As a morphological index to assess blade production by Zostera marina L., the previous growth was determined from measurements of the distance from the ligula to the first node. The test took place as a two-step process: first, the long version of the previous growth analytical technique, in which shoots are dissected and old growth substracted from new growth, was run in parallel with a technique in which the displacement of a needle mark represents growth. Data were analyzed on a sampling interval, seasonal and annual basis. Second, growth and production values obtained with the long version of the previous growth analytical technique were compared and regressed against values obtained with the rapid version of the same technique, in which only the field value of the distance from the ligula to the first node is used. Results of the first comparative analysis indicated that in half of the sampling intervals no significant difference between techniques existed. On a seasonal basis, the difference between techniques ranged from 0 to 30% for growth, and from 0 to 55% for production. Although in most cases higher values were obtained with the technique that assessed growth from the needle mark displacement, both techniques can be used to describe variations in blade growth and production through time. Regression lines between the rapid and the long version of the previous growth analytical technique, were both significant, with corresponding correlation coefficients of 0.64 and 0.83 for growth and production. These results confirm the possibility of using the rapid version of the previous growth analytical technique as a morphological index to assess blade growth and production in a non-destructive manner.