ALBERT

Description: Global warming in the Arctic region causes alterations in the composition and structure of marine communities. Such changes are particularly pronounced in the transitional zones such as Fram Strait where the increased inflow of warm Atlantic waters accelerates this process. In other ecoregions of the world’s oceans, warming has caused an increase in the biomass of gelatinous zooplankton (or jellies). Jellies are versatile predators in diverse marine ecosystems. Despite the potential impact of jelly communities on the Arctic food webs, their ecological roles have been poorly studied. We hypothesise that the Arctic pelagic community consists of a significant component of gelatinous fauna, some of which are expanding from the North Atlantic. To test this hypothesis, we obtained baseline data on vertical distribution and diversity of Arctic jellies using towed camera video transects during expeditions to the HAUSGARTEN LTER in Fram Strait in 2019, 2020 and 2021. The data include the abundance of 17 groups of gelatinous zooplankton, among which the most abundant were the hydrozoan family of Rhopalonematidae, mainly consisting of Aglantha and Rhopalonema, and the siphonophore suborders Physonectae and Calycophorae. Based on the obtained abundance data, we fitted bayesian joint species distribution models (JSDMs) to understand current patterns of species distributions at different depth layers and to provide predictive insights into community assembly processes. Variance partitioning over the explanatory variables showed that depth and temperature explained a substantial amount of variation for most of the taxa. The trained models were later coupled with climate change scenarios, which allowed us to forecast spatial niche range shifts in ecosystems.

Description: Gelatinous zooplankton or “jellies” (ctenophores, cnidarians, tunicates) are known to be major drivers of ecosystem changes. Increases in jelly biomass, referred to as “jellification”, have been observed in several marine ecosystems, causing, amongst others, the collapse of major fisheries. For the Arctic region, abundance data on jellies are virtually non-existent, impeding our ability to detect changes of a similar magnitude. To better understand the role of jellies in the Arctic seas, the Helmholtz Young Investigator Group ARJEL aims to combine the most recent technologies in optics, acoustics, and environmental DNA (eDNA) analyses. Based on data collected during recent international campaigns, we attempt to link distributional patterns of jellies to oceanographic features and sea ice. Furthermore, we apply species distribution models to a broad set of archived data to understand observed species and community patterns and to predict changes under future climate-change scenarios. The role of jellies in the Arctic food web and their importance as prey for planktonic predators and fish is assessed with molecular diet studies, which will improve food web models currently neglecting jellies as major predators and prey. We also explore the genetic connectivity of dominant jelly species across the Arctic Ocean and its adjacent seas. An overview of the project’s goals, methods and first results will be given. Our ongoing research foci include: 1. the comparison of species composition and abundances of ctenophores and cnidarians in Arctic vs. Atlantic-influenced Svalbard fjords to better understand the impact of the ongoing Atlantification of the Arctic; and 2. the comparison between optical methods, net catches and eDNA for assessing jelly diversity and abundances.

Description: Gelatinous zooplankton are known to play an important role in World Ocean ecosystems. As climate change continues to cause profound environmental shifts in Fram Strait, a key transitional zone between the North-Atlantic and the Arctic Ocean, the lack of understanding of how gelatinous zooplankton are affected by these environmental changes creates a significant gap in knowledge about the future state of Arctic ecosystems. In this study, we used in situ observations obtained by the towed underwater camera system PELAGIOS (Pelagic In situ Observation System) to establish one of the first regional baselines of large gelatinous zooplankton diversity and abundance in mesopelagic and bathypelagic zones. Our data included 16 taxa of gelatinous zooplankton, with the most abundant being from the family Rhopalonematidae (Aglantha digitale and Sminthea arctica) and the suborders Physonectae and Calycophorae. We used a joint species distribution modelling approach to better understand their three-dimensional distribution patterns and assess the environmental drivers of gelatinous community structures. The most significant drivers were temperature and depth. Spatial distribution modelling based on in situ measurements revealed that the highest abundance and diversity of jellyfish are expected at the edges of the West Spitsbergen and East Greenland current systems. The near-future projections indicate that with continued temperature increase, the gelatinous zooplankton community in the Fram Strait will become less diverse but more abundant. Among taxa of the Rhopalonematidae family, we expect the abundance of Aglantha digitale to increase by 2% throughout the water column, while Sminthea arctica will experience a loss of up to 60% by 2050.

Description: Deep-sea benthic communities depend on food that reaches the seafloor from the overlying water column as well as from in-situ autotrophic production. Sinking carcasses (food falls) from jellyfish and squid contribute to this nutrient flux, but natural medium-sized food falls are rarely observed. Consequently, little is known about scavenging communities associated with invertebrate food falls. The Arctic Ocean is known for rapid environmental change and strong benthopelagic coupling. To investigate if scavenging responses in the Arctic deep sea differ between different medium-sized food fall species we performed experiments in the Fram Strait at ∼2500 m depth. Baited free fall landers were equipped with a time-lapse camera (n = 5) and traps (n = 4) to document and capture scavengers. Squid (Loligo vulgaris) and jellyfish (Periphylla periphylla) were used as bait. Image analysis showed that the amphipod Eurythenes gryllus arrived within minutes and was the main scavenger on squid (MaxN = 166 individuals) while it was almost absent (MaxN = 3 individuals) on jellyfish. Nine additional scavenger taxa were identified in total, including Scopelocheirus and stegocephalid amphipods, various crustaceans and the gastropod Mohnia. The jellyfish bait was consumed 7.6 times slower than squid (jellyfish: 142 g d−1, squid: 1,294 g d−1), and almost three times slower than during similar experiments in the North Atlantic. Squid experiments incited higher consumption rates and scavenger diversity, but lower maximum abundances than similar experiments in the North Atlantic. Despite a small sample size of our experiments, differences in consumption rates, scavenger diversity and successional stages between food falls were apparent supporting that scavenging response depends on carcass species.