Seasonal Variations in Invertebrates Sheltered among Corallina officinalis (Plantae, Rodophyta) Turfs along the Southern Istrian Coast (Croatia, Adriatic Sea)

Abstract

Available research on invertebrates in Corallina officinalis settlements shows a high level of biodiversity due to a complex habitat structure. Our aim was to examine seasonal changes in the invertebrate population, considering the algae’s growth patterns. Nine locations with over 90% algal coverage were selected in southern Istria, where quantitative sampling was performed using six replicates of 5 × 5 cm quadrats in each location. Results showed that 29,711 invertebrates were found during winter (maximum algae growth) and 22,292 during summer (minimum algae growth), with an extrapolated average density of 220,000 and 165,200 individuals per square meter, respectively. The total number of individuals showed a linear increase as the algae biomass increased. The highest density, 586,000 individuals, was recorded in the Premantura area during winter. Dominant groups such as amphipods, polychaetes, bivalves and gastropods made up over 80% of the invertebrates. Our study confirms high invertebrate richness in the C. officinalis settlements, with the maximum density being the highest when compared to previously published data.