AN ASSESSMENT ON GROWTH RATE OF RELOCATED NEPTUNE �S CUP SPONGE (CLIONA PATERA) IN SINGAPORE

Abstract

Sponges constitute an important component of reef and benthic communities, but their role and interactions with other species in the marine environment have not been well-studied in Singapore and the region. The rediscovery in Singapore of Neptune’s Cup Sponge (Cliona patera)—a massive sponge that was thought to be extinct globally since 1912—shone the limelight on conservation for sponges for the first time locally. Since 2014, six individuals of this rare species have been relocated to Sisters’ Islands Marine Park as part of National Parks Board’s species recovery efforts. Ad-hoc monitoring of these sponges revealed that they were being preyed upon as bite marks were observed. This study aims to understand the growth rate of the relocated sponges and assess the effectiveness of the relocation, as well as to provide recommendations for future conservation actions.

The growth rate of each sponge was determined by measuring the total height monthly (from June to December 2020) using photographs taken from a fixed distance and angle. The number of fresh, non-fresh and recovered bite marks from predators were recorded to quantify predation rate. A GoPro was also deployed overnight to detect the sponges’ predators. Past photos of the sponges from ad-hoc monitoring surveys since relocation were also used to investigate growth rate qualitatively and predation rate quantitatively. For comparison, one individual that was discovered in 2018, but not re-visited nor relocated since, was surveyed during the study period to determine its growth and predation rate. Recovery times of the relocated sponges from damages were estimated by coring a 2 cm diameter hole through each cup and observing them weekly until full recovery.

Overall, sponges with an intact cup structure survived well post-relocation. Total height of the sponges fluctuated during the study period, except for one (Sponge C) that consistently increased and another (Sponge G) that consistently decreased. The growth rate of the relocated sponges ranged from -1.5 cm/month to 1.2 cm/month, with 3 sponges each registering positive and negative growth rates. The non-relocated individual grew at 0.1 cm/month. At the end of the study, the cup structures of two of the six relocated individuals were lost nearly entirely from predation. Predation by Map Pufferfish (Arothron mappa) and Copperband Butterflyfish (Chelmon rostratus) was observed, and predation rate appears to be higher at the relocated site than the source site. Recovery rate was slowest for the smallest individual (Sponge G), and similar among the other five which recovered within three weeks.

Given that the sponges may not recover fast enough to overcome the predation intensity at the Marine Park, it is recommended that sponges not be relocated save for exceptional circumstances. Future relocation approaches must consider the impact of spongivory, and to identify new sites for relocation if possible. Furthermore, additional protection measures against predation may need to be taken when relocating smaller sponges.