The following details may be seen with a microscope after being dissected. Each colony of Didemnum spp. consists of many small individuals called zooids, each about a millimetre in length, embedded in the sheet-like matrix. Each zooid pumps water through its body, filtering out food particles, and along with neighboring zooids discharges the filtered water into a common space from which it exits the colony. Embedded in a thin layer in the surface of the matrix are tiny, spiny, calcareous balls, each one shaped like the head of a medieval mace (Cohen, 2005).
Principal source: USGS-WHSC, 2005 Genus Didemnum: colonial tunicate; ascidian; sea squirt
Cohen, 2005Guide to the Exotic Species of San Francisco Bay
Compiler: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Review: Andrew N. Cohen San Francisco Estuary Institute Oakland California USA
Publication date: 2007-05-31
Recommended citation: Global Invasive Species Database (2024) Species profile: Didemnum spp.. Downloaded from http://iucngisd.org/gisd/species.php?sc=946 on 01-09-2024.
While Didemnum spp. has been observed primarily colonizing artificial substrates in harbors and manmade structures there are fears that natural reefs may become susceptible. Healthy natural ecosystems such as coral reefs comprise a high biodiversity, with complex interactions among the species, and this is thought to be an important factor in preventing the establishment of Didemnum spp. and other invading species. However, many coral reef areas are becoming degraded due to anthropogenic activities, global warming, natural events like El Nin˜ o, and perhaps other causes. Didemnum spp. is spreading to various temperate and tropical regions of the world. The reasons for this species sudden invasiveness are not known.To add to these fears, Didemnum spp. have not declined with the return of cooler water; on the contrary they continue to proliferate (Lambert, 2002).