Desmarestia tropica

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]

Desmarestia tropica
Desmarestia tropica A small portion of a branch tip to show the serration, the young branchlets, and the hair tufts on the teeth near the tips. In most collections the hair tufts have been lost, probably by damage due to the inevitably rough handling resulting from dredging.
Scientific classification Edit this classification
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Stramenopiles
Phylum: Gyrista
Subphylum: Ochrophytina
Class: Phaeophyceae
Order: Desmarestiales
Family: Desmarestiaceae
Genus: Desmarestia
Species:
D. tropica
Binomial name
Desmarestia tropica

History

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]

Description

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]

Habitat

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]

References
  1. Miller, K.A.; Garske, L.; Edgar, G. (2007). "Desmarestia tropica". IUCN Red List of Threatened Species. 2007: e.T63585A12684515. doi:10.2305/IUCN.UK.2007.RLTS.T63585A12684515.en. Retrieved 20 November 2021.
  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. Archived from the original on 14 December 2017. 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. Archived from the original on 14 December 2017. Retrieved 12 December 2017. Rightly named "Acid Weed," the internal pH of Desmarestia has been estimated as low as 0.6 pH.
  4. Ramírez, María Eliana; Peters, Akira F. (December 1992). "The South American species of Desmarestia (Phaeophyceae)". Canadian Journal of Botany. 70 (12): 2430–2445. doi:10.1139/b92-301. ISSN 0008-4026. OCLC 5140406657.
  5. Taylor, William Randolph (May 1945). "Pacific marine algae of the Allan Hancock Expeditions to the Galapagos Islands" (PDF). Allan Hancock Pacific Expeditions. 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". Global Change Biology. 16 (10): 2876–2890. Bibcode:2010GCBio..16.2876E. doi:10.1111/j.1365-2486.2009.02117.x. ISSN 1354-1013. OCLC 660819334. S2CID 83795836. Desmarestia tropica Tropical acidweed * EF$, herbivore overgrazing associated with interactions between El Niño and overfishing
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