Introduction of Mysis relicta (Mysida) reduces niche segregation between deep-water Arctic charr morphs

Abstract

Niche diversification of polymorphic Arctic charr can be altered by multiple anthropogenic stressors. The opossum-shrimp (Mysis relicta) was introduced to compensate for reduced food resources for fish following hydropower operations in Lake Limingen, central Norway. Based on habitat use, stomach contents, stable isotopes (δ 13 C, δ 15 N) and trophically transmitted parasites, the zooplanktivorous upper water-column dwelling 'normal' morph was clearly trophically separated from two sympatric deep-water morphs (the 'dwarf' and the 'grey') that became more abundant with depth (>30m). Mysis dominated (50-60%) charr diets in deeper waters (>30m), irrespective of morph. Mysis and/or zooplankton prey groups caused high dietary overlap (>54%) between the 'dwarf' morph and the two other 'normal' and 'grey' morphs. After excluding Mysis, the dietary overlap dropped to 34% between the two profundal morphs, as the 'dwarf' fed largely on deep-water zoobenthos (39%), while the 'grey' morph fed on fish (59%). The time-integrated trophic niche tracers (trophically transmitted parasites and stable isotopes) demonstrated only partial dietary 2 segregation between the two deep-water morphs. The high importance of Mysis in Arctic charr diets may have reduced the ancestral niche segregation between the deep-water morphs and thereby increased their resource competition and potential risk for hybridization.

The biology and feeding ecology of Arctic charr in the Kerguelen Islands

“…In Arctic charr, the development of resource polymorphisms is common and in the absence of competition from other species may develop into stable niches under conditions of intense intra‐specific competition (Jonsson & Jonsson, 2001). Notably absent in the Kerguelen sample was any suggestion of morphological variation, which has been described extensively from both North American (Guiguer et al ., 2002; Power et al ., 2012) and European lakes ( e.g ., Hindar & Jonsson, 1982; Klemetsen et al ., 2003; Knudsen et al ., 2019; Pavlov, 1997; Snorrason et al ., 1994). Time may explain the absence of morphological and feeding correlates, although examples of the incipient divergence of traits related to prey use in contemporary time frames exist ( e.g ., Michaud et al ., 2008).…”

Environmentally Modulated Repeat Evolution of Polymorphic Arctic Charr Life History Traits

“…Lake Limingen (64 • 42 13 N, 13 • 32 40 E) is located in central Norway in Trøndelag county while the remaining four lakes are located in Troms county in Northern Norway (Figure 1). These lakes have been described in other work (Klemetsen et al, 1997;Smalås et al, 2013;Knudsen et al, 2019;Moccetti et al, 2019) and the following is an overview of previous descriptions. Lakes in Troms county are typically ice covered from November/December to May/June and are described as being dimictic and oligotrophic (Klemetsen et al, 1997;Smalås et al, 2013;Moccetti et al, 2019).…”

“…trimorphic Arctic charr (LO, PB, and PP) and brown trout and is 53 m deep and 3.21 km 2 (Moccetti et al, 2019). Lake Limingen has a surface area of 95.7 km 2 and a maximum depth of 192 m. It is described as being dimictic and oligotrophic and contains in addition to the trimorphic Arctic charr (LO, PB, and PP), brown trout, minnow (Phoxinus phoxinus L. 1758; introduced in 1980s), and three-spined stickleback (Knudsen et al, 2019).…”

“…In general the LO morph is described as having greater lengths at age and delayed age at maturation relative to their small profundal (PB/PZ) conspecifics (Klemetsen et al, 1997;Smalås et al, 2013;Knudsen et al, 2015;Moccetti et al, 2019). Available estimates of the maximum attainable length [i.e., von Bertalanffy growth parameter for asymptotic length (L)] from the studied populations exceed 330 mm in the LO morph and are under 200 mm for the PB/PZ morph (Smalås et al, 2013;Knudsen et al, 2019). In instances where three morphs are present both the LO and PB/PZ morphs cooccur in addition to a piscivorous (PP) morph (Smalås et al, 2013;Moccetti et al, 2019).…”

Assessing the impact of charr research past, present, and future

“…The effect was ascribed to differences in foodchain length that was longer in the monomorphic whitefish lakes, and the keystone predator role of Arctic charr in the monomorphic whitefish lakes. Second, Knudsen et al (2019), examining the impacts of anthropogenic stressors on polymorphic Arctic charr, noted that introduction of the opossum-shrimp Mysis relicta (Lovén 1862) had reduced ancestral niche segregation between or among two deep-water morphs and thereby increased resource competition, and possibly, the risk of hybridization. Third, Henriksen et al (2019) found that growth rate of Arctic charr was linearly related to abundance of a less harmful parasite, Crepidostomum spp., and non-linearly related to abundance of a more harmful parasite, Eubothrium salvelini (Schrank 1790), perhaps because the negative effect of a high-cost parasite was outweighed by the energy gained from feeding on the intermediate host.…”