Sea Slugs’ Survival Secrets 

A recent study conducted by the University of Groningen, investigated how three species of solar-powered sea slugs exhibit unique photoprotection strategies against excessive light, revealing connections between light intensity, photoprotection, and oxidative stress. The study underscores the necessity of exploring aquatic photosynthesizers under natural lighting conditions. 

E crispata blue- Photo credit: L. Burgués Palau – all rights reserved.

This study sheds light on the photoprotective strategies employed by three sea slug species—Elysia crispata (lettuce sea slug), Elysia velutinus, and Elysia ornatae (ornate leaf slug)—living in high-light environments. These slugs steal chloroplasts (the organelle that makes energy from sunlight in plants and algae) from the algae that they eat. These stolen chloroplasts (kleptoplasts) keep making energy once they are inside the slug. In this paper, they showed that these slugs protect their kleptoplasts from too much light, allowing them to make more energy, which the slug then uses.

Meet the Team 

Elysia crispata, more commonly known as the lettuce sea slug, was typically found at depths between 5 and 15 meters.  These sea slugs have diverse coloration, which can suggest population-specific variations in light-seeking behavior. Unlike previous reports of hiding behavior, this study observed lettuce sea slugs exposed to full sunlight and using its own body to provide shading. This behavior demonstrated the species’ ability to physically control light reaching its kleptoplasts. 

E crispata  (green)-Photo credit: Elise M. J. Laetz- all rights reserved.

 

Elysia velutinus, was found to prefer depths of 4–6 meters and relied on macroalgal food for camouflage, exhibited a light-avoidance response in laboratory trials. The study suggests that these slugs likely avoid excess light by seeking shelter among algae, displaying a unique photoprotective strategy. 

Elysia ornata, or ornate leaf slug, typically resides in shallow waters and is associated with Bryopsis plumosa (green) algae.  These sea slugs displayed a strong negative phototactic response, indicating a preference for darkness. Despite having the highest optimal light intensity among the studied species, ornate leaf slugs showed signs of oxidative stress, possibly due to limited photoprotective mechanisms. 

The sea slug species were collected from the reefs in Curaçao. 

The sacoglossan and algal species used in this study. A. Elysia crispata—specimens ranged from~4–14 cm in length, B. Elysia velutinus—specimens ranged from~0.1–1 cm in length, C. Halimeda sp.—thalli ranged from~5–15 cm in height from the substrate, D. Elysia ornata—specimens ranged from~0.6–1.5 cm in length, and E. Bryopsis plumosa—specimens ranged from 5 to 10 cm in height from the substrate. Photo credit: Laia Burgués Palau, Giulia Senna, Elise M. J. Laetz- all rights reserved.

 

Implications 

The study emphasizes the need to consider natural light conditions when studying photosymbiotic organisms, revealing a disparity between laboratory experimental conditions and field reality. The intricate photoprotective adaptations observed in these sea slug species provide valuable insights into their interactions with high-light environments and highlight the importance of understanding the ecological context for accurate research findings. 

DCNA 

TheDutch Caribbean Nature Alliance (DCNA)supports (science) communication and outreach in the Dutch Caribbean region by making nature related scientific information more widely available through amongst others theDutch Caribbean Biodiversity Database, DCNA’s news platformBioNewsand through the press. This article contains the results from several (scientific) projects but the projects themselves are not DCNA projects. No rights can be derived from the content. DCNA is not liable for the content and the in(direct) impacts resulting from publishing this article. 

More info in the Dutch Caribbean Biodiversity Database

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