Coral reefs are one of the most productive ecosystems in the world and are heavily replied upon by ecosystem goods and services, yet they are increasingly at risk of bleaching as a result of anthropogenic impacts and global warming. Oxybenzone is an ingredient commonly found in personal care products, particularly sunscreen, which is having a significant impact on the rate of coral bleaching. Sponges are incredibly effective biological filters and are vital to the health of coral reefs. I studied the effects of sunscreen on Pocillopora damicornis in the presence of Amorphinopsis sp. to determine whether the sponge could act as an effective filter of oxybenzone and protect the coral from bleaching in order to be an effective management option. The results clearly showed that sunscreen has a considerable impact on the rate of bleaching of coral reefs, however the sponge did not appear to be an effective filter of oxybenzone. This does not necessarily mean that it is not possible with other species or under different conditions, however there are other management options that could reduce the impact of oxybenzone on coral reefs.

Coral reefs are becoming increasingly endangered with the current global climate change and the ever-growing number of anthropogenic stressors, including overfishing and pollution as a result of development and agriculture. It is estimated that approximately 20% of the world’s coral reefs are already lost (Riegl et al. 2009), and up to 60% are projected to be lost by 2030 (Hughes et al. 2003). Significant coral bleaching has occurred over the past 20 years, increasing both spatially and in frequency (Danovaro et al. 2008).

Coral reefs are one of the most biologically productive ecosystems in the world (Danovaro et al. 2008) and maintain a huge array of marine life. They sustain a range of ecosystem good and services that directly support around half a billion people (Danovaro et al. 2008), including food, recreational activities, tourism opportunities, coastal protection etc. (Moberg and Folke 1999). Current management has been unable to sustain coral reefs on a global scale thus far, and we are continually finding new factors affecting their resilience (Bellwood et al. 2004).

With increasing awareness about sun safety and skin cancer, particularly in Australia, there has been an unprecedented rise in the production of cosmetic sun products being developed, which have the potential to significantly influence environmental contamination (Danovaro et al. 2008). Oxybenzone is an active ingredient found in many sunscreen lotions and personal care products that is designed to protect against the damaging UV rays (Downs et al. 2015). It is estimated that between 6000 and 14,000 tons of sunscreen containing oxybenzone are released around coral reefs every year, putting 10% of the global reefs at risk of exposure, targeting 40% of the coastal reefs (Downs et al. 2015). Oxybenzone has been shown to increase the rate of coral bleaching (Downs et al. 2015), to the extent that some coastal tourist destinations have banned its use (Danovaro et al. 2008).

Sponges are key to maintaining coral reef health, due to the incredible filtration ability they exhibit, maintaining water movement around coral reefs and retaining approximately 80% of the suspended particles (Stabili et al. 2006). I therefore proposed that the presence of sponges may reduce the risk of coral bleaching when exposed to oxybenzone in sunscreen. To evaluate this, I studied the effect of oxybenzone on coral alone, as well as on coral in the presence of a sponge over a period of five days, and also compared this to coral and sponges that had not been treated with oxybenzone.

The coral was collected from Moreton Bay and was identified as Pocillopora damicornis (Davie 2011), a species common in the indo-pacific but only really prevalent around Amity point in Moreton Bay. This particular species was characterized by brown tissue and many small branching polyps, making it ideal for fragmentation.

The sponge was also collected from Moreton Bay and was identified as Amorphinopsis sp. (Davie 2011) and is found on sandy mudflats and intertidal rocky reefs. This particular species has only been found in Moreton Bay, however related species are found throughout Australasia.

The experiment was conducted in the aquarium at The University of Queensland, St. Lucia campus. The species used were collected from Moreton Bay and kept in the same aquarium under constant light and temperature conditions. Coral were removed from the aquarium and fragmented into even-sized pieces before being re-mounted on Moreton Bay rock fragments from which they were removed, using UHU superglue (Fig 1). The sponges were gently sliced from the substrate using a sterile scalpel blade and pinned onto petri dishes that had been filled with agarose gel and left to set (Fig 2). 

The experiment contained two controls; one coral fragment on its own, and one in the presence of the sponge. The two treatments included the addition of 1.42g Neutrogena Sport sunscreen containing 6% w/w Oxybenzone. The quantity of sunscreen was determined based on the lethal dose determined by Downs et al. (2015) and was dissolved in seawater produced at the aquarium before being added to the containers holding the species to make up 750mL of the treated sea water. Three replicates were carried out (Fig 3).

Bleaching was quantified by visually analyzing 240 photos, four photos from each treatment for five days.

All coral controls showed no change for the first two to three days, and for replicates one and three, only slight bleaching occurred on the tips of the nubbins. None of the coral and sponge controls showed any change until day four. Once again, for replicates one and three only the tips were affected, however replicate two showed significant bleaching down one side.

The coral that had been treated with oxybenzone showed a response from day two in replicates one and three, however replicate two did not show a change until day three. Once bleaching began it was rapid and extreme, with all three replicates almost entirely white by day six. The biggest change observed was between days three and four for all replicates.

The coral and sponge that had been treated with oxybenzone showed a response from day two across all treatments and significant bleaching occurred by day six, with the biggest change observed being between days three and four.

Coral bleaching occurs when the symbiotic zooxanthellae hosted by the coral are lost as a result of adverse environmental conditions (Danovaro et al. 2008). Oxybenzone has clearly been shown to increase the rate of coral bleaching (Danovaro et al. 2008; Downs et al. 2015) and the results here clearly corroborate this. However, the addition of sponges does not seem to have benefited the coral in any way, nor has it reduced the ability of the coral to survive.

There are a number of reasons as to why the sponges may have been unable to process the oxybenzone so that it didn’t affect the coral, including it’s health, the close confines of the container, and it’s filtering mechanism. The sponges used that were collected from the aquarium were not entirely healthy and may not have been able to filter effectively. This may have been due to air exposure resulting in the shutting down of water flow (Rutzler 1995), either during the collection of the sponges, or the transfer from the aquarium to the experimental containers. This is also observed in unfavourable aquarium conditions (Rutzler 1995). Another factor affecting its sponge health may be a lack of food particles of an appropriate size. The sponges were very small, and may have rapidly used what food resources were present within the containers. Many aquarium keeping information websites also note a lack of food for sponges in aquariums.

The fact that the sponges and coral were in close confines, and there was no water change over the six day period, may also have resulted in the results seen. Sponges are extremely effective filters (Bell 2008), and in the open ocean they may be able to process the oxybenzone and exhale these secondary metabolites much further out into the water column and away from the coral. However, in the experimental system, these organic compounds would have been released back near the coral, making the process ineffective by still allowing the oxybenzone to affect the coral.

It may also be that the aquiferous system of the sponge just did not allow it to filter the oxybenzone and, despite dissolving the sunscreen first, the thick consistency of the sunscreen may have blocked some of the oscula of the sponge, reducing the efficiency of filtration, which would explain both the declining health of the sponge and its inability to protect the coral.

Oxybenzone toxicity is not just limited to corals, some studies carried out on invertebrates showed that oxybenzone caused oxidative injuries to the protozoan Tetrahymena thermophila including reducing cell viability and reducing glutathione content (an important antioxidant) (Gao et al. 2013). It is also toxic to fish, causing endocrine disruption, leading to decreased fecundity and reproduction (Coronado et al. 2008; Fent et al. 2010) and even on humans, with an correlation between exposure to oxybenzone and an increase in the occurrence of endometriosis in women (Kunisue et al. 2012). With such a wide range of species affected, it would not be surprising to discover that oxybenzone is directly toxic to sponges as well. Microscopic observations would have to be carried out in order to test this, and is something that should be considered for future management of coral reefs.

Due to the fact that Amorphinopsis sp. is only found in Moreton Bay, there is very little literature on it, therefore it is difficult to establish ideal conditions for this sponge apart from basing it on it’s habitat, and also to know how effective it may be at filtering different substances, studies using other more commonly known sponges may be more effective at determining which sponge has the most potential to protect the coral from the effects of oxybenzone.

Despite the fact that the sponges did not appear to have an effect on the rate of bleaching and survival of the coral, the results still clearly show that oxybenzone in sunscreen has a significant effect on coral reefs. In all replicates, the rate of bleaching of the controls was much slower than those treated with oxybenzone.  The first and third replicates only showed bleaching of the tips of the coral polyps, this may be due to how close the polyps are to the surface here. Throughout the experiment evaporation occurred and the polyps became very close to exposure. The water would be warmer at the surface and even very small temperature changes can elicit bleaching (Goreau & Hayes 1994). Replicate two showed bleaching of both controls on day six, however red slime algae (cyanobacteria) was found on both coral fragments which would explain this degradation. Studies show that algae is competitively dominant over adult coral, often resulting in mortality (Kuffner et al. 2006) and is commonly found in aquariums with poor flow and few water changes. In this case, there were no water changes and it is possible that the flow in these particular containers were not enough to prevent the cyanobacteria from establishing. The lack of water change allows accumulation of nutrients that result in this bloom, and explains why it took a while to show and effect.

Previous studies have shown that it is oxybenzone in sunscreen, rather than other ingredients that have a significant effect on the rate of coral bleaching (Danovaro et al. 2008), therefore it is unlikely that it was the other ingredients in the Neutrogena Sport sunscreen that was causing this effect, however testing ingredients separately would be required to confirm this assumption. It is also shown that a range of oxybenzone concentrations affect coral reefs, and although I selected a high lethal dose based on experiments done by Downs et al. (2015), all doses used in their study showed an increase in the rate of coral bleaching, therefore it is unlikely that a different dose would elicit a different response.

With the increasing awareness of the need for sun protection, the risk to coral ecosystems is growing dramatically and management options need to be considered to reduce these effects. Mexico’s ecoreserves are leading the way by banning products that contain oxybenzone entirely (Xcaret Ecopark 2007; Xel-ha Ecopark 2007). This would be the most effective option and is entirely reasonable, as there is whole ranges of personal care products out there that don’t contain Oxybenzone (Goodguide 2016). It is also entirely cost effective, however may be difficult to monitor.

Another option is to increase awareness through educational programs and information in coastal areas to inform tourists about the effects of Oxybenzone on coral reef systems and encourage them to use products that don’t contain oxybenzone. Encouraging companies to stop using oxybenzone in their products would also be very effective, however the cost of converting may dissuade producers from complying.

I’d like to thank the University of Queensland for the provision of facilities and materials required for this study to take place. I’d also like to thank Professor Bernie Degnan for his assistance in assessing the logistics of the experiment I proposed and the tutors of BIOL3211 for giving advice and providing access to the aquarium, particularly Jabin for sharing his knowledge on sponge and coral collection and help in acquiring the required material.

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