Australia recently hosted the 9th World Sponge Conference, bringing together international experts in all things spongy. Spanning advances in molecular biology, taxonomy, symbioses and ecology, the meeting was a chance to hear the latest science on these strange and fascinating animals that play key roles in marine systems all around the globe.
I was invited to attend and provide a plenary presentation on the reef manager’s perspective on sponges. My experience working with coral reef managers and scientists from the Caribbean – and a few dives on reefs dominated by sponges - had recently tuned me in to the potential importance of sponges to reef management.
Often not as prominent as hard corals, sponges are abundant in all reef systems. Once you start looking though, you’ll see them everywhere. In some reefs, such as those I saw in the Caribbean, sponges can be visually dominant and very hard to ignore.
It is the bold shapes and intricate structures of sponges that capture a diver’s attention, but swimming over these huge barrel sponges I couldn’t help thinking about their potential importance to reef ecosystem health. Questions buzzed through my mind...
Are sponges good or bad for coral reefs?
How important are they to reef resilience?
Should we be incorporating sponges more explicitly into our coral reef management plans and strategies?
One thing I do know: sponges rarely have a place in our monitoring programs, and they almost never feature as components of the reef ecosystem worthy of special management attention. As corals decline in reefs all around the world, sponges are likely to become increasingly important for the many functions they fulfill.
Understanding the roles of different sponges, and being able to recognize situations when these roles are important to reef health, is an important first step to assessing their significance to management – and planning for it. The conference provided a timely opportunity to identify emerging opportunities for sponge research to contribute to the management of coral reefs under a changing climate.
Hot off the science presses were important discoveries about the importance of sponges to fundamental ecosystem processes.
· Jasper de Goeij shared an exciting new discovery of a ‘sponge-loop’ in the nutrient cycling of reefs. Recently published in Science, the work he and colleagues have been doing demonstrates that sponges play a critical and unique role that enables coral reefs to persist in low-nutrient environments. By converting dissolved organic carbon resulting from photosynthetic processes to particulate forms (detritus) available to other organisms, sponges prevent the majority of nutrients ‘escaping’ into surrounding waters.
· Manuel Maldonado presented compelling evidence that sponges are an important contributor to the ocean’s silicon cycle. Silicon is a limiting element for diatoms, which are a major contributor to global ocean productivity. Previously, diatoms have been assumed to be the dominant player in the processing of silicon, but it looks like sponges may play a crucial function in this cycle on a global scale.
· Chris Battershill showed just how vulnerable sponge populations can be, with large and important sponge beds drowning under floods of mud following major erosion events in New Zealand.
Other presentations, including a talk by Janie Wulff, highlighted the diversity of roles played by sponges, their importance in reef ecosystems and the alarming signs that sponges, too, may be in decline in many areas. It was apparent that not all sponges are equal, and that increasingly sponge populations are going to require management actions to protect or restore their helpful functions and reduce their negative impacts on reefs.
What we need are tools to help coral reef managers understand and communicate the importance of sponges, quickly assess the importance and health of sponge communities in their reef systems and decide what types of actions, and when to implement them.
For more information on the World Sponge Conference and to view abstracts, visit www.spongeconference2013.org