Laurie L. Richardson

Coral diseases: what is really known?

Reports of new and emerging coral diseases have proliferated in recent years. Such coral diseases are often cited as contributing to coral reef decline. Many of these diseases, however, have been described solely on the basis of field characteristics, and in some instances there is disagreement as to whether an observed coral condition is actually a disease. A disease pathogen has been identified for only three coral diseases, and for only two of these has the pathogen been shown (in the laboratory) to be the disease agent. In one case, the same disease name has been used for several widely varying coral syndromes, whereas in another multiple disease names have been applied to symptoms that may be caused by a single disease. Despite the current confusion, rapid progress is being made.

Florida's mystery coral-killer identified

An unusual coral disease appeared on the Florida Reef Tract in June 1995. It was distinct in its microbiology, its pattern of tissue degradation, the species susceptible to it, and its regional distribution. Symptoms included a sharp line between healthy and diseased tissue, as occurs with other coral diseases, but the pathogen responsible for the new outbreak seemed more virulent, affected a wider variety of species, and destroyed tissue much more rapidly than these other ‘line’ or ‘band’ diseases. We have identified the pathogen responsible for this new disease as a new species of Sphingomonas.

African and Asian Dust: From Desert Soils to Coral Reefs

Abstract Many hypotheses have been proposed to explain the decline of coral reefs throughout the world, but none adequately accounts for the lack of recovery of reefs or the wide geographical distribution of coral diseases. The processes driving the decline remain elusive. Hundreds of millions of tons of dust transported annually from Africa and Asia to the Americas may be adversely affecting coral reefs and other downwind ecosystems. Viable microorganisms, macro- and micronutrients, trace metals, and an array of organic contaminants carried in the dust air masses and deposited in the oceans and on land may play important roles in the complex changes occurring on coral reefs worldwide.

Ecological aspects of black band disease of corals: relationships between disease incidence and environmental factors

Abstract. Eleven environmental factors (salinity, water depth, water temperature, nitrate, nitrite, ammonium, soluble phosphate, total phosphate, turbidity, coral diversity, and percent coral cover) were measured at 190 sites on 12 patch reefs of the Florida Keys. Each (2-m-diameter) site was centered around a coral colony with active black band disease (n=21) or a haphazardly selected healthy coral of a species known to be susceptible to black band disease (n=169). Statistical analysis was performed to detect any relationship between each environmental factor and black band disease incidence. Five factors (water temperature, water depth, coral diversity, and concentrations of ortho-phosphate and nitrite) exhibited statistically significant relationships with black band disease. These are discussed in terms of the etiology of the disease as well as the reef environment.

Microbial communities in the surface mucopolysaccharide layer and the black band microbial mat of black band-diseased Siderastrea siderea.

ABSTRACT Microbial community profiles and species composition associated with two black band-diseased colonies of the coral Siderastrea siderea were studied by 16S rRNA-targeted gene cloning, sequencing, and amplicon-length heterogeneity PCR (LH-PCR). Bacterial communities associated with the surface mucopolysaccharide layer (SML) of apparently healthy tissues of the infected colonies, together with samples of the black band disease (BBD) infections, were analyzed using the same techniques for comparison. Gene sequences, ranging from 424 to 1,537 bp, were retrieved from all positive clones (n = 43 to 48) in each of the four clone libraries generated and used for comparative sequence analysis. In addition to LH-PCR community profiling, all of the clone sequences were aligned with LH-PCR primer sequences, and the theoretical lengths of the amplicons were determined. Results revealed that the community profiles were significantly different between BBD and SML samples. The SML samples were dominated by γ-proteobacteria (53 to 64%), followed by β-proteobacteria (18 to 21%) and α-proteobacteria (5 to 11%). In contrast, both BBD clone libraries were dominated by α-proteobacteria (58 to 87%), followed by verrucomicrobia (2 to 10%) and 0 to 6% each of δ-proteobacteria, bacteroidetes, firmicutes, and cyanobacteria. Alphaproteobacterial sequence types related to the bacteria associated with toxin-producing dinoflagellates were observed in BBD clone libraries but were not found in the SML libraries. Similarly, sequences affiliated with the family Desulfobacteraceae and toxin-producing cyanobacteria, both believed to be involved in BBD pathogenesis, were found only in BBD libraries. These data provide evidence for an association of numerous toxin-producing heterotrophic microorganisms with BBD of corals.

Abundance and distribution of black band disease on coral reefs in the northern Florida keys

The abundance and distribution of black band disease on the reef building coralsMontastraea annularis, M. cavernosa, Colpophyllia natans, Diploria clivosa, D. labyrinthiformis andD. strigosa were determined at Algae Reef, Grecian Rocks and Key Largo Dry Rocks in the Key Largo National Marine Sanctuary, Florida, USA. During July and November of 1992 and July 1993, surveys of permanently marked sites covering 9424m2 of reef tract showed that up to 0.72% of 1397 coral colonies of these species were infected with black band disease. The distribution of the disease among the thirty 20-meter diameter sites was clumped, suggesting that the disease is infectious. Year-round monitoring revealed that seasonal disease patterns varied between reefs. Three seasonal patterns were apparent: some coral colonies were infected year round; several colonies exhibited previously unreported reinfection on a seasonal basis; and some exhibited the widely reported pattern of infection limited to the warmer months of the year (sea water temperatures 25 °C or higher).

Remote Sensing of Algal Bloom DynamicsNew research fuses remote sensing of aquatic ecosystems with algal accessory pigment analysis

mhe last decade has seen rapid advances in two technologybased approaches to the study of algal biology: the use of remote sensing, which quantitatively measures light reflected from the surface of the earth, as a tool to study regional-scale aquatic ecosystem dynamics, and the refinement of techniques to identify and quantify algal pigments. Although research in remote sensing has been driven by the ongoing development of new sensors, advances in pigment analysis have essentially evolved from continual research in algal population dynamics, ecology, and physiology. Recent innovative results in both

Black Band Disease

Black band disease (BBD) was the first coral disease to be reported in the literature (Antonius 1973). It was first noted on reefs of Belize in the western Caribbean, and was described as a striking microbial assemblage that formed a band which moved across apparently healthy coral colonies, actively destroying coral tissue and leaving behind the bare coral skeleton (Fig. 18.1). The band appeared dark, which was the basis of the descriptive name. During this same decade, two additional coral diseases were reported, white plague (Dustan 1977) and white band (Gladfelter et al. 1977). BBD differed from the other two in that a very obvious microbial biomass was associated with the pathology, whereas no discernible microorganisms were observable for white plague or white band. Despite the distinct presence of a dense microbial community associated with active coral tissue lysis, identification of the BBD pathogen has proven to be challenging and is still the subject of ongoing investigation.

Ecological physiology of the black band disease cyanobacterium Phormidium corallyticum

Abstract Laboratory studies were carried out to assess the photosynthetic and nitrogen-fixing capabilities of the gliding, filamentous cyanobacterium Phormidium corallyticum. This species is found on coral reefs, and is one of the members of a pathogenic microbial consortium called black band disease of corals, a unique horizontally migrating microbial mat with an active sulfuretum. It was determined that P. corallyticum can perform oxygenic photosynthesis in the presence or absence of sulfide, but cannot conduct (DCMU-forced) anoxygenic photosynthesis with sulfide as electron donor. Photosynthesis vs. irradiance curves revealed a very low threshold for Pmax of <30 muE m(-2) s(-1). Temperature optima for photosynthetic activity were at and above 30 degrees C. Neither a laboratory culture of P. corallyticum nor freshly collected samples of the black band microbial consortium were capable of fixing N(2). Results are discussed in terms of the ecology of this coral disease.

Molecular Detection and Ecological Significance of the Cyanobacterial Genera Geitlerinema and Leptolyngbya in Black Band Disease of Corals

ABSTRACT Black band disease (BBD) is a pathogenic, sulfide-rich microbial mat dominated by filamentous cyanobacteria that infect corals worldwide. We isolated cyanobacteria from BBD into culture, confirmed their presence in the BBD community by using denaturing gradient gel electrophoresis (DGGE), and demonstrated their ecological significance in terms of physiological sulfide tolerance and photosynthesis-versus-irradiance values. Twenty-nine BBD samples were collected from nine host coral species, four of which have not previously been investigated, from reefs of the Florida Keys, the Bahamas, St. Croix, and the Philippines. From these samples, seven cyanobacteria were isolated into culture. Cloning and sequencing of the 16S rRNA gene using universal primers indicated that four isolates were related to the genus Geitlerinema and three to the genus Leptolyngbya. DGGE results, obtained using Cyanobacteria-specific 16S rRNA primers, revealed that the most common BBD cyanobacterial sequence, detected in 26 BBD field samples, was related to that of an Oscillatoria sp. The next most common sequence, 99% similar to that of the Geitlerinema BBD isolate, was present in three samples. One Leptolyngbya- and one Phormidium-related sequence were also found. Laboratory experiments using isolates of BBD Geitlerinema and Leptolyngbya revealed that they could carry out sulfide-resistant oxygenic photosynthesis, a relatively rare characteristic among cyanobacteria, and that they are adapted to the sulfide-rich, low-light BBD environment. The presence of the cyanotoxin microcystin in these cultures and in BBD suggests a role in BBD pathogenicity. Our results confirm the presence of Geitlerinema in the BBD microbial community and its ecological significance, which have been challenged, and provide evidence of a second ecologically significant BBD cyanobacterium, Leptolyngbya.