Friday, March 6, 2015

The Amazing Sponges - Glue of the Reef

Orange Mycale armata sponge commonly found around Moku o Lo'e.
Photo taken by the Bishop Museum.

Sponges have been on our mind the past few weeks thanks to the newest visitor in the Jokiel lab, Dr. Janie Wulff from Florida State University.  After having the privilege to learn from her about her extensive sponge research, we decided to spruce up our own marine life post on sponges with the information we know now.
Sponge pore-bearing structure.
As mentioned in our previous sponge posts, they are quite fascinating creatures.  Belonging to the phylum, Porifera, they are named for their network of pores and channels through which they filter feed. As a defense, they possess spiny spicules that vary in shape but can be sharp and may help deliver the many toxins that sponges tend to produce.  The multicellular masses of sponge have the ability to morph and alter themselves due to unique cells that can transform to serve different purposes in the sponge anatomy.  These cells allow for quick healing of damaged tissue after being picked at by sponge-feeding fish.  Even fish that do not feed on sponges may approach eaten areas to pick at the newly exposed organisms that live in the sponge.  Many tiny critters seek protection in the small and deep pores of sponges.  However, these are just a few of the countless interactions sponges maintain with other marine organisms.

In addition to providing food and protection to numerous fish and invertebrates, they perform a number of services necessary for a coral reef to thrive.  Sponges help to stabilize coral colonies by growing through nooks and crannies at their base and affixing them to the reef creating additional support during times of increased wave action.  This also provides a barrier against organisms known for excavating into coral skeletons.  Sponges promote the reformation of corals following physical damage by gathering the leftover carbonate rubble from the broken skeletons and facilitating the reshaping of this carbonate through bioerosion, molding them back into the reef.

Orange Mycale sponge attacking a coral colony to the reef at Moku o Lo'e.
Photo taken by Mark Heckman

Despite their obvious plasticity in shape and size, and although they may look similar to each other, sponge species, like other marine animals, have variable growth rates and defenses particular to each environment in which they live which isolate them to specific marine ecosystems.  Dr. Janie Wulff tested habitat specificity of mangrove versus shallow reef sponges in Belize. Despite looking very similar at times, 78% of the sponge species  were only found in one location or the other, but not both suggesting a firm divide. By transplanting the most abundant sponge species in each habitat to the other habitat and observing interactions with spongivores and sponges naturally residing at each site, some interesting results came forward.  

Within 3 days of the experiment, 100% of all mangrove sponges transplanted to the shallow reef were consumed by predators.  The mangrove sponge species were unable to survive without protection from the mangrove roots. In turn, transplanted shallow reef sponges were quickly overgrown and out-competed by mangrove sponges due to their slower growth rates.  Mangrove trees are present in the shallow reef site normally, but less dense, allowing spongivores to access them easily and combat the rapid growth of the mangrove sponge species.  As a result, slowly growing reef sponges are not overtaken by the mangrove sponges in the shallow reef site.  It is clear that the sponge species in Belize, and probably on most tropical reefs have distinct characteristics allowing them to differentially thrive in specific habitats, which also boosts sponge diversity.

Photo taken by Candy Feller, Smithsonian Environmental Research Center
Tedani ignis, one of the mangrove sponges in Belize under study.
Photo taken by Candy Feller, Smithsonian Environmental Research Center 

In another study, mangrove sponges were removed from their native habitat and offered to grey angelfish and redband parrotfish for 12 days.  It was noted that the most quickly consumed sponges also had the fastest growth rates.  This suggests a possible relationship between growth rates and predator defense.  Perhaps for mangrove sponges in their protected habitat within the thick maze of mangrove roots,  faster growth rates are more important than slower growth and more complex chemical defenses against grazers, as are found in the open habitat shallow reef sponges.   However, more experimentation is required to look into this prospect.    

Unlike fish, invertebrates and corals, sponges are difficult to quantify and identify.  Thus, many scientists neglect to consider them in monitoring and assessment activities, giving us a lowered understanding of their importance.  In addition, past studies on interactions between sponges and reef fish have been questioned due to flawed scientific methods.  Dr. Janie Wulff is looking to use her own research to offset these weaknesses and provide a more realistic view of the role of sponges in reef ecology.  Her work has convinced many in the marine science community that routine surveying of sponges would prove valuable and should not be overlooked.  Healthy sponge populations are indicators of a thriving coral reef.  The poriferans have demonstrated their worth by cleaning the reef water (a basic sponge can filter up to 4 times its own volume every minute) and servicing the reefs in many other ways. In turn, we should do everything we can to ensure they remain there.

Sponges in Belize.  Photo taken by Florida State University.
 Written by Casey Ching and Mark Heckman

Bioerosion- The gradual removal or degradation of a material through action by an organism.

Wulff J (2005) Trade-offs in resistance to competitors and predators, and their effects on the diversity of tropical marine sponges. Journal of Animal Ecology. 74: 313-321.  Accessed 3-3-15. 

Wulff J (2006) Ecological interactions of marine sponges. Canadian Journal of Zoology. 84(2): 146-166.  Accessed 3-3-15.

Wulff J (2001) Assessing and monitoring coral reef sponges: why and how? Bulletin of Marine Science. 69(2): 831-846. Accessed 3-3-15.

Wulff J (1997) Parrotfish predation on cryptic sponges of Caribbean coral reefs. Marine Biology. 129(1): 41-52. Accessed 3-3-15. 

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