W. H. ADEY Division of Paleobotany, U.S. National Museum, Washington, D.C. 20560 I. G. MACINTYRE Division of Sedimentology, U.S. National Museum, Washington, D.C. 20560 Crustose Coralline Algae: A Re-evaluation in the Geological Sciences ABSTRACT Therefore an understanding of crustose coral- line taxonomy and habitat preferences is The crustose coralline algae are well known critical to quantitative ecological and pale- in shallow tropical waters as reef frame-builders oecological studies. This paper is intended to and sediment producers. Although their abun- develop a "fresh start," realistic viewpoints, dance at greater depths and in arctic waters and even an optimism toward the crustose has been previously recorded, this knowledge corallines in the geological sciences, where con- in recent decades has been largely ignored by siderable confusion prevails. geologists and marine scientists in general. Much of the existing confusion concerning Many erroneous or misleading ecological and the crustose coralline algae stems from either paleoecological statements and conclusions a misunderstanding of terminology or a general have resulted, and we have endeavored to failure to consider the wide generic and specific clarify matters through the citation of the older variation within the group. Perhaps more literature along with more recent ecological serious are the widely held misconceptions studies. about habitat, which can lead to wholly A parallel tendency to "simplify" the erroneous paleoecological conclusions. taxonomic structure of crustose corallines has As a result of these problems, many scientists threatened to add considerable confusion to are reluctant to undertake detailed studies modern marine studies. We have discussed involving the crustose corallines. Their in- recent work on anatomy, reproduction, and creasing frustration is well illustrated in the taxonomy. These and classical data are sum- following statements: "It is doubtful whether marized in the form of keys and an evolutionary the genera of crustose melobesioids can be tree, which are intended to provide the geo- differentiated in the field" (Marsh, 1970); logist and marine biologist with a working and, "Because most of these algae resemble facility with the group. each other so closely in their appearance, A number of quantitative ecological studies habitat requirements and their roles as herma- treating crustose corallines have appeared types, we have combined them for sake of during the past decade; these results are dis- convenience into an artificial group called the cussed and possibilities for future ecological lithothamnioid algae" (Goreau, 1963). Identi- work indicated. The occurrence of rhodoliths fications in the field are possible, however, and (maerl, free corallines) and the factors con- it has been shown that quantitative ecological trolling the development of these deposits are studies also can be accomplished both in also noted. northern waters (Adey, 1971) and in the tropics (Littler, 1971; Adey and W. T. INTRODUCTION Boykins, in prep.). The crustose corallines, which form three subfamilies (Melobesioideae, Lithophylloideae, MISNOMERS AND and Mastophoroideae) of the family Coral- MISUNDERSTANDINGS linaceae (Adey and Johansen, 1972), play Present-day problems concerning classifica- a major role in the ecology and development tion of the crustose corallines originated in the of most photic hard bottoms as well as some early 19th century when the term Nullipore sediment bottoms throughout the world. was applied loosely to crustose corallines and Geological Society of America Bulletin, v. 84, p. 883-904, 31 figs., March 1973 883 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/84/3/883/3433487/i0016-7606-84-3-883.pdf by guest on 29 September 2021 884 ADEY AND MACINTYRE superficially similar animals. Later, even up Some attempts, however, have been made to to the present, all crustose corallines frequently clarify the terminology. The ridge on Raroia "pass[ed] under the widely inclusive generic Atoll in the Pacific, for example, was described name 'Lithothamnion' " (Howe, 1912, p. 839), as an "Algal Ridge" rather than "Litho- or "lithothamnioid algae" (Goreau, 1963). thamnion Ridge" because ". the dominant Lithothamnium (correct spelling), however, is coralline is Porolithon onkpdes not Lithotham- primarily an arctic genus; in the tropics, it is nion' (Newell, 1956, p. 344). A subsequent dis- common only in deep water. Recently, there cussion of the "Lithothamnion Ridge" misno- has been a trend to call crustose corallines "the mer indicated tha: in the tropical Pacific these melobesioid algae" (Lee, 1967), but this term ridges are constructed mainly by species of the also leads to further confusion. In fact, it genus Porolithon, and that "species belonging refers to only the typically arctic-antarctic to the genus Lithothamnium are seldom pres- Melobesioideae of the three crustose coralline ent" (Johnson, 1961, p. 25). More recently, it subfamilies. was suggested that these algal ridges have a Crustose corallines generally have been rather simple crust ose coralline assemblage be- considered shallow-water tropical organisms cause only two gsnera, Porolithon and Neo- goniolithon, were reported on the reef flats of (see below), but various species and genera are Rongelap Atoll, Marshall Islands (Lee, 1967). known to occur from the tropics to the polar Collections from reef flats on Bikini, Guam and regions. Perhaps crustose corallines are most Palau, however, show a greater variety, in- important in the polar regions where they are cluding considerable numbers of Lithophyllum commonly the main calcifiers, particularly mollucense and Lithophyllum kotschyanum (J. on hard bottoms. Also, their depth of occur- H. Johnson collections in the U.S. Geol. Sur- rence ranges from the intertidal to the lower vey; Adey, unpub.). Although upper Tertiary limit of the photic zone. In addition, a strong and Pleistocene collections of crustose coral- specific depth zonation has been observed in lines from Saipan (johnson, 1957) contained a northern waters (Adey, 1966a, 1968, 1971); number of species of Lithothamnium, at least in the tropics, depth zonation appears to be some of these belong to Mesophyllum (Adey, on the generic level (Adey, 1966b; Adey and personal observation), and no paleoenviron- W. T. Boykins, in prep.). mental data v/ere given. Recent shallow-water Lithothamnion Ambiguity plants in the same study included species of Porolithon, Neogonhlithon, Lithophyllum, and The consistent use of Lithothamnion as a Lithoporella (Lithothamnium was not reported). generic term for all crustose corallines has given rise to ambiguous terminology. One A shallow-water ''Lithothamnion'' bank was result is that the spectacular growth of crus- reported to have b:en constructed by Meso- tose coralline algae which form wave-resistant phyllum (Lithothamnion) erubescens off Bonaire ridges in many Pacific reefs were named in the Caribbean (Zaneveld, 1958). This "Lithothamnion Ridges." The ridge on Bikini identification may b; questioned, particularly Atoll, for example, was said to be "conposed as anatomical data were lacking and Neo- mainly of pink and dark-red Lithothamnion' goniolithon strictum occurs abundantly in simi- (Tracey and others, 1948, p. 867). Kuenen lar environments. In fact, recent collections (1950, p. 421-422) stated: "Most important from the Caribbean area show a general are the family of red algae called Coralliraceae, absence of the Melcoesioideae. Shallow-water generally termed nullipores, encrusting coral- (to 15 m) reef collections from Jamaica (Adey, lines or Lithothamnium. But other genera., such unpub.) consisted of 41 percent Neogonio- as Lithophyllum and Archeolithothamnium, are lithon, 25 percent Porolithon, 12 percent Litho- also of importance." Later, the algae on some phyllum (the remainder being about equally Pacific ridges were described as "encrusting divided among Arctieolithothamnium, Litho- calcareous algae 'Porolithon and other litho- porella, Hydrolithon, Heteroderma, and Lepto- thamnia' " (Ladd, 1961, p. 705). During an phytum. In deeper water (>27 m), Hydrolithon investigation of the Great Bahama Bank in the (45 percent) and Lithoporella (22 percent) Caribbean area, Newell and Rigby (1957, p. were the major elements. Another shallow- 47) noted that "a well-defined algal rim is water collection, patcii reef and lagoon, from lacking, but encrusting Lithothamnion is con- the southeastern Bahamas (Adey, unpub.) in- spicuous over the shallowest part, or crest, of cluded three species of Porolithon, two species some of the reefs." each of Neogoniolithon and Tenarea, and one Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/84/3/883/3433487/i0016-7606-84-3-883.pdf by guest on 29 September 2021 CRUSTOSE CORALLINE ALGAE 885 species each of Lithophyllum and Heteroderma. and Curray, 1956; Menzies and others, 1966). Archeolithothamnium is, however, important Algal balls from a bank off the Canary Islands, below 30 m in the Bahamas and the Virgin however, were found to contain algae of the Islands; also, a Lithothamnium and a Mesophyl- genera Goniolithon and Porolithon, and were lum species occur cryptically in small amounts referred to as oncolites (McMaster and Cono- in shallow water. Lithothamnium occidentale has ver, 1966). The term oncolite properly refers been described in shallow water in Bermuda to spheroidal forms of algal stromatolitic struc- (Bosellini and Ginsburg, 1971).