Growth and feeding resilience of green sea urchin (Strongylocentrotus droebachiensis) to visible-light quantity and quality

We used a 298-day (July to April) laboratory mesocosm experiment with Newfoundland green sea urchins (Strongylocentrotus droebachiensis) to test the prediction that growth and feeding are largely unaffected by light quantity and quality within the visible-light spectrum. Sea urchins experienced either of three light environments simulating differences in illuminance and red/blue light ratios among common habitats for the species: tide pool, shallow subtidal, and deeper subtidal habitats. Sea urchins were fed exclusively kelp (Alaria esculenta) and exposed to natural photoperiod. Light had no effect on body diameter and weight. Diameter, but not weight, changed over time with a low, yet statistically significant, 3% increase from August to February. Gonadosomatic index (GSI) of sea urchins in the mesocosms doubled from similar to 10% in Aug to similar to 20% in February, with no further change in April, independently of light. GSI of sea urchins in the field was comparatively lower throughout the experiment, being similarly low, similar to 5%, in August, December, and April, and peaking significantly higher at similar to 9% in February. Light also did not affect feeding on kelp, which, however, differed significantly among the three sampling months, peaking in November. Seasonal patterns of feeding in the mesocosms followed that in natural habitats. Our findings speak highly to the relative insensitivity of the species to its visible-light environment within the range tested. They also reinforce the paradigm that in green sea urchin, visible-light quantity and quality have a much lesser impact on somatic and gonadic growth and feeding than food quality and availability.

Automated summary

The experiment showed that green sea urchins are relatively insensitive to their visible-light environment, with light quantity and quality having minimal impact on their growth and feeding. Food quality and availability were found to have a greater influence on somatic and gonadic growth and feeding in the species.