Artificial structures cover a considerable part of the Mediterranean coasts. In the Aegean Sea, most studies related to artificial structures have focused in vagile fauna on harbors and marinas but little attention has been given to the sessile biota on coastal defense structures. The aim of this work was to describe for the first time the shallow sublittoral sessile benthos on coastal defense structures in Crete (Eastern Mediterranean Sea) in order to identify potential differences in comparison to natural rocky substrates, adopting both a taxonomic and functional (i.e. macroalgal structural complexity) approach. Three shallow (1-3 m) localities were studied in the north coast and three in the south coast of the island (six localities in total). At each locality, two types of hard substrate were selected: an artificial coastal defense structure (rip-rap) and the nearest natural rocky substrates. The percent cover of sessile taxa was calculated using random points counts over photoquadrats (20 x 20 cm). The structure of the assemblage differed between artificial and natural habitats. Values of Shannon-Wiener’s diversity index and number of taxa were higher in natural substrates. In addition, cover of arborescent macroalgae was lower on artificial substrates. In conclusion, rip-raps do not function as surrogates of natural hard substrates in the study area since their shallow subtidal assemblages differ in terms of community structure, diversity and functionality. The deficient performance of such artificial structures could be attributed to the combined effects of abiotic factors and biotic processes, including substrate nature and roughness as well as differential grazing pressure.

The colonization of artificial structures by benthic organisms in the marine realm is known to be affected by the general trophic patterns of the biogeographical zone and the prevailing environmental traits at the local scale. The present work aims to present quantitative data on the early settlement progress of macrofaunal benthic assemblages developing on artificial reefs (ARs) deployed at the Underwater Biotechnological Park of Crete (UBPC) in the oligotrophic Eastern Mediterranean. Visual census and subsequent image analysis combined with scraped quadrats were used to describe the establishment of the communities and their development over three consecutive campaigns, spanning 5 years post-deployment. Macroalgae consistently dominated in terms of coverage, while sessile invertebrates displayed different patterns over the years. Polychaeta and Bryozoa were gradually replaced by Cnidaria, while Porifera and Mollusca displayed an increasing trend over the years. Motile benthos was mainly represented by Mollusca, while the abundance of Polychaeta increased in contrast to that of Crustacea. For both sessile and motile assemblages, significant differences were observed among the years. The results of this study indicate that ecological succession is still ongoing, and further improvement in the monitoring methodology can assist towards a more accurate assessment of the community composition in complex AR structures.

Ports and recreational marinas are established hotspots for the introduction and secondary spread of non-indigenous species (NIS), mainly via vessel transport and biofouling on artificial substrates. In the AlienPorts project, we surveyed fouling and associated macrobenthic assemblages in four major Greek marinas across distinct marine regions—Rhodes (Levantine), Heraklion and Piraeus–Zea (Aegean), and Patra (Ionian)—from 2021 to 2022, applying two complementary protocols: (i) photoquadrat surveys and (ii) scraped assemblage sampling. The photoquadrats recorded twelve NIS and seven cryptogenic species, which were dominated by sessile fouling taxa, especially ascidians. The scraped samples revealed 106 polychaete and amphipod species, including 25 taxa (23 NIS, two cryptogenic). Six of the polychaetes are new NIS for the Mediterranean, and thirteen of the taxa are newly recorded as NIS in Greek waters. Heraklion had the highest NIS richness (18 NIS + two cryptogenic), while the other marinas hosted approximately ten NIS/cryptogenic taxa. In contrast, NIS often dominated the population densities, with Zea being the most impacted based on the NIS to native species ratios for both diversity and abundance. The two methods detected largely distinct biodiversity components and shared only one NIS, underscoring a strong complementarity. The multivariate analyses confirmed significant differences among marinas (ANOSIM, p < 0.01). These results support integrated, multi-method monitoring to enhance the early detection and impact assessment under MSFD Descriptor 2.

The Gulf of Heraklion is one of the most well-studied coastal marine ecosystems in the eastern Mediterranean. It is an oligotrophic area, exposed to wave action where muddy sediments prevail and its coastal zone is relatively unaffected by major riverine inputs. However, it faces pressures deriving from urbanisation, tourism, small-scale fisheries and climate change. Amongst its biological components, macrobenthos is an important component of soft-bottom habitats of the continental shelf and considered to be an indicator of environmental and human-induced disturbance. Nevertheless, long-term data are limited, thus restricting our understanding of their temporal trends. This is of particular importance for the Mediterranean Sea which is characterised as a hot spot of biodiversity and climate change impacts on its biota. The macrοbenthic faunal communities were investigated in the continental shelf of Heraklion Bay within the framework of the European funded project entitled MARine Biodiversity and Ecosystem Functioning leading to Ecosystem Services (MARBEFES), with the objective to enhance the understanding of marine biodiversity, ecosystem functioning and the ecosystem services they provide. Additional studies, with the same objectives, were carried under national and local monitoring programmes. Samples were collected from a specific transect of stations, named H2 (10, 20, 30, 40, 50, 100 and 200 m depth), located in the wider marine area of the wastewater treatment plant of Heraklion City. The transect was sampled during three different sampling surveys and periods: June 2010, June 2015 and August 2024. A total of 30,280 individuals were examined belonging to the taxonomic groups of Annelida, Crustacea, Mollusca, Echinodermata, Nemertea and varia. The identification of the key taxonomic classes (Polychaeta, Bivalvia, Gastropoda, Scaphopoda and Malacostraca) revealed 231 macrobenthic taxa. Out of the 231 taxa, only 30 were common amongst all the three sampling periods, while Polychaeta was the most abundant macrobenthic group in all sampling periods.