Seagrass detritus in the Mediterranean: A preferred habitat for harpacticoid copepods. Is there an active migration towards seagrass detritus?
Agusto, L.E. (2014). Seagrass detritus in the Mediterranean: A preferred habitat for harpacticoid copepods. Is there an active migration towards seagrass detritus? MSc Thesis. Marine Biology, Ghent University/Université de Liège: Ghent, Liège. 56 pp.
An in-situ experiment was conducted within a seagrass macrophytodetritus field in the Bay of Calvi, Corsica. The species-specific migration of harpacticoid species towards macrophytodetritus was studied. Defauntated macrophytodetritus was used to attract harpacticoids migrating either through the water column or from the sediment in separate experimental cores. The colonization process was allowed for a period of 24 hours and for a period of 96h. These two time experiments were done independent from each other.In the Mediterranean Sea, harpacticoid copepods occur in high numbers in the endemic seagrass Posidonia oceanica L. Delille meadows (Danovaro et al. 2002) and detritus accumulations (Mascart et al. 2013). Detritus accumulations form new ephemeral habitats which can remain present from days to months and occur at relative large distances from live seagrass. The morphology of copepods gives an indication of the habitat in which they occur. Four different copepod morphological types, or morphotypes, can be distinguished in a seagrass habitat: 1) mesopsammic types which are found mainly in the sediment. They have slender vermiform bodies with non-protruding appendages. 2) Phytal types live attached to the seagrass leaves and have developed clinging appendages like prehensile legs. 3) Phytal-swimmers are well capable of swimming but live inside the phytal habitat. 4) pelagic types possess long antennae and large swmming legs. Colonization capacities are suggested to be related to species-specific swimming abilities. Harpacticoids are well known emergers and colonize new habitats fast. Their presence in detritus accumulations preludes the fact that they that they are capable of colonizing new habitats at large distances. However knowledge on how colonization of novel structures occurs by harpacticoids is lacking. Migration toward new habitats can occur through active mechanisms, swimming or crawling, or passive patterns governed by hydrodynamics. Colonization of detritus can occur by active migration through the water column of from the sediment by an upwards migration. Results showed an influence of the experimental core on the species composition for the 96h colonization experiment. The study found a higher amount of species to migrate from the sediment upwards. Active migration was dominated by phytal-type species. A reclassification of phytal-types migrating through the water column is proposed as they show a good swimming ability. Three species, Amphiascus minutus, Sarsamphiascus tenuiremis and Ectinosoma cf. dentatum were identified as migrating both through the water column as from the sediment.
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