MEPS 524:185-196 (2015)  -  DOI: https://doi.org/10.3354/meps11184

ABSTRACT: Sedimentary habitats show large variation in physical and ecological conditions that can influence microbial abundance and composition. Such variation can place resident organisms under different risks of microbial infestation and thereby select for different levels of anti-microbial defense. The egg masses deposited by a diversity of marine organisms in these environments may be especially vulnerable to microbial colonization. Previous studies have demonstrated interspecific variation in the level of anti-microbial activity in egg masses, but have not examined whether intraspecific variation among populations relates to variation in risks among habitats. We compared anti-bacterial activity in egg masses among populations of the opisthobranch mollusc Melanochlamys diomedea in relation to sediment features, including bacterial load, particle size, and organic content. Egg masses were extracted with ethyl acetate and methanol to derive fractions with relatively low and high polarity, respectively. The extracts were then tested in a bacterial growth assay for anti-microbial activity against the bacteria Vibrio harveyi and Bacillus subtilis. Sediment characteristics and bacterial load were all highly correlated and varied significantly among sites, with organic content appearing to be a stronger predictor of bacterial load than sediment size. Among populations, the level of anti-bacterial activity within egg masses also correlated as expected with these sediment characteristics and with bacterial load. These results support the hypothesis that anti-microbial defenses in egg masses are related to the environmental risks of microbial exposure. Thus, microbial interactions appear to drive an important component of the reproductive biology of sediment-dwelling organisms.

KEY WORDS: Egg mass · Anti-bacterial activity · Sediment · Bacterial load · Population · Benthic development · Organic content · Grain size