EFFECT OF WIDESPREAD ENVIRONMENTAL DISTURBANCES ON MEIOFAUNA AND FREE-LIVING NEMATODES

Natural and human disturbances may affect ecosystems compromising their functioning. It is, therefore, important to define prevention strategies to avoid irreparable damages, where the first action implicates the identification of possible environmental criticalities followed by the management actions. For this purpose, it is necessary to identify reliable and easily applicable bioindicators that can give an early response to potential environmental disturbance and define the ecological quality of marine coastal systems. Meiofauna (animals from 500 μm to 45 μm in size), and in particular free-living nematodes, appear good candidates in the framework of the ecological assessment because they have all the above cited characteristics along with a wide distribution in all the types of environments and substrata. Thus, the present Ph. D. project takes into consideration six study cases set in a wide geographical span and under environmental disturbances frequently occurring in the coastal systems. The primary project aims are i) to demonstrate that meiofauna and nematodes can be efficiently used for the assessment of the health status in marine habitats; ii) to increase the number of meiobenthic indicator taxa that can be regarded as “sentinels” of human disturbance; iii) to further calibrate the tools so far available for the classification of Ecological Quality (EcoQ) to encourage the use of meiofauna in the assessment of the status of underwater life. The first study case was carried out in the Maldivian Archipelago (Indian Ocean), where human activities such as dredging and infilling are common practices, which led to a decrease in the taxonomic diversity of many animal species. In this context, the study of nematode communities shows that their taxonomical composition and functional traits (i.e. trophic and life strategy) are mainly influenced by the reef exposure and topography (i.e., lagoon and ocean reefs) and the depth gradient. The high abundance of k-strategists in ocean reefs might indicate a higher EcoQ when compared to lagoon reefs; however, the absence of significant differences in life strategy functional diversity and functional redundancy indicates that a recovery process is underway. The results obtained suggest that nematodes could add important information to the vulnerability and resilience of the benthos and, therefore, should be included in the biomonitoring activities of the Coral Degradation Zones (CDZs) along with the reef bioconstructors. The second case study from the Indian Ocean (Indonesia), was carried out in two seagrass meadows characterized by different sedimentological regimes and anthropogenic pressure. The lowest meiobenthic abundance and diversity found at the Barat meadow along with the major sediment modifications suggested a higher anthropogenic pressure in this site. Rare meiobenthic taxa (<1% of the total abundance in all investigated samples) revealed significant differences in the composition of the meiobenthic assemblage suggesting the key role of rare meiobenthic taxa as possible indicators of spatial variability generated by engineer species and different environmental conditions. The third study concerned the Southern Ocean at Terra Nova Bay (Antarctica), where the effects of the human activities in the Mario Zucchelli Research Station were compared with the natural disturbance occurring in the penguin colony located at Adelie Cove. Here, the high contribution of r- strategists corroborates the hypothesis that the chronic impact of the penguin colonies may have stronger effects on the meiobenthos than the human activities at the research station and, as reported in the Indonesian study, the assemblage structure of rare meiobenthic taxa is confirmed to be more susceptible to environmental variations, rather than the whole assemblage structure. In the fourth study, a commercial port of the Ligurian Sea, nematode communities were investigated in stations at an increasing distance from the port. The stations selected at an increasing distance from the port outlet aim to detect how ports may influence the benthic nematodes from surrounding coastal areas. The taxonomical and functional distribution of the nematode species appeared influenced by the contamination level, granulometry, and organic load of sediments. According to these results, the nearest stations to the port outlet appeared to be the most polluted, while the coast close to Bergeggi Marine Protected Area seemed as the most pristine area. Furthermore, the study indicated a selection of the genera that may be considered as sentinels of sediment contamination and organic enrichment. The maturity index suggested that the different proportion of the nematode life-strategies is an effective tool to assess the EcoQ of sediments. In the fifth study the sediments within three commercial ports from the Adriatic Sea (Ancona and Trieste, Italy; Koper, Slovenia) were investigated, the nematode analysis indicated that r-strategist genera were dominant in all three study areas. Despite the high contamination levels, Trieste showed high nematode biodiversity which suggests a potential adaptation of nematodes to a long-standing contamination. A co-occurrence analysis was performed to further implement the sets of bioindicator genera concerning their different opportunistic behaviors and to identify which genera cohesively respond to site-specific environmental conditions. The results encourage the use of nematodes for the EcoQ assessment of port seabeds. Despite the good response of meiofauna and nematodes as bioindicators of anthropogenic disturbance, the taxonomic identification of these organisms remains a time-consuming activity and requires the supervision of experienced taxonomists. To overcome this problem, in the sixth study, was proposed a combination of morpho-functional traits (i.e. amphids, cuticles, buccal cavities, and tail shapes) as an alternative to the taxonomic identification of the nematode specimens. The approach was tested by employing a meta-analysis of a data set of study cases from the Mediterranean Sea. The statistical results revealed that the trait combination perfectly mirrors the changes in the taxonomic community structure at the genus level which makes it possible to suggest this approach as a rapid test of nematode fauna changes for biomonitoring purposes.