Impact scenario for an introduced decapod on Arctic ... - Springer Link

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Norwegian College of Fishery Science, University of Tromsø, Norway; Present address: ... foraging, invasion, Norway, Paralithodes camtschaticus, red king crab.
Biological Invasions (2005) 7: 949–957 DOI 10.1007/s10530-004-2996-1

 Springer 2005

Impact scenario for an introduced decapod on Arctic epibenthic communities Lis Lindal Jørgensen Norwegian College of Fishery Science, University of Tromsø, Norway; Present address: Institute of Marine Research, 9091 Tromsø, Norway (e-mail: [email protected]; fax: +47-77609701) Received 27 May 2003; accepted in revised form 12 July 2004

Key words: Chlamys islandica, foraging, invasion, Norway, Paralithodes camtschaticus, red king crab Abstract The intentional introduction of a species for the enhancement of stock or establishment of new fisheries, often has unforeseen effects. The red king crabs, Paralithodes camtschaticus, which was introduced into the Barents Sea by Russian scientists, has established a self-sustaining population that has expanded into Norwegian waters. As top benthic predators, the introduced red king crabs may have possible effects upon native epifaunal scallop (Chlamys islandica) communities. These benthic communities may be a source of prey species in late spring, when the red king crabs feed most intensively. Foraging rates (consumption, killing or severely damaging) of red king crab on native prey organisms were measured by factorial manipulation of crab density (0.5, 1.5 and 3 per m2), size classes (immature, small mature, and large mature crabs), and by evaluating prey consumption after 48 h, in order to extrapolate a scenario of the likely impacts. Foraging rates of the red king crab on scallops ranged between 150 and 335 g per m2 within 48 h. These rates did not change when crab density was altered, though an increased amount of crushed scallops left uneaten at the tank floor, were correlated with high density of small mature crabs. Foraging rate changed significantly with crab size. Consequently, the susceptibility of native, shallow water epibenthic communities to red king crab predation in the early life history stages, and during the post-mating/molting spring period, must be considered significant when foraging rates are contrasted with natural scallop biomass between 400 and 1200 g scallops per m2.

Introduction There has been a rapid acceleration of biological introductions due to human-aided movement of species across and between continents in the late 20th century, (Carlton and Geller 1993; Lodge 1993; Mills et al. 1993; Cohen and Carlton 1998; Ruiz et al. 2000). There is a growing recognition that nonindigenous species are both common and may strongly interact with the members of marine and estuarine recipient communities throughout the world (e.g. Carlton 1996; Ruiz et al. 1997; Walton et al. 2002). Introduced predators are hypothesised to have the largest

impact on native communities (Elton 1958; Lodge 1993; Ross et al. 2003), yet numerous top predators have been intentionally introduced for the purpose of fisheries establishment. The red king crab, Paralithodes camtschaticus (Tilesius, 1815), which is among the world’s largest arthropods (weighing over 10 kg and 22 cm in carapace length, Powell and Nickerson, 1965) is native to the northern Pacific Ocean and the Bering Sea. Russian scientists intentionally introduced the predatory red king crab from the western Kamchatka peninsula to the Barents Sea (Figure 1) during the period 1961–1969 to establish a fishery. Ten years later, a reproductive

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Figure 1. Map showing the northern part of Norway (Finmark coast). The spreading of the introduced red king crab in year 2003 was from Russian Barents Sea (east) and west along the Norwegian coast to island ‘Sørøya’. The small map of the Arctic shows the distribution of the red king crab (in light grey) in the native northern Pacific, Sea of Okhotsk and Bering Sea and the nonnative distribution in the Russian and Norwegian southern Barents Sea.

population of red king crabs was established in the Barents Sea (Orlov and Ivanov 1978). Migration by mature crab which can reach 20 years of age (Matsuura and Takeshita 1990), and the pelagic period of the zoea larvae, make a continuing range expansion likely. The crab has become abundant along the Finmark coast of northern Norway (Figure 1), with a population of 2.9 million in year 2001 and 3.5 million crabs larger than 70 mm carapace length in 2003 (Hjelset et al. 2003). The red king crab is known to

reproduce at several places in Norwegian waters with frequently abundant year-classes, and steadily increasing numbers of red king crabs are invading new coastal areas (Sundet 1999). Sexually immature crabs (smaller than 120 mm in carapace length) generally remain in shallow water along the coast at 20–50 m depth (Wallace et al. 1949). Maturing crabs and adults primarily reside at a depth of 100–300 m, however, in late winter and early spring, adults migrate shoreward to shallow waters (10–30 m) to mate and

951 breed (Powell and Nickerson 1965). A migratory feeding movement into progressively deeper water (300 m) follows the termination of spawning activities (Cunningham 1969). In northern (native) areas with low temperatures, the red king crab undergoes a marked spring spawning migration to shallow water; in southern areas with higher temperatures, the spring spawning is widely distributed from the shore to 100–120 m depth (Rodin 1989). Adult red king crabs are opportunistic omnivores (Cunningham 1969) feeding on the most abundant benthic organisms. At least one food or species group tend to dominate their diet, and the diet composition is usually area-specific (Jewett and Feder 1982). Red king crabs have two distinct ways of feeding: (1) grasping and tearing apart larger invertebrates and (2) filtering organisms using the third maxillipeds, from substrate scooped up by the lesser chela. Scooping of sand by the red king crabs, was often observed by Cunningham (1969) during periods when no evident food material was immediately available. Although the significance of this behaviour is obscure, he suggests this as an alternative method of feeding when larger prey is unavailable. Red king crabs feed most intensively in late spring, probably to replace energy recently expended during molting and mating (Jewett and Feder 1982). However, laboratory studies show that the crab completely stopped feeding during ecdysis and fed at lower rate before and after ecdysis with no sign of compensatory feeding (Zhou et al. 1998). Food appears to be the sole factor that could limit the increase in abundance of red king crabs within the Southern Barents Sea (Gerasimova 1997). Stomach analyses from the invaded area show that the crab feeds on a diverse range of molluscs, sea urchins (Strongylocentrotus droebachiensis) and other echinoder crabs, worms (Polychaeta and Sipunculida) and fish (Sundet et al. 2000). Gerasimova (1997) concluded that the non-native red king crab reflects much of the same behaviour as in the native areas of the Bering Sea and northern Pacific. This behaviour includes seasonally variable consumption of prey such as bivalves and echinoderms (spring and summer) and polychaetes (autumn and winter). Following and quantifying the potential impact of the red king crab on native benthic communi-

ties along the coast of northern Norway is of high priority. Conspicuous native epibenthic species such as the commercial Iceland scallop Chlamys islandica (O.F. Mu¨ller) are particularly exposed to risk of local extinction. Both the red king crab and the scallop have a sub-Arctic distribution. The Iceland scallop has a life span of 30 years, and matures after 3–6 years. It reaches a shell height of 40 mm after 5 years, 70 mm after 10 (Vahl 1981), and 120 mm after 30 years. The Iceland scallop is found at 10–100 m depth (Wiborg 1962) and overlaps the depth distribution of the red king crab. The scallop beds are patchy and found on sand/gravel bottom at localities with strong current (Ekman 1953). Sundet (1996) recorded eight such areas of scallop bed (