In the last decades, blooms of Ostreopsis ovata are increasingly frequent in several Mediterranean coastal areas, sometimes causing problems to the public health. The quantification of O. ovata abundances is generally performed by quantifying the number of cells per gram of macroalga, often preventing the comparison of abundances from different sites if cell quantifications are performed on different algal species. In this paper we propose a sampling method based on the use of a modified plastic syringe designed to quantify benthic cells abundances independently from the type of substratum. The method was tested in the O. ovata monitoring carried out in the Gulf of La Spezia (Ligurian Sea) and along the Apulian coasts (Southern Italy) since 2007. In 2009 the “syringe” method was compared with the classic methodology used in national monitoring of O. ovata. The syringe method seems interesting in terms of time costs and effectiveness, both for sample collection and processing, allowing quick and simple sampling of several sites along the coastline. The technique turned out to be adequate when a fast and reliable estimate of O. ovata “reservoir” near the bottom was required, in order to forecast toxic algal blooms in coastal areas.