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

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.

KELPEX has provided a wealth of new empirical and modeled data on kelp forests and the role of kelp detritus in fueling adjacent benthic communities. In the academic sector, KELPEX's results are being used by other ongoing research projects as baseline data for their investigations (e.g. NFR's KELPPRO, Blåttskog, NBFN). Internationally, KELPEX has established a strong network of kelp scientists (DK, AU, CA, UK). KELPEX has provided an excellent framework for a highly productive postdoctoral fellow, a component of a PhD thesis and 3 MSc projects. In the non-academic sector, KELPEX has produced data that are of importance to regional and national authorities working on the management of natural seascapes and resources. The results will also be important to better understand potential regime shifts in kelp forests driven by climate-change stressors, thus providing scientifically-robust data to inform the UN SDGs, such as SD14 (Life Below Water) and SDG13 (Climate Action).

Kelp forests are one of the most emblematic ecosystems in the world, forming complex systems that provide a major source of primary production and support rich and diverse communities. However, dramatic changes have occurred in Norwegian kelp forests in the last 4 decades, where about 2000 km2 have become barren under the overgrazing pressure of sea urchins. In the 1990s, a recovery of barren grounds started in mid-Norway and is moving northwards, driven by a decrease in grazing sea urchins. Up to 80% of the kelp production is exported to adjacent ecosystems, but the role played by kelp detritus in fuelling adjacent benthic communities is poorly understood. Quantifying this trophic relationship between kelp forests and benthic ecosystems is timely in northern Norway, where kelp forests both play a major ecological role and are experiencing major regime shifts. KELPEX is a multidisciplinary project integrating research in kelp forest, biodiversity, coastal and deep-sea ecology and modelling, to determine the role played by kelp export in shaping the structure (abundance, biodiversity) and function (trophic webs) of adjacent ecosystems. KELPEX will quantify experimentally kelp production and export (WP1) and the effect of kelp export will be assessed in shallow-water (WP2) and deep-sea (WP3) communities. We will integrate all results from the field and lab experiments into newly developed ecological models (WP4). KELPEX will take a bulk step forward to determine the role played by kelp export in fuelling adjacent habitats, including effects on benthic ecosystem services (e.g. sustaining commercially exploited species) and will develop a predictive tool from which to assess ecosystem change associated with kelp regime shifts. KELPEX results will thus provide robust scientific knowledge to support decision making and management of arctic ecosystems under different natural and climatic stressors, addressing Norway?s strategic priorities for the Arctic.