Rhodolith

Rhodoliths are colorful, unattached, branching, crustose benthic marine algae that resemble coral. (Images: [1] [2]) Rhodolith beds create biogenic habitat for diverse benthic communities. Common rhodolith species include Lithophyllum margaritae, Lithothamnion muellerii, and Neogoniolithon trichotomum (source: Riosmena-Rodriguez et al. 2007).

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Rhodoliths belong to a group known as coralline red algae that deposit calcium carbonate within their cell walls to form hard structures that closely resemble beds of coral. Unlike coral, rhodoliths do not attach themselves to the rocky seabed. Rather, they drift like tumbleweeds along the seafloor until they grow heavy enough to settle and form brightly colored beds (Image: [3]). While corals are animals that filter plankton and other organisms from the water for food, rhodoliths produce energy through photosynthesis. Scientists believe rhodoliths have been present in the world's oceans since at least the Eocene epoch, some 55 million years ago (source:Science Daily, September 23, 2004).

Habitat

Rhodolith beds have been found throughout the world's oceans, including in the Arctic near Greenland and in waters off British Columbia, Canada. Globally, rhodoliths fill an important niche in the marine ecosystem, serving as a transition habitat between rocky areas and barren, sandy areas. Rhodoliths provide a stable and three-dimensional habitat onto which a wide variety of species can attach, including other algae, commercial species such as clams and scallops, and true corals (source:Science Daily, September 23, 2004). Living rhodolith beds are widely distributed throughout the Gulf of California, Mexico (source:Diana Steller, Moss Landing Marine Laboratories). Rhodoliths are resilient to a variety of environmental disturbances, but can be severely impacted by harvesting of commercial species.

In June 2004, living specimens of Phymatolithon calcareum were recovered from Prince William Sound, Alaska. Rhodoliths had not previously been documented in Alaska waters (source:Science Daily, September 23, 2004, Konar et al 2006).

Geologic Significance

Rhodoliths are a common feature of modern and ancient carbonate shelves worldwide. Rhodolith communities contribute significantly to the global calcium carbonate budget, and fossil rhodoliths are commonly used to obtain paleoecologic and paleoclimatic information.(source: Hetzinger et al, 2006). Under the right circumstances, rhodoliths can be the main carbonate sediment producers, often forming rudstone or floatstone beds consisting of large pieces of rhodoliths in grainy matrix.