It appears that eutrophication - a type of aquatic pollution - has been associated with fibropapillomatosis (FP), a disease that triggers the formation of tumors in sea turtles around the world [Figure 1.].
|Figure 1. Green turtle riddled with fibropapillomatosis (Van Houtan et al. 2014)|
First, some background info on FP: Previous research on the disease by Lackovich et al. (1999) had revealed the presence of DNA from α-herpesviruses in FP-affected tissue. Because the herpes DNA was not found in the surrounding healthy tissue, researchers suggested the disease to have a viral origin. However, further studies showed that the viruses were found in every turtle tested, whether healthy or otherwise, indicating that the viruses are dormant and require a certain trigger to promote the formation of FP tumors (Alfaro-Núñez and Gilbert 2014).
The new study is a follow up investigation from a 2010 paper that revealed FP to be more prevalent in areas with high levels of nitrogen runoff (Van Houtan et al. 2010). At the time, the authors hypothesised it could have something to do with how the algae the turtles eat store the excess nitrogen.
The researchers decided to test the amino acid profiles of green turtles, as well as those from a range of native and non-native algae found in both eutrophic and oligotrophic sites off Hawaii. Arginine, an amino acid known to play a role in "cell inflammation and immune dysfunction, and in promoting viral tumors" was specifically tested for in the algae. The results showed that arginine levels were elevated in eutrophic sites in all the algal species, and that the invasive species Hypnea musciformis showed especially high levels of arginine compared to the other species in both eutrophic and oligotrophic sites [Figure 2.] (Van Houtan et al. 2014).
|Figure 2. Arginine levels in three non-native species and the native Rhodophyta in eutrophic (Hi) and oligotrophic (Lo) sites; note the high levels of arginine in H. musciformis in both sites compared to other algal species (Van Houtan et al. 2014)|
The authors proposed that the excess environmental nitrogen from anthropogenic nutrient pollution is stored preferentially as arginine by the algae, which are then consumed by the turtles. Significantly, the aforementioned trigger required by the α-herpesviruses to rise from their dormant state is in fact arginine.
Moreover, H. musciformis grows more readily than the native species and thus the turtles are more likely to consume it, indicating it could potentially make up a huge propertion of the turtles' diet. It is also energy-poor compared to the native species so the turtles have to eat twice as much of it to get the same amount of energy from it.
So not only are the turtles eating arginine-rich algae, they are also consuming it in huge quantities. All this from nutrient pollution!!
The study highlights two important environmental issues - eutrophication and invasive species - and provides just one example of the effects of one type of marine pollution.