Species richness and interacting factors control invasibility of a marine community.

Anthropogenic vectors have moved marine species around the world leading to increased invasions and expanded species' ranges. The biotic resistance hypothesis of Elton (in The ecology of invasions by animals and plants, 1958) predicts that more diverse communities should have greater resistance to invasions, but experiments have been equivocal. We hypothesized that species richness interacts with other factors to determine experimental outcomes. We manipulated species richness, species composition (native and introduced) and availability of bare space in invertebrate assemblages in a marina in Monterey, CA. Increased species richness significantly interacted with both initial cover of native species and of all organisms to collectively decrease recruitment. Although native species decreased recruitment, introduced species had a similar effect, and we concluded that biotic resistance is conferred by total species richness. We suggest that contradictory conclusions in previous studies about the role of diversity in regulating invasions reflect uncontrolled variables in those experiments that modified the effect of species richness. Our results suggest that patches of low diversity and abundance may facilitate invasions, and that such patches, once colonized by non-indigenous species, can resist both native and non-indigenous species recruitment.

Breaking up and getting together: evolution of symbiosis and cloning by fission in sea anemones (Genus Anthopleura).

Clonal growth and symbiosis with photosynthetic zooxanthellae typify many genera of marine organisms, suggesting that these traits are usually conserved. However, some, such as Anthopleura, a genus of sea anemones, contain members lacking one or both of these traits. The evolutionary origins of these traits in 13 species of Anthopleura were inferred from a molecular phylogeny derived from 395 bp of the mitochondrial 16S rRNA gene and 410 bp of the mitochondrial cytochrome oxidase subunit III gene. Sequences from these genes were combined and analyzed by maximum-parsimony, maximum-likelihood, and neighbor-joining methods. Best trees from each method indicated a minimum of four changes in growth mode and that symbiosis with zooxanthellae has arisen independently in eastern and western Pacific species. Alternative trees in which species sharing growth modes or the symbiotic condition were constrained to be monophyletic were significantly worse than best trees. Although clade composition was mostly consistent with geographic sympatry, A. artemisia from California was included in the western Pacific clade. Likewise, A. midori from Japan was not placed in a clade containing only other Asian congeners. The history of Anthopleura includes repeated shifts between clonality and solitariness, repeated attainment of symbiosis with zooxanthellae, and intercontinental dispersal.

Cryptic invasions of the crab Carcinus detected by molecular phylogeography.

Coastal marine ecosystems world-wide are threatened by invasions of nonindigenous species. The ubiquity of marine sibling species identifiable only by genetic analysis suggests that many invasions are cryptic and therefore undetected, causing an underestimation of the actual number and impacts of invading species. We test this hypothesis with European crabs in the genus Carcinus that have invaded five regions globally. Partial 16S ribosomal RNA gene sequences confirm sibling species status of morphologically similar Atlantic C. maenas and Mediterranean C. aestuarii. Based on 16S rRNA haplotypes, crabs from California, New England and Tasmania were all C. maenas. However, we report the cryptic multiple invasion of both species in Japan and South Africa, where only C. aestuarii and C. maenas, respectively, were previously recognized.

Zoogeographic Distributions of the Sibling Species Mytilus galloprovincialis and M. trossulus (Bivalvia: Mytilidae) and Their Hybrids in the North Pacific.

Diagnostic length differences in a PCR amplified fragment of the gene for byssal adhesive protein were used to study the zoogeographic distribution of Mytilus galloprovincialis and M. trossulus along the west coast of North America and in Japan. The distributions of M. galloprovincialis and M. trossulus are patchy, although an overall geographic pattern emerges. M. galloprovincialis was the only species found on either Kyushu or Honshu, and it was the most abundant mussel from Tomales Bay to San Diego, California. M. trossulus was the only bay mussel found on Hokkaido and in Alaska, and it was by far the most abundant mussel along the coasts of Washington and Oregon. Mytilus galloprovincialis and M. trossulus are sympatric and hybridize near Whidbey Island, Washington, in San Francisco Bay, and in San Diego Bay. A second diagnostic anonymous nuclear PCR marker was used to examine the extent of hybridization at Palo Alto, California. At this site, genotypes appeared to be a mixture of M. galloprovincialis, F1 hybrids between M. galloprovincialis and M. trossulus, and backcrosses between the F1's and M. galloprovincialis. The discontinuity between the zoogeographic distributions of these two species at about 40{deg}-41{deg}N latitude in both the eastern and western Pacific suggests that temperature is a factor in determining their present distribution and limiting their dispersal to other regions.

Ecological roulette: the global transport of nonindigenous marine organisms.

Ocean-going ships carry, as ballast, seawater that is taken on in port and released at subsequent ports of call. Plankton samples from Japanese ballast water released in Oregon contained 367 taxa. Most taxa with a planktonic phase in their life cycle were found in ballast water, as were all major marine habitat and trophic groups. Transport of entire coastal planktonic assemblages across oceanic barriers to similar habitats renders bays, estuaries, and inland waters among the most threatened ecosystems in the world. Presence of taxonomically difficult or inconspicuous taxa in these samples suggests that ballast water invasions are already pervasive.

Interspecific and intrapopulation variation in mitochondrial ribosomal DNA sequences of Mytilus spp. (Bivalvia: Mollusca).

A 560-base pair portion of the mitochondrial 16S ribosomal DNA (16S rDNA) from three morphologically similar mussels, Mytilus edulis, M. galloprovincialis, and M. trossulus, was amplified with the polymerase chain reaction, and 349 base pairs were sequenced. These data showed that this gene in M. edulis and M. galloprovincialis has not diverged; however, the north Pacific mussel, M. trossulus, showed fixed differences from M. edulis and M. galloprovincialis at 5 nucleotide positions. Furthermore, the population of M. trossulus at Tillamook Bay, Oregon, was found to contain two very divergent 16S rDNA genotypes that differ at 37 nucleotide positions. Thus, intraspecific variation in this gene in M. trossulus is greater than that seen interspecifically in M. edulis and M. galloprovincialis. Despite this large difference, in the absence of evidence of genetic isolation between these groups of M. trossulus, no taxonomic changes are proposed. These data are consistent with a north Pacific origin of the genus with subsequent dispersal to the Atlantic Ocean across the Artic Sea, giving rise to M. edulis in northern Europe and subsequently M. galloprovincialis in southern Europe and the Mediterranean Sea.

Aphasia in multiple sclerosis.

In a 17-year-old woman, motor aphasia developed during her second bout of multiple sclerosis, characterized by absent spontaneous speech, paraphasias in naming and repetition, and marked orofacial apraxia, with relative preservation of written language and intact auditory comprehension. A mild right hemiparesis was associated. Bilateral cerebral lesions were demonstrated on a computerized tomographic brain scan. The aphasia remitted over 1 month.