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In light of increasing sea surface temperatures, quantifying the expression of stress- inducible genes in coastal organisms is imperative to identify early biomarkers of thermal stress. In the present study we developed a quantitative PCR (qPCR) assay to test the molecular response to heat stress in the Great Barrier Reef sponge Rhopaloeides odorabile. Suitable reference genes (cod- ing for α-tubulin, 28S rRNA and ubiquitin) were identified among 5 candidates and then used to nor- malise expression of target genes (actin-related protein, calmodulin, ferritin, ubiquitin-conjugating enzyme, heat shock protein 90 (Hsp90) and heat shock protein 40 (Hsp40)) in samples exposed to high temperatures (31 and 32°C) for 1, 3, 14 and 15 d. A rapid down-regulation of most genes (actin- related protein, ferritin, calmodulin and Hsp90) was observed at both temperatures within 24 h, indi- cating an initial shut-down of the sponge's molecular systems in response to thermal stress. The increased expression of Hsp40 and Hsp90 in sponges at 32°C after 1 and 3 d respectively indicates an activation of the heat shock response system and is consistent with their role as chaperones for direct- ing degraded proteins to proteolysis, this last process being sustained by an induction of the ubiqui- tin-conjugating enzyme gene at this temperature. While sponges kept at 32°C only survived for the first 3 d, none of the genes in sponges kept at 31°C were significantly different from those in the 27°C controls after 14 d. This indicates a very strict thermal threshold for R. odorabile between 31 and 32°C and is consistent with previous findings based on sponge necrosis and symbiotic disruptions in this species.

Bacteria were isolated seasonally from the Mediterranean sponges Chondrilla nucula and Petrosia ficiformis and screened for antibacterial activities. Selected isolates were taxonomically identified by 16S rRNA gene sequencing. A total of 416 different bacterial strains were isolated, 60 (14.4%) of which displayed variable degrees of antimicrobial activity. Of the bioactive strains, 58.3% were able to inhibit Staphylococcus aureus, 6.7% were active against Bacillus subtilis, 11.7% against both Enterococcus faecalis and Escherichia coli, 38.3% against Pseudoalteromonas atlantica and 33.3% against Pseudomonas elongata. 16S rRNA gene sequence analysis showed that 2 isolates, 1 from seawater samples and 1 from P. ficiformis, were most closely related to Bacillus subtilis (99% similarity) and that another isolate from P. ficiformis was most closely related to a previously described sponge-associated Alphaproteobacterium NW001 (98% similarity). Two isolates from C. nucula were most closely related to Brachybacterium paraconglomeratum (99% similarity) and She- wanella algae (89% similarity). The high percentage of bioactive isolates derived from the 2 sponges suggests that marine microorganisms, whether animal-associated or planktonic, are promising sources for drug discovery.

Coral reefs are declining worldwide due to increased incidence of climate-induced coral bleaching, which will have widespread biodiversity and economic impacts. A simple method to measure the sub-bleaching level of heat-light stress experienced by corals would greatly inform reef management practices by making it possible to assess the distribution of bleaching risks among individual reef sites. Gene expression analysis based on quantitative PCR (qPCR) can be used as a diagnostic tool to determine coral condition in situ. We evaluated the expression of 13 candidate genes during heat-light stress in a common Caribbean coral Porites astreoides, and observed strong and consistent changes in gene expression in two independent experiments. Furthermore, we found that the apparent return to baseline expression levels during a recovery phase was rapid, despite visible signs of colony bleaching. We show that the response to acute heat-light stress in P. astreoides can be monitored by measuring the difference in expression of only two genes: Hsp16 and actin. We demonstrate that this assay discriminates between corals sampled from two field sites experiencing different temperatures. We also show that the assay is applicable to an Indo-Pacific congener, P. lobata, and therefore could potentially be used to diagnose acute heat-light stress on coral reefs worldwide.