Does pigmentation provide protection to bdelloid rotifers in a high ultraviolet B environment?

Aquatic species found in habitats with limited shade and little dissolved organic carbon (DOC) have increased vulnerability to ultraviolet radiation (UVR) damage. Pigmentation is a common mechanism used by animals for protection from UVR. A pigmented bdelloid rotifer, Philodina, occurs in high densities in shallow rock pools in El Paso Co., TX, and is subject to repeated desiccation and high UVR. To understand the roles of DOC, pigmentation, and dormancy in reducing the effects of UVR exposure in these rotifers: (1) DOC levels in rock pools were measured before and after the summer monsoon season and (2) hydrated or dormant bdelloids (desiccated for 0, 1, 7, or 32 d) that differed in degree of pigmentation (highly, moderately, lightly, and none) were exposed to three intensities of UVB radiation (low, mid, or high) and monitored for survival after 48 h. Pigmented bdelloids were found in rock pools with lower DOC concentrations. Logistic regression analysis indicated that pigmentation level, desiccation time, and UVB intensity all affected survival. Bdelloids in the dormant form for 1 d were more resistant to UVB exposure at all pigmentation levels. However, as desiccation time increased, the odds of surviving decreased. Hydrated highly pigmented bdelloids were three times more likely to survive desiccation, UVB radiation, and their combined effects. Prolonged periods of drought due to the changing climate will alter DOC concentrations, causing photoprotection to become an increasingly important survival strategy for aquatic invertebrates, especially those inhabiting shallow waters.