In spite of being one of the most relevant components of the biosphere, the plankton-benthos network is still poorly studied as such. This is partly due to the irregular occurrence of driving phenomena such as gelatinous plankton pulses in this realm. Gelatinous plankters rely on their life cycles and histories to exploit temporarily abundant resources with an undeniable, but often overlooked, impact on marine food webs. Dramatic increases of gelatinous filter-feeders and/or carnivores (both native and nonindigenous species) are frequently observed, and explanations of these blooms alternatively invoke ecosystem variability, climate change, unspecified anthropogenic perturbation or removal of top predators from trophic networks. Gelatinous plankters, however, are not anomalies in plankton dynamics: the recognition of the ecological importance of their pulses, based on their life cycle patterns (often involving benthic stages), is a critical breakthrough to understand the cycling diversity of plankton in space and time. The current study focuses on the many neglected aspects of the ecology and biology of gelatinous zooplankton, describes how life cycle patterns are central in marine ecology, as are the pulses of gelatinous organisms, and highlights how such a dramatic lack of knowledge can affect our understanding of the marine ecosystem as a whole.

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Hydroidolina is a group of hydrozoans that includes Anthoathecata, Leptothecata and Siphonophorae. Previous phylogenetic analyses show strong support for Hydroidolina monophyly, but the relationships between and within its subgroups remain uncertain. In an effort to further clarify hydroidolinan relationships, we performed phylogenetic analyses on 97 hydroidolinan taxa, using DNA sequences from partial mitochondrial 16S rDNA, nearly complete nuclear 18S rDNA and nearly complete nuclear 28S rDNA. Our findings are consistent with previous analyses that support monophyly of Siphonophorae and Leptothecata and do not support monophyly of Anthoathecata nor its component subgroups, Filifera and Capitata. Instead, within Anthoathecata, we find support for four separate filiferan clades and two separate capitate clades (Aplanulata and Capitata sensu stricto). Our data however, lack any substantive support for discerning relationships between these eight distinct hydroidolinan clades.

Invasions mediated by humans have been reported from around the world, and ships' ballast water has been recognized as the main source of marine invaders worldwide. Some invasions have dramatic economic and ecological consequences. On the other hand, many invasions especially in the marine realm, can go unnoticed. Here we identify a human mediated, worldwide introduction of the hydrozoan species Turritopsis dohrnii. The normal life cycle of hydrozoans involves the asexual budding of medusae from colonial polyps. Medusae of Turritopsis, however, when starved or damaged, are able to revert their life cycle, going back to the polyp stage through a process called transdifferentiation. They can thus easily survive through long journeys in cargo ships and ballast waters. We have identified a clade of the mitochondrial 16S gene in Turritopsis which contains individuals collected from Japan, the Pacific and Atlantic coasts of Panama, Florida, Spain, and Italy differing from each other in only an average of 0.31% of their base-pairs. Fifteen individuals from Japan, Atlantic Panama, Spain, and Italy shared the same haplotype. Turritopsis dohrnii medusae, despite the lack of genetic differences, are morphologically different between the tropical and temperate locations we sampled, attesting to a process of phenotypic response to local conditions that contributes to making this grand scale invasion a silent one.

The Hydractiniidae are a family of globally distributed marine hydrozoans (class Hydrozoa, phylum Cnidaria). Despite being one of the most well‐studied families of the Hydrozoa, their genus and species‐level taxonomy is unsettled and disputed. The taxonomic difficulties of the Hydractiniidae are due to many inadequate species descriptions, a paucity of available morphological characters, many cryptic species, and the often‐extreme plasticity seen when colonies of the same species are found at different stages of growth or different environmental conditions. This confusion over species identity is especially important because some species of the family Hydractiniidae are well‐established model organisms for a wide array of studies ranging from gene expression to developmental biology and colony growth. Here we report the species‐level implications of 226 mitochondrial large ribosomal subunit (16S) rDNA sequences from around the world and 52 nuclear DNA sequences (Elongation Factor 1α) with the intent to reconcile described morphospecies with genealogical lineages. Our data show that Podocoryna carnea and P. exigua are distinct and geographically disjunct species, P. borealis is paraphyletic with respect to Podocoryna sp. from South Africa and P. bella from New Zealand. Podocoryna australis, from New Zealand form a distinct monophyletic group. Podocoryna from New England, New York and Florida all fall into a distinct monophyletic group (P. americana) and fail to support the existence of a distinct, P. selena in the Gulf of Mexico. Hydractinia pruvoti is the only species within the Podocoryna clade without fully formed medusae. We identify a Clava clade closely related to other algae dwelling Hydractiniidae. Our data do not recover Stylactaria inabai from Japan as a distinct species from S. misakiensis, and S. carcinicola as distinct from H. epiconcha. Also, 10 colonies identified as S. carcinicola fall into a distantly related clade that is close to the American S. hooperi. Finally, we identify Janaria mirabilis as the sister group to the H. echinata species complex and clarify the relationships between the H. echinata, H. symbiopollicaris, H. polyclina, H. symbiolongicarpus and H. [GM].

At least six morphospecies of vestimentiferan tubeworms are associated with cold seeps in the Gulf of Mexico (GOM). The physiology and ecology of the two best-studied species from depths above 1000 m in the upper Louisiana slope (Lamellibrachia luymesi and Seepiophila jonesi) are relatively well understood. The biology of one rare species from the upper slope (escarpiid sp. nov.) and three morphospecies found at greater depths in the GOM (Lamellibrachia sp. 1, L. sp. 2, and Escarpia laminata) are not as well understood. Here we address species distributions and boundaries of cold-seep tubeworms using phylogenetic hypotheses based on two mitochondrial genes. Fragments of the mitochondrial large ribosomal subunit rDNA (16S) and cytochrome oxidase subunit I (COI) genes were sequenced for 167 vestimentiferans collected from the GOM and analyzed in the context of other seep vestimentiferans for which sequence data were available. The analysis supported five monophyletic clades of vestimentiferans in the GOM. Intra-clade variation in both genes was very low, and there was no apparent correlation between the within-clade diversity and collection depth or location. Two of the morphospecies of Lamellibrachia from different depths in the GOM could not be distinguished by either mitochondrial gene. Similarly, E. laminata could not be distinguished from other described species of Escarpia from either the west coast of Africa or the eastern Pacific using COI. We suggest that the mitochondrial COI and 16S genes have little utility as barcoding markers for seep vestimentiferan tubeworms.

Speciation remains one of the most controversial and least understood topics in evolution. About 75% of the earth's surface is covered by oceans. However, most of what we currently know about speciation is strongly biased toward terrestrial and freshwater organisms. Here, we discuss some of the major advances of the past two decades in our understanding of speciation in the sea and outline promising future directions that were gathered during the 2011 SICB Symposium "Speciation in the Sea."

Medusae of Turritopsis dohrnii undergo reverse development in response to physical damage, adverse environmental conditions, or aging. Senescent, weakened or damaged medusae transform into a cluster of poorly differentiated cells (known as the cyst stage), which metamorphose back into a preceding life cycle stage, the polyp. During the metamorphosis, cell transdifferentiation occurs. The cyst represents the intermediate stage between a reverting medusa and a healthy polyp, during which cell transdifferentiation and tissue reorganization take place. Here we characterize and compare the transcriptomes of the polyp and newborn medusa stages of T. dohrnii with that of the cyst, to identify biological networks potentially involved in the reverse development and transdifferentiation processes. The polyp, medusa and cyst of T. dohrnii were sequenced through Illumina RNA-sequencing and assembled using a de novo approach, resulting in 92,569, 74,639 and 86,373 contigs, respectively. The transcriptomes were annotated and comparative analyses among the stages identified biological networks that were significantly over-and under-expressed in the cyst as compared to the polyp and medusa stages. Biological processes that occur at the cyst stage such as telomerase activity, regulation of transposable elements and DNA repair systems, and suppression of cell signaling pathways, mitotic cell division and cellular differentiation and development may be involved in T. dohrnii’s reverse development and transdifferentiation. Our results are the first attempt to understand T. dohrnii’s life-cycle reversal at the genetic level, and indicate possible avenues of future research on developmental strategies, cell transdifferentiation, and aging using T. dohrnii as a non-traditional in vivo system.