###### Abstract  
Tropical coral reefs are considered one of the most diverse and productive ecosystems on the planet. Corals heavily rely on the symbiotic relationships with photosynthetic dinoflagellates of the Symbiodiniaceae family, receiving photosynthates in exchange for inorganic nutrients. The breakdown of this symbiosis leads to coral bleaching, resulting in major coral reef losses. Despite the fact that the environmental stressors causing coral bleaching are well known, the cellular and molecular mechanisms underlying this endosymbiosis are not well understood. The upside-down jellyfish _Cassiopea_, similarly to corals, has a mutualistic relationship with Symbiodinaceae. However, unlike corals, this upside-down jellyfish has a closed sexual reproductive cycle, can be easily maintained in laboratory conditions, and has a short generation time. The use of _Cassiopea_ as a model organism to investigate symbiosis with Symbiodinaceae would provide us with a better understanding of Cnidarian symbiosis and would bring us a step closer to the development of a cnidarian symbiosis model. _Cassiopea_ polyps can stay aposymbiotic and propagate if fed regularly. To understand the molecular mechanisms behind this symbiosis, gene expression profiles between aposymbiotic and symbiotic _Cassiopea_ polyps were compared, revealing genes and pathways putatively involved in symbiosis. We identified 1227 differentially expressed genes out of 63,340 transcripts, of which 560 were upregulated and 667 were downregulated in symbiotic polyps. GO enrichment analysis indicated that processes linked to lipids, sterols, cholesterol, and membrane transport were upregulated in symbiotic _Cassiopea_ polyps. We also compared GO enriched terms between _Cassiopea_ and _Aiptasia_ upon symbiosis, revealing shared enrichment in processes related to steroid hormone receptor activity and sterol homeostasis. Sterols are essential cell components that cannot be synthesized by cnidarian hosts, which rely on symbionts or on prey consumption for their acquisition. Symbiodinaceae can produce and transfer a variety of sterols to the host, including dinosterol, cholesterol, and gorgosterol, among others. Our results show that two genes annotated as NPC intracellular cholesterol transporter 2 were also increased during symbiosis, suggesting that sterol transport via Symbiodiniaceae may potentially play an essential function in _Cassiopea_.  
keywords: _Cassiopea_; Symbiodinaceae; symbiosis; bleaching; transcriptomics  
###### Abstract  
The Verde Island Passage (VIP) is a region in the Philippines with a high index of biodiversity. Baseline coral reef assessments were conducted in four provinces along the VIP (Batangas, Marinduque, Occidental Mindoro, and Oriental Mindoro) to compare coral reef abundance and biodiversity in marine protected area (MPA) and non-MPA sites. The average abundance of coral and other substrates (e.g., macroalgae, sponges, rock, sand/rubble) were measured, and the numbers of coral genera were identified for each site. Batangas showed equal coral cover and coral species richness for MPA and non-MPA sites. Marinduque showed equal coral cover for MPA and non-MPA sites, and the non-MPA site had higher species richness. Occidental Mindoro showed higher coral cover and species richness in the non-MPA site compared to the MPA site. Oriental Mindoro was the only exception, showing higher coral cover and species richness in the MPA site compared to the non-MPA site. The findings indicate that many non-MPA coral reefs in the VIP have potential to become MPAs, thus warranting their protection and conservation. Continued monitoring and assessment should be conducted to build on the growing database of biodiversity data that are being compiled for the VIP.  
coral reef; biodiversity; Verde Island Passage; marine protected areas (MPA)