Why is a Shell Considered to Be Biotic
In many marine environments, hard surfaces are a limiting resource (Jackson, 1977; Kuklinski et al., 2008; Wahl, 2009), but some organisms have difficult externa which provide a surface for colonization. Such epibiosis is common and widespread across many groups of sessile taxa. Numerous living organisms, called basibionts, thus become the substrate for settlement and evolution of others (Wahl, 1989; Harder, 2009). An instance of potential basibionts is decapod crustaceans, which are a species-rich and abundant group with a broad geographical distribution (Hayward & Ryland, 1999). They are long-lived, tiresome-moving and big plenty to provide considerable substrate for other invertebrates. On soft substrata they are ofttimes ane of the few providers of difficult substrates (Gili et al., 1993; Di Camillo et al., 2008; Balazy & Kuklinski, 2013). Their calcified exoskeletons are physiologically inactive with respect to filtration or osmoregulation (Fernandez-Leborans, 2010). Not surprisingly therefore, decapods are one of the most oft used substrates for epibionts which is reflected in the literature as focus for ecologists studying epibiosis (Connell & Keough, 1985; Dick et al., 1998; Hayward & Ryland, 1999; McGaw, 2006; Dvoretsky & Dvoretsky, 2008, 2009, 2010).
Among Decapoda, the superfamily Paguroidea (hermit crabs) is a archetype instance of difficult mobile substrate providers (Sandberg & McLaughlin, 1988; Balazy & Kuklinski, 2013). Their naked abdomens are not calcified, and to protect themselves hermit crabs must notice and occupy empty gastropod shells or other materials such as bivalve and scaphopod shells, polychaete tubes, sponge, corals, wood or even hollowed-out fragments of stones (Lancaster, 1988; Williams & McDermot, 2004 and references therein). Thus, in the example of hermit crabs not only the body surfaces only also other non-living resource used by these animals can serve equally a new substrate for colonization. Williams & McDermot (2004) and McDermott et al. (2010) found >550 invertebrate species associated with over 180 species of hermit crab species worldwide. The about arable epifaunal groups include arthropods, polychaetes and cnidarians. Epibiont assemblages of the common hermit crab
(Linnaeus, 1758) include nearly 120 epifaunal species in the North Sea (Skagerrak-Kattegatt area, Jensen & Bough, 1973; Reiss et al., 2003).
Even if some hermit crab species together with their associates are well known and often host higher biodiversity compared to other surrounding hard substrates (Balazy & Kuklinski, 2013), factors affecting the composition and multifariousness of these assemblages remain poorly understood (Williams & McDermot, 2004). This is also true for epibiosis of other crustaceans (Fernandez-Leborans, 2010) and hard mobile substrates in general. The recognition of the factors correlating with diversity of these rich assemblages could be of import to aid understanding biodiversity drivers in coastal systems. Even though some factors affecting biodiversity on hard mobile substrates have been already recognized by manipulative experiments, they accept largely been performed in isolated, homogeneous environments that have not incorporated various environmental parameters. Thus, the extent to which such factors dominate what happens in real environments is unknown. Typically, a wide range of abiotic factors, biological processes and their interplay tin influence epifaunal assemblages (Dayton, 1984; Menge & Sutherland, 1987; Smith & Witman, 1999). Among them, substrate size (Barnes & Clarke, 1995; McGaw, 2006; Kuklinski et al., 2008), host and shell species identity (Conover, 1979), its condition (documented in the case of decapods other than hermit crabs, Dvoretsky & Dvoretsky, 2010) seem to play of import roles. Secondary factors reported to date include host gender or depth of occurrence, although these accept been rarely investigated (Fernandez-Leborans, 2010; Dvoretsky & Dvoretsky, 2010). To our knowledge, the about comprehensive work concerning various factors has been on two sympatric hermit crab species:
Say, 1817 and
Say, 1817, from Tampa Bay, Florida (Conover, 1979). This showed that epifaunal species richness increased with trounce size but without altering their density. The identity of the host crab as well strongly influenced the epibiota, whilst the identity of gastropod shell was of piffling importance.
Our study aims to depict factors affecting epifaunal species limerick and affluence (i.e. epifaunal aggregation construction), diverseness (Southward,
H′) and full abundance (N) on gastropod shells used past hermit crabs from Northern Kingdom of norway, across Barents Sea’s shallow banking concern (Svalbard Bank) to Spitsbergen Island (Svalbard Archipelago). This is the northern latitudinal extreme of hermit crab ranges, where the ecologies of host and epifauna remain poorly understood (Barnes et al., 2007). Besides investigating the potential impacts of substrate size, crab and shell identity, we additionally include factors that have been rarely investigated before, such as crab gender and location. In the cold, ice-scoured, glacier-dominated Arctic shallows, environmental weather are severe—then nosotros hypothesize that on Svalbard, location (that reflects the variability in ecology conditions and the local species puddle of potential colonizers) is a fundamental determinant, while factors like crab species and gender, shell expanse or its identity become more of import in boreal Norwegian fjords.
Materials and methods
Report sites were three littoral locations (Isfjord, Kongsfjord, Smeerenburg) in the west of Spitsbergen Island, the largest i of the Svalbard Archipelago, i offshore location to the south on Svalbard Bank and two littoral locations in Northern Norway (Mjosund and Kvalsund, Fig. i). All locations are inside the warm and saline (T > three°C,
S > 35, Loeng, 1991) Due north Atlantic Electric current which, through its extension—the West Spitsbergen Electric current (WSC)—influences due west Atlantic latitudes as loftier equally 76–80°N, giving them a mild ‘sub-Arctic’ character (Hop et al. 2002; Svendsen et al., 2002). Withal, Svalbard waters are also strongly influenced by cold freshened Arctic water (T < 0°C,
34.iii–34.8) transported by the Eastward Spitsbergen Electric current (ESC), and glacial and riverine arrival (Loeng, 1991; Cottier et al., 2010).
Hydrographic conditions inside the Spitsbergen fjords remain in dynamic balance between these 2 large h2o masses and local water, and tin vary considerably between locations depending on fjord shape, bathymetry at the mouth (sill presence), tidal currents and wind directions (Svendsen et al., 2002; Basedow et al., 2004). Iceberg scouring, sedimentation and fresh h2o runoff grade steep environmental gradients visible along the fjord’s axis from the inner-most, glacier-influenced part of the fjords towards its mouth (Włodarska-Kowalczuk & Pearson, 2004). Fjordic seabeds of Svalbard are typically covered with soft sediments and drib stones. The macrobenthic assemblages in that location are mostly dominated past infaunal bivalves and polychaetes (Włodarska-Kowalczuk, 2007). Wherever hard bedrock is nowadays, dense kelp forest (Saccharina latissima
(Linnaeus) C.Due east. Lane, C. Mayes, Druehl & 1000.W. Saunders, 2006;
spp. J.V. Lamouroux, 1813) and rich epibenthic assemblages of echinoids, cnidarians, ascidians, sponges, barnacles, bryozoans and sedentary polychaetes are abundant (Barnes & Kuklinski, 2005; Barnes et al., 2007). Spider (Hyas
spp. Leach, 1814) and hermit crabs (Pagurus
spp. Fabricius, 1775) are commonly found beyond these areas in big numbers (Kaczmarek et al., 2005; Berge et al., 2009, Balazy et al., 2015).
spp. occurs also ~50 nm southeast of Spitsbergen—at Svalbard Banking company. This ascent in the seabed that peaks at merely 30–40 1000 depth is covered more often than not by a thick layer of barnacle and clam shell fragments overlying fibroid sand and gravel. In a front end between North Atlantic and Chill water masses, with stiff tidal currents and vertical mixing, Svalbard Bank is considered to be a very productive area (Elverhoi & Solheim, 1983; Sakshaug et al., 2009).
The study sites in Northern Norway were located in Mjosund and Kvalsund. These narrow, shallow sounds connect the open sea with fjords that cutting deep into the country. Without significant influence of glaciers, rivers and creeks are the primary source of freshwater input (Wassmann et al., 1996). Water masses are, even so, well mixed vertically due to strong tidal currents (Holte & Oug, 1996). Sea temperature varies from ~iii.v to 8°C; thus, water rarely freezes and salinity ranges from 31 to 34 (Loeng, 1991; Oug, 1998). The seabed is characterized, similarly to Spitsbergen, by a mix of cobbles and boulders overlying mud and silt. On patches of mud/silt polychaetes, bivalves and gastropods boss (Holte & Oug, 1996). Hard bedrock is typically overgrown past leaf-shaped red, green and coralline algae and serpulid polychaete reefs (Haines & Maurer, 1980; Oug, 2001). Barnacles, ascidians, bryozoans and sponges are too mutual and abundant epifaunal taxa. Among decapods, along with the edible crab
Linnaeus, 1758 and two species of
Hyas, three pagurid species occur [Pagurus pubescens Krøyer, 1838;
(Lilljeborg, 1856); Bahr & Gulliksen, 2001; Barnes et al., 2007].
Hermit venereal were collected in August 2009 in ii ways: haphazardly picked by SCUBA defined (Mjosund, Kvalsund, Isfjord, Kongsfjord, Smeerenburg) and by triangular dredge (1 grand each side, Svalbard Banking concern). Samples were preserved in 4% formaldehyde buffered with seawater, and transported to the laboratory. Crab identity, gender and gastropod shell identity were adamant for each individual. The external surface area (SA) of a shell was estimated post-obit the technique of Bergey & Getty (2006). A shell was advisedly wrapped in a sparse layer of stock aluminium foil and all overlapping or excess areas were trimmed off. The foil was and then weighed (B) and the SA was calculated from the equation SA = 0.0495 + 413.59 * B,
2 = 0.948 (this equation was obtained subsequently weighing pieces of foil of known surface area). All animate being larger than 1 mm constitute on the beat surface, including the shell aperture, were identified to the lowest possible taxonomic level, typically to species. Determination of polychaete species was made according to Jirkov (2001) using tube morphology (Kupriyanova & Jirkov, 1997). However, identification of Spirorbinae mostly requires inspection of morphological characteristic of soft trunk parts and some of the spirorbids were classified into morpho-groups:
sp., Spirorbinae juvenile, Spirorbinae undetermined. The number of individuals in each group/species was counted, with each colonial organism considered every bit i ‘individual’.
Epifaunal assemblages colonizing hermit crab-inhabited shells were analysed separately at Svalbard (fjords and the offshore location, Fig. i.) and separately in Northern Norway due to strong differences between those regions (the 2 hermit crab species were recorded together only in Northern Norway). Non-parametric PERMANOVA procedures were used to test for differences in both multivariate (species composition and abundance) and univariate (species number, total abundance and Shannon–Wiener variety) characteristics of the epifauna in groups of samples defined by three or 4 factors. For cloth collected at Svalbard, three stock-still factors were included: (1) location, (2) crab gender and (three) shell identity (i.east. family). For Northern Kingdom of norway, four stock-still factors were considered: (ane) location, (2) crab species, (3) crab gender and (4) vanquish identity (i.e. family). Because epifaunal diversity and abundance can be strongly related to the area of the substrate (Conover, 1979; McGaw, 2006; Kuklinski et al., 2008), gastropod shell area was included as a covariable in all analyses. The statistical significances of each of the multivariate and univariate variance components were tested using 9999 permutations of residuals nether a reduced model (Anderson & ter Braak, 2003).
Prior to the multivariate analysis for epifaunal species composition and abundance (i.e. epifaunal assemblage structure), data were square-root transformed to assure a more balanced view of the assemblage construction equally this transformation reduced the influence of the nearly numerous taxa (Clarke & Gorley, 2001). The analyses were conducted on a zero-adjusted Bray–Curtis dissimilarity matrix. To visualize and compare the importance of each cistron, their Sqrt values of PERMANOVA, given in Tabular array one, were plotted. Sqrt values are the square-root transformed sizes of the variance components, expressed as a per centum of the total variation. Variance components were obtained using mean squares (MS, Table 1) from PERMANOVA (Anderson et al., 2008). Significant effects of factors documented past PERMANOVA principal tests were further examined with the utilize of post hoc, pair-wise tests. When both a significant outcome of a factor and pregnant interaction between two factors were detected, pair-wise tests for differences between different levels of a factor were performed separately within each level of the other factor, as recommended by Anderson et al. (2008). However, at Svalbard, due to limited number of samples, the furnishings of the gene location were analysed only for Buccinidae shells (they were most abundant and distributed in all the investigated fjords), while the furnishings of Crush identity were examined for samples nerveless in Isfjord (the largest fjord with all crush groups present). SIMPER routine (similarity percentages—species contributions) was used to reveal which species were responsible for the differences among epifaunal assemblages. Only species with contributions >10% were reported. In order to remove the confounding effect of dissimilar gastropod beat out areas for SIMPER analyses, abundance data for each epifaunal species were averaged by shells full abundance prior to the analyses.
As univariate descriptors of the epifaunal assemblages, species number (S), total affluence (N) and Shannon–Wiener diversity index (H′) were calculated. PERMANOVA primary and pair-wise tests in this instance were conducted on Euclidean-distance similarity matrices (untransformed data, Clarke et al., 2006; Anderson et al., 2008). Spearman’s rank correlations (Sokal & Rohlf, 1981) were used to decide human relationship between the gastropod shell expanse and
The epifauna abundance data in SIMPER assay and graphical visualizations of number of individuals (N) were expressed equally the number of individuals per cmtwo
of surface area, but in all other analyses (S,
H′), as the number of individuals per beat out.
PERMANOVA main and pair-wise exam, calculation of diversity measures (South,
H′) were performed in PRIMER v6 with the PERMANOVA+ add-on (Clarke & Gorley, 2001; Anderson et al., 2008). Spearman’s rank correlations analyses were done in STATISTICA v. x (StatSoft Inc.). Significance level for all statistical tests used was
P = 0.05.
The 439 gastropod shells nerveless across both areas (Svalbard—302, Northern Norway—137) were inhabited by ii hermit crab species (Pagurus pubescens
P. bernhardus). At Svalbard, only
was plant. In Northern Norway, it was dominant (P. pubescens
P. bernhardus 38%). In total, 36,736 epifauna individuals from 102 taxa were recorded (31,851 individuals from 92 taxa at Svalbard, and 4885 individuals and 55 taxa in Northern Norway). Shells used by
in Northern Norway hosted in total 3263 individuals from 48 taxa, whereas those of
hosted 1622 individuals and 41 taxa. Shells collected at Svalbard were colonized by 1665 individuals (one–24 species), whilst in Northern Norway 1223 individuals (1–14 species) colonized the shells. Although gastropod shells nerveless at Svalbard were significantly larger than those from Northern Norway (1.4–87.7 cmtwo
at Svalbard vs. 0.9–forty.2 cmtwo
in Northern Kingdom of norway), the range of Shannon–Wiener diversity index for epifauna for both areas was the same (0–2.iii). Among all epifaunal taxa, Bryozoa and Polychaeta were represented by the highest numbers of species (67 and 15, respectively). Epifaunal assemblages at Svalbard were dominated by the barnacle
(Linnaeus, 1767) and sedentary polychaetes [Circeis armoricana
(Bush, 1905) and
sp. Caullery & Mesnil, 1897]. The next most arable species were bryozoans [Myriozoella plana
sp. Gray, 1848;
sp. Grey, 1848] and the foraminifer
(Walker & Jacob, 1798). In Northern Kingdom of norway’south assemblages, sedentary polychaetes [juvenile forms of Serpulidae;
sp.] and ii foraminiferan species [Discorbis rosacea
(d’Orbigny, 1826) and
L. lobatula] prevailed.
Multivariate analysis showed that hermit crab epifaunal community construction differed significantly betwixt locations, crab species and trounce identity, and that there were significant interactions between factors (Tabular array 1). The structure of these assemblages also showed a highly pregnant human relationship with shell area. Multivariate variations indicated by Sqrt values (see M&K), in both report areas, were greatest from 1 beat replicate to the other (remainder), followed by investigated factors in order of decreasing contribution to the total variability: location, crab sp. (just Northern Norway), shell identity and shell area. Interactions between location and shell identity (merely Svalbard) every bit well as location and crab sp. (Northern Norway) were also a significant sources of variation in hermit crab epifaunal assemblages, simply were less important (Table 1; Fig. 2).
Pair-wise tests indicated differences in epifaunal assemblage structure among all the four Svalbard locations (Table 1). Dissimilarity revealed by SIMPER analysis, ranged from 55.9% (Svalbard Bank vs. Isfjord) to 86.7% (Svalbard Bank vs. Kongsfjord). For each pair of locations, species that contributed the about to the observed differences were the barnacle
and the sedentary polychaetes:
Circeis armoricana, or both of these species (Table two; Fig. 3a). Meaning differences in species number, affluence and multifariousness index were as well found among Svalbard’s locations (Fig. 4). Pair-wise analyses indicated that the nigh various hermit crab epifaunal assemblages were establish on the shells from Kongsfjord and Smeerenburgfjord, still these shells hosted the lowest number of individual epibionts (Fig. 4b, c). Svalbard Banking company was the location with the highest number of epifaunal individuals only the lowest diverseness index (Fig. 4b, c).
Differences in epifaunal assemblage structure between the two Northern Norway locations were present considering both
(Table 1; Fig. 3b). Dissimilarity between Kvalsund and Mjosund revealed past SIMPER analyses reached 81.9% (P. pubescens) and 84.9% (P. bernhardus). The differences observed were due to higher relative abundances of sedentary polychaetes (Circeis armoricana, juvenile forms of Serpulidae) in Kvalsund and foraminiferans (Lobatula lobatula,
Discorbis rosacea) in Mjosund (Table 2; Fig. 3b). The number of species and individuals were college in Mjosund than in waters of Kvalsund, but each time these differences were constitute only for one crab species—Southward
(Fig. 4a, b). Values of Shannon–Wiener diversity indices were similar in both locations, regardless of the crab species (Fig. 4c).
Hermit crab species
Two hermit crab species (P. pubescens
P. bernhardus) occurred simply in Northern Norway. SIMPER analyses performed separately for two Northern Kingdom of norway locations showed 73.ix% (Kvalsund) and 68.iv% (Mjosund) dissimilarity between the assemblages overgrowing shells of the 2 hermit crabs. In Kvalsund, SIMPER identified sedentary polychaetes (juvenile forms of Serpulidae and
C. armoricana) as taxa responsible for differences in epifauna, although differences in their relative affluence between the two hermit venereal were small (Table two; Fig. 3b). In Mjosund, juvenile forms of Serpulidae and
prevailed on shells used by
P. bernhardus, while foraminiferans (Discorbis rosacea, Lobatula lobatula) dominated on
P. pubescens-inhabited shells. Shells carried by
supported larger number of epifaunal species and individuals and a higher diverseness than
P < 0.05, private examination values not shown, Fig. four).
Beat out identity
There were meaning differences in the structure of epifaunal assemblages among gastropod beat families (Tabular array 1). Pair-wise tests showed significant effects in seven out of 10, pair-wise comparisons of gastropod vanquish families (Table i). Contrast revealed by SIMPER analysis ranged from 57.6% (Buccinidae vs. Naticidae) to 84.v% (Naticidae vs. Trochidae). Species with the largest contributions to observed differences were
(prevailing on Naticidae shells),
(prevailing on Muricidae shells),
(predominating on Trochidea shells) and
(on Muricidae, Table two; Fig. 5a). More epifaunal species were found on Buccinidae and Muricidae than on Trochidae shells (Fig. 6a). Buccinids supported college diversity than Trochidae and Naticidae (Fig. 6b).
In Northern Norway, irrespective of hermit crab identity, pair-wise tests indicated significant differences betwixt the epifaunal communities on shells from Littorinidae and Muricidae, Littorinidae and Buccinidae (Table 1). SIMPER analyses showed 78.7% contrast between Littorinidae and Muricidae, and 79.ii% betwixt Littorinidae and Buccinidae. Species that played the greatest part in discriminating these groups of samples were juvenile forms of Serpulidae, prevailing on Muricidae and Buccinidae shells, and
and foraminiferans (Discorbis rosacea,
Lobatula lobatula), ascendant on Littorinidae shells (Tabular array two; Fig. 5b). In Northern Norway, Shell identity had no influence on the number of species, individuals nor biodiversity (PERMANOVA
P > 0.05).
Trounce surface area
All assemblage parameters studied varied significantly (PERMANOVA
P < 0.05) with gastropod beat expanse in both written report areas, except for biodiversity at Svalbard (Table 1, individual test values for
H’ not shown). In that location were more epifaunal species with increasing vanquish size in Northern Kingdom of norway (r
s = 0.31,
t = 3.84,
P < 0.001), more than individuals (r
s = 0.18,
t = 2.09,
P = 0.039) and the diversity index was higher (r
due south = 0.25,
t = three.06,
P = 0.003). Like patterns were observed at Svalbard where the number of epifaunal species (r
s = 0.68,
t = xvi.32,
P < 0.001) and number of individuals increased with trounce size (r
s = 0.78,
t = 21.28,
P < 0.001). In Northern Norway the average shell had a surface area of xiv.5 cm2
and diversity of ane.one and was the substrate for 35.7 epifaunal individuals belonging to 5.ix species. The average shell plant at Svalbard was larger (23.7 cm2), and hosted more than epibiont individuals (mean 105.5) and species (eight.4), whilst the diversity of epibionts was the same (one.1). When numbers were converted to values per cm2
of shell expanse, the number of species wes equal (0.4 sp. cm−2), but the number of individual epibionts was higher at Svalbard (4.5 ind. cm−two) than in Northern Norway (2.5 ind. cm−2).
Despite the common pattern of autocorrelation in marine ecological samples (i.e. tendency of samples collected closer to each other to be more similar than those further autonomously, due east.k. Underwood & Chapman 1996), the greatest multivariate variations in hermit crab epifaunal assemblages from the two regions in the current written report occurred betwixt their replicates (i.due east. from sample to sample). This has been constitute in other studies of benthic invertebrates (Underwood & Chapman, 1996; Anderson et al., 2005; Wlodarska-Kowalczuk & Weslawski, 2008). In hermit crab assemblages, where on a small surface the first colonist is able to occupy the majority of available space and dominate, outcompete or prevent recruitment of other species (McLean, 1983), priority furnishings (Sutherland, 1974) may serve as a potential mechanism for the observed design. Large overall number of species that occurred across all gastropod shells sampled might be likewise responsible for this. Although during this study we did not tape as many epifaunal species equally listed in the literature (e.g. Jensen & Bender 1973, p. 120 taxa), we even so found 92 taxa at Svalbard and 55 in Northern Norway. Taking into business relationship that typical gastropod shell was the substrate for 8.4 (Svalbard) or five.9 (Northern Kingdom of norway) species, and assuming the random selection of first colonizers and in result—the dominant epibiont species, the probability that on the side by side shell there will be different species prepare is big.
Regardless of large ecology differences between Northern Norway and Svalbard, variations observed in epifaunal assemblages were the greatest between locations (i.e. fjords) not equally hypothesized just on Svalbard merely in both of these regions. Local species diversity draws from regional species pools, simply has been found by some studies to exist driven by small scale, local ecology settings (Witman et al., 2004; Renaud et al., 2009). The Svalbard locations used in the current study differed largely in their physical (e.g. hydrology, bathymetry, water ice action, distance from country and glaciers, influence of terrigenous material input, sediment or freshwater discharge and lesser substratum), and thus biological settings (Jorgensen & Gulliksen, 2001; Włodarska-Kowalczuk & Pearson, 2004; Kuklinski & Porter, 2004). This was clearly reflected in the samples collected. Svalbard Banking company, for example, mainly comprises barnacle and mollusc shell fragments (Elverhoi & Solheim, 1983). Epifaunal assemblages there had the highest number of individuals and the lowest Shannon–Wiener diversity alphabetize (Fig. 4b, c) due to mass occurrence of barnacles [generally
(Linnaeus, 1758) and
Bruguière, 1789; Fig. 3a] overgrowing each other and forming dense clusters. The highest richness of epibiont species and amongst the highest epifaunal diversity occurred at Kongsfjord probably due to the intermediate oceanographic conditions in that location, supporting an Chill and boreal species mix (Hop et al., 2002; Svendsen et al., 2002). Northern Norway, also subjected to the Due north Atlantic Electric current, is a more homogenous environment, yet in its Kvalsund waters serpulid polychaete reefs dominate the macrobenthos (Haines & Maurer, 1980) and were also apparent on hermit crab shells (Fig. 3b). Known for their gregarious behaviour (Scheltema et al., 1981) and potent spatial competition (Kuklinski & Barnes, 2008), they are able to monopolize a pocket-size surface such as a hermit crab shell in a short time, probably hindering other epibionts from colonization. This might explain the smaller number of species recorded in Kvalsund. In Mjosund, foraminiferans (Lobatula lobatula
Discorbis rosacea) contributed to the larger number of epifaunal individuals observed there. Species similar
prefer hard substrates and strong currents that ensure well mixed water and reduced sedimentation (Klitgaard Kristensen & Sejrup, 1996). In full general, such conditions prevail in both the Northern Norway study locations (Holte & Oug, 1996), and then perhaps local variations in sedimentation rates, as at Tanafjord (Corner et al., 1996), could be responsible for the differences observed.
The differences in epifaunal assemblages between the hermit crab species (Pagurus pubescens
P. bernhardus) documented in this study contrast with reports from the North Bounding main (Reiss et al., 2003), where, except several cases, no major departure in the mean number of species or abundance of epifauna between these two hermit crab hosts was found. On the other mitt Conover (1979), studying
from Florida, observed such differences and attributed them to a charge per unit at which hermit crabs modify their shells. Species which abandon shells less oftentimes offer more stable and predictable habitat for epibionts. In our written report, shells inhabited by
were covered by a larger number of species and individuals and had higher diversities than those used by
P. bernhardus. The ecology (e.g. habitat, convenance and behaviour) of the 2 hermit crab species seems similar (Samuelsen, 1970; Hazlett, 1981; Lancaster, 1988, 1990), and at that place were no detectable influences of gastropod beat type (interaction of crab sp. × shell identity was not significant), so these differences could exist caused by the fact that the two hermit crabs change shells in a different manner. This is possible as bulk of hermit crab populations are shell limited (Kellogg, 1976; Barnes et al., 2007) and frequency of moulting/irresolute shells can vary even betwixt specimens of the same kind kept in similar conditions (Thruway & Williamson, 1958). Differences in epifaunal assemblages between hermit crab hosts may be finally region specific (Norwegian Ocean vs. N Sea) and future studies are needed to assess this.
Although host gender influence on epifaunal communities seems unlikely, such effects have been documented in the literature. Virtually of them are related to true venereal (Brachyura) and attributed to differences between the sexes in migratory habits, growth rate, length of intermoult period, beat out use or abrasion during mating (Abelló, 1986; Abrams, 1988; Lancaster, 1990; Ingle, 1996; Key et al., 1997; Gherardi, 2004; Fernandez-Leborans, 2010). Genders may also exhibit specific preferences concerning epibionts (e.g. female preference of shells without
sp. Van Beneden, 1844; Damiani, 2003). In our study, both hermit crab species genders occurred in the same habitats. We did non observe any major differences in the frequency of occurrence in
Hydractinia-covered shells betwixt males and females of either crab species in Northern Norway or Svalbard. Shell utilize (number of shell types and their percentage) also did not differ. Consequently, in that location were no significant variation acquired by gender of
in these areas (Tabular array ane). These findings correspond with previous studies on anomuran decapods belonging to the family Lithodidae (e.g. red king crab
(Tilesius, 1815) from the Barents Sea, Dvoretsky & Dvoretsky, 2010; but this may besides vary, come across Klitin, 2003).
Epifaunal assemblages in the waters of Tampa Bay, Florida varied fiddling between the different shell species, suggesting that shell identity may non be an of import cistron direct influencing epifauna (Conover, 1979). Our results approve these findings—shell identity was indicated by PERMANOVA every bit ane of the least influential factors, merely withal significant. Many of the epibiotic species larvae driven by specific preferences (e.g. substrate texture and contour, bio-mineralogy, presence of biofilms) practise not randomly attach to exposed surfaces but instead actively seek suitable places for settlement (Crisp & Barnes, 1954; Wahl, 1989; Bavestrello et al., 2000; Berntsson et al., 2000). One of the spatial dominants from Svalbard, for example,
Semibalanus balanoides, exhibits so-called “rugophilic” tendency, i.e. the tendency for settlement in grooves and concavities (Crisp & Barnes, 1954). In the present written report, however, this species was characteristic both for irregular Buccinidae shells (Buccinum glaciale
Kiener, 1834) and for smooth shells of Naticidae [Cryptonatica affinis
(Broderip & Sowerby, 1829)]. Other species indicated by SIMPER assay to be those contributing almost to observed differences between the shell types were non specific to whatever shells and were recorded also on other substrates (e.g. polychaete
were found on stones and pebbles, carapaces of various crustaceans, or algae; Hayward & Ryland, 1999; Jirkov, 2001; Włodarska-Kowalczuk et al., 2009). In the case of other species, reports in the literature propose broad occurrences without substrate-specific allegiance (Keough & Downes, 1982). In general however, for the majority of epibionts, rough surfaces seem to be more attractive than smooth (Crisp & Ryland, 1960; Teitelbaum, 1966; Crisp, 1974; Mils, 1976; Köhler et al., 1999; Herbert & Hawkins, 2006). Pits and grooves of irregular shells ensure larger number of refuges, lowered probability of destruction by physical disturbance (e.g. overturning) and college adhesion (Barry & Dayton, 1991; Pech et al., 2002). This was too the instance in our study where large, irregular Buccinidae shells supported higher diversities than smooth Naticidae.
Previous studies take shown that for well-nigh epifaunal species, the near important unmarried factor influencing their presence or affluence is availability of suitable substrata (Kuklinski et al., 2006, 2008; Dvoretsky & Dvoretsky, 2009). Here shell area was not the virtually important factor only withal had a significant influence on virtually all investigated parameters (S,
H’ in Northern Norway;
at Svalbard; Table 1). Larger shells provide a larger target area for settling larvae, just are too inhabited by older hermit crabs which alter their shells less frequently considering they grow more slowly (Tendal & Dinesen, 2005). Prolonged, undisturbed time for growth and development is advantageous for colonization of epifauna. Therefore, unsurprisingly, the number of epifaunal species and individuals increased with shell size.
Summing up, regardless of the written report region (Svalbard vs. Northern Norway), local environmental settings, that is the hydrology, physical weather and local species pools, had the greatest influence on epifaunal assemblages occurring on hard mobile substrate. Apparently, the relative importance of unlike factors depends on the spatial scale of the investigation, and one might expect that when the conditions are similar (e.g. study sites are located close to each other), other factors, such as shell area and its identity, or crab species, might gain in importance.
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Why is a Shell Considered to Be Biotic