ABSTRACT. – Seasonal variation in clutch size of multi-brooded vertebrates in intermediate latitudes follow a parabolic trend that could be coupled to seasonal variation in environmental factors so that maximal clutch size is attained at times of higher resources availability. To test whether this trend may be observed in aquatic invertebrates, we monitored the clutch size and related ecological traits of a crangonid decapod Philocheras trispinosus population on the Western Mediterranean coast of Spain for more than two years. Unlike other northernmost studies, the monitored population presented ovigerous females throughout the year without interruption. The analysis of sex-ratio, size-frequency distribution and percentage of ovigerous females allowed the period of maximum recruitment and reproduction to be assigned between April and June. Pooling all the samples analyzed into one theoretical reproductive year starting on 1 September (minimal clutch size) showed a second order polynomial (parabolic) trend with maximum sizes and clutch size corresponding to early spring. We suggest that the response of P. trispinosus’ reproductive effort to habitat variability over time is similar to that of clutch size in birds. This could be a general trend in organisms living in habitats with strong seasonal habitat variability.