- Scientific name: Spongilla aspinosa
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Special Concern (MA Endangered Species Act)
Description
The smooth branched sponge can be found in freshwater ponds, encrusting surfaces, or as a finger-like branching structure growing on rock or wood. The sponge is typically bright green in color but may be drab brown or grayish under low-light conditions. Close observation with a hand lens or the naked eye will reveal the spicules – hard, thin, supporting structures that form the “skeleton” of the sponge. The smooth branched sponge contains both megascleres – large skeletal spicules – and smaller microscleres.
Identification of the smooth branched sponge requires use of a microscope. The genus Spongilla is distinguished by its thin finger-like growth form, smooth megascleres, and pointed microscleres, which in S. aspinosa also appear smooth. The closely related S. lacustris generally displays microscleres which are minutely spined, though in acidic waters, the spines may be absent. The two species are best distinguished by the arrangement and appearance of the gemmules, spherical structures which allow for asexual reproduction. Mature specimens of S. lacustris contain large numbers of gemmules, which are concentrated at the base of the sponge in a single layer. These gemmules are reinforced with coarsely-spined gemmoscleres, a specialized class of spicule. Gemmules are rarely found in S. aspinosa. Where present, they are distributed in rough clusters throughout the tissue of the sponge and are not supported by true gemmoscleres.
Life cycle and behavior
Sponges are filter-feeders, taking in water and directing it through feeding canals. Food particles are absorbed by cells lining the canal through phagocytosis and transferred to other cells for digestion.
Sexual reproduction is carried out by specialized cells that develop from normal tissue during specific times of year. Sperm are released by male sponges into the open water and ingested into female sponges during water uptake associated with feeding. Fertilized eggs develop into larvae, which undergo extensive development within the female sponge. They are then released and swim freely until they find a suitable substrate, where they metamorphose into stationary adults. Little research has been done on the smooth branched sponge in particular, but individuals of the closely-related species S. lacustris have been shown to switch sexes between years.
Asexual reproduction can occur through simple fragmentation of the parent sponge, or through the formation of spherical gemmules, which are resistant to environmental stresses like low oxygen or cold temperatures. Many freshwater sponges undergo a dormancy period in the winter months, in which the mature sponge dies back and much of the tissue is converted into hardy gemmules. The smooth branched sponge is unusual in that it rarely forms gemmules. This sponge may be more resistant to cold temperatures than related species. Potts (1887) noted the verdant growth of this sponge: “even after February has for weeks covered it with a thick sheet of ice, the sponge has been seen still green and in apparently as healthy growth as ever.” The bright green color of this and other sponges is attributable to symbiotic relationships formed with photosynthetic algae.
Distribution and abundance
The true range of this species is unknown. The smooth branched sponge has been collected in scattered localities, including ponds in Massachusetts, New Jersey, Virginia, Indiana, and eastern Canada. Only two populations of smooth branched sponge have been found in Massachusetts, in ponds in the Blackstone River and Martha’s Vineyard watersheds. This species is listed under the Massachusetts Endangered Species Act as a species of Special Concern. All listed species are protected from killing, collecting, possessing, or sale and from activities that would destroy habitat and thus directly or indirectly cause mortality or disrupt critical behaviors. In addition, listed animals are specifically protected from activities that disrupt nesting, breeding, feeding, or migration.
Habitat
Sites in Massachusetts show little to no human disturbance and are naturally acidic sites, with a pH ranging around 4-5.0. Nationwide, smooth branched sponge has only been reported from acidic waters, with a pH range of 4.0-5.5.
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Threats
Since this species occupies undisturbed ponds, it is expected to be sensitive to changes in water chemistry from pollution and shoreline disturbance.
Conservation
Survey and monitoring
The smooth branched sponge has not been positively identified since the late 1980s. The difficulty in identification and limited survey effort have contributed to the lack of knowledge about its distribution and status in Massachusetts. Surveys are needed to redocument this species at its historical sites and in new waterbodies that may support the species. Monitoring is recommended every five years or to the extent practical at its historical sites.
Management
Pollution of the naturally acidic ponds where smooth branched sponges are found should be avoided, mitigated, or eliminated. Human disturbance of these habitats should be avoided.
Research needs
Surveys should target historical but also identify new wetlands and streams to better understand its distribution and habitat requirements in Massachusetts. Effort to identify DNA sequences to aid in species identification would increase our knowledge of its distribution and status in Massachusetts.
References
Potts, E. 1887. Fresh water sponges: A monograph. Proc. Acad. Nat. Sci. Phila.
Smith, D.G. 1991. Keys to the freshwater macroinvertebrates of Massachusetts. Douglas G. Smith, Department of Zoology, University of Massachusetts, Amherst, Massachusetts.
Thorp, J.H., and A.P. Covich, editors. 2001. Ecology and Classification of North American Freshwater Invertebrates, Second Edition. San Diego: Academic Press.
Contact
| Date published: | April 11, 2025 |
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