Growth, morphology and reproductive phenology of Gelidium adriaticum (Gelidiales, Rhodophyta) from the Slovenian coast (Gulf of Trieste, northern Adriatic)

The occurrence, growth, external morphology and reproductive phenology of a Gelidium adriaticum settlement from the midlittoral zone in St. Simon Bay (Slovenian coast, Gulf of Trieste, northern Adriatic Sea) were investigated. The study was based on monthly sampling conducted for one year, from January to December 2023. The studied settlement was well developed in shaded rock crevices, forming dense turfs with a very patchy and irregular distribution. It was characterized by a slight predominance of tetrasporic thalli, with a ratio between the three reproductive stages (tetrasporic:sterile:cystocarpic) of 1.19:1.04:1.00. The mean values of the morphological characteristics studied (height and width of the thallus, width of the widest part of the thallus axis, width of the apical, middle and basal parts of the erect axes) varied between seasons and reproductive stages. In general, these values were lower in the cystocarpic thalli than those in the tetrasporic and sterile stages in all seasons.