]. tenor. https://tenor.com/view/fisharefriendsnotfood-findingnemo-shark-gif-12512103