RESEARCH ARTICLE Disturbance to conserved bacterial communities in the cold-water gorgonian coral Eunicella verrucosa Emma Ransome1,2,3, Sonia J. Rowley2,4,5, Simon Thomas1, Karen Tait1 & Colin B. Munn2 1Plymouth Marine Laboratory, Plymouth, UK; 2School of Marine Science and Engineering, Plymouth University, Plymouth, UK; 3Smithsonian National Museum of Natural History, Washington, DC, USA; 4Bernice Pauahi Bishop Museum, Honolulu, HA, USA; and 5University of Hawai’i at Manoa, Honolulu, HI, USA Downloaded from https://academic.oup.com/femsec/article/90/2/404/2680460 by guest on 27 September 2021 Correspondence: Emma Ransome, Abstract Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian The bacterial communities associated with healthy and diseased colonies of the Institution, Washington, DC 20560, USA. cold-water gorgonian coral Eunicella verrucosa at three sites off the south-west Tel.: (+1) 202 633 9075; coast of England were compared using denaturing gradient gel electrophoresis fax: (+1) 202 357 2343; (DGGE) and clone libraries. Significant differences in community structure e-mail: [email protected] between healthy and diseased samples were discovered, as were differences in the level of disturbance to these communities at each site; this correlated with Received 3 March 2014; revised 12 July 2014; accepted 27 July 2014. Final version depth and sediment load. The majority of cloned sequences from healthy coral published online 01 September 2014. tissue affiliated with the Gammaproteobacteria. The stability of the bacterial community and dominance of specific genera found across visibly healthy colo- DOI: 10.1111/1574-6941.12398 nies suggest the presence of a specific microbial community. Affiliations included a high proportion of Endozoicomonas sequences, which were most Editor: Patricia Sobecky similar to sequences found in tropical corals. This genus has been found in a number of invertebrates and is suggested to have a role in coral health and in Keywords the metabolisation of dimethylsulfoniopropionate (DMSP) produced by zoo- coral microbiology; Eunicella verrucosa; coral xanthellae. However, screening of colonies for the presence of zooxanthellae disease; Endozoicomonas spp.; DGGE; clone libraries. produced a negative result. Diseased colonies showed a decrease in affiliated clones and an increase in clones related to potentially harmful/transient micro- organisms but no increase in a particular pathogen. This study demonstrates that a better understanding of these bacterial communities, the factors that affect them and their role in coral health and disease will be of critical impor- tance in predicting future threats to temperate gorgonian communities. such as nitrogen fixation, nitrogen cycling and sulphur Introduction cycling (Lesser et al., 2004; Raina et al., 2009). They also Recent marine disease epizootics have reduced the abun- confer resistance to the host by producing antibacterial dance of a variety of endangered, commercially valuable agents (Nissimov et al., 2009; Shnit-Orland & Kushmaro, and habitat-forming species (Harvell et al., 1999). This 2009), which are compromised during disease (Ritchie, includes a number of corals from tropical and subtropical 2006). Increased host susceptibility (Lesser et al., 2007) systems, where an increasing number of coral diseases are and increased pathogenicity of coral-associated microor- being described (Bourne et al., 2009). Investigations into ganisms (Rosenberg & Ben-Haim, 2002; Bruno et al., bacterial associations with corals have established that 2007) have both been proposed to be driving incidences these communities are often species specific (e.g. Ritchie of disease. In addition, disturbance to the fragile relation- & Smith, 1997; Littman et al., 2009), spatially and tempo- ships between the coral host and their bacterial commu- rally stable (Knowlton & Rohwer, 2003; Sharp et al., nities has been linked to a variety of environmental 2012) and different from surrounding water and sediment factors, including thermal abnormalities (Harvell et al., MICROBIOLOGY ECOLOGY MICROBIOLOGY communities (Frias-Lopez et al., 2002; Carlos et al., 2002; Rosenberg & Ben-Haim, 2002), increased nutrients 2013). There is strong evidence that these bacterial com- (Bruno et al., 2003) and sedimentation (Voss & Richard- munities have a beneficial effect, carrying out functions son, 2006). With an increasingly changing marine ª 2014 Federation of European Microbiological Societies. FEMS Microbiol Ecol 90 (2014) 404–416 Published by John Wiley & Sons Ltd. All rights reserved Disturbed bacterial communities in E. verrucosa 405 environment and an increase in the frequency and inten- ecology of the benthic environment in which it is found sity of disease (Garrabou et al., 2009), it is essential to (Hall-Spencer et al., 2007). Colonies were monitored for understand the progression of disease and its link to envi- disease at three sites, chosen for differences in depth and ronmental stress. Documenting the alteration of coral substratum, off the SW coast of England, during 2008, bacterial communities is necessary to provide accurate and healthy and diseased colonies were sampled in June diagnosis of coral disease for researchers and ecosystem and September of 2008. Sedimentation, temperature and managers (Ainsworth et al., 2007). irradiance were also recorded. Recently, disease outbreaks have been noted in gorgo- nian corals (Order: Alcyonacea) in temperate waters of Materials and methods the NW Mediterranean (Cerrano et al., 2000; Martin et al., 2002; Garrabou et al., 2009) and in SW England Downloaded from https://academic.oup.com/femsec/article/90/2/404/2680460 by guest on 27 September 2021 Field observation and sample collection (Hall-Spencer et al., 2007). Mass mortality by tissue necrosis has been observed for several species and Two sediment traps were deployed at each site for although the cause of this tissue loss has not been clearly 12 days in June and September 2008 (English et al., defined, opportunistic pathogenic bacteria have been 1997). Seawater temperature and irradiance were mea- implicated in a number of gorgonians (Cerrano et al., sured at each site every 15 min throughout the monitor- â 2000; Harvell et al., 2001; Martin et al., 2002). Using cul- ing period (HOBO data loggers, Onset, MA). On 7 ture-based methods Hall-Spencer et al. (2007) found an June, E. verrucosa colonies at each site were evaluated for increase in the diversity of culturable bacteria from visual signs of necrotic tissue, epibiont cover and fouling healthy to diseased Eunicella verrucosa tissue, many of to determine colony health (see Table 1 for site details) which were a close match to Vibrio splendidus. Members via a stratified videographic survey using closed circuit of the family Vibrionaceae are associated with disease in rebreather diving technology (AP Diving Inspiration Clas- other coral species (e.g. Godwin et al., 2012), including sic). Each individual colony encountered within four per- infections correlated with temperature stress (e.g. Kush- manent 10 m 9 2 m belt transects per site was filmed maro et al., 1996; Ben-Haim & Rosenberg, 2002). A Vib- face on with a scaled back board aligned appropriately rio strain showing thermo-dependent virulence has also for scale. Fouling was determined by the percentage cover been isolated from diseased colonies of the gorgonian per colony quantified from videographic frame grabs in coral Paramuricea clavata (Bally & Garrabou, 2007) and ImageJ64 (Abramoff et al., 2004) and was defined as has been shown to be involved in mass mortality events established, and therefore nontemporary (e.g. not snagged of this coral in the NW Mediterranean (Vezzulli et al., on colony temporarily due to water current dynamics) 2010). Hall-Spencer et al. (2007) demonstrated that these matter covering the coral axis. Abundance data were Vibrio isolates induced tissue necrosis at 20 °C but not at quantified in ImageJ64 from scaled frame grabs (using 15 °C in the laboratory, suggesting a possible link belt transects, as above) and counts of colonies ≤ 2cm between E. verrucosa disease and temperature. tall were used to determine the previous years recruit- Details of the nonperturbed microbial communities ment (Munro, 2004). Five healthy colonies and two dis- thought to associate with temperate anthozoans are scant eased colonies (depending on presence) of similar size in comparison with tropical anthozoans (Bayer et al., from each site were tagged. Evaluation of visual condition 2013), as is information concerning how these communi- of colonies was repeated on 16 September. Recruitment ties change with the progression of disease. Given a greater of E. verrucosa was assessed using abundance data from knowledge of these communities we may further our 2007 and 2008 surveys. understanding of multispecies mutualism, the effect that Branches 4 cm in length were collected from each of environmental conditions have on these associates and aid 37 tagged colonies for analysis. In June, five healthy colo- our identification of species that play a key role in both nies from each site and one diseased colony from site 1 maintaining coral health and progressing disease. Further, (16 in total) and in September, five healthy colonies and documenting shifts in microbiota, if they occur prior to two diseased colonies from each site (21 in total) were signs of visible stress, may also allow the use of microbiol- collected. Only one colony found at site 1 showed signs ogy