Kelp export: fuel for adjacent communities in changing arctic ecosystems?

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2016

End date

12/31/2018

Budget

953,004 EUR

Fundings

Abstract

Kelp forests support high production and provide habitat for a wide variety of species globally. On average 80% of the primary production can be exported to adjacent ecosystems as kelp detritus, but the role of this potential food source to faunal communities on the seafloor is poorly understood. KELPEX has investigated the production and export of kelp detritus at the entrance of the Malangen fjord (northern Norway) to assess the role played by this detritus in fueling adjacent benthic communities, both shallow and deep. Understanding this trophic relationship is particularly important in the current scenario of changing oceans, where environmental stressors have resulted in important kelp regime shifts in Norway, with large areas becoming barren grounds. Research groups from 5 national and 5 international partners participated in the project between 2016 and 2018. The mouth of the Malangen fjord has a deep basin (450 m) surrounded by steep walls and healthy kelp forests in the shallows, and a shallow sill separating the basin from the shelf. KELPEX has studied the Malangen kelp forests, adjacent shallow water communities and two deep (450 m) areas: the deep fjord basin assumed to be an area receiving significant kelp detritus and an area of similar environmental conditions but 15 km offshore on the shelf, assumed to be an area not receiving kelp detritus. KELPEX showed that high annual blade production in kelp forests (465 g C m-2) was lost each year as detritus produced from continuous erosion of blades, dislodgment of whole plants, and annual shedding of old blades in spring. The annual loss of blades corresponds to ca. 57% of the total detrital production. Kelp detritus formed dense accumulations in kelp forests and shallow reefs. Tagging experiments showed that 50% of the large detritus was retained by sea urchins in the shallows, but abundant kelp detritus was observed down to 60 m depth. Kelp blades were also observed at 450 m in the fjord basin, but not on the shelf. Sea urchins were shown to transform kelp detritus from large blades into small particles (faces). The transportation of these small particles was modelled, showing that kelp carbon can reach the seafloor 100s km away from the kelp forest. This was confirmed by the presence of small kelp particles in the grab samples both from the fjord basin but also from the deep shelf offshore. The KELPEX findings support arguments for a significant contribution from kelp forests to subsidizing adjacent benthic communities. Through experiments in aquaria, we have shown that mussels grow equally well when fed phytodetritus or kelp detritus, suggesting that mussels can potentially use small kelp particles as food. The biomass and abundance of the deep faunal communities (meio-, macro-, and mega-fauna) were similar on the fjord basin and the shelf, but the community composition and structure was different between the two areas. The amount of kelp detritus only explained part of the differences for the macrofauna, but not for the mega- and meiofauna. No patterns of biodiversity related to kelp detritus were detected for any of the faunal groups. A food web model has been developed for the Malangen fjord and initial results show that kelp is used mainly by the lower trophic levels. The food web model represents a baseline from where we are developing scenarios of future change that will enable us to assess the effects of kelp regime shifts or kelp recovery on the Malangen ecosystems. This is particularly important in the current climate change scenario, which can influence the disappearance of kelp forests in certain areas. KELPEX results will be published in 14 papers (6 published, 8 in preparation) and have been presented at 4 international symposia. 3 master theses have been defended. The KELEPX website has maintained a blog with information on field work and project progress and we have collaborated with an artist working on kelp.