Competitive dominance among sessile marine organisms in a high Arctic boulder community

In most hard substrate environments, space is a limiting resource for sessile organisms. Competition for space is often high and is a structuring force within the community. In the Beaufort Sea’s Boulder Patch, crustose coralline red algae are major space occupiers. This research determined if coralline algae were competitively dominant over other sessile organisms. To test this hypothesis, overgrowth was documented in terms of “winners” and “losers” on the contact borders between different species. Crustose corallines occurred in over 80% of the observed interactions but were only winners in approximately half of them. Most frequently, bryozoans, tunicates, and sponges were superior competitors over crustose corallines, while at the same time these invertebrate groups were among the least abundant space occupiers.     

FIELD MEASUREMENTS OF INORGANIC NITROGEN UPTAKE BY EPIFLORA COMPONENTS OF THE SEAGRASS POSIDONIA OCEANICA (MONOCOTYLEDONS,POSIDONIACEAE)1

Crustose corallines, crustose and erect brown algae, and sessile animals are major components of the epiphytic community of the Mediterranean seagrass Posidonia oceanica (L.) Delile. Production, biomass, and specific composition of this epiphyte–seagrass association are impacted by anthropogenic increase of nutrient load in this oligotrophic area. In this context, nitrogen uptake by P. oceanica and its epiflora was measured using the isotope ¹⁵N at a 10 m depth in the Revellata Bay (Corsica, Mediterranean Sea). Epiflora components showed various seasonal patterns of biomass and abundance. The epiphytic brown algae appeared at the end of spring, later than the crustose corallines, and after the nitrate peak in the bay. Because of their later development in the season, epiphytic brown algae mostly rely on ammonium for their N needs. We hypothesize that the temporal succession of epiphytic organisms plays a crucial role in the N dynamics of this community under natural conditions. The epiphytic brown algae, which have a growth rate one order of magnitude greater than that of crustose corallines, showed lower N‐uptake rates. The greater N‐uptake rates of crustose corallines probably reflect the greater N requirements (i.e., lower C/N ratios) of red algae. We determined that the epiflora incorporated ammonium and nitrate more rapidly than their host. Nevertheless, when biomass was taken into account, P. oceanica was the most important contributor to N uptake from the water column by benthic macrophytes in this seagrass bed.     

Arctic rhodolith beds and their environmental controls (Spitsbergen, Norway)

Coralline algae (Corallinales, Rhodophyta) that form rhodoliths are important ecosystem engineers and carbonate producers in many polar coastal habitats. This study deals with rhodolith communities from Floskjeret (78°18′N), Krossfjorden (79°08′N), and Mosselbukta (79°53′N), off Spitsbergen Island, Svalbard Archipelago, Norway. Strong seasonal variations in temperature, salinity, light regime, sea-ice coverage, and turbidity characterize these localities. The coralline algal flora consists of Lithothamnion glaciale and Phymatolithon tenue. Well-developed rhodoliths were recorded between 27 and 47 m water depth, while coralline algal encrustations on lithoclastic cobbles were detected down to 77 m water depth. At all sites, ambient waters were saturated with respect to both aragonite and calcite, and the rhodolith beds were located predominately at dysphotic water depths. The rhodolith-associated macrobenthic fauna included grazing organisms such as chitons and echinoids. With decreasing water depth, the rhodolith pavements were regularly overgrown by non-calcareous Polysiphonia-like red algae. The corallines are thriving and are highly specialized in their adaptations to the physical environment as well as in their interaction with the associated benthic fauna, which is similar to other polar rhodolith communities. The marine environment of Spitsbergen is already affected by a climate-driven ecological regime shift and will lead to an increased borealization in the near future, with presently unpredictable consequences for coralline red algal communities.     

Bioerosion of gastropod shells: with emphasis on effects of coralline algal cover and shell microstructure

Organisms boring into fifty nine species of gastropod shells on reefs around Guam were the bryozoan Penetrantia clionoides; the acrothoracian barnacles Cryptophialus coronorphorus, Cryptophialus zulloi and Lithoglyptis mitis; the foraminifer Cymbaloporella tabellaeformis, the polydorid Polydora sp. and seven species of clionid sponge. Evidence that crustose coralline algae interfere with settlement of larvae of acrothoracian barnacles, clionid sponges, and boring polychaetes came from two sources: (1) low intensity of boring in limpet shells, a potentially penetrable substrate that remains largely free of borings by virtue of becoming fully covered with coralline algae at a young age and (2) the extremely low levels of boring in the algal ridge, a massive area of carbonate almost entirely covered by a layer of living crustose corallines. There was a strong negative correlation between microstructural hardness and infestation by acrothoracian barnacles and no correlation in the case of the other borers. It is suggested that this points to a mechanical rather than a chemical method of boring by the barnacles. The periostracum, a layer of organic material reputedly a natural inhibitor of boring organisms, was bored by acrothoracican barnacles and by the bryozoan. The intensity of acrothoracican borings is shown to have no correlation with the length of the gastropod shell.     

Limited flexibility in resource use in a coral reef grazer foraging on seasonally changing algal communities

Feeding ecology of three life phases of the parrotfish Scarus ferrugineus was studied on a southern Red Sea fringing reef by comparing availability and consumption of benthic algae during the monsoon hot and cool seasons. Dominant biota covering dead carbonate substrates were in decreasing order of importance: turfs on endoliths, turfs on crustose corallines, and crustose corallines. On the reef crest and shallow fore reef, composition of the biota changed seasonally. Cover of turfs on endoliths and turfs on crustose corallines was higher during the hot season, while crustose corallines and macroalgae (only on reef crest) increased during the cool season. Biota in the deep fore reef did not show seasonal variation. All life phases used similar resources and showed selective feeding in all zones. Turfs on endoliths, followed by turfs on crustose corallines, was the primary feeding substrate. These two sources represented over 92% of bites during both seasons. Crustose corallines, macroalgae, and living corals were negligible components being strongly avoided at all zones and seasons. Resource use varied seasonally on the reef crest and shallow fore reef, while it remained unchanged on the deep fore reef. Turfs on endoliths were consistently preferred in both seasons but their contribution increased from 45% in the cool to 70% of bites in the hot season. Electivity for turfs on crustose corallines shifted from random feeding in the hot (27% of bites) to selection in the cool season (47% of bites). Feeding pattern changed diurnally with more bites taken from crustose corallines and turfs on crustose corallines during morning. During the rest of the day, bites from turfs on endoliths predominate. S. ferrugineus shows limited capacity to exploit seasonal increases in the biomass of foliose and canopy forming macroalgae, despite indications of energetic limitation during the cool season.     

QUANTIFYING GROWTH AND CALCIUM CARBONATE DEPOSITION OF CALLIARTHRON CHEILOSPORIOIDES (CORALLINALES,RHODOPHYTA) IN THE FIELD USING A PERSISTENT VITAL STAIN1

Growth and calcium carbonate deposition rates of the coralline alga Calliarthron cheilosporioides Manza were quantified by monitoring fronds in the intertidal zone that had been chemically labeled with the nontoxic fluorescent brightener Calcofluor white. This vital stain effectively labeled apical meristems of coralline thalli in the field: fronds exposed for only 5 min had detectable chemical marks at least 1.5 years later. By distinguishing portions of thalli that developed before and after exposure, this methodology permitted accurate measurement of growth and calcium carbonate deposition at each meristem. In Calliarthron, meristematic activity declined with increasing frond size. However, because growing fronds dichotomize, the total number of meristems and the deposition rate of new calcified tissue both increased with frond size. Growth rates reported here suggest that large fronds may not be as old as previously estimated. The Calcofluor white method may improve demographic studies of corallines by resolving growth and age of fronds in the field and may facilitate studies of climate change on calcium carbonate deposition in these ecologically important, calcifying algae.     

植物分类学在化石珊瑚藻(珊瑚藻目,红藻门)中的应用

最近有人认为将化石藻类的分类归入现生藻类分类单元有利于珊瑚藻作为古环境的标志,便于理解该类群的演化。然而,这样分类可能很难,因为并不是所有现生藻类分类特征都能在化石种中保存下来。Sporolithacea科的钙化部分(独立或者聚集的孢子囊群)的出现,可以把它们与这个类群的另一个现生科Corallinaceae区别开,这个科在生殖窠中产生孢子囊。节片的有无,丝间细胞的联系类型,生殖窠中孢子囊释放的数目都是用来划分Coral1inaceae科的亚科的标准,在化石样品中也可以用合适的条件进行观察。在大多数情况下,对现生珊瑚藻类属的划分特征可以在化石藻类中鉴别出来,但在几种现生珊瑚藻没有钙化的生殖结构或发育特征。因此,它们生殖结构无法与相应的化石藻类进行对比,也不能进行化石藻类的分类。近年来的趋势认为生殖结构和发育特征是对现生珊瑚藻进行分类的优先鉴定标准,然而,某些特征的稳定性在属的划分上仍然存在争论。在许多情况下,现生藻类的分类标准特征都不能在化石中保存,对古生物化石的分类标准的最佳选择是在化石藻类中选择辅助的,并且可以识别的其它鉴定特征,或者应用非正式的比现生藻类代表定义更宽的属名。     

Kelp and sea urchin settlement mediated by biotic interactions with benthic coralline algal species

Species interactions can influence key ecological processes that support community assembly and composition. For example, coralline algae encompass extensive diversity and may play a major role in regime shifts from kelp forests to urchin-dominated barrens through their role in inducing invertebrate larval metamorphosis and influencing kelp spore settlement. In a series of laboratory experiments, we tested the hypothesis that different coralline communities facilitate the maintenance of either ecosystem state by either promoting or inhibiting early recruitment of kelps or urchins. Coralline algae significantly increased red urchin metamorphosis compared with a control, while they had varying effects on kelp settlement. Urchin metamorphosis and density of juvenile canopy kelps did not differ significantly across coralline species abundant in both kelp forests and urchin barrens, suggesting that recruitment of urchin and canopy kelps does not depend on specific corallines. Non-calcified fleshy red algal crusts promoted the highest mean urchin metamorphosis percentage and showed some of the lowest canopy kelp settlement. In contrast, settlement of one subcanopy kelp species was reduced on crustose corallines, but elevated on articulated corallines, suggesting that articulated corallines, typically absent in urchin barrens, may need to recover before this subcanopy kelp could return. Coralline species differed in surface bacterial microbiome composition; however, urchin metamorphosis was not significantly different when microbiomes were removed with antibiotics. Our results clarify the role played by coralline algal species in kelp forest community assembly and could have important implications for kelp forest recovery.     

Effects of elevated seawater temperature and phosphate enrichment on the crustose coralline alga Porolithon onkodes (Rhodophyta)

Both global and local environmental changes threaten coral reef ecosystems. To evaluate the effects of high seawater temperature and phosphate enrichment on reef‐building crustose coralline algae, fragments of Porolithon onkodes were cultured for 1 month under laboratory conditions. The calcification rate of the coralline algae was not affected at 30°C, but it decreased to the negatives at 32°C in comparison to the control treatment of 27°C, indicating that the temperature threshold for maintaining positive production of calcium carbonate lies between 30 and 32°C. Phosphate enrichment of 1–2 μmol L ^?1 did not affect the calcification rate. The net oxygen production rate was enhanced by phosphate enrichment, suggesting that the photosynthetic rate was limited by the availability of phosphate. It was concluded that moderate phosphate enrichment does not directly deteriorate algal calcification but instead ameliorates the negative effects of high seawater temperature on algal photosynthesis.     

Discovery of the mineral brucite (magnesium hydroxide) in the tropical calcifying alga Polystrata dura (Peyssonneliales,Rhodophyta)

Red algae of the family Peyssonneliaceae typically form thin crusts impregnated with aragonite. Here, we report the first discovery of brucite in a thick red algal crust (~1 cm) formed by the peyssonnelioid species Polystrata dura from Papua New Guinea. Cells of P. dura were found to be infilled by the magnesium‐rich mineral brucite [Mg(OH)₂]; minor amounts of magnesite and calcite were also detected. We propose that cell infill may be associated with the development of thick (> ~5 mm) calcified red algal crusts, integral components of tropical biotic reefs. If brucite infill within the P. dura crust enhances resistance to dissolution similarly to crustose coralline algae that infill with dolomite, then these crusts would be more resilient to future ocean acidification than crusts without infill.     

Biomineralization of calcium carbonate in the cell wall of Lithothamnion crispatum (Hapalidiales,Rhodophyta): correlation between the organic matrix and the mineral phase

Over the past few decades, progress has been made toward understanding the mechanisms of coralline algae mineralization. However, the relationship between the mineral phase and the organic matrix in coralline algae has not yet been thoroughly examined. The aim of this study was to describe the cell wall ultrastructure of Lithothamnion crispatum, a cosmopolitan rhodolith‐forming coralline algal species collected near Salvador (Brazil), and examine the relationship between the organic matrix and the nucleation and growth/shape modulation of calcium carbonate crystals. A nanostructured pattern was observed in L. crispatum along the cell walls. At the nanoscale, the crystals from L. crispatum consisted of several single crystallites assembled and associated with organic material. The crystallites in the bulk of the cell wall had a high level of spatial organization. However, the crystals displayed cleavages in the (104) faces after ultrathin sectioning with a microtome. This organism is an important model for biomineralization studies as the crystallographic data do not fit in any of the general biomineralization processes described for other organisms. Biomineralization in L. crispatum is dependent on both the soluble and the insoluble organic matrix, which are involved in the control of mineral formation and organizational patterns through an organic matrix‐mediated process. This knowledge concerning the mineral composition and organizational patterns of crystals within the cell walls should be taken into account in future studies of changing ocean conditions as they represent important factors influencing the physico‐chemical interactions between rhodoliths and the environment in coralline reefs.     

CHIHARAEA AND YAMADAIA (CORALLINALES,RHODOPHYTA) REPRESENT REDUCED AND RECENTLY DERIVED ARTICULATED CORALLINE MORPHOLOGIES1

Phycologists have hypothesized that the diminutive fronds produced by species in the genera Chiharaea and Yamadaia, which are composed of comparatively few genicula and intergenicula, represent morphological intermediates in the evolution of articulated corallines from crustose ancestors. We test this “intermediate frond hypothesis” by comparing rbcL sequences from the generitype species Chiharaea bodegensis and Yamadaia melobesioides to sequences from other coralline genera. We demonstrate that Chiharaea includes two other NE Pacific species, Arthrocardia silvae and Yamadaia americana. Chiharaea species are characterized morphologically by inflated intergenicula and axial conceptacles with apical or acentric pores. Although relationships among the three species are unresolved, Chiharaea bodegensis, C. americana comb. nov., and C. silvae comb. nov. are distinguished from one another by DNA sequences, morphology, habitat, and biogeography. Chiharaea occurs together with Alatocladia, Bossiella, Calliarthron, and Serraticardia macmillanii in a strongly supported clade of nearly endemic north Pacific articulated coralline genera and species that have evolved relatively recently compared to other articulated corallines. In contrast, NW Pacific Yamadaia melobesioides belongs in a clade with Corallina officinalis, the generitype species of Corallina, and therefore we reduce Yamadia to a synonym of Corallina and propose Corallina melobesioides comb. nov. We reject the ‘intermediate frond hypothesis’ and conclude that Chiharaea and Yamadaia are recently derived taxa that evolved from articulated coralline ancestors and represent a reduction in the number of genicula and intergenicula.     

Experimental effects of kelp canopies on subtidal coralline algae

Plants are often grouped as canopy species or understorey species because it is thought that that these sets of taxa interact in predictable ways. Mensurative experiments in southern Australia demonstrated that the percentage cover of encrusting coralline algae was greater, and articulated (branching) coralline algae less, on boulders under a canopy of dense kelp (>7 plants per m²), Ecklonia radiata, than on boulders without kelp. Experimental clearances of kelp and reciprocal transplants of boulders between patches of E. radiata and patches without kelp showed that canopies maintained and facilitated the growth of encrusting coralline algae and reduced the cover of articulated coralline algae. Potential artefacts associated with clearing kelp and transplanting boulders were not detected when tested with a series of translocation controls. These results reject the model that the co‐occurrence of E. radiata and encrusting corallines is just an assemblage of plants caused by spatial and temporal coincidence. Instead, they support the model that kelp facilitates the growth and survival of understorey algae.     

Natural inducers for coral larval metamorphosis

 Coral gametes from Acropora millepora (Ehrenberg, 1834) and from multi-species spawning slicks provided larvae for use in metamorphosis assays with a selection of naturally occurring inducer chemicals. Four species of crustose coralline algae, one non-coralline crustose alga and two branching coralline algae induced larval metamorphosis. However, one additional species of branching coralline algae did not produce a larval response. Metamorphosis was also observed when larvae were exposed to skeleton from the massive coral Goniastrea retiformis (Lamarck, 1816) and to calcified reef rubble, demonstrating metamorphosis is possible in the absence of encrusting algae. Chemical extracts from these algae and the coral skeleton, obtained using either decalcification or simple methanol extraction procedures, also contained active inducers. These results extend the number of crustose algal species known to induce coral metamorphosis, suggest that some inducers may not necessarily be strongly associated with the calcified algal cell walls, and indicate that inducer sources in reef habitats may be more diverse than previously reported. Accepted: 21 May 1999     

Deep-water rhodolith distribution, productivity, and growth history at sites of formation and subsequent degradation

This study provides the first quantitative measures of deep-water (i.e., below scuba depths) rhodolith development, distribution, abundance, and primary productivity at sites of both active formation and breakdown. The 1.27-km² upper platform surface of San Salvador Seamount, Bahamas, ranges in depth from 67 to 91 m and averages 95.8% cover of rhodoliths that contribute an estimated 391 t organic C·yr⁻¹ to deep-sea productivity. The predominant nongeniculate coralline alga of the slope environment has an extremely narrow PI curve (photosynthesis vs. irradiance) of net primary production (0.005) to slightly beyond 0.24 μmol·m⁻²·⁻¹ PAR) suggesting that some deep-water benthic algae may be acclimated to restricted light ranges. Platform areas contain up to fice-deep accumulations (≈45 cm thick) of rhodoliths with their visible, planar (2-D), crustose algal cover (68.5%) composed of 41% Lithophyllum sp., 14.9% average nongeniculate corallines, and 12.6% Peyssonnelia sp. Platform rhodoliths also contain ≈25% average planar cover of the foraminiferan Gypsina sp. overlying the rock-penetrating chlorophyte Ostreobium sp.

On the steep slopes of the seamount, to a depth of 290 m, rhodoliths that have spilled down from the relatively flat platform average 17.4% cover. These nodules tend to be concentrated in fan-shaped deposits that are most prevalent (33.3% cover) on the west side (leeward) of the mount where they are more abundant near the top of the slope than on the other three sides. Cover of living crustose algae on the deeper slope rhodoliths averages only 22.8% and is made up of 14.8% unidentified nongeniculate corallines, 6% Lithophyllum sp., and 2% Peyssonnelia. Gypsina sp. is not an important component of the slope nodules. Biotic overstory on the seamout slopes is greatly reduced relative to the platform, restricted mainly to bedrock, and consists mostly of Halimeda, gorgonians, and sponges along with scattered patches of small frondose algae.

Over platform depths from 67 to 91 m, rhodoliths are fairly uniform in composition and abundance. Ranging from 4 to 15 cm in diameter, with an average of ≈ 9 cm, they are roughly spherical with smooth living surfaces. The rhodoliths spilling down the steep slopes of the seamount to depths below 200 m are characteristically smaller (mean of ≈5 cm diameter), much rougher, and pittend by boring organisms. As shown by cross sections through the centers of the platform nodules, outer, relatively thin (1–3 cm thick), well-preserved envelopes overlie dead laminated crustose layerse. These layers surround much thicker cores of biotically altered carbonate (mostly coralline, foraminiferan, and coral) that have been extensively reworked by boring sponges, algae, polychaetes, and pelecypods. Borings have been infilled with carbonate detritus and are lithified to various degrees ranging from porous to dense and stony.

Radiocarbon dates indicate that the outermost unaltered envelopes that underlie actively growing crusts are 112–880 yr old ( ), while the innermost unaltered layers average 731 ybp (range = 200–1100 ybp). The consistently abrupt transitions from the intact underlying layers of living.     

Effects of kelp canopies on bleaching and photosynthetic activity of encrusting coralline algae

Canopy-forming algae often coexist with an understorey of encrusting coralline algae that bleach following the loss of canopies. We tested the hypothesis that canopy loss causes a reduction in photosynthetic activity of encrusting coralline algae concomitant with their bleaching. When canopies were experimentally removed, corallines bleached and their photosynthetic activity was rapidly reduced to half their activity observed under canopies. This result prompted us to test, and subsequently accept, the hypothesis that exposure of understorey corallines to enhanced light intensity per se (simulation of canopy loss) acts as a mechanism that causes bleaching and reduced photosynthetic activity. Despite bleaching, encrusting corallines maintained reduced levels of photosynthetic activity, and this may explain why, under certain conditions, bleached corallines can persist in the absence of canopy-forming algae. Nevertheless, our data provide evidence that the positive association between canopy-forming algae and encrusting coralline algae is maintained because of shade provided by the canopy.     

COMPOSITION,DISTRIBUTION, AND ABUNDANCE OF DEEP‐WATER (>30 m) MACROALGAE IN CENTRAL CALIFORNIA1

The deep‐water macroalgal assemblage was described at 14 sites off the central California coast during 1999 and 2000 from SCUBA and remotely operated vehicle sampling. The stipitate kelp Pleurophycus gardneri Setchell & Gardner, previously thought to be rare in the region, was abundant from 30 to 45 m, forming kelp beds below the well‐known giant kelp forests. Macroalgae typically formed three broadly overlapping zones usually characterized by one or a few visually dominant taxa: 1) the upper “Pleurophycus zone” (30–45 m) of stipitate kelps and Desmarestia spp. with a high percent cover of corallines, low cover of uncalcified red algae, and rare green algae; 2) a middle “Maripelta zone” (40–55 m) with other uncalcified red algae and infrequent corallines and green algae; and 3) a zone (55–75 m) of infrequent patches of nongeniculate coralline algae. The green alga Palmophyllum umbracola Nelson & Ryan, not previously reported from the Northeast Pacific, was found over the entire geographical range sampled from 35 to 54 m. Year‐round profiles of water column irradiance revealed unexpectedly clear water with an average K₀ of 0.106·m ^{? 1} Received 18 January 2002. Accepted 16 December 2002. . The low percent surface irradiance found at the average lower macroalgal depth limits in this study (0.56% for brown algae, 0.12% for uncalcified red algae, and 0.01% for nongeniculate coralline algae) and lack of large grazers suggest that light controls the lower distributional limits. The ubiquitous distribution, perennial nature, and similar lower depth limits of deep‐water macroalgal assemblages at all sites suggest that these assemblages are a common persistent part of the benthic biota in this region.     

The population and community structure of Hawaiian fringing-reef crustose Corallinaceae (Rhodophyta,Cryptonemiales)

Measurements of cover, relative density, and frequency are given for the major reefbuilders on the Waikiki fringing reef. Crustose coralline algae cover 39% of the reef surface and exceed all other organisms as the major builders and consolidators of reef materials. An unidentified coralline (melobesioid C) covers the greatest area (17 %), but Hydrollthon reinboldii (Weber-van Bosse & Foslie) Foslie (11 % cover) because of its thicker thalli and higher relative density (45 %) and frequency (68 %) values is the primary limestone former. Melobesioid C ranks second and Sporolithon erythraeum (Rothpletz) Kylin (6 % cover) third in relative importance. Porolithon onkodes (Heydrich) Foslie (3 % cover), although shown by its low density (4 %) and frequency (6 %) to have a comparatively restricted distribution, is more important than P. gardineri (Foslie) Foslie (2 % cover). P. onkodes maintains and provides the surf-resistant reef edge and is, therefore, of great ecological importance. Coelenterate corals cover less than 1 % of the total area and are relatively unimportant on the fringing reef. The hypothesis is developed that the high ratio (200 : 1) of crustose corallines to corals at Waikiki may be partly due to increases in eutrophication.Experimental evidence shows that P. onkodes can withstand intense illumination and is thereby unique among Hawaiian crustose Corallinaceae. Sporolithon erythraeum is more typical of other crustose corallines since it is physiologically adapted to low-light habitats.     

Weathering of calcite,pyrite, and sulfur by Thermothrix thiopara in a thermal spring

The mineral weathering capabilities of Thermothrix thiopara were investigated by scanning electron microscopy and energy dispersive X‐ray analysis. Thermothrix thiopara is an extremely thermophilic, sulfur‐oxidizing bacterium that grows in a thermal spring whose principal minerals are calcium carbonate, pyrite, and sulfur. Crystals of these minerals were incubated in situ for periods up to eight days, removed, and examined. Results indicated that T. thiopara is partially responsible for weathering calcium carbonate by the production of sulfuric acid, thereby contributing to the formation of a porous tufa mound. Examination of ultravioletirradiated control crystals indicated that the sulfuric acid produced by T. thiopara caused solubilization of calcium carbonate even in the absence of direct bacterial colonization. Pyrite and sulfur were not visibly weathered, but instead were coated with calcium carbonate precipitate. During eight days incubation, growth forms of T. thiopara colonizing the minerals progressed from unicells to filaments to nets of filaments. Bacteria other than T. thiopara appeared after eight days, indicating an increased diversity.