We examined the functional response of the Japanese brush-clawed shore crab ( Hemigrapsus takanoi ) towards blue mussels ( Mytilus sp.) across four seasons for an ambient and +6 °C future warming scenario in the Baltic Sea. The experiment was carried out as a laboratory experiment at the GEOMAR Helmholtz Centre for Ocean Research Kiel. Crabs were sampled in the innermost part of the Kiel Fjord, Germany (54°19′44.8″ N, 10°08′55.5″ E) between Summer 2021 and Spring 2023 during the respective season. The experimental design used a fully factorial approach, examining the functional response across two temperatures, two sexes, and eight prey densities (1, 2, 4, 6, 8, 16, 32, 64) across four seasons. Each crab was subjected to a pre-experiment 48-hour starvation period and then exposed to a fixed number of mussels for a 72-hour feeding trial. The number of mussels consumed was recorded, providing data on the predatory impact of H. takanoi under varying temperature scenarios and across seasons.
We conducted two experiments to assess the predation of female H. takanoi (a non-native species in the Baltic) on a native gammarid (Gammarus duebeni) and a non-native analogous gammarid (Gammarus tigrinus). In the first experiment, we examined the functional response of female H. takanoi to G. duebeni and G. tigrinus. The experiments were conducted at the GEOMAR Helmholtz Centre for Ocean Research Kiel. Crabs were sampled in the innermost part of the Kiel Fjord, Germany (59°19'44N, 10°08'55.5E) during the summer of 2021. The experimental design utilized a fully factorial approach. One temperature (16°C) and one salinity (10) across five prey densities (1, 2, 4, 8, 16) were used. Each combination was replicated three times, alongside three replicates of predator-free controls at each prey density to quantify background prey mortality. The crabs were starved for 48 hours ahead of the experiment and were exposed to the respective number of gammarids for a 6-hour feeding period. The number of gammarids consumed was recorded.
One of the motivations for the study of trophic relations is the necessity to predict how ecological mommunities will respond to major perturbations like global warming or nutrient enrichment. Ecological communities can be modelled as webs in which each species is represented by a variable and each trophic link by a dynamic equation. Properties of model food webs depend on the form of the trophic interactions. The project aims to explore the alternative forms of the trophic interactions using three approaches. (a) Food web theory. The consequences of the alternative forms of the trophic interactions on food web structure and on responses to large perturbations will be explored. (b) Plankton time series. Models with alternative forms of the trophic interactions will be fitted to non-equilibrium plankton time series. This should help determine which form of the trophic interactions better applies to lakes. (c) Behavioural mechanisms. The echanistic background of trophic interactions will be explored.^L'etude des realtions trophiques est motivee par la necessite de predire comment des communautes ecologiques reagiront a de grandes perturbations comme le rechauffement du climat ou l'apport de nutriments. Les communautes ecologiques peuvent etre modelisees comme des reseaux trophiques ou chaque espece est representee par une variable et chaque interaction trophique par une equation dynamique. Les proprietes du modele dependent de la forme des interactions trophiques. Le but du projet est d'explorer les formes alternatives des interactions trophiques en utilisant trois approches. (a) Theorie des reseaux trophiques. On etudiera leurs effets sur la structure trophique et sur les reponses a de grandes perturbations. (b) Series temporelles. Des modeles alternatives seront ajustes a des series temporelles de plancton. Cela aidera a determiner quelle forme des interactions trophiques s'applique mieux aux lacs. (c) Mecanismes comportementaux. On etudiera les fondations'mecanistiques' des interactions trophiques. (FRA)