Desmarestia tropica

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Desmarestia tropica
Scientific classification e
Kingdom: Chromista
Phylum: Ochrophyta
Class: Phaeophyceae
Order: Desmarestiales
Family: Desmarestiaceae
Genus: Desmarestia
Species: D. tropica
Binomial name
Desmarestia tropica
W. R. Taylor, 1945

Desmarestia tropica, sometimes called tropical acidweed, is a species of seaweed in the family Desmarestiaceae. It is critically endangered, possibly extinct, and one of only fifteen protists evaluated by IUCN.[1] Endemic to the Galápagos Islands,[1] the specific epithet tropica alludes to its tropical habitat, rare for members of Desmarestiales.[1] The common name acidweed applies to members of the genus Desmarestia,[2] generally characterized by fronds containing vacuoles of concentrated sulfuric acid,[3] but it is unclear if this species also produces acid.[4]


D. tropica was first collected by William Randolph Taylor on 19 January 1935, and twice more later that month.[5] He published a description of the species ten years later in May 1945.[5] The organism was last collected in 1972, and not seen since despite efforts to search the sighted locations and other possible habitats in the archipelago.[1] Because of its preference for deep, cold water in a tropical location, it was likely severely affected by El Niño, especially the 1982–83 El Niño event.[1] This event killed much of the macroalgae in the area,[1] and D. tropica likely declined from overgrazing by herbivores resulting from El Niño and overfishing of predator fish.[6] There is a small possibility that the species still lives in deeper water in a cryptic gametophyte stage, but if so it has yet to return to the more visible sporophyte stage.[1] The gametophyte has also never been observed.[4]


The thallus of D. tropica can be about 40 centimetres (16 in) tall and is soft, bushy, and light brown in color.[5] The holdfast is tiny and not very differentiated.[5] The stipe is 3 millimetres (0.12 in) in diameter and short, fleshy, and firm.[5] It continues up as the rachis where it flattens out, only visible underneath the blade, and widens to 5–8 millimetres (0.20–0.31 in).[5] Opposite branching starts 1–2 centimetres (0.39–0.79 in) from the base with wide-angled branches every 1–3 centimetres (0.39–1.18 in), and continues from each branch for several degrees.[5] The blades have short, broad teeth which on the younger blades include short brown filaments.[5] These filaments are oppositely branched.[5]

D. tropica differs from D. latifrons by being more bushy and having more of a gradation in branches from the apex to the base.[5] The branches are also more expansive in D. tropica than in D. latifrons or similar species.[5] D. tropica is in the section Herbacea of Desmarestia, but compared to other North American species it is less membranous.[5]


Tropical acidweed has been found in only two locations: Post Office Bay off Floreana Island[5] and Caleta Tagus (Tagus Cove) off Isabela Island.[1] At the former site it was found at depths from 14–60 metres (46–197 ft).[5] It was once thought to be found off the mainland coast of Peru, but these specimens are considered instead to be D. firma.[4][1]

Despite its tropical range, it prefers the cold, deep water[1] of upwelling areas of the lower sublittoral zone.[4]


  1. ^ a b c d e f g h i j k "Desmarestia tropica". IUCN Red List of Threatened Species. 2007. doi:10.2305/IUCN.UK.2007.RLTS.T63585A12684515.en. Retrieved 10 December 2017. 
  2. ^ Watson, Jane (30 April 2014). "Spatial and temporal variation in kelp forest composition off the NW coast of Vancouver Island, British Columbia". Salish Sea Ecosystem Conference. Bellingham, WA: Western Washington University. Retrieved 12 December 2017. In general, annual species such as Acid Weed (Desmarestia spp,) were highly variable in abundance 
  3. ^ Warneke, Alex (5 December 2014). "These are a few of my favorite species: Desmarestia". Deep Sea News. Deep Sea News. Retrieved 12 December 2017. Rightly named “Acid Weed,” the internal pH of Desmarestia has been estimated as low as 0.6 pH. 
  4. ^ a b c d Ramírez, María Eliana; Peters, Akira F. (December 1992). "The South American species of Desmarestia (Phaeophyceae)". Canadian Journal of Botany (PDF). Ottawa, Ontario: NRC Research Press. 70 (12): 2430–2445. doi:10.1139/b92-301. ISSN 0008-4026. OCLC 5140406657. 
  5. ^ a b c d e f g h i j k l m n Taylor, William Randolph (May 1945). "Pacific marine algae of the Allan Hancock Expeditions to the Galapagos Islands" (PDF). Allan Hancock Pacific Expeditions. Los Angeles, CA: University of Southern California Press. 12: 106–107, 352–353. LCCN 42021995. OCLC 1321112. Retrieved 11 December 2017. 
  6. ^ Edgar, G. J.; Banks, S. A.; Brandt, M.; Bustamante, R. H.; Chiriboga, A.; Earle, S. A.; Garske, L. E.; Glynn, P. W.; Grove, J. S.; Henderson, S.; Hickman, C. P.; Miller, K. A.; Rivera, F.; Wellington, G. M. (19 August 2010). "El Niño, grazers and fisheries interact to greatly elevate extinction risk for Galapagos marine species" (PDF). Global Change Biology. Blackwell Publishing. 16 (10): 2876–2890. Bibcode:2010GCBio..16.2876E. doi:10.1111/j.1365-2486.2009.02117.x. ISSN 1354-1013. OCLC 660819334. Retrieved 12 December 2017. Desmarestia tropica Tropical acidweed * EF$, herbivore overgrazing associated with interactions between El Niño and overfishing 

External links

  • Media related to Desmarestia tropica at Wikimedia Commons
  • Data related to Desmarestia tropica at Wikispecies
  • Image of type specimen at University of Michigan
  • Different image of type specimen from UC Berkeley
  • D. tropica on the Charles Darwin Foundation Galapagos Species Checklist
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