Sponge Mass Mortalities in a Warming Mediterranean Sea: Are Cyanobacteria-Harboring Species Worse Off?

Abstract

Mass mortality events are increasing dramatically in all coastal marine environments. Determining the underlying causes of mass mortality events has proven difficult in the past because of the lack of prior quantitative data on populations and environmental variables. Four-year surveys of two shallow-water sponge species, Ircinia fasciculata and Sarcotragus spinosulum, were carried out in the western Mediterranean Sea. These surveys provided evidence of two severe sponge die-offs (total mortality ranging from 80 to 95% of specimens) occurring in the summers of 2008 and 2009. These events primarily affected I. fasciculata, which hosts both phototrophic and heterotrophic microsymbionts, while they did not affect S. spinosulum, which harbors only heterotrophic bacteria. We observed a significant positive correlation between the percentage of injured I. fasciculata specimens and exposure time to elevated temperature conditions in all populations, suggesting a key role of temperature in triggering mortality events. A comparative ultrastructural study of injured and healthy I. fasciculata specimens showed that cyanobacteria disappeared from injured specimens, which suggests that cyanobacterial decay could be involved in I. fasciculata mortality. A laboratory experiment confirmed that the cyanobacteria harbored by I. fasciculata displayed a significant reduction in photosynthetic efficiency in the highest temperature treatment. The sponge disease reported here led to a severe decrease in the abundance of the surveyed populations. It represents one of the most dramatic mass mortality events to date in the Mediterranean Sea.

Effects of thermal stress on early developmental stages of a gorgonian coral

“…These large events were accompanied by several others, affecting fewer species or being more localized, e.g. in summers of (Bensoussan et al 2010, Maldonado et al 2010, Cebrian et al 2011, Huete-Stauffer et al 2011, Stabili et al 2012. In general, gorgonians, which are structurally important elements of Mediterranean hard-bottom communities, were among the most affected species (Cerrano et al 2000, Pérez et al 2000).…”

Host-specificity among abundant and rare taxa in the sponge microbiome

“…They can provide additional nutrients and produce secondary metabolites that improve the defense of the host against predation, fouling and diseases (Hentschel et al, 2006;Taylor et al, 2007a). Several recent studies also correlate environmental parameters such as elevated seawater temperatures (Webster et al, 2008;Cebrian et al, 2011) or the presence of heavy metals (Webster et al, 2001;Selvin et al, 2009) with shifts in microbial communities and declines in sponge health.…”

Pruning treatment: A possible method for improving the conservation status of a Ellisella paraplexauroides Stiasny, 1936 (Anthozoa, Alcyonacea) population in the Chafarinas Islands?

“…All this reveals that the absence of colonies smaller than 15 cm in our study is the result of a low rate of population regeneration by sexual reproduction (low recruitment), and this is also supported by our results on growth after pruning (Table 1), where the maximum growth detected for a colony branch was 5.8 cm/year. Moreover, all these negative effects on the Chafarinas Islands E. paraplexauroides population can be magnified as a consequence of mortality episodes due to rising temperature events, such as those in 1999 and 2003 (Cerrano et al, 2000;Cupido et al, 2009;Cebrian et al, 2011), which affected other species of gorgonians in other locations in the Mediterranean. Additionally, in the Chafarinas Islands, in summer 2015, mass mortality of E. singularis and increased epibiosis in P. clavata were detected (unpublished data).…”

“…In recent years, mass mortality events in infralittoral and circalittoral communities have become increasingly frequent (e.g., Cerrano et al, 2000;Cupido et al, 2009;Cebrian et al, 2011;Rubio-Portillo et al, 2016). Among the direct or indirect anthropogenic or natural drivers, increases in water temperatures have been noted as the main cause, while the regeneration of beaches, organic and inorganic spills, different types of professional and recreational fishing, etc., have also played a role in increasing such mortality, likely interacting synergistically (Gaino et al, 1992;Bianchi & Mori, 2000;Cerrano et al, 2001;Coma et al, 2004;Templado, 2014).…”