# Environmental drivers of Catostylus tagi polyp survival and reproduction: unlocking the role of temperature and salinity, supported with citizen science data

## TL;DR

This study explores how temperature and salinity affect the survival and reproduction of a jellyfish polyp, using lab experiments and citizen science data to better understand its environmental preferences.

## Contribution

The study identifies optimal environmental conditions for C. tagi polyp survival and reproduction, integrating controlled experiments with long-term citizen science data.

## Key findings

- Polyp survival was highest at intermediate salinities (17.5–25) and temperatures (17–20°C).
- Strobilation and asexual reproduction were enhanced at specific temperature and salinity ranges.
- Citizen science data showed medusae peak between July and January in the lower Tagus estuary.

## Abstract

Catostylus tagi is a scyphozoan jellyfish native to Portuguese waters. While its life cycle is known, the environmental conditions that support polyp survival, trigger strobilation, and promote asexual reproduction remain unclear. Field observations from the citizen science GelAvista project indicate that C. tagi occurs year-round in the Tagus estuary, suggesting tolerance to broad temperature and salinity ranges. However, polyps and ephyrae have not been observed in the wild, and their natural habitats and environmental preferences remain unknown. This study aims to fill these knowledge gaps by investigating how temperature and salinity affect C. tagi polyps under controlled conditions and integrating these results with field data.

Ninety-six polyps were cultured for 71 days in well plates at four temperature treatments (14, 17, 20, 23 °C) and four salinity levels (10, 17.5, 25, 35). Survival, asexual reproduction, and strobilation were monitored. Seven years of citizen science data were analysed with environmental parameters to assess estuarine distribution.

Polyp survival was high, except at salinity 35, where mortality increased regardless of temperature. Podocyst production was enhanced at higher temperatures (20–23 °C) and intermediate salinities (17.5–25), although podocyst development into new polyps occurred at lower salinities (10–17.5). Strobilation occurred predominantly at intermediate temperatures (17–20 °C) and salinities (17.5–25). Medusae are most frequently found in the lower Tagus estuary and coastal adjacent areas, exhibiting a peak between July and January. Results showed that wind intensity was negatively correlated with medusa stranding abundances on the shores, possibly displacing individuals away from coastal areas during periods of strong winds. Sea surface temperature (SST), measured two to four months prior to medusae occurrence, was positively correlated with C. tagi abundance.

Optimal polyp performance occurred at 17–20 °C and 17.5–25 salinity. When considered alongside citizen science observations, these findings suggest that polyps may occur in estuarine areas where such conditions prevail, such as upper estuary inlets and marinas. It is further hypothesized that ephyrae could disperse to downstream and adjacent coastal zones via wind and tides. The correlation between sightings and past SSTs indicates the ephyrae and young medusae dispersal rate. Furthermore, this study highlights C. tagi’s adaptability to varying environmental conditions and contributes to identifying optimal parameters for polyp well-being and reproduction, with potential applications in jellyfish farming.