National Inventory and Ecological status ofMarine Crustaceans in Libyan Waters,Southern Mediterranean

Abstract
The Libyan coast provides an ecological habitat supporting a diversity of marine crustaceans. This study aims to assess the diversity, spatial distribution, and ecological status of crustacean species inhabiting Libyan marine waters. Data were compiled from a comprehensive review of unpublished scientific surveys, technical reports, and biological samples collected along various parts of the Libyan coast during two main sampling periods: January 2005 to March 2006, and January 2013 to January 2017. Additional benthic samples were obtained from a shipwreck site located on a sandy seabed at a depth of 31 meters off the coast of Tripoli during both winter and summer seasons in 2020. A total of 357 crustacean species were identified, encompassing five taxonomic classes and 138 families. Species richness was highest in the eastern coastal region. The class Malacostraca represented the most taxonomically diverse group, comprising 62.32% of the identified families and 162 species (45% of the total species count). This was followed by Hexanauplia, which accounted for 31.88% of the families and included 183 species (50.83%). The majority of recorded species (94.40%) were native to Libyan waters, while 5.60% were classified as non-indigenous. These non-indigenous species, primarily localized along the coast, offer critical insights into patterns of marine bio-invasion and species establishment in the south-eastern Mediterranean Sea. This study provides a comprehensive evaluation of crustacean biodiversity along the Libyan coast, contributing significantly to baseline data for regional marine biodiversity assessments. It also highlights key distributional patterns and potential ecological implications of nonindigenous species in this underexplored sector of the Mediterranean basin.

Key Findings :

1.ignificant Influx of Non-Indigenous Species (NIS)Substantial Expansion: Recent marine checklists show a dramatic increase in non-indigenous marine biodiversity along the Libyan shoreline. Major comprehensive revisions (such as Shakman et al., Mediterranean Marine Science) added over 100 newly documented bony fish species, bringing the total list to 304 taxa.
Dominance of Lessepsian Migrants: The primary source of non-indigenous species is Lessepsian migration (species originating from the Red Sea/Indo-Pacific via the Suez Canal).
In addition, several Atlantic-origin taxa are expanding their range eastward from Gibraltar.

2. East-to-West Biodiversity GradientBiodiversity metrics and non indigenous species richness are significantly higher in the Eastern sector of Libya (Cyrenaica). Due to its proximity to the Suez Canal, the eastern region acts as the primary initial hub for Lessepsian species before they spread westward toward central and western assessment zones (e.g., Tripoli and Farwa Lagoon).

3. Established Populations & Ecological ImpactMany non-indigenous species have transitioned from casual sightings to fully established breeding populations.Invasive species (e.g., Siganus rabbitfish, Pterois miles lionfish, and Lagocephalus sceleratus pufferfish) actively alter local food webs, outcompete native species, and impact local coastal fisheries.

4. Integration of Novel Survey MethodsCombining traditional scientific field surveys with citizen science and social media mining (monitoring fishermen’s catches via social groups) has proven essential for detecting non-indigenous species early in under-monitored southern Mediterranean waters.

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