• Energy Research

A two year survey of benthic primary production during periods of emersion was performed on two stations of an intertidal mudflat (a muddy-sand station and a muddy station) in the Seine Estuary (English Channel, France). The goals of this study were to investigate the seasonal variations of metabolism, to estimate daily potential primary production variation at the annual scale and to estimate the annual potential primary production of the mudflat. Primary production and respiration were estimated by in situ measurements of carbon dioxide fluxes. Chlorophyll a concentration exhibited a great variability on both locations. Gross community production ranged from ca. 0 to 77 mg C m(-2) h(-1) at the muddy-sand location and from ca. 0 to 122 mg C m(-2) h(-1) at the muddy location. Community respiration showed a seasonal trend following temperature variations (up to 28.51 mg C m(-2) h(-1) in the muddy-sand and up to 23.40 mg C m(-2) h(-1) in the mud). Daily potential primary production was calculated, according to seasonal variations of photosynthetic parameters calculated using three photosynthesis versus irradiance curves obtained for the muddy location. The annual gross community primary production was 135 g C m(-2) yr(-1), leading to a low autotrophic annual budget, considering an annual community respiration of 110 g C m(-2) yr(-1).

A two year survey of benthic primary production during periods of emersion was performed on two stations of an intertidal mudflat (a muddy-sand station and a muddy station) in the Seine Estuary (English Channel, France). The goals of this study were to investigate the seasonal variations of metabolism, to estimate daily potential primary production variation at the annual scale and to estimate the annual potential primary production of the mudflat. Primary production and respiration were estimated by in situ measurements of carbon dioxide fluxes. Chlorophyll a concentration exhibited a great variability on both locations. Gross community production ranged from ca. 0 to 77 mg C m(-2) h(-1) at the muddy-sand location and from ca. 0 to 122 mg C m(-2) h(-1) at the muddy location. Community respiration showed a seasonal trend following temperature variations (up to 28.51 mg C m(-2) h(-1) in the muddy-sand and up to 23.40 mg C m(-2) h(-1) in the mud). Daily potential primary production was calculated, according to seasonal variations of photosynthetic parameters calculated using three photosynthesis versus irradiance curves obtained for the muddy location. The annual gross community primary production was 135 g C m(-2) yr(-1), leading to a low autotrophic annual budget, considering an annual community respiration of 110 g C m(-2) yr(-1).

In aquatic environments, habitat complexity influences community species composition at a local scale by partitioning physical niches, mediating water motion and retaining organic matter. Stratified into several microhabitats, kelp forests represent one of the most complex biotopes in coastal waters. These microhabitats are generally made of biogenic structures characterised by species-specific life cycles and their complexity is expected to change over time. In a Laminaria hyperborea forest near Roscoff (Brittany, France), we tested whether temporal changes differed among strata (lamina, stipe, holdfast and rock) in terms of habitat complexity, richness and species abundance distributions. At the scale of the study, the epiphytic habitat was relatively stable over four sampling dates, whereas epilithic structures of the understorey appeared particularly unstable in terms of habitat size and distribution among morpho-functional groups of habitat-formers. Unlike sessile species, mobile fauna experienced substantial temporal changes in richness and abundance distribution in all microhabitats studied. Although mobile fauna distribution varies in part with habitat complexity, additional factors likely come into play such as seasonal and stochastic variation in direct and indirect food resources.

In aquatic environments, habitat complexity influences community species composition at a local scale by partitioning physical niches, mediating water motion and retaining organic matter. Stratified into several microhabitats, kelp forests represent one of the most complex biotopes in coastal waters. These microhabitats are generally made of biogenic structures characterised by species-specific life cycles and their complexity is expected to change over time. In a Laminaria hyperborea forest near Roscoff (Brittany, France), we tested whether temporal changes differed among strata (lamina, stipe, holdfast and rock) in terms of habitat complexity, richness and species abundance distributions. At the scale of the study, the epiphytic habitat was relatively stable over four sampling dates, whereas epilithic structures of the understorey appeared particularly unstable in terms of habitat size and distribution among morpho-functional groups of habitat-formers. Unlike sessile species, mobile fauna experienced substantial temporal changes in richness and abundance distribution in all microhabitats studied. Although mobile fauna distribution varies in part with habitat complexity, additional factors likely come into play such as seasonal and stochastic variation in direct and indirect food resources.

SummaryKelps are dominant primary producers in temperate coastal ecosystems. Large amounts of kelp biomass can be exported to the seafloor during the algal growth cycle or following storms, creating new ecological niches for the associated microbiota. Here, we investigated the bacterial community associated with the kelp Laminaria hyperborea during its accumulation and degradation on the seafloor. Kelp tissue, seawater and sediment were sampled during a 6‐month in situ experiment simulating kelp detritus accumulation. Evaluation of the epiphytic bacterial community abundance, structure, taxonomic composition and predicted functional profiles evidenced a biphasic succession. Initially, dominant genera (Hellea, Litorimonas, Granulosicoccus) showed a rapid and drastic decrease in sequence abundance, probably outcompeted by algal polysaccharide‐degraders such as Bacteroidia members which responded within 4 weeks. Acidimicrobiia, especially members of the Sva0996 marine group, colonized the degrading kelp biomass after 11 weeks. These secondary colonizers could act as opportunistic scavenger bacteria assimilating substrates exposed by early degraders. In parallel, kelp accumulation modified bacterial communities in the underlying sediment, notably favouring anaerobic taxa potentially involved in the sulfur and nitrogen cycles. Overall, this study provides insights into the bacterial degradation of algal biomass in situ, an important link in coastal trophic chains.

SummaryKelps are dominant primary producers in temperate coastal ecosystems. Large amounts of kelp biomass can be exported to the seafloor during the algal growth cycle or following storms, creating new ecological niches for the associated microbiota. Here, we investigated the bacterial community associated with the kelp Laminaria hyperborea during its accumulation and degradation on the seafloor. Kelp tissue, seawater and sediment were sampled during a 6‐month in situ experiment simulating kelp detritus accumulation. Evaluation of the epiphytic bacterial community abundance, structure, taxonomic composition and predicted functional profiles evidenced a biphasic succession. Initially, dominant genera (Hellea, Litorimonas, Granulosicoccus) showed a rapid and drastic decrease in sequence abundance, probably outcompeted by algal polysaccharide‐degraders such as Bacteroidia members which responded within 4 weeks. Acidimicrobiia, especially members of the Sva0996 marine group, colonized the degrading kelp biomass after 11 weeks. These secondary colonizers could act as opportunistic scavenger bacteria assimilating substrates exposed by early degraders. In parallel, kelp accumulation modified bacterial communities in the underlying sediment, notably favouring anaerobic taxa potentially involved in the sulfur and nitrogen cycles. Overall, this study provides insights into the bacterial degradation of algal biomass in situ, an important link in coastal trophic chains.