Myrmica rubra microhabitat selection and putative ecological impact

1. Myrmica rubra (European fire ant) has invaded northern latitude coastal areas in North America. This macroscale distribution suggests that M. rubra is moisture‐ and temperature‐limited, but the distribution of the invaded range may reflect the legacy of original introduction locations preserved by limited dispersal. 2. This study examined a two‐decade population change in M. rubra (1994–2015) and the microscale abiotic (moisture and temperature), biotic (plants), anthropogenic (pesticide) and physiological (thermal tolerance) limits on the invasion at the Tifft Nature Preserve in Buffalo, NY (U.S.A.). Changes in the abundance of native ants and other invertebrates were also examined. 3. Despite localised declines with pesticide treatments, overall M. rubra forager abundance increased 27% between 1994 and 2015. Abundance increased the most in the warmest areas (native ants were unaffected by temperature), but M. rubra colony locations were strongly linked to higher soil moisture and lower soil temperature. Myrmica rubra ants also exhibited relatively low thermal tolerances consistent with high‐latitude and high‐elevation ants. 4. Where local M. rubra populations increased the most, native ant species decreased, and where local M. rubra populations declined, native ant species increased. Some arthropod species had lower abundance with M. rubra presence, but the impacts were less striking. 5. Myrmica rubra population growth was promoted at the microhabitat scale where relatively higher temperatures prompted foraging, and relatively lower temperatures and high moisture supported nesting. These results suggest that macroscale M. rubra invaded‐range distributions in northern climates near coastal areas are replicated at the microscale where the ant prefers cooler, moister microsites.     

Density‐ and trait‐mediated top–down effects modify bottom–up control of a highly endemic tropical aquatic food web

Benthic invertebrates mediate bottom–up and top–down influences in aquatic food webs, and changes in the abundance or traits of invertebrates can alter the strength of top–down effects. Studies assessing the role of invertebrate abundance and behavior as controls on food web structure are rare at the whole ecosystem scale. Here we use a comparative approach to investigate bottom–up and top–down influences on whole anchialine pond ecosystems in coastal Hawai‘i. In these ponds, a single species of endemic atyid shrimp (Halocaridina rubra) is believed to structure epilithon communities. Many Hawaiian anchialine ponds and their endemic fauna, however, have been greatly altered by bottom–up (increased nutrient enrichment) and top–down (introduced fish predators) disturbances from human development. We present the results of a survey of dissolved nutrient concentrations, epilithon biomass and composition, and H. rubra abundance and behavior in anchialine ponds with and without invasive predatory fish along a nutrient concentration gradient on the North Kona coast of Hawai‘i. We use linear models to assess 1) the effects of nutrient loading and fish introductions on pond food web structure and 2) the role of shrimp density and behavior in effecting that change. We find evidence for bottom–up food web control, in that nutrients were associated with increased epilithon biomass, autotrophy and nutrient content as well as increased abundance and size of H. rubra. We also find evidence for top–down control, as ponds with invasive predatory fish had higher epilithon biomass, productivity, and nutrient content. Top–down effects were transmitted by both altered H. rubra abundance, which changed the biomass of epilithon, and H. rubra behavior, which changed the composition of the epilithon. Our study extends experimental findings on bottom–up and top–down control to the whole ecosystem scale and finds evidence for qualitatively different effects of trait‐ and density‐mediated change in top–down influences.     

Predator-dependent diel migration by <Emphasis Type="Italic">Halocaridina rubra</Emphasis> shrimp (Malacostraca: Atyidae) in Hawaiian anchialine pools

Diel migration is a common predator avoidance mechanism commonly found in temperate water bodies and increasingly in tropical systems. Previous research with only single day and night samples suggested that the endemic shrimp, Halocaridina rubra, may exhibit diel migration in Hawaiian anchialine pools to avoid predation by introduced mosquito fish, Gambusia affinis, and perhaps reverse migration to avoid the predatory invasive Tahitian prawn, Macrobrachium lar. To examine this phenomenon in greater detail, we conducted a diel study of H. rubra relative abundance and size at 2-h intervals in three anchialine pools that varied in predation regime on the Kona-Kohala Coast of Hawai‘i Island. We found two distinct patterns of diel migration. In two pools dominated by visually feeding G. affinis, the abundance of H. rubra present on the pool bottom or swimming in the water column was very low during the day, increased markedly at sunset and remained high until dawn. In contrast, in a pool dominated by the nocturnal predator M. lar, H. rubra density was significantly lower during the night than during the day (i.e., a pattern opposite to that of shrimp in pools containing fish). In addition, we observed that the mean body size of the shrimp populations varied among pools depending upon predator type and abundance, but did not vary between day and night in any pools. Our results are consistent with the hypothesis that H. rubra diel migratory behavior and size distributions are influenced by predation regime and suggest that diel migration may be a flexible strategy for predator avoidance in tropical pools where it may be a significant adaptive response of endemic species to introduced predators.     

Abundance decline in the narrow-ridged finless porpoise population off the Pacific coast of eastern Japan

The narrow-ridged finless porpoise Neophocaena asiaeorientalis is a small-toothed whale with a coastal habitat and is sensitive to human activity. Aerial sighting surveys were conducted in 2012 to evaluate the abundance and distribution of the Sendai Bay-Tokyo Bay population off the Pacific coast of eastern Japan. We flew along 35 east–west transects at intervals of 11.6 km over the study area between 34°57′ and 38°21’ N. In total, 25 groups were detected by two observers. The mean group size was 1.44 individuals. Porpoise abundance was estimated to be 1,491 individuals (coefficient of variation = 32.4%), which was lower than the abundance estimated in 2000 (z test, p < 0.05). A population decline trend during 2000–2012 was also detected using four available abundance estimates (Bootstrapping linear regression, p = 0.040). A possible cause of this decline was coastal habitat disturbance and deaths by tsunami waves caused by the 2011 Great East Japan Earthquake. Density was as low as 0.221 individuals/km², which is among the lowest levels in Japanese waters. Furthermore, distributional gaps reconfirmed by the present study and past genetic studies show that the population should be divided into at least two populations: northern (“Sendai Bay-Fukushima”) and southern. Density decline was detected in the northern population between 2000 and 2012. Unlike the earthquake, human activities may continue to affect the porpoises. Viability analyses of these small populations should be conducted in the future.     

Limited evidence for ecosystem‐level change on reefs exposed to Haliotis rubra (‘blacklip abalone’) exploitation

It is increasingly recognized that fisheries must take the broader ecosystem into account for sustainable management of marine systems, requiring an understanding of the interaction between fished species and other organisms. This study uses a correlative approach to investigate potential interactions between benthic organisms and Haliotis rubra, a dominant herbivore that is the subject of a large and valuable commercial fishery in south‐eastern Australia. Specific emphasis was placed on understanding associations between H. rubra and understorey organisms, because particular understorey algae (crustose coralline algae) provide critical habitat for H. rubra larval recruitment and juvenile ecology. Broad‐scale surveys along the 6–8 m depth contour (the depth range where H. rubra fishing activity is intense) were conducted across four regions (separated by 10⁴?10⁵ m), including at least 10 sites (separated by 10²?10³ m) within each region. Positive correlations between H. rubra and crustose coralline algae were found, while negative correlations were observed between H. rubra and sessile invertebrates and understorey algae. While significant, these associations were weak and H. rubra abundance generally only explained a small proportion of the variability in the abundance of understorey organisms (r² 0.02–0.30). H. rubra abundance also had a minor influence on community‐level understorey patterns in comparison with differences in community structure attributable to regional variation. Patterns of H. rubra abundance and benthic community structure were also examined in relation to depth at a restricted number of sites. At sites where differences in understorey groups were evident, H. rubra abundance also varied significantly, highlighting the issue of confounding when contrasting patterns of understorey abundance using a correlative approach. Further manipulative experiments are required to confirm causal relationships; however, the available correlative evidence suggests limited ecosystem effects of H. rubra depletion at the scale of individual reefs.     

Habitat requirements and niche selection of Maculinea nausithous and M. teleius (Lepidoptera: Lycaenidae) within a large sympatric metapopulation

Identifying the factors determining the distribution and abundance of species is a fundamental question in population ecology. Based on habitat characteristics, we sought to identify factors affecting the abundance of two vulnerable large blue butterflies, Maculinea teleius and Maculinea nausithous. Both species often occur in sympatry and thus seem to have very similar requirements with regard to their wetland habitats. Even though, M. nausithous is usually far more widespread and abundant than M. teleius in Central Europe. For understanding this difference despite a similar ecology, more data is needed on the niche selection of both species. We have recorded Maculinea numbers, vegetation structure, food-plant abundance and ant community for 120 patches within a large sympatric metapopulation of both species in the Westerwald area (Germany). Unexpectedly (based on previous data), both species were equally common in the study area, reaching high densities of up to 61 (M. teleius) and 58 (M. nausithous) individuals per 50 m2. In 116 out of 120 patches both species occurred sympatrically. The preferred habitat was extensively managed grassland, being mown or grazed twice a year. The abundance of both Maculinea species was positively related to vegetation height, food-plant and Myrmica rubra abundance. There was no association between M. teleius and its putative main host-ant Myrmica scabrinodis, indicating that M. rubra may serve as an important host in the Westerwald area. The positive effect of food-plant abundance was more pronounced for M. teleius, coinciding with a higher food-plant abundance at sites dominated by M. teleius compared to those dominated by M. nausithous. Thus, M. teleius seems to be slightly more demanding than M. nausithous in terms of food-plant availability.     

Geographic range determinants of two commercially important marine molluscs

Aim We modelled the spatial abundance patterns of two abalone species (Haliotis rubra Donovan 1808 and H. laevigata Leach 1814) inhabiting inshore rocky reefs to better understand the importance of current sea surface temperature (SST) (among other predictors) and, ultimately, the effect of future climate change, on marine molluscs. Location Southern Australia. Methods We used an ensemble species distribution modelling approach that combined likelihood‐based generalized linear models and boosted regression trees. For each modelling technique, a two‐step procedure was used to predict: (1) the current probability of presence, followed by (2) current abundance conditional on presence. The resulting models were validated using an independent, spatially explicit dataset of abalone abundance patterns in Victoria. Results For both species, the presence of reef was the main driver of abalone occurrence, while SST was the main driver of spatial abundance patterns. Predictive maps at c. 1‐km resolution showed maximal abundance on shallow coastal reefs characterized by mild winter SSTs for both species. Main conclusions Sea surface temperature was a major driver of abundance patterns for both abalone species, and the resulting ensemble models were used to build fine‐resolution predictive range maps (c. 1 km) that incorporate measures of habitat suitability and quality in support of resource management. By integrating this output with structured spatial population models, a more robust understanding of the potential impacts of threatening human processes such as climate change can be established.     

SEQUESTRATION,PERFORMANCE, AND FUNCTIONAL CONTROL OF CRYPTOPHYTE PLASTIDS IN THE CILIATE MYRIONECTA RUBRA (CILIOPHORA)1

Myrionecta rubra (Lohmann 1908, Jankowski 1976 ) is a photosynthetic ciliate with a global distribution in neritic and estuarine habitats and has long been recognized to possess organelles of cryptophycean origin. Here we show, using nucleomorph (Nm) small subunit rRNA gene sequence data, quantitative PCR, and pigment absorption scans, that an M. rubra culture has plastids identical to those of its cryptophyte prey, Geminigera cf. cryophila (Taylor and Lee 1971, Hill 1991). Using quantitative PCR, we demonstrate that G. cf. cryophila plastids undergo division in growing M. rubra and are regulated by the ciliate. M. rubra maintained chl per cell and maximum cellular photosynthetic rates (P_max^cell) that were 6–8 times that of G. cf. cryophila. While maximum chl‐specific photosynthetic rates (P_max^chl) are identical between the two, M. rubra is less efficient at light harvesting in low light (LL) and has lower overall quantum efficiency. The photosynthetic saturation parameter (E_k) was not different between taxa in high light and was significantly higher in M. rubra in LL. Lower Chl:carbon ratios (θ), and hence P_max^C rates, in M. rubra resulted in lower growth rates compared with G. cf. cryophila. G. cf. cryophila possessed a greater capacity for synthesizing protein from photosynthate, while M. rubra used 3.2 times more fixed C for synthesizing lipids. Although cryptophyte plastids in M. rubra may not be permanently genetically integrated, they undergo replication and are regulated by M. rubra, allowing the ciliate to function as a phototroph.     

Variability of cnidae within a small clonal sea anemone (Isactinia sp.)

The cnidom and intraspecific variability of cnidae within the small sea anemone Isactinia sp. were verified. The specific cnidae within the cnidom of four discrete morphological structures (tentacle, actinopharynx, mesenterial filaments, and body column) within Isactinia sp. was investigated. Microbasic b-mastigophores, microbasic p-mastigophores, basitrichs, microbasic p-amastigophores, and spirocysts were found in this species. In addition, two morphologically distinct basitrich forms, distinguishable only in a discharged state, were also found, of which basitrichs with the distinctly shorter thread were found predominately only on the body column. The distribution and abundance of cnidae types differed significantly around the body in the sea anemones, as did the length of basitrichs and spirocysts among tissue types. Cnidae length also differed significantly among individuals. Correlations between cnidae length and sea anemone size were variable, whereby cnidae size was significantly negatively correlated to sea anemone size in seven cnidae–tissue combinations, positively correlated in one, and not correlated in two. Linear regression revealed that sea anemone size was able to explain 33%–68% of variation in size of b-mastigophores, p-amastigophores, and small basitrichs from within the mesenterial filaments. Correlations were negligible or not significant in remaining cnidae–tissue combinations, however. While providing key taxonomic cnidae information, this study also highlights the variability of cnidae that may occur within a species of Isactinia.     

Ontogenetic diet shifts of bull-rout, Myoxocephalus scorpius (L.), in the south-western Baltic Sea

The stomach contents of 533 bull‐rout, Myoxocephalus scorpius (L.), were collected during February–March and October–November 1997 in the south‐western Baltic Sea in order to study the feeding ecology and investigate diet changes between seasons and with the increasing size of the fish. The isopod Mesidotea entomon, and herring Clupea harengus, were the dominant species in the diet, accounting for 99% in weight of all bull‐rout sampled in spring and autumn. Mysis mixta was frequent but less important in weight; analysis of the ontogenetic diet shift showed the presence of M. mixta essentially in the smaller size‐classes. Herring was eaten almost exclusively by individuals larger than 21 cm total length; its importance increased with increasing size of bull‐rout. The isopod M. entomon was abundant in all size‐classes examined. Prey‐size and the size of the principal prey, M. entomon, showed a significant increase with increasing bull‐rout size. The diet shift from mysids to fish was followed by a change in the weight‐length relationship. Cluster analysis confirmed two distinct size groups of >26 cm and <24 cm. In conclusion, the data indicate that the diet of bull‐rout partially overlaps with that of herring in the first trophic stage, and with that of cod in the second part of the bull‐rout life cycle.     

Size‐structured vulnerability of the colonial cyanobacterium,Microcystis aeruginosa,to grazing by zebra mussels (Dreissena polymorpha)

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Distribution and salinity tolerance of marine mysids from a subtropical estuary,Brazil

We studied the spatial and temporal distribution pattern of three marine mysids (Chlamydopleon dissimile, Metamysidopsis elongata atlantica and Mysidopsis coelhoi) from the Cananeia-Iguape Coastal System, southeast Brazil, in relation to environmental variables and zooplankton abundance. We also analysed mysid reproductive traits, and tested their tolerance to salinity gradients in laboratory experiments. Salinity was identified as a major factor influencing mysid spatial and temporal distribution, selectively limiting their distribution within the estuary. Chlamydopleon dissimile and M. coelhoi were common, but occurred at low abundances throughout the year, whereas the numerically dominant M. elongata atlantica had abundance peaks in spring, when thermohaline conditions were more favourable. Mysid brood size varied interspecifically; the occurrence of juveniles throughout the year indicated that mysids breed continuously in the region. The high biomass of M. elongata atlantica observed in spring confirms the importance of mysids in coastal regions' food webs.     

Highlighting patterns of fungal diversity and composition shaped by ocean currents using the East China Sea as a model

How ocean currents shape fungal transport, dispersal and more broadly fungal biogeography remains poorly understood. The East China Sea (ECS) is a complex and dynamic habitat with different water masses blending microbial communities. The internal transcribed spacer 2 region of fungal rDNA was analysed in water and sediment samples directly collected from the coastal (CWM), Kuroshio (KSWM), Taiwan warm (TWM) and the shelf mixed water mass (MWM), coupled with hydrographic properties measurements, to determine how ocean currents impact the fungal community composition. Almost 9k fungal operational taxonomic units (OTUs) spanning six phyla, 25 known classes, 102 orders and 694 genera were obtained. The typical terrestrial and freshwater fungal genus, Byssochlamys, was dominant in the CWM, while increasing abundance of a specific OTU affiliated with Aspergillus was revealed from coastal to open ocean water masses (TWM and KSWM). Compared with water samples, sediment harboured an increased diversity with distinct fungal communities. The proximity of the Yangtze and Qiantang estuaries homogenizes the surface water and sediment communities. A significant influence of ocean currents on community structure was found, which is believed to reduce proportionally the variation explained by environmental parameters at the scale of the total water masses. Dissolved oxygen and depth were identified as the major parameters structuring the fungal community. Our results indicate that passive fungal dispersal driven by ocean currents and river run‐off, in conjunction with the distinct hydrographic conditions of individual water masses, shapes the fungal community composition and distribution pattern in the ECS.     

Distribution,habitat use,and abundance of the endangered franciscana in southeastern and southern Brazil

The franciscana (Pontoporia blainvillei) is endemic to coastal waters from Brazil to Argentina. The species is regarded as one of the most threatened cetaceans in South America due to high bycatch levels. Four management units (FMAs) were defined throughout the species’ range. FMA II includes states along southeastern and southern Brazil, and represents one of the least known units. Recently, genetic analysis proposed that FMA II comprises two distinct populations and its range should be divided into FMA IIa and IIb. In December 2008 and January 2009 aerial surveys were conducted to assess the distribution and to estimate abundance of franciscanas off FMA II. A total of 54 groups were seen (average group size = 2.76, SE = 0.17) in shallow (mean depth = 7.15 m, SE = 7.08) coastal habitats (average distance from the shore = 6.48 km, SE = 6.28). Abundance corrected for perception and availability bias was estimated at 6,827 (CV = 0.26) franciscanas in FMA II, and at 1,915 (CV = 0.32) and 4,353 (CV = 0.24) franciscanas in FMA IIa and FMA IIb, respectively. This study indicates that, at least during the summer, franciscanas aggregate in shallow coastal habitats. Current estimates of incidental mortality in FMA II correspond to 4.4%–7.3% of the estimated stock size, suggesting high, likely unsustainable bycatch.     

Ecology of mysid shrimps in the Bornholm Basin (central Baltic Sea)

Mysid shrimps are an important trophic link in the food web of the Baltic Sea. In 2002 and 2003 we investigated species composition, distribution, life cycle and prey in the Bornholm Basin (central Baltic). Three species and one genus were identified: Mysis mixta, Neomysis integer, Mesopodopsis slabberi and Praunus sp. The dominant M. mixta and N. integer occurred in the whole study area but were more abundant in the peripheral, more shallow regions. Size frequency distribution indicated one generation for M. mixta and probably two for N. integer. Main prey of all size classes in both species was the cladoceran Bosmina coregoni maritima during summer and autumn. In spring and winter also copepods of the species Temora longicornis and Pseudocalanus acuspes were important prey items. Detritus and phytoplankton cells were of minor importance and many individuals had empty guts. Mysid shrimps in the deep basin might be advected from more shallow areas, as the abundance of all species was much lower than in coastal regions. The deep Bornholm Basin does not seem to be a favourable habitat, probably due to the inaccessibility of the oxygen deficient bottom layer. Under current hydrographic conditions mysids are probably not important predators of zooplankton and thus not competitors of planktivorous fish in the Bornholm Basin.     

Habitat variation,mutualism and predation shape the spatio‐temporal dynamics of tansy aphids

1. Spatially distributed resources can lead to the formation of metapopulations, where individual subpopulations are often small and can experience frequent local extinction events followed by recolonisation. An example of terrestrial metapopulations are specialised phytophagous insects on their patchily distributed host plants. 2. The present study investigated the population dynamics of a specialised aphid (Metopeurum fuscoviride) on its patchily distributed host plant (Tanacetum vulgare) and associated community of mutualistic ants and predators in a small‐scale field site. Furthermore, aphid habitat differences (plant size, C/N ratio, location and surrounding vegetation) were quantified, and seasonal timing and precipitation were considered. 3. Seasonal timing and precipitation both had effects on aphid colonisation, extinction events and aphid colony persistence. Towards the end of the season, and after higher precipitation, aphid colonisation events decreased and extinction events increased. Plant size and location as well as aphid within‐field dispersal determined the spatio‐temporal distribution of aphid colonies. 4. Mutualistic ants (Lasius niger and Myrmica rubra) increased the chance of establishment of aphid colonies. However, when M. rubra was tending, aphid colony persistence was reduced. Aphid persistence and extinction were dependent on aphid abundance, as a higher colony size reduced the probability of extinction by predation. 5. The results emphasise the importance of dispersal limitation, population growth and the presence of mutualists when studying the spatio‐temporal dynamics of tansy aphids, particularly in a small‐scale field site.     

Use of the coastal areas adjacent to the Douro estuary as a nursery area for pouting, Trisopterus luscus Linnaeus, 1758

In the present study, the nursery role of the coastal areas adjacent to the Douro estuary for pouting, Trisopterus luscus Linnaeus, 1758, was analysed. The distribution and abundance patterns, diet and growth of T. luscus were studied based on samples collected on seven occasions from November 2000 to March 2002 using a 12 m otter‐trawl with 18 mm mesh size at 12 sites within the estuary and six sites in the adjacent coastal areas. This species occurred only in the coastal areas adjacent to the estuary and a marked seasonal pattern was reported, which reflected the peak abundance of juveniles that use this area as a nursery ground. No marked relationships were obtained between T. luscus abundance and the environmental variables considered. Nonetheless, the highest densities of pouting were recorded at sites where water temperature was high compared with the other sampling areas. Diet of T. luscus juveniles was mainly composed of crustaceans Decapoda, Mysidacea and Amphipoda. The growth rate determined for T. luscus juveniles off the Portuguese coast was higher than those reported for North European areas, and was similar to those obtained in the eastern Mediterranean.     

Soil Microbial Communities Associated with Douglas-fir and Red Alder Stands at High- and Low-Productivity Forest Sites in Oregon, USA

Communities of archaea, bacteria, and fungi were examined in forest soils located in the Oregon Coast Range and the inland Cascade Mountains. Soils from replicated plots of Douglas-fir (Pseudotsuga menziesii) and red alder (Alnus rubra) were characterized using fungal ITS (internal transcribed spacer region), eubacterial 16S rRNA, and archaeal 16S rRNA primers. Population size was measured with quantitative (Q)-PCR and composition was examined using length heterogeneity (LH)-PCR for fungal composition, terminal restriction fragment length (T-RFLP) profiles for bacterial and archaeal composition, and sequencing to identify dominant community members. Whereas fungal and archaeal composition varied between sites and dominant tree species, bacterial communities only varied between sites. The abundance of archaeal gene copy numbers was found to be greater in coastal compared to montane soils accounting for 11% of the prokaryotic community. Crenarchaea groups 1.1a-associated, 1.1b, 1.1c, and 1.1c-associated were putatively identified. A greater abundance of Crenarchaea 1.1b indicator fragments was found in acidic (pH 4) soils with low C:N ratios under red alder. In coastal soils, 25% of fungal sequences were putatively identified as basidiomycetous yeasts belonging to the genus Cryptococcus. Although the function of these yeasts in soil is not known, they could significantly contribute to decomposition processes in coastal soils distinguished by rapid tree growth, high N content, low pH, and frequent water-saturation events.     

Ant species distribution in a sandy coastal plain

Abstract.

• 1 Three species of ants, Lasius niger, Myrmica rubra and Myrmica scabrinodis, have been recorded in a 20-year-old coastal plain on the Dutch Wadden Zee island, Schiermonnikoog.
• 2 The habitats of these species appeared to be clearly segregated, both horizontally (different parts of the plain) and vertically (along dune slope gradients in the plain).
• 3 Lasius niger is distributed throughout the plain in sparsely vegetated sand-dunes and in mounds covered with turf of Festuca rubra ssp. litoralis, but always in areas that are only waterlogged or inundated in winter.
• 4 Myrmica rubra is limited to Festuca-turf, occurring in a distinct zone along the bases of small dunes and on isolated mounds.
• 5 Myrmica scabrinodis only occurs in mounds covered with Festuca-tutf and rarely in the small dunes.
• 6 Analysis of soil, vegetation, inundation and salinity of the ground-water demonstrated that Myrmica scabrinodis is dominant in areas with more silt and salt in the soil, characterized by a vegetation with more typical halophytes, whereas Myrmica rubra occurs most frequently in sandy habitats without much salt stress. The populations of both Myrmica species and Lasius niger do not seem to be affected by inundation during winter.
• 7 The distribution of the ant species is discussed in relation to data about ants in more stable habitats. In particular, attention is given to the absence, in this coastal plain, of Lasius flavus which is a dominant species in the sand-dunes and neighbouring parts of the salt-marsh on Schiermonnikoog.

     

Mussel and dogwhelk distribution along the north‐west Atlantic coast: testing predictions derived from the abundant‐centre model

Aim We performed the first test of predictions from the abundant‐centre model using north‐west Atlantic coastal organisms. We tested the hypotheses that the density of intertidal mussels (Mytilus edulis and M. trossulus) and dogwhelks (Nucella lapillus) and mussel age and size would peak at an intermediate location along their distribution range. We also assessed the latitudinal variation in critical aerial exposure time. Location North‐west Atlantic coast between Newfoundland (Canada) and New York (USA), covering 1800 km of shoreline. Methods Using a nested design, we measured mussel density, age and size and dogwhelk density in 60 wave‐exposed rocky intertidal sites spread evenly in six regions. Critical aerial exposure times were determined using online data. Results Mytilus edulis peaked in abundance in Maine and was much less abundant in the other regions. Mytilus trossulus peaked in abundance in southern Nova Scotia and Maine, was less abundant in the other regions to the north, and was absent in the southernmost region (New York). Both mussel species were least abundant in a northern region (Cape Breton), although not in the northernmost region (Newfoundland). Critical aerial exposure times were negatively correlated with overall mussel density. Mussel age and size were similar among regions. Dogwhelks peaked in abundance in Maine and were much less abundant in the other regions, being positively correlated with overall mussel density across regions. Main conclusions Density data for M. edulis and N. lapillus provide limited support for an abundant‐centre pattern, while M. trossulus shows a clear ramped‐south distribution. Critical aerial exposure times suggest that physiological stress during summer and winter low tides may be lowest in Maine and southern Nova Scotia, which might partially explain mussel predominance in those regions. Winter ice scour in Cape Breton may explain the abundance trough observed there. Mussel size and age may be more limited by wave exposure at our sites (as they all face open waters) than by regional differences in environmental stress. Dogwhelks, which prey on mussels, seem to respond positively to prey density at the regional scale. Our study supports the notion that, while the abundant‐centre model is a useful starting point for research, it often represents an oversimplification of reality.