Laminaria digitata (Marine Algae of Cape Cod, Massachusetts and Adjacent Islands)

Laminaria digitata

Summary ¹¹

Laminaria digitata is a large brown alga in the family Laminariaceae, also known by the common name Oarweed. It is found in the sublittoral zone of the northern Atlantic Ocean.

Description ¹²

L. digitata is a tough, leathery, dark brown seaweed that grows to two or three metres. The holdfast which anchors it to the rock is conical and has a number of spreading root-like protrusions called rhizoids. The stipe or stalk is flexible and oval in cross section. The blade is large and shaped like the palm of a hand with a number of more or less regular finger-like segments. This seaweed can be distinguished from the rather similar Laminaria hyperborea by being darker in colour and having a shorter stipe that does not easily snap when bent.

Distribution ¹²

L digitata occurs in the north west Atlantic from Greenland south to Cape Cod and in the north east Atlantic from northern Russia and Iceland south to France. It is common round the coasts of the British Isles except for much of the east coast of England.

Ecology ¹²

L digitata is found mostly on exposed sites on shores in the lower littoral where it may form extensive meadows and can be the dominant algal species. It has a fairly high intrinsic growth rate compared to other algae, 5.5% per day, and a carrying capacity of about 40 kg wet weight per square meter. It may reach lengths of about 4 m. It overlaps to a small degree in distribution with Fucus serratus and Alaria esculenta. It is highly susceptible to grazing by sea urchins, among other species. It has low and high light limitation values of about 5 and 70 W per square meter respectively. Its distribution is also limited by salinity, wave exposure, temperature, desiccation and general stress. These and other attributes of the alga are summarized in the publications listed below.

Uses ¹²

L digitata was traditionally used as a fertiliser and spread on the land. In the 18th century it was burnt to extract the potash it contained for use in the glass industry. In the 19th century it was used for the extraction of iodine. Both these uses died out when cheaper sources for these products became available. It is still used as an organic fertiliser but also for the extraction of alginic acid, the manufacture of toothpastes and cosmetics, and in the food industry for binding, thickening and moulding. It is used in Japan and China for making dashi, a soup stock, and for other culinary purposes.

Historically, the dried stalks of L digitata, called sea-tangle tents were used as an abortifacient and for inducing labour.

Habitat ¹³

Depth range based on 281 specimens in 1 taxon.
Water temperature and chemistry ranges based on 130 samples.

Environmental ranges
  Depth range (m): 0 - 23.77
  Temperature range (°C): -0.536 - 14.527
  Nitrate (umol/L): 0.987 - 28.246
  Salinity (PPS): 33.712 - 35.363
  Oxygen (ml/l): 5.750 - 8.011
  Phosphate (umol/l): 0.191 - 1.817
  Silicate (umol/l): 0.958 - 30.934

Graphical representation

Depth range (m): 0 - 23.77

Temperature range (°C): -0.536 - 14.527

Nitrate (umol/L): 0.987 - 28.246

Salinity (PPS): 33.712 - 35.363

Oxygen (ml/l): 5.750 - 8.011

Phosphate (umol/l): 0.191 - 1.817

Silicate (umol/l): 0.958 - 30.934

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