Search

Seagrasses colonise coastal areas worldwide. Despite their high primary production, a considerable proportion becomes detritus that can be used as food, physical habitat and occasional or permanent shelter by several benthic macroinvertebrates. In turn, macroinvertebrates can contribute to regulating seagrass decomposition, and represent an important trophic link between primary producers and higher consumers. Nonetheless, several factors could modify colonizer responses to this habitat. In this study, we tested if colonisation of the seagrass detritus of Zostera noltei Hornemann, 1832 was related to substrate availability rather than food and whether the colonising assemblages were similar according to the structural complexity of the meadow. We used artificial seagrass detritus to mimic the physical structure of the natural detritus while disentangling the effect of food attractiveness vs. physical habitat availability. Litterbags were filled with natural or artificial detritus and deployed within a seagrass meadow in Thau lagoon (Étang de thau, France) in areas of different structural complexity. During two field experiments, detritus decomposition and litterbag colonisation were analysed. A total of 11270 individuals belonging to 26 taxa were identified (including polychaetes, crustaceans, molluscs, and chironomids larvae). Habitat structural complexity shows no effects on the colonisation of the detritus, but there were clear differences between empty and filled litterbags, which had a higher number of species and individuals, but without a general preference for the natural or artificial detritus substrate. In conclusion, colonisation appeared to be driven by the presence of debris material, and not by its type. The natural and artificial detritus acts as an attractor for macroinvertebrates, which use opportunistically one or the other type, with no differences according to the seagrass habitat complexity, probably indicating a supply of individuals from further distances. These findings show that the detritus, acting as a faunal magnet, can be colonised by a rich and diverse benthic community, highlighting its important role in maintaining the biodiversity within the seagrass meadows.

Seagrass detritus can attract numerous invertebrates as it provides food and substrate within the meadow or in adjacent environments. Nonetheless, several factors could modify the invertebrate response to this habitat. In this study, we tested if epifaunal colonisation of Zostera noltei detritus was related to substrate availability rather than food and whether colonising assemblages were similar according to the meadow structural complexity. Litterbags filled with natural or artificial detritus were deployed within an eelgrass meadow in a Mediterranean coastal lagoon (Thau lagoon, France). Colonisation appeared to be driven by the presence of detritus, with similar assemblages in natural and artificial substrate, but with more individuals than the empty bags, used as controls. There were also no differences according to habitat complexity. These findings show that detritus, acting as a faunal magnet, plays an important role in maintaining biodiversity, as epifauna is a critical trophic link between primary producers and consumers.

Peracarid crustaceans (orders Amphipoda, Isopoda and Mysida) represent one of the most important group of invaders in European freshwaters that largely contribute to the homogenization of macroinvertebrate fauna. The aims of this study were to investigate distribution, density and assemblages of native and alien Peracarida in Croatian large rivers, their relationship with physico-chemical parameters and their proportion in total density of benthic macroinvertebrates as preliminary assessment of their impact. Hand net sampling (25×25 cm, mesh size 500 μm) was conducted twice (in 2015 and in 2016 or 2017), at 48 locations on four major large rivers (Danube-4 sites, Sava-21, Drava-20, Mura-3). Quantitative samples (20×0.0625 m2) were collected at each site in a shallow bank area of rivers (44 sites) or two reservoirs on Drava (2 sites), while deeper parts of the same reservoirs were sampled using Ekman grab (3×0.0225 m2 at 2 sites). In a total, 16 species were recorded, five native (Amphipoda- 4, Isopoda-1) and 11 alien species (Amphipoda- 8, Isopoda-1, Mysida-2). The highest number (10 spp., all alien species) were found in the Danube River, while subsets of alien species were found in the Sava (5) and Drava Rivers (6). The Mura River and the most upstream reaches of the Drava and Sava Rivers in Croatia have not yet been colonized by invasive peracarids and native species still thrive there. The most widespread alien species, present in the Danube, Sava and Drava Rivers, were isopod Jaera istri (29 sites) and amphipods Dikerogammarus villosus (24) and Chelicorophium curvispinum (22). The most upstream distributed species were amphipod D. haemobaphes in the Sava (631 rkm) and D. villosus in Drava River (270 rkm). Characteristic species for Sava were D. haemobaphes and C. sowinskyi, for Drava and Danube D. villosus and C. curvispinum, and additionally C. robustum for Danube. Significant differences were found in peracarid assemblages between all four rivers. Interestingly, extremely cold winter in January 2017 caused decrease of invasive amphipod D. villosus and enabled native species G. fossarum and S. ambulans to become more abundant than D. villosus at two sites in Drava. Proximity to the Danube River, as source of all invaders, and colonization history together with physico- chemical parameters, explained observed variation in peracarid assemblage between studied rivers. Proportions of alien Peracarida in total density of benthic macroinvertebrate was very spatially variable with the highest average and maximum values in the Drava River and lowest in the Sava River. Long-term monitoring of the distribution and abundance of invasive peracarid species is essential prerequisite for better understanding of the changes in macroinvertebrate assemblages in Croatian large rivers.

The isopod Ligia baudiniana is reported for the first time from the Caribbean coast of Colombia. Specimens of this species were collected on a rocky, intertidal substrate on the beaches of Marbella, Cartagena de Indias. A diagnosis is included along with illustrations of main taxonomic characters.