Effects of an experimental resource pulse on the macrofaunal assemblage inhabiting seagrass macrophytodetritus

Abstract

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.

Seasonal dependence on seagrass detritus and trophic niche partitioning in four copepod eco-morphotypes

“…epiphytic and microbial biomass) (Mascart et al, 2015b), but also quality (detritus ageing, enrichment by microbial biomass, fatty acid composition), are probably the main drivers of trophic competition and trophic niche partitioning between these two eco-morphotypes, tightly associated to phytal habitats. These resource pulses have been demonstrated to have an important effect on macrofauna biodiversity in studied EMAs (Remy et al, 2017).…”

“…In addition, EMAs are seasonally pulse-sourced by dead seagrass leaves and the epiphytic community covering them (Mascart et al, 2015b;Remy et al, 2017). Therefore, food item availability fluctuates over time, and this could have consequences for copepod trophic ecology and food partitioning between the different copepod ecomorphotypes (Mascart et al, 2015b).…”

Trophic ecology of macrofauna inhabiting seagrass litter accumulations is related to the pulses of dead leaves

“…The extreme abundance of this resource, despite poor digestibility, allows invertebrates that are capable of using them directly (or in an early phases of decomposition) to increase their biomass and abundance (Remy et al, 2017b). Moreover, this study demonstrates that resource increases induce diet modifications in some dominant macrofaunal herbivores, detritus feeders, and omnivores.…”

“…Mesocosm experiments showed that the input of a moderate amount of dead P. oceanica leaves had large and rapid effects on macrofauna community (i.e., changes in specific diversity and total and relative abundances) (Costa et al, 2019;Remy et al, 2017b).…”

Decomposition rate and invertebrate colonization of seagrass detritus along a hydrodynamic gradient in a Mediterranean coastal basin: The Stagnone di Marsala (Italy) case study

“…Duarte and Krause‐Jensen () pointed out as the potential sequestration of seagrass carbon exported beyond the meadows may approach 30% of the carbon sequestered within meadows. Detritus act as faunal magnets (Duggins et al, ; Remy, Gobert, & Lepoint, ), attracting fungi and bacteria, but also benthic invertebrates that use them as food and shelter (Heck et al, ; Remy, Mascart, De, Loïc, & Lepoint, ). Detritus undergoes decomposition and recycling that allows it to be channelled to higher trophic levels (Michel et al, ).…”