Pines for the Sea

Black pine Neorhodomela larix growing alongside lighter-coloured Analipus japonicus on a beach in California, copyright Peter D. Tillman.

There aren't many types of algae that receive their own vernacular name. Despite the fact that thousands of different species of macroscopic algae exist in the world, the majority tend to get lumped under the catch-all term of 'seaweed'. Among those seaweeds that are visible enough to stand out from the general crowd is Neorhodomela larix, the 'black pine'.

Neorhodomela larix is a common seaweed species on the west coast of North America. It has also been recorded from the western side of the Pacific Ocean, but it should be noted that it might not always be readily distinguished from related species (indeed, N. larix was not distinguished at species level from the primarily western Pacific N. aculeata until the revision of this genus by Masuda, 1982). The name 'black pine' that has been bestowed on it reflects its overall appearance. Black pine grows as erect axes radiating from a small basal holdfast. These primary axes give rise to regular branches arranged in a spiral fashion; most of these side branches, at least in young individuals, only grow to a fixed, short length and remain unbranched or only bifurcate (in more mature individuals, some of the side branches become indeterminate in length and grow in a similar manner to the primary axes). The overall effect is to make the seaweed stems look like a bottlebrush or, with a bit of imagination, like a pine-tree branch (or at least like a plastic-Christmas-tree branch). Black pine is particularly common on horizontal, wave-exposed beaches about a foot above the mean low-tide mark; in some places it may form large, continuous stands. It is most abundant where said shorelines are swept by sand, probably because the action of the sand's movement keeps away grazers such as urchins (D'Antonio 1986).

Neorhodomela larix was previously included in the closely related genus Rhodomela, and some sources still refer to it as 'Rhodomela larix'. Masuda (1982) established Neorhodomela as a separate genus from Rhodomela due to differences in vegetative structure. Both genera possess hair-like branchlets known as trichoblasts, but in Rhodomela these arise from the main branches spirally whereas in Neorhodomela they are positioned dorsally and arise in a zig-zag arrangement. Spermatangia are produced from trichoblasts in Neorhodomela, whereas in Rhodomela the spermatangia are produced directly on the unspecialised branches and the trichoblasts are only vegetative structures. In N. larix, few vegetative trichoblasts are produced until shortly before the production of reproductive trichoblasts bearing spermatangia; other Neorhodomela species (such as N. aculeata) may start producing vegetative trichoblasts soon after germination.

Apart from the ecological role it presumably plays in providing food and shelter to other coastal lifeforms, Neorhodomela larix does not have much of a direct impact economically. Like many macroalgae, black pine produces chemical compounds known as bromophenols that have been subject to some investigation due to their potentially beneficial (such as anti-microbial or anti-oxidant) activities. However, to date no practical pharmaceutical products have been developed from algal bromophenols, in part because the amount of these compounds produced by the algae in vivo is fairly low (Liu et al. 2011). For now, there is little to disturb these little pine forests by the sea.

REFERENCES

D'Antonio, C. M. 1986. Role of sand in the domination of hard substrata by the intertidal alga Rhodomela larix. Marine Ecology—Progress Series 27: 263–275.

Liu, M., P. E. Hansen & X. Lin. 2011. Bromophenols in marine algae and their bioactivities. Marine Drugs 9: 1273–1292.

Masuda, M. 1982. A systematic study of the tribe Rhodomeleae (Rhodomelaceae,Rhodophyta). Journal of the Faculty of Science, Hokkaido University, Series 5: Botany 12 (4): 209–400.