Abstract
Physical disturbances and resource pulses are major structuring drivers of terrestrial and aquatic ecosystems. The accumulations of exported dead leaves from the Neptune grass, Posidonia oceanica (L.) Delile are ephemeral and highly dynamic detrital habitats offering food sources and shelter for vagile macrofauna community. These habitats are frequently subject to wind and storms which can add “new” detrital material to previous accumulations; these can be defined as resource pulses and could potentially impact the associated macrofauna. This study assesses the impact of an experimental resource pulse on the macrofauna associated with exported P. oceanica litter accumulations. The experimental design consisted of two pulse treatments (the addition of dead leaves with and without the associated fauna), and two controls (one procedural, and one total control), where the added material was left underwater for 14 days. Invertebrates then present in the sampled detritus were all identified and counted. Our data suggest that the responses of these invertebrates to resource pulses present intermediate characteristics between aquatic and terrestrial ecosystems responses. Inputting a moderate amount of dead P. oceanica leaves into experimental mesocosms had a non-negligible impact and rapidly affected the macrofauna community. Specialist detritivores species were boosted while herbivore/detritivore species dramatically decreased. Predators also showed a modest but significant density increase, demonstrating the fast propagation of the pulse response throughout the entire community and through several trophic levels. Strict hypoxia-tolerant species were also only observed in the treated mesocosms, indicating the strong influence of resource pulses on physico-chemical conditions occurring inside litter accumulations.
Highlights
In terrestrial, estuarine and marine ecology, disturbances are regarded as playing a central structuring role in ecosystems (Giller 1996; Lake 2000)
The two controls showed no significant difference between each other either, demonstrating that the effect of the experimental design was quite negligible compared to the effect of the treatments. This experiment showed that diversity (H’) and dominance (1-λ’) in pulsed litter were influenced by both pulse treatments, and that diversity increased significantly with the addition of dead leaves, with or without the associated macrofauna
The Nebalia genus (Okey 2003) and the species N. strausi is known to be highly tolerant to hypoxia (Gallmetzer et al 2005; Remy 2016), indicating that the addition of dead leaves to the treatment mesocosms potentially induced a certain level of hypoxia. This experimental study provides insights into the impact of a resource pulse on the vagile macrofauna associated with an exported dead P. oceanica litter accumulation
Summary
Estuarine and marine ecology, disturbances are regarded as playing a central structuring role in ecosystems (Giller 1996; Lake 2000). Resource pulses have recently been defined as “rare, brief and intense episodes of increased resource availability in space and time” (Ostfeld & Keesing 2000; Yang et al 2008). They can take place in many different ecosystems (e.g., massive floods in arid ecosystems or floodplains, dead leaf litter input in mangroves or forests, massive emergence of insects, mass seeding events or storm driven nutrient runoffs).
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