Northeast Atlantic species distribution shifts over the last two decades

Marine species are widely shifting their distributions in response to
global changes, and it is commonly expected they will move northward and
to greater depths to reach cooler, less disturbed habitats. However, local
manifestations of global changes, anthropogenic pressures, and species
characteristics may lead to unanticipated and varied responses by
individual species. In this regard, the Celtic-Biscay Shelf is a
particularly interesting study system because it has historically been
heavily fished and occurs at the interface between two distinct
biogeographic provinces, its community is thus comprised of species with
diverse thermal preferenda. In the context of rapidly warming temperatures
and intense fishery exploitation, we investigated the distribution shifts
of 93 taxa (65 Actinopteri, 10 Elasmobranchii, 11 Cephalopoda, 5
Malacostraca, and 2 Bivalvia), which were sampled annually from 1997 to
2020 during a scientific bottom trawl survey. We used a set of 11
complementary spatial indices to quantify taxon distribution shifts over
time. Then, we explored the relative effect of taxon abundance, fishing
pressure, and climatic conditions on taxon’s distribution shift when a
significant shift was detected. We observed that 56% of the taxa
significantly shifted. Not all taxa will necessarily shift northward and
to deeper areas, as is often expected. Two opposite patterns were
identified: taxa either moving deeper and to the southeast, or moving
closer to the surface and to the northwest. The main explanatory factors
were climate change (short- and long-term temperatures) and taxon
abundance. Fishing pressure was the third, but still significant,
explanatory factor of taxa of greater commercial importance. Our research
highlights that taxa are displaying complex distribution shifts in
response to the combined anthropogenic disturbances and underscores the
need to conduct regional studies to better understand these responses at
the ecosystem scale to develop more suitable management plans and
policies.