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Hidden Diversity in Arctic Crustaceans. How Many Roles Can a Species Play?

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Hidden Diversity in Arctic Crustaceans. How Many Roles Can a Species Play? vol. 31, no. 3, pp. 205–216, 2010 doi: 10.2478/v10183−010−0001−5 Hidden diversity in Arctic crustaceans. How many roles can a species play? Jan Marcin WĘSŁAWSKI1, Artur OPANOWSKI2, Joanna LEGEŻYŃSKA1, Barbara MACIEJEWSKA3, Maria WŁODARSKA−KOWALCZUK1 and Monika KĘDRA1 1 Instytut Oceanologii PAN, Powstańców Warszawy 55, 81−712 Sopot, Poland <[email protected]> 2 Zachodnio−Pomorski Uniwersytet Technologiczny, K. Królewicza 4, 71−550 Szczecin, Poland <[email protected]> 3 Ecological Consultancy Services Limited (EcoServe), B23 KCR Industrial Estate, Kimmage, Dublin 12, Ireland <[email protected]> Abstract: The life modes and sizes of 98 species of higher crustaceans (Malacostraca) from Hornsund and Kongsfjorden (Svalbard fjords) were analyzed. The majority (90%) of the species were perennial, K strategists, with eight− to tenfold size differences between newborn and adult specimens. The largest species are carnivores and carrion feeders, while the smallest are sediment−dwelling suspension and deposit feeders. Compared with the crustacean fauna of northern Norway (over 500 species), the Svalbard fjord crustacean fauna is less diverse (below 150 species). The crustacean species populations from the Arctic fjord are more numerous (average number of ind./species/m2) compared to those of the northern Norway boreal fjords. Crustaceans with long life cycles and distinct size dif− ference between juveniles and adults represent three to five ecologically different func− tional “species” each, since the smaller size groups of the same species differ with regard to their mobility, food and habitat use. Thus, crustaceans are ecologically and functionally more diverse than expected from simple species count. Key words: Arctic benthos, Crustacea, biodiversity, life cycles. Introduction On numerous occasions in the history of taxonomy juveniles, males, or fe− males of the same species have been described as separate taxa by naturalists unfa− miliar with their biology. Even when morphological differences are not very strik− ing, marine invertebrate juveniles being much smaller than adults, are nursed in separate habitats to avoid cannibalism. Typically, mobility changes with onto− genic development, and juveniles are slower and less mobile than adults, as is the Pol. Polar Res. 31 (3): 205–216, 2010 Unauthenticated Download Date | 1/10/18 1:45 AM 206 Jan Marcin Węsławski et al. case, for example, with euphausiids and mysids (Mauchline 1980). Since juveniles and adults are separated by habitat and niche, they act as separate species in terms of their functional roles in a given ecosystem. For the scope of this paper there are two well−established ecological observa− tions about the Arctic: (1) Thorson’s (1936) rule describes the tendency of Arctic species to modify life cycles, reducing larval stages, and investing energy in larger and less−dispersed off− spring. This phenomenon was later identified as one of the effects of K breeding strategy in cold waters (Clarke 1980, 1999, 2003). Recent, extensive studies on Arc− tic benthos confirmed the prevalence of direct development, brooders, and short− −lived lecitotrophic larvae over planktotrophic pelagic stages (Piepenburg et al. 2006, 2007; Fetzer and Arntz 2008). (2) Rapoport’s rule (Stevens 1989) states that Arctic ecosystems are species poor since the ranges of occurrence of particular species in high latitudes tend to be very wide. In consequence Arctic species are less specialized and niches are not densely packed. Recent attempts to confirm this observation have been somewhat dubious; although this seems to be true for benthos in general, and specifically for some taxa, like Mollusca and Bryozoa, other taxa (e.g. Amphipoda) are not at all impoverished in polar waters (Palerud and Vader 1991; Jażdżewski et al. 1995). The aim of the present paper is to propose a new idea that polar water ecosys− tems might be more diverse than previously thought, because of the ecological ef− fects of the prevailing K strategy in macrobenthos populations. This is based on the assumption that the larger the size difference is between adults and offspring, then the larger their ecological separation is. As typical K strategists polar animals are characterized by low mortality and long life spans. Since cold water species grow more slowly and attain larger sizes, the separation of ecological roles within them is stronger compared to inhabitants of warm waters. In effect, in cold−water populations single taxa can be represented by numerous “eco−species” that physi− cally occupy different places in the ecosystem. In warm waters, among the prevail− ing small species, there are usually lesser size differences between juveniles and adults, higher mortality rates, and less numerous populations, all of which means that there is competition among true species. Based on these assumptions, the aim of this paper is to explain why polar shelf waters, which are so productive, are also typically species poor in comparison with warmer waters. Methods Macrozoobenthos species were collected with different types of gear from two polar fjords (Hornsund 77°N, and Kongsfjorden 79°N, Svalbard archipelago) (Fig. 1) during summer campaigns of r/v Oceania between 2000 and 2007. Crusta− cean length was measured in a specific way – Amphipoda, Decapoda, Isopoda, Unauthenticated Download Date | 1/10/18 1:45 AM Hidden diversity in Arctic crustaceans 207 10o E 20o E 30o E 80o N Kongsfjord Spitsbergen Hornsund 1000m Svalbard archipelago 100m 75o N Atlantic Waters Arctic Coastal Waters Fig. 1. Study area. Mysidacea, Euphausiacea, Cumacea length were measured from the tip of the rostrum to the end of telson, except of Brachyura where the width of carapax was measured. Only malacostracan Crustacea were selected for the present paper since their measurements were the most numerous and complete. Twelve pelagic Crustacea species were also included since most hyperiids and euphausiids are ob− served near the bottom, often feeding at the seabed, and are found frequently in benthic dredges. The minimal taxon size is that of newborn animals commencing independent life. In brooders this is the size after leaving the brood pouch, while in larval developers it is the size of the larvae. “Mean individual size” refers to the av− erage size of an animal in the samples and, although this might be misleading, since samples are always collected from an unknown fraction of the population, it does indicate what size of a given species is most frequent in the system analyzed. “Maximal individual size” is the largest size of a species recorded in the sample collection from a study area, and it represents the ability of a given species to grow to a certain limit if conditions are appropriate. The percentage relation between minimal and maximal size (i.e., what percentage juvenile size is of adult body size) Unauthenticated Download Date | 1/10/18 1:45 AM 208 Jan Marcin Węsławski et al. Table 1 Summary table of crustacean species characteristics. Length in mm, feeding types: c – car− nivore, s – suspension feeder, h – herbivore, f – filtrator. Mobility types: m – mobile, dm – discretely mobile, nb – nectobenthic, p – pelagic. Zoogeographic types: A – Arctic, AB – arcto−boreal, B – boreal. max/ zoogeo− mean min max feeding mobility n min graphic length length length type type index type AMPHIPODA Acanthostepheia malmgreni (Goës, 1866) 21 7 5 36 7 c m A Ampelisca eschrichtii Krøyer, 1842 11.6 29 3 37 12 s dm AB Anonyx laticoxae Gurjanova, 1962 16 21 3 33 11 c nb A Anonyx nugax (Phipps, 1774) 18.3 19 3.5 44 13 c nb A Anonyx sarsi Steele et Brunel, 1968 17 90 3 30 10 c nb A Apherusa sarsii Shoemaker, 1930 9 9 3 15 5 h m A Apherusa glacialis (Hansen, 1887) 8 91 2 17 9 h m A Arrhis phyllonyx (M. Sars, 1858) 8 95 3.1 19.25 6 s m A Atylus carinatus (Fabricius 1793) 9 12 3 21 7 c m A Byblis gaimardi (Krøyer, 1846) 10 12 3 18 6 s dm AB Calliopius laeviusculus (Krøyer, 1838) 9 10 3 18 6 c m AB Caprella septentrionalis Krøyer, 1838 16 38 3.4 26 8 s dm AB Gammarellus homari (Fabricius, 1779) 21 86 5 35 7 c m AB Gammarus oceanicus Segerstråle, 1947 11 98 4 38 10 s m B Gammarus setosus Dementieva, 1931 12.7 93 4.2 34 8 s m AB Gammarus wilkitzkii Birula, 1907 12 120 3.5 40 11 c m A Goesia depressa (Goës, 1866) 4 6 2.5 11 4 s/f dm AB Halirages fulvocinctus (M. Sars, 1858) 7 11 3 17 6 s m AB Haploops tubicola Liljeborg, 1855 6.4 46 2.5 21 8 s dm AB Harpinia propinqua (G.O. Sars, 1895) 4 9 3 6 2 s m AB Hyperia galba (Montagu, 1815) 4 10 3 7 2 c p B Hyperoche medusarum (Krøyer, 1838) 5 11 3 9.5 3 c p B Idunella aequicornis (G.O. Sars, 1876) 4 3 3 8 3 s m A Ischyrocerus anguipes Krøyer, 1938 8 100 3 17 6 s m AB Lepidepecreum umbo (Goës, 1866) 3.8 8 2 7 4 s m A Melita dentata (Krøyer, 1842) 12 23 3 28 9 s m AB Melita formosa Murdoch, 1866 10.2 38 6 26.5 4 s m A Melita quadrispinosa Vosseler, 1889 8.1 130 4.4 12.9 3 s m AB Menigrates obtusifrons (Boeck, 1861) 5 11 2.5 10 4 c m B Metopa boeckii G.O. Sars, 1892 3.5 5 2.5 4 2 s m A Monoculodes borealis Boeck, 1871 8 21 2.5 15 6 s m AB Monoculodes longirostris (Goës, 1866) 9 20 3 18 6 s m A Monoculodes packardi Boeck, 1871 4.55 28.5 3 9 3 s dm AB Neohela monstrosa (Boeck, 1861) 11 4 3 25 8 f dm AB Onisimus caricus Hansen, 1886 16 84 3 24 8 c m A Onisimus edwardsi (Krøyer, 1846) 9 90 4 14 4 c m AB Onisimus litoralis (Krøyer, 1845) 8 200 3 25 8 c m A Orchomenella minuta (Krøyer, 1846) 5 30 4 9 2 c m A Parapleustes bicuspis (Krøyer, 1838) 9 7 3 12 4 s m AB Parapleustes monocuspis (G.O.
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