Composition and Seasonal Variation of Macro-benthic Invertebrate Species Caught by Bottom Trawling in Yumurtalık Bight (Iskenderun Bay-Türkiye)

Abstract

This study aims to determine the distribution and species diversity of macro-benthic invertebrates captured by bottom trawling at different depth layers in Yumurtalık Bight, a critical breeding and feeding ground for numerous species. Sampling was conducted monthly between September 2017 and August 2018 at depths of 0–10 m, 10–20 m, and 20–50 m. The lowest water temperature (15.9°C) was recorded at 0–10 m depth in January and the highest (30.13°C) at the same depth in July. Salinity ranged from 36.6 PSU in March to 39.4 PSU in October at 10–20 m depth. A total of 28 macro-benthic invertebrate taxa were identified, 20 at the species level and 8 at the phylum or class level. The majority of identified species belonged to the orders Decapoda (11 species), Stomatopoda (3 species), and Littorinimorpha (2 species). These species were classified into seven different phyla: Arthropoda, Mollusca, Echinodermata, Cnidaria, and Porifera. A significant proportion of the identified species were exotic, primarily of Indo-Pacific origin. The Shannon-Wiener Diversity Index (H') varied by month and depth, peaking at 1.90 in March (20–50 m) and 1.82 in September (0–10 m). The Simpson Dominance Index (D) ranged from 0.19 to 1.0, while the Pielou Index (J') ranged between 0.5 and 0.9 from July to November, dropped sharply in December and January, and increased again from April to June. According to the Soyer Dominance Index, the most abundant species were Charybdis (Archias) longicollis (13.13%), Sepia officinalis (12.12%), Erugosquilla massavensis (11.62%), Loligo vulgaris (11.11%), and Penaeus semisulcatus (11.11%). The Shannon-Wiener Diversity Index (H'), Simpson Dominance Index (D), and Pielou’s Evenness Index (J') showed no statistically significant differences across depths and months, indicating a generally homogeneous ecological structure in the Yumurtalık Bight.