by Kyle Jensen
For most of the Quaternary Period the inhospitable environment north of the Arctic Circle has served as a biotic barrier between Northern portions of the Atlantic and Pacific oceans. Through it is known that interchange across the Northwest and Northeast passages has occurred, currently only 135 of over 800 fish species found above 50° of latitude are found in both oceans. Continued warming may result in the reopening of these passages resulting an accelerated interchange of species between the Atlantic and Pacific as species follow favorable conditions into higher latitudes. This may also lead to increased movement of fishing and shipping vessels through these channels, which could facilitate further interchange. This has the potential to impact the food webs and biodiversity of systems in both of these oceans, the consequences of which would affect ecosystems currently comprising 39% of global marine fish landings. To analyze potential impacts of future species interchange, Wisz et al (2015) has made forecasts of potential distributions for 515 fish species.
All species used in the study had been observed north of 50° latitude to a sufficient numerical degree. Niche-based models were used under climate change scenarios to simulate the progression of species through the passages over time. The models were implemented with occurrence data matched to monthly oceanographic condition records, such that the model fit the species’ bioclimatic requirements. This type of analysis is well suited to studying species distribution shifts as the range of arctic species is strongly determined by measurable abiotic factors such as temperature and salinity. The interchange potential of given species was determined by that species predicted occupancy of a given area based on the availability and suitability of habitat within each passage. Potential impacts on community and trophic structures for a given species were evaluated by assessing the length and current trophic level of the species in question. The models were run to the year 2100 and divided geographic area into ‘pixel’ units, giving a 1, 10, or 50% predicted occupancy for a given pixel.
Results indicate likely shifts in diversity and restructuring of high-latitude ecosystems. By 2050 species will have begun to approach the passages, the majority approaching the Atlantic from the Pacific along the NE passage. By 2100 the number of potentially interchanging species will have increased sharply, as even more Pacific and some Atlantic species find more suitable conditions in the passages. Conservative estimates (based on 50% predicted occupancy) find that 13 species from the Pacific may reach the Atlantic, while 16% may reach the Pacific from the Atlantic, with almost all species moving across the NE passage. With more relaxed requirements (10% predicted occupancy), 44 species reach the Atlantic while 41 reach the Pacific, again mostly across the NE passage. Few species were considered likely to change the trophic structure or size of existing communities with the exception of the apex predators the Lingcod and Atlantic cod, which have the potential to dominate new ecosystems.
As of now, it is unclear what the final result of this interchange will be, though it will certainly continue well past 2100. The potential impacts as considered by this model are preliminary, and the authors call for further development in this area. Accounting for the interaction of species, as well as the mechanisms of spawning and dispersal, will allow for more accurate predictions of future species dispersal and community change. Such modeling will allow us to more accurately assess and analyze the potential impacts on biodiversity and environment future interchange may have on these hugely important populations.
Wisz, M. S., Broennimann, O., Grønkjær, P., Møller, P. R., et al., 2015. Arctic warming will promote Atlantic-Pacific fish interchange. Nature Climate Change. 10.1038/nclimate2500