Sponge monitoring: Moving beyond diversity and abundance measures

Monitoring has become a critical component of managing marine environments world-wide in the face of local and global anthropogenic impacts. Typically the focus of most monitoring programmes has been to quantify temporal and spatial variation in the abundance of organisms, along with the diversity and composition of biological communities to assess acute and chronic impacts. However, while such measures provide important indicators of change, they are less useful when trying to identify more chronic impacts, especially for species that are long-lived. Sponges are an important component of marine systems world-wide and they have received increased focus in recent years as a result of global reports of changing sponge abundance, particularly in tropical systems. While many studies have reported spatial and temporal variation in sponge assemblage composition and abundance, far fewer studies have considered specific monitoring of other aspects of sponge ecology, particularly ecological processes, or physiology. Here we identify a range of different potential indicators, primarily focused on shallow water (<40 m) sponges that could be applied to provide more-comprehensive sponge monitoring, and the potential for these indicators to respond to different local and global scale anthropogenic impacts. While we focused on sponges, these indicators and our approach could be easily adapted to other marine groups. Applying broader and more comprehensive monitoring approaches will enable both chronic and sub-chronic impacts to be detected, and provide a more holistic view of overall ecosystem health and population fitness.