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Didymo Natural Diversity Section June 2011 Aquatic Invasive Species Action Plan Didymo Natural Diversity Section June 2011 Aquatic Invasive Species are resistant to degradation by bacteria or (AIS) Action Plan: fungi. Didymo This action plan is a living document and will be updated, as needed, to reflect the status of the species in Pennsylvania. Natural History Description: “Didymo” is a microscopic diatom alga also colloquially known as ‘rock snot’. Taxonomy Common name: Didymo Family : Gomphonemataceae Species: Didymosphenia geminata ITIS Taxonomic Serial Number: 591283 ITIS-Integrated Taxonomic Information System. Morphology: Didymosphenia geminata (Bascillariophyta) is a very large (>100 microns), single-celled, ‘coke-bottle’ shaped alga known as a diatom (Figure 1a.). Diatoms are structurally unique because their cell walls contain silica (SiO2). This gives mats of the species a characteristic ‘wet cotton’ feel when handled, which distinguishes it from species of filamentous algae which generally are slimy to the touch. D. geminata cells produce an extracellular, Figures. branched stalk which can form strong 1a (Top). Stalked didymo cells. (Photo: Walt Butler Maryland attachments to a variety of substrates, DNR). including plants (epiphytic) and hard 1b (Middle). Didymo clump from substrates such as stones (epilithic) (Figure upper Delaware River. 1b.). This branched stalk is comprised of (Photo: by Tim Daley PA DEP). complex polysaccharides and proteins that Page | 1 Aquatic Invasive Species Action Plan Dydimo Natural Diversity Section June 2011 Origin: Didymo is thought to be native to survive outside of a stream in cool, damp, the northern regions of Europe, Asia, and dark conditions for at least 40 days. other cool water areas in the northern Recreational equipment that may sustain D. hemisphere; however, in recent years it has geminata environments suitable for survival expanded in range and habitat tolerance to include: neoprene waders, wetsuits, felt- include streams in warmer climates. soled wading boots, fishing tackle and compartments on boats and other equipment. Food Preferences: Photosynthetic organism that can be both phosphorus and nitrogen Preferred Habitat: The ecological limited. distribution for D. geminata appears to have expanded from more boreal, montane Reproductive behavior: The life history of habitats (nutrient-poor) to aquatic habitats most diatoms includes both vegetative and with higher nutrient levels. Limited sexual reproduction although the sexual information is available on the thermal stage has not so far been documented in D. requirements for successful vegetative geminata. When a D. geminata cell divides reproduction but suggested water via vegetative cell division, the stalk also temperatures range from 4-27° C (39-80° F) divides, forming dense mats (nuisance (Kilroy et al. 2005; Stoddard et al. 2005). D. blooms) under certain environmental geminata appears to thrive in streams and conditions (Spaulding and Elwell 2007). rivers with stable substrates, particularly hard rock catchment areas (larger substrates Notable Characteristics: Stalked D. resistant to higher stream velocities) and geminata consolidate in mats of up to 20 cm regulated rivers (smaller substrates but (~ 8 inches) in thickness on the bottom of stable flow regimes). D. geminata can infected waterways. tolerate high water velocity (>1 m3/s) but the diatoms appear to become dislodged during Historic Vectors: The method(s) by which storm events which cause significant D. geminata spread across northern North bedload shift and downstream mobilization America approximately 100 years ago are of sediment. Specific minimum water unknown. The earliest record of D. geminata velocity requirements for D. geminata are in North America is from Cleve (1894-1896) currently unknown (Kilroy 2004). D. who reported it from Vancouver Island, geminata requires high light conditions for British Columbia. Boyer, 20 years later, growth, and reports generally indicate that reported D. geminata in the Delaware River shaded environments may limit growth. in the vicinity of Philadelphia, Pennsylvania Turbidity may also be a factor limiting (1916). In general, historical reports of D. growth (Kilroy 2005). Noga (2003) noted geminata are sparse and voucher specimens that brown-stained water from peat bogs uncommon (Spaulding and Elwell 2007). appeared to limit D. geminata growth and suggested that water clarity may be limiting. Current Pathways/Vectors: Dispersal Reported didymo pH requirements vary but, mechanisms are not well understood but in general, the alga seems to prefer relatively likely are tied to angling and other stream high pH streams. recreation activities. Kilroy (2005) documented the ability of D. geminata to Page | 2 Aquatic Invasive Species Action Plan Dydimo Natural Diversity Section June 2011 Distribution and Status Pennsylvania Legal Status: Currently not regulated in 58 Pa. Code §71.6 and §73.1. Distribution: Nationally, D. geminata has been confirmed in at least 14 states. The Threats majority of confirmed occurrences are in Colorado, Idaho, and Montana. Ecological: D. geminata appears to cause macroinvertebrate community shifts due to D. geminata has been confirmed in the East the diatom’s extensive coverage of exposed and West Branches of the Delaware River substrates. These shifts are generally (New York and Pennsylvania) as well as in characterized by the reduction of the Delaware River mainstem as far south as Ephemeroptera (mayflies), Plecoptera Callicoon, New York (Daley and Silldorff, (stoneflies) and Trichoptera (caddisflies) personal communication). The extent of the (aka EPT taxa) due to habitat loss and species’ distribution in Pennsylvania beyond replacement by more pollution-tolerant taxa the upper 27.5 miles of the Delaware River (e.g. chironomids) (Spaulding and Elwell mainstem and the West Branch is unknown 2007). Another unpublished study in (Figure 2). The status of D. geminata in the Montana demonstrated an increase in Delaware River could be considered a range dipteran taxa (e.g. chironomids) and loss of expansion, although natural occurrences EPT taxa. have not been reported previously for this stretch of river and range expansion by The effect of D. geminata on freshwater natural causes should be considered mussel populations is unknown. However, unlikely. D. geminata has also been due to the ability of nuisance blooms to confirmed in Maryland just south of the cover stream substrates to a depth of 20cm Pennsylvania border at Gunpowder Falls in (about 8 inches), mussels may suffer from Baltimore County and in the Savage River reduced ability to suspension feed, and in western Maryland (Maryland DNR, reduced ability to move during low flow personal communication). periods may lead to their desiccation. Sediment accumulating on top of D. geminata mats may bury mussels completely. Although D. geminata blooms have been observed to have supersaturated dissolved oxygen levels within the concentrated stalk masses (Larned et al. 2006), mussel kills could occur if mass D. geminata die-off produces anoxic conditions associated with decomposition. Of particular concern are the effects of D. geminata on Pennsylvania’s population of endangered dwarf Figure 2. Pennsylvania distribution of Didymo wedgemussel (Alasmidonta (Didymosphenia geminata) (April, 2011). Page | 3 Aquatic Invasive Species Action Plan Dydimo Natural Diversity Section June 2011 heterodon) in the upper Delaware River. management of the species needs to focus Studies examining the effects of D. on containing or eliminating the existing geminata on freshwater mussel communities populations to prevent their spreading to are needed. additional waterways. The direct effects of D. geminata on sport Containment and Prevention Options: fish, primarily trout, and other fish species Efforts to stop the spread of D. geminata have not been well studied. However, within Pennsylvania need to focus on community shifts in benthic containing the existing Delaware River macroinvertebrates and reduction of their population and to closely monitor the biomass may have a ripple-effect throughout Maryland populations at Gunpowder Falls higher trophic levels. As with freshwater and the Savage River and the Pennsylvania mussels, D. geminata die-offs could cause waters near those areas. fish mortality due to low dissolved oxygen levels. • Initiate a public education effort to acquaint the populace with the threat of Economic: While detailed economic threat and measures to prevent the spread of studies of D. geminata impacts in the United didymo. States evidently have not yet been conducted, a 2006 report to Biosecurity New • Advocate inclusion of didymo on the Zealand identified seven potential didymo invasive species lists in 58 Pa. Code related economic threats to that country. §71.6 and §73.1. Potential economic impacts to many of the following, due to the effects of D. geminata, • Encourage the incident reporting of are likely applicable to Pennsylvania: 1) aquatic invasive species within commercial and sport fisheries; 2) Pennsylvania. Online reporting can now municipal, industrial and agricultural water be conducted at the following PFBC web intake; 3) community, municipal and site: domestic drinking water; 4) local recreation http://www.fish.state.pa.us/promo/form/ values; 5) tourism expenditures; 6) local ais_reporting.htm existence values; and 7) existence values associated with extinction of native species • Advocate development of water hauler (New Zealand 2006). disinfection procedures and regulations
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