The introduction of Pacific oysters to the sedimentary south-eastern North Sea coast and their establishment on intertidal native blue mussel beds has caused the development of mixed reefs of mussels and oysters with extensive tidepools. Tidepools have been intensively studied at rocky shores where they show community structures, which usually differ from that of the surrounding emerging substrates. Tidepools at sedimentary coasts, however, have received less attention. We compared the community structure and species interactions inside and outside tidepools in oyster reefs by determining densities of snails, barnacles and amphipods. Snail densities were similar in and outside tidepools. Barnacle coverage on bivalve shells, however, was lower inside tidepools, which may be caused by higher predation pressure and increased snail grazing under permanently submerged conditions, as was revealed by field and laboratory experiments. Additionally, we studied the occurrence of copepod and trematode parasites in blue mussels inside and outside tidepools. Prevalence and intensity of parasitic copepods was higher in mussels inside tidepools. Trematode parasites, by contrast, showed a lower intensity in mussels inside tidepools. This can be explained by high amphipod densities found inside tidepools because trematode larvae represent a food source of amphipods. Our study suggests that the community structure of oyster reefs within tidepools is not a submerged equivalent to that of intertidal reefs. As their counterparts at rocky shores, they show their own species distribution patterns with particular species interactions and only provide refuge for specific species such as parasitic copepods.

Species interactions are often context-dependent, where outcomes require an understanding of influences among multiple biotic and abiotic factors. However, it remains unclear how abiotic factors such as temperature combine with important biotic factors such as density-dependent food limitation and predation to influence species interactions. Using a native grassland – grasshopper – wolf spider model food chain in tallgrass prairie, we conducted a manipulative field experiment to examine how predator–prey interactions respond to manipulations of temperature, grasshopper density, and food chain length. We find that grasshopper performance responses to temperature and predator treatments were density dependent. At high densities, grasshopper survival decreased with increased temperature when no spiders were present. When spiders were present, grasshopper survival was reduced, and this effect was strongest in the cooled treatment. In contrast, grasshopper survival did not vary significantly with spider presence or among temperature treatments at low grasshopper densities. Our results indicate that context-dependent species interactions are common and highlight the importance of understanding how and when key biotic and abiotic factors combine to influence species interactions.

Introduction of species is a major driver of global change and loss of biodiversity in ecosystems. The Mediterranean Sea is the most heavily invaded region in the world by introduced seaweeds. The fan mussel Pinna nobilis is the largest Mediterranean bivalve, and a protected species, present at depths from 0.5 m to 60 m. In Cabrera National Park marine protected area (MPA) (Balearic Islands, north-western Mediterranean) the population of P. nobilis is affected by the invasive seaweeds Lophocladia lallemandii and Caulerpa racemosa; however the extent of this colonization on the bivalve is unknown. Therefore, the main aims of the present study were to: (1) determine the extent of invasion of L. lallemandii and C. racemosa on the P. nobilis population; and (2) test if this invasion showed differences with depth. This is the first study assessing invasion by seaweeds on a large bivalve in a high density P. nobilis population. Pinna nobilis was distributed in all seagrass meadows surveyed within the MPA; we found a total of 872 live P. nobilis individuals, 449 and 423 of which were found at 10 and 20 m depth, respectively. High cover of L. lallemandii and low presence of C. racemosa were detected in the P. nobilis population, being quantified in 49.37% and 1.38% of the population of P. nobilis, respectively. Bathymetric differences on Lophocladia epizoism over P. nobilis has been recorded in this study; with increasing values of L. lallemandii cover index, biomass and volume at deeper depths. Pinna nobilis could be a preferential substratum for L. lallemandii in Posidonia oceanica meadows in deeper waters, acting as a stepping-stone for invasive seaweeds and facilitating the invasion throughout seagrass meadows.

Detailed molecular data of Artemia (Crustacea, Anostraca) from South Africa are scarce. Here, we provide for the first time genetic data on the species status and phylogeography of Artemia from this region after an extensive sampling expedition. Our 16S rRNA RFLP analysis of 27 Artemia populations, including seven from South African sites, provides evidence for the presence of a mixed bisexual and parthenogenetic component in this area. Phylogenetic and network analyses reveal that three (out of seven) Artemia populations from South Africa belong to the invasive A. franciscana, two of them belong to A. salina while the last two contain both parthenogenetic and bisexual (A. salina) individuals. From a total of 18 haplotypes identified, seven were recorded from South Africa. To our knowledge, this is the first confirmed report of A. franciscana in this region. Its invasiveness is reaffirmed by evidence for the complete replacement of the native A. salina population from Velddrif Saltworks. However, in other cases, parthenogens seem to modify the capacity of A. franciscana to replace natives. Results on the genetic identification of South African Artemia provide insights into the dynamics of invasion and co-occurrence and highlight effects on species interactions and on biodiversity in inland aquatic invertebrates.

Stratford Shoal is a topographic high dividing the west and central basins of Long Island Sound (north-west Atlantic). The southern end of the shoal has a linear, north–south-tending boulder reef along the crest. Repeated observations of the reef using remote and diver-held cameras from 1991 to 2010 found an apparently stable epibenthic community dominated by Haliclona oculata (branching sponge), Astrangia poculata (northern star coral), Mytilus edulis (blue mussel) and erect bryozoa. In 2012, when the boulder reef area was imaged as part of a benthic habitat mapping project, A. poculata was still abundant, but no H. oculata was found. A number of mechanisms (e.g. species interactions, disease, recruitment failure, thermal stress, sediment loading, freshwater input and physical disturbance) may have contributed, individually or synergistically, to the community shift. However, because of the ad hoc and aperiodic nature of the observations, drivers of the shift are indeterminate. As a result, whether the observed changes reflect a short-term disturbance or a long-term community state remains unclear, as do the effects of changes in the identity of the dominant species.

Lichens are a fascinating example of a symbiotic mutualism. It is still uncertain which processes guide fungal-photobiont interactions, and whether they are random or of a more complex nature. Here, the fungal-algal interactions in Ramalina menziesii and co-occurring taxa are analyzed by using DNA sequences of the algal Internal Transcribed Spacer region (ITS), to investigate fungal-algal associations in juvenile R. menziesii and allied species. Algal species were identified by a combination of BLAST searches, median-joining network analysis, and Bayesian phylogenetics. Fungal-algal networks were analyzed for nestedness, both at the species and haplotype level (fungal species vs. algal haplotypes), and the networks were inspected for evidence of compartmentalization. Bayesian phylogenetic trees indicated that the widespread green alga Trebouxia decolorans associated with R. menziesii, as well as six other fungal species. Four additional fungal species interacted with four different species of Trebouxia. Only in one out of ten samples were algal haplotypes shared with the nearest neighbours of juvenile R. menziesii. Fungal-algal species interactions were compartmentalized, while at the level of algal haplotypes, nestedness was found. This pattern is similar to the compartmentalization found in other intimately interacting mutualists.

Patterns of infection among hosts in a population are often driven by intrinsic host features such as age or sex, as well as by positive or negative interactions between parasite species. We investigated helminth parasitism in 2 South American rodent species, Ctenomys australis and C. talarum (Octodontidae), to determine whether the unusual solitary and subterranean nature of these hosts would impact their patterns of infection. We applied generalized linear models to infection data on a total of 7 helminth species (1 in C. australis and 6 in C. talarum). Host age and season of capture influenced infection levels in some of the helminth species, but none were influenced by host body condition. In C. talarum, 4 pairs of helminth species showed significant associations, either asymmetrical or symmetrical, and with 3 of the 4 being positive; strong inter-specific facilitation appears likely in 1 case. Also, we found that female hosts, especially non-pregnant ones, harboured heavier infections of 2 nematode species than male hosts. This is in sharp contrast to the general male-bias reported for most studies of nematodes in wild mammals, and we develop explanations for these results based on the unusual ecology of these subterranean rodents.

This study focuses on the synchronous blooms of the coccolithophore Emiliania huxleyi and three dinoflagellates Prorocentrum micans, Ceratium furca var. furca and Ceratium fusus var. seta observed between 7 June and 11 July 2003 in the Dardanelles. An analysis of the vertical distribution of the E. huxleyi population size with respect to various environmental parameters was discussed. Additionally, inorganic nutrients and phytoplankton interactions were investigated in relation to the bloom conditions and hydrography of the Dardanelles. The algal bloom started in nearby Izmit Bay (eastern end of the Sea of Marmara) in early June, then quickly spread through the Sea of Marmara and continued until mid-July. Thermal stratification was observed between different water masses at the time of sampling. During the bloom period, cell density of E. huxleyi ranged from 3.58 × 107 to 2.55 × 108 cells l−1 in the superficial layer. Prorocentrum micans was the second most-abundant species and the cell numbers ranged from 1.0 × 106 cells l−1 to 3.3 × 106 cells l−1. Other abundant species in this area included C. furca var. furca and C. fusus var. seta.

We describe a laboratory model using Eimeria falciformis and E. pragensis to investigate some of the interactions in double-species infections of Eimeria. Mice were given trickle infections by oral inoculation of 100 sporulated oocysts of one species at 3 or 4 day intervals throughout the experiments and, once immunity had developed, as indicated by cessation of oocyst production, the animals were challenged with a single inoculation of the other species. A trickle infection of E. falciformis gave a significant enhancement of oocyst output from E. pragensis infection as compared with animals that had not received E. falciformis. Histological examination of the mice infected with E. pragensis showed significantly more asexual parasites and a significantly higher female/male ratio in the mice that had received trickle E. falciformis infections than in those that had not. There was no evidence to suggest that extra asexual generations were occurring in these mice. In the converse experimental protocol, trickle E. pragensis infections had no significant effect on a single E. falciformis infection. We discuss the possible mechanisms for the interactions and also how these interactions may influence multiple species infections in animals in their natural habitats.