# The Effects of Salinity on the Survival, Growth, and Eco-Physiological Parameters of Juvenile Sea Urchin Diadema setosum

## TL;DR

This study finds that juvenile sea urchins Diadema setosum thrive best in salinity levels of 32–36, which is crucial for their aquaculture and conservation.

## Contribution

The study identifies the optimal salinity range for juvenile D. setosum growth and survival, filling a gap in understanding their eco-physiological responses.

## Key findings

- Juvenile D. setosum showed 100% survival at salinities of 32–36 in winter and across all salinities in spring.
- Optimal growth occurred at salinities of 32–36, with negative growth at lower salinities during winter.
- Higher oxygen consumption and ammonium excretion at 32–36 salinity indicate carbon-based metabolism, while protein metabolism dominates under salinity stress.

## Abstract

Diadema setosum holds both economic and ecological significance. Economically, it is not only valued for its medicinal properties but also for its gonad, which can be processed into various seafood products, making it an important commercial sea urchin species. Ecologically, D. setosum plays a vital role in maintaining marine ecosystem balance by feeding on algae and organic debris, thereby facilitating nutrient cycling and energy flow within benthic ecosystems. However, overfishing and environmental changes have led to a decline in its population. Previous studies have shown that salinity significantly affects the reproduction and larval development of D. setosum, but its impact on juveniles remains unclear. In this study, we investigated the effects of salinity on the survival, growth, and eco-physiological parameters of juvenile D. setosum. Our results demonstrate that salinity has a substantial influence, with an optimal range of 32–36. This work provides valuable insights for the breeding and aquaculture of D. setosum.

Diadema setosum is an economically important species in tropical and subtropical waters. To determine the optimal salinity for D. setosum aquaculture, we examined six salinity levels (20, 24, 28, 32, 36, and 40) during winter and spring, assessing their effects on survival, growth, and eco-physiological parameters of juvenile D. setosum. Results showed that (1) in winter, the survival rate of juvenile D. setosum was highest at salinities of 28–36, with 100% survival at salinities of 32–36. During spring, all salinity groups reached 100% survival. (2) Juveniles exhibited optimal growth performances at salinities of 32–36 across all seasons, and negative growth occurred at lower salinities (20–24) during winter. (3) The juveniles exhibited higher oxygen consumption rate and ammonium excretion rate with an atomic O:N ratio > 25 at salinities of 32–36, indicating that carbon-based substrates were the primary catabolic substrate. Under salinity stress (<24 or >40), the O:N ratio declined significantly, reflecting that proteins were the main metabolic substrate. (4) Fecal excretion was higher in winter than in spring, possibly due to size and digestive efficiency differences. Studies confirmed that salinity and temperature exert significantly combined effects on D. setosum, with an optimal salinity range of 32–36. This work provides valuable insights for the breeding and aquaculture of this species.