Ecological Partitioning and Morphometric Analysis of Two Sympatric Intertidal Gastropods (Phorcus turbinatu and Patella caerulea) in the Southern Mediterranean shore (Al-Hanyiah, Libya)

This study investigated the distribution, abundance, and morphometric characteristics of two dominant intertidal marker species, the gastropods, Phorcus turbinatu and Patella caerulea, along the rocky shores of Al-Hanyiah in eastern Libya. Using 20 transects (1×1 m quadrats) spanning lower-mid littoral and shallow subtidal zones, we quantified population densities during autumn and measured key shell parameters (length, height, weight, base dimensions). P. turbinatus exhibited a conical shell (3–6 whorls; mean height = 19.19 mm, weight = 3.69 g) with distinctive black spiral markings and an operculum used to seal the shell aperture during low tide, conserving moisture and deterring predators, while P. caerulea displayed a whorl-less, striated shell (mean length = 19.93 mm, weight = 2.01 g). Both species showed negative allometric growth (b = 2.231 and 2.498, respectively), with strong correlations among morphometric traits.Spatial partitioning was evident: P. turbinatus dominated lower intertidal zones (peak abundance 0–3 m from shore), avoiding areas beyond 12 m landward or 3 m seaward. In contrast, P. caerulea distributed more broadly across mid-intertidal elevations (up to 14 m landward), with higher densities near the shoreline. Both species were completely absent from sandy substrates and exhibited no size gradients across their ranges. Behavioral differences reinforced niche separation—P. turbinatus utilized crevices and tidal pools for diurnal refuge, whereas P. caerulea relied on home scars and nocturnal activity.These patterns reflect adaptations to abiotic stressors (turbulence at high tide and overheating and desiccation at low tide) and resource competition, with P. turbinatus prioritizing mobility and P. caerulea optimizing attachment strength. Despite current minimal anthropogenic threats, future conservation efforts should monitor these keystone grazers, given their role in maintaining algal balance and microhabitat diversity. The study provides baseline data for assessing climate change impacts (e.g., ocean acidification, warming) on Mediterranean intertidal ecosystems.