Occurrence and Ecological Significance of Microalgae Species Associated with Egg Clutches of Aquatic Animals

The association of microalgae with aquatic animal egg masses plays an important role in the reproductive ecology of several species. The first descriptions of this phenomenon were reported in 1888 for the egg masses of the spotted salamander Ambystoma maculatum. The microalgae most commonly associated with animal egg masses are green algae belonging to the genus Oophila. For many years, Oophila sp. was considered the only known intracellular endosymbiont in vertebrates; however, subsequent research has expanded the list of microorganisms capable of forming such associations. Here, we reviewed 69 English-language scientific publications on the occurrence of microalgae in the egg clutches of aquatic animals. This clearly indicates that current knowledge of these organisms remains incomplete and requires further investigation. This review presents a general characterization of the occurrence of microalgae in aquatic animal egg clutches, summarizes the locations where this phenomenon has been documented, describes both the animal hosts and the microalgae involved, examines the benefits resulting from the presence of photosynthetic microorganisms within egg masses, and highlights future research directions, including potential practical applications of these associations.