According to our findings, climate change does not result in increased habitat suitability for commercially important squid species. Models for commercial squid around north America forecast that most species (except Doryteuthis opalescens in 2100 for RCP 6.0 and 8.5) may benefit from warming (borealization) of the Arctic (Polyakov et al 2020). However, a decline in habitat suitability is expected for all other species, especially those on the Southern Hemisphere. Although the squid considered here fall into two taxonomic groups (Myopsida and Oegopsida) with different spawning strategies, these groups did not consistently differ in future habitat suitability changes.
Limitations
We found high resemblance between (ensemble) models’ predictions for the present-day distribution of the studied squid and their documented distributions (Jereb and Roper, 2010). However, caution should be taken into the future projections here made, as there are limitations of the species distribution models (SDM), that may explain differences between (future) projections of habitat suitability and future observed species distribution. First, it should be noted that while we considered multiple variables in our analysis, we only had one biotic variable which was primary productivity (chlorophyll) with both present and future values. This productivity at the local habitat level, limits the resources available to sustain metazoan biomass, including squid. Second, prey biomass predictions and other species (predators and competitors) were not included in our models, potentially leading to an overprediction of habitat suitability. Squid prey, predators and competitors may limit squid distribution. Third, our models do not consider key abiotic factors. For example, dissolved oxygen is affected by climate change and may limit the distribution and habitat suitability of vertically migrating squid and their competitors (Rosa and Seibel 2008, 2010). One of the species here studied, D. gigas, can cope with a wide range of dissolved oxygen and as a result, has been expanding along with the oxygen minimum zones in the Pacific (Arkhipkin et al 2015; Rosa and Seibel, 2010). Likewise, pH represents an abiotic factor worth considering, as previous climate change studies have highlighted the potentially negative effects of ocean acidification on squid physiology and behavior (Rosa & Seibel 2008; Rosa et al 2012, 2014) and hence, an important environmental determinant for their distribution. Finally, many species selected in this study have either few occurrence points available online (below 100 points; T. pacificus, D. gahi and D. gigas) or have their sampling skewed to the waters of countries with extensive resources for surveys (particularly the U.S.A coastlines), with limited to no information in other areas of their range (D. pealeii, D. gahi, I. illecebrosus and D. gigas). Furthermore, due to the difficulty in distinguishing some of these squids from closely related species (e.g.: D. pealeii vs. D. pleii, D. gahi vs. D. sanpaulensis, N. sloanii vs. N. gouldii, L. vulgaris vs. L. forbesii; Jereb and Roper., 2010), many occurrence points may represent cases of misidentification, especially in areas where the distribution of two similar species overlaps. This issue may disproportionally affect D. pealeii, likely contributing to an underestimation of the habitat suitability for this species within the Caribbean basin.
Species specific and regional changes in habitat suitability
The 11 squid species here studied did not change their distribution equally (as mentioned in the beginning of this discussion), and the consequences of climate change seemed species specific. However, within the same region, squid presented similar patterns of future habitat suitability change.
The Jumbo squid (D. gigas) in the Pacific East coast, is projected to expand poleward, which is in line with the documented patterns of migration towards higher latitudes during el Niño and recent slight expansion of their northern range (Field et al. 2007; Arkhipkin et al 2015). This poleward shift is strongest in the northern hemisphere, where habitat suitability will potentially increase along the shores of Canada and USA. On the other hand, a decrease in suitability is projected for the Sea of Cortez and the areas from the Costa Rica Dome upwelling system towards the 140°W longitude, where this species is thought to follow the pacific equatorial current (Wormuth, 1998; Jereb and Roper, 2010). Indeed, across all future scenarios, this species may potentially be extirpated from tropical areas. Therefore, with these predicted extirpations and poleward expansion, future conditions may favor the split of this species into two different stocks without geographic continuity. Different size stock structures have been suggested in the past, either a 3 different sizes stocks (Nigmatullin et al. 2001) or a size continuum (Hoving et al. 2013). With a decrease in both area of habitat as well as its suitability, smaller animals could be benefitted (specially on the lower latitudes where habitat suitability loss concentrates), as these ecosystems carrying capacity will decrease, favoring smaller individuals. This has already been observed in this species (Hoving et al. 2013) and other squid in less favorable years (D. opalescens; Zeidberg et al 2006; Jackson and Domeier, 2003). The opposite (larger individuals) may also happen locally at higher latitudes, where the species is expanding into new habitat (Hoving et al. 2013). Finally, the gains in habitat suitability obtained at higher latitudes are less than the losses around the tropical regions. As a result, there is an overall loss of habitat for D. gigas under all future scenarios.
In the North Pacific, a northward increase in habitat suitability is expected for both B. magister and D. opalescens, with suitability decreasing in their southern limit. For B. magister, gains in the north will surpass the losses in the south, as there are large areas of low-depth high primary production continental shelves in the north, on the pacific coast of Canada, the Bering Sea and Okhotsk Sea. Although the squid occurs between 0-1500 m, the highest densities of B. magister are generally found at depths greater than 200 m, near the bottom on the continental slope and in the mesopelagic zone (Jereb and Roper 2010) where they spawn. In this context, their depth use may limit their ability to take advantage of the habitat projected to become suitable (specifically on the northern parts of the Bering Sea). This may ultimately even lead to a population decrease, as spawning grounds on the southern limits of this species (mostly continental slopes) are negatively affected. D. opalescens is projected to experience a net loss of suitable habitat in 2100 for the two worst RCP scenarios, which is in line with the pattern observed during el Niño years, when the species’ abundance (and size) decreases throughout their home range (Zeidberg et al 2006; Jackson and Domeier, 2003).
Northward increase is experienced in squid species found on the northwest Atlantic Ocean, where projected squid habitat suitability increased poleward. Both I. illecebrosus and D. pealeii occur in this region, with I. illecebrosus preferentially using the colder northern waters and D. pealeii the warmer waters, in the South (Brodziak and Hendrickson, 1999). Under future climate scenarios, both species are projected to shift their distribution poleward. Meanwhile, their northern limits of distribution are expected to increase in habitat suitability, where I. illecebrosus may gain new habitat on the continental platforms around Greenland, Iceland and Baffin Island. A habitat increase is also projected for D. pealeii around the great banks off Newfoundland, a pattern which has already been observed in warmer years (Dawe et al 2007). These gains compensate for the losses projected in the southern distribution range of both species, with net gains increasing along with the severity of RCP scenarios. Should the borealization of the Arctic (i.e.: increase in temperature, salinity and decrease in ice cover much like the surrounding temperate waters) continue for the next few hundred years, the models suggest that squids may be able to cross the Artic Ocean and settle in new ocean basins, as it has been hypothesized for the cuttlefish Sepia officinalis (Xavier et al 2016b). In fact, this suggestion is supported by the recent evidence of squid migrating northwards around the North American continent (Arkhipkin et al 2015; Burford et al 2022).
In the southern hemisphere, climate change is likely to pose a considerable threat to squid (i.e. I. argentinus, D. gahi, N. sloanii and L. reynaudii). With no nearby poleward continental platforms to colonize or facing other oceanographic features likely to prevent their expansion (e.g. Antarctic circumpolar current), these squid species stand at an oceanographic dead-end. Furthermore, the areas with the highest abundance of I. argentinus, D. gahi and N. sloanii (around 40ºS; Jereb and Roper, 2010; Haimovici et al 1998) overlap with those projected to face the steepest decline in habitat suitability. The habitat of L. reynaudii is projected to decrease in size particularly offshore and in the southeast where currently two-thirds of the adult biomass is found (Augustyn, 1989, 1991; Augustyn et al 1993). As a result, the population may be found closer to shore along the Namibian coast (Shaw et al 2010). However, should milder RCP scenarios come to pass, L. reynaudii, D. gahi and I. argentinus may rebound (or even prosper, in the case of the latter) by 2100, with models predicting the overall habitat suitability for that period to values like those currently observed.
Lastly, the habitat suitability for northeastern Atlantic loliginid squids (L. vulgaris and L. forbesii; Hastie et al. 2009) is projected to decrease substantially, primarily around the Mediterranean basin and off the coast of northeast Africa, aligning with previous projections for L. vulgaris under climate change (Schickele et al 2021). L. forbesii may be extirpated from the Mediterranean Sea, the northeast coast of Africa and the Atlantic islands, following the temperature-driven northerly abundance shift registered for this species since the 1990’s (Chen et al. 2006). This trend is also observed, albeit to a lesser degree, for L. vulgaris in the south Adriatic, east Mediterranean, and Mauritanian upwelling - the areas where this species is most abundant (da Cunha et al. 1995).
Potential foodweb and exploitation effects
Assuming that habitat suitability is likely to translate into squid abundance, many squid predators (like marine mammals and seabirds; Klages 1996; Clarke, 1996; Croxal & Prince, 1996) dependent on the studied squid species may face in the future difficulties to find enough prey biomass on their current feeding grounds, having to either migrate to new areas (poleward), change target prey, decrease in number/biomass, or a combination of these options. In regards of fisheries, we may witness a change in the location of economically relevant fishing grounds for many of the commercial squid studied here. Additionally, a decrease in abundance (and therefore available stock) for several of these species is likely (assuming that habitat suitability is translate into squid abundance). The two most important squid fisheries worldwide (D. gigas and I. argentinus) can be hard hit, as they could experience both effects (range and abundance change) and their fisheries are currently unregulated on the high seas (Arkhipkin et al 2022). Other locally important squid (N. sloani, genus Loligo and Doryteuthis opalescens) will experience the same effect. If local extirpations are to happen, many fishing communities may face economic hardship (Downey et al 2010; Arkhipkin et al. 2015), having to look for other marine resources to compensate for the loss of a profitable fishery.
Future studies
In the future, studies of SDMs in the pelagic environment should strive to produce three-dimensional projections of habitat suitability (Duffy and Chown, 2017; Aspillaga et al 2019), namely by using present day environmental data from repositories such as Copernicus marine services (Le Traon et al 2019), which already provides marine information with depth resolution, and in terms of presence occurrence points, further effort should be put on providing depth information. Also, as different life stages of squid (i.e. eggs, paralarvae, juveniles and adults) require different environmental conditions (and therefore migrate during their lifetimes; Jereb and Roper 2010), different models should be made for each stage (which also implies further data collection on their life stage on the occurrence points). This is especially relevant within squid, as there are two different egg laying strategies for myopsids and oegopsids. Myopsids fix their eggs into the substrate, and therefore their eggs are more sessile and benthic (and dependent on seabed environmental conditions) while oegopsids release their eggs into the water column or even transport and care for them (Jereb and Roper 2010). The environmental stability provided by the water masses where oegopsid eggs are released and parental care that some squid provide can save many of these species from the nefarious effects that warming and acidification have on early life stages in contrast with myopsid’s eggs that can be exposed to different water masses that pass the seabed where they are settled. For myopsid embryos, lowered survivability (from normal 92–96–47% with + 2ºC; Rosa et al. 2014) and increased occurrence of developmental abnormalities (Rosa et al 2012, 2014) are expected with future warming, and hatchlings, having to deal with an increased metabolic rate and higher energy demands (however, this last point could be also applied to the oegopsid paralarvae; Rosa et al 2012). Additionally, higher temporal resolution (i.e. Seasons or months) should be obtained for the environmental rasters. The decade average rasters used mask all the variation happening during the year cycle (during which squid migrate and change locations to follow the most suitable habitat; Jereb and Roper 2010), but also provide wrong information when collecting environmental data from the occurrence points during the model construction. Finally, this kind of studies in the future should cover a wider variety of animals, not only because there are others that have key roles in the ecosystem, but also to use as layers for other species distribution models.