Seawater temperatures are increasing, with many unquantified impacts on marine diseases. While prolonged temperature stress can accelerate host-pathogen interactions, the outcomes in nature are poorly quantified. We monitored eelgrass wasting disease (EWD) from 2013-2017 and correlated mid-summer prevalence of EWD with remotely sensed seawater temperature metrics before, during, and after the 2015-2016 marine heatwave in the northeast Pacific, the longest marine heatwave in recent history. Eelgrass shoot density declined by 60% between 2013 and 2015 and did not recover. EWD prevalence ranged from 5-70% in 2013 and increased to 60-90% by 2017. EWD severity approximately doubled each year between 2015 and 2017. EWD prevalence was positively correlated with warmer temperature for the month prior to sampling while EWD severity was negatively correlated with warming prior to sampling. This complex result may be mediated by leaf growth; bigger leaves may be more likely to be diseased, but may also grow faster than lesions, resulting in lower severity. Regional stressors leading to population declines prior to or early in the heatwave may have exacerbated the effects of warming on eelgrass disease susceptibility and reduced the resilience of this critical species.

A new syndrome in sea fans Gorgonia ventalina consisting of multifocal purple spots (MFPS) has been observed in the Caribbean Sea. Surveys of MFPS on sea fans were conducted from 2006 to 2010 at a shallow and deep site in La Parguera, Puerto Rico (PR). At the shallow site, MFPS increased between 2006 and 2010 (site average ranged from 8 to 23%), with differences found at depths over time using an analysis of covariance (ANCOVA, p < 0.0001). As a potential causative agent we examined a Labyrinthulomycota-like ovoid parasite that was observed to be abundant in MFPS lesions in light micrographs. Labyrinhylomycetes were successfully isolated, cultured and characterized in sea fans from Florida and PR. Sequence information obtained from the small subunit (SSU) rRNA gene indicated that Labyrinthulomycetes in most sea fans (healthy and MFPS sea fans from Florida; MFPS from PR) and the cultured microorganism are in the genus Aplanochytrium, although some healthy sea fans from PR contained members of the genus Thraustochytrium. Both genera fall within the family Thraustochytriidae. Histology confirmed ob servations of thraustochytrids within apparently healthy and MFPS sea fans from PR, and specific staining indicated a host melanization response only in colonies containing Labyrinthulomycetes or fungal infections. Growth trials indicate that the temperature-growth optima for the cultured microorganism is ~30°C. In inoculation experiments, the cultured Aplanochytrium did not induce purple spots, and histology revealed that many of the apparently healthy recipients contained Labyrinthulomycetes prior to inoculation. Taken together, these results indicate that the Labyrinthulomycetes associated with sea fans is likely an opportunistic pathogen. Further studies are needed to understand the pathogenesis of this microorganism in sea fans and its relationship with MFPS.KEY WORDS: Labyrinthulomycota · Caribbean sea fan · Gorgonia ventalina · Multi-focal purple spots · MFPS Resale or republication not permitted without written consent of the publisherDis Aquat Org 101: [1][2][3][4][5][6][7][8][9][10][11][12] 2012 increase in the number of purple sclerites and is a generalized response to invading pathogens or other biotic agents (Petes et al. 2003, Alker et al. 2004, Smith & Weil 2004. Necrotic lesions, surrounded by purple halos in G. ventalina, have been described as aspergillosis (Smith et al. 1996, Nagelkerken et al. 1997, Kim & Harvell 2001. The terrestrial fungus Aspergillus sy dowii was isolated from fans with these signs and Koch's postulates fulfilled in controlled laboratory experiments (Smith et al. 1996, Geiser et al. 1998). More recently, culture-dependent sampling showed that fungal species other than A. sydowii can be associated with lesions (ToledoHernández et al. 2008). During field surveys in Mexico, Florida, and Puerto Rico, a new type of lesion was identified (Weil & Hooten 2009, Weil & Rogers 2011 our Fig. 1) that is characterized by small (1 to 3 mm in diameter), circular to oblong multi-focal...