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Appendicularians, pelagic tunicates that are common in world oceans, periodically produce new mucus houses and discard old ones. Discarded houses form macroscopic aggregates that constitute sites of biological activity in the water column and also contribute to the transport of organic matter to deeper water. In this study, we measured the house renewal rates of 10 appendicularian species cultivated in 30 µm-mesh-screened seawater at 17 to 29°C. In addition, the carbon content of the tunicates (C B ), their newly secreted houses (C NH ) and their discarded houses (C DH ) were concurrently examined for some of the oikopleurid species. , and that the first 3 species could discard houses corresponding to 380, 708 and 174% of their biomass d -1 , respectively. The individual lifetime production of C NH and C DH for all 3 species was estimated to be 1.1 to 3.6 and 2.7 to 12 times greater than the C B of mature individuals. This high houseproductivity, combined with large population sizes, indicates that appendicularians are major producers of macroscopic aggregates in marine ecosystems. KEY WORDS: Appendicularians · House · House renewal rate · Carbon content · Macroscopic aggregatesResale or republication not permitted without written consent of the publisher

The phyllosoma, a larva of spiny and slipper lobsters, has an exceptionally flat body and long appendages. It is known to associate with several species of cnidarian jellyfish, a behavior that is not rare in crustaceans. Indeed, phyllosomas clinging onto jellyfish have been observed both in the laboratory and in the natural environment. Wild phyllosomas have been found to contain jellyfish tissues in their hepatopancreas and feces, suggesting that the larvae utilize jellyfish as a food source; however, how they capture jellyfish and what species of jellyfish they prefer have rarely been investigated. The few previous studies conducted have suggested that phyllosomas have a high specificity for jellyfish (preying on only a few species); in contrast, the results of our study indicate that specificity is low. We show that phyllosomas prey on a variety of jellyfish species including deadly stinging types, on a variety of jellyfish developmental stages, and on various parts of the jellyfish body. When making contact with a jellyfish, phyllosomas first cling onto its exumbrella, feed on its tentacles or oral arms, and then consume the exumbrella. Phyllosomas may be capable of defending themselves against any types of nematocyst sting, and it is likely that they have evolved to utilize venomous jellyfish as a food in the open sea, where food may be scarce.

To test the validity of intron-exon structure as a phylogenetic marker, the intron-exon structure of EF-1alpha genes was investigated for starfish, acornworms, ascidians, larvaceans, and amphioxus and compared with that of vertebrates. Of the 11 distinct intron insertion sites found within the coding regions of the deuterostome EF-1alpha genes, 7 are shared by several taxa, while the remainder are unique to certain taxa. Examination of the shared introns of the deuterostome EF-1alpha gene revealed that independent intron loss or intron insertion must have occurred in separate lineages of the deuterostome taxa. Maximum parsimony analysis of the intron-exon data matrix recovered five parsimonious trees (consistency index = 0.867). From this result, we concluded that the intron-exon structure of deuterostome EF-1alpha has evolved more dynamically than previously thought, rendering it unsuitable as a phylogenetic marker. We also reconstructed an evolutionary history of intron insertion-deletion events on the deuterostome phylogeny, based on several molecular phylogenetic studies. These analyses revealed that the deuterostome EF-1alpha gene has lost individual introns more frequently than all introns simultaneously.

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Liu, H., Dagg, J. M., Napp, J. M., and Sato, R. 2008. Mesozooplankton grazing in the coastal Gulf of Alaska: Neocalanus spp. vs. other mesozooplankton. – ICES Journal of Marine Science, 65: 351–360. Three species of large calanoid copepod, Neocalanus flemingeri, Neocalanus plumchrus, and Neocalanus cristatus, dominate the spring biomass of mesozooplankton in the Subarctic Pacific. We compared the grazing impact of Neocalanus species on phytoplankton with grazing by the remainder of the mesozooplankton community in the coastal and shelf waters of the Gulf of Alaska during spring and summer 2003. Neocalanus spp. and other mesozooplankton fed mainly on particles >20 µm, and phytoplankton in the smaller size-fractions (<20 µm) increased in the presence of mesozooplankton, possibly because of a trophic cascade resulting from mesozooplankton consumption of microzooplankton. Neocalanus spp. accounted for most of the mesozooplankton biomass and herbivory in the shelf water of the Gulf of Alaska and in the Prince William Sound (PWS) during April/May. The biomass of other mesozooplankton (mostly small copepods) varied seasonally and spatially; it did not increase in summer after the descent of Neocalanus spp. from the surface layer. On the basis of the clearance rates obtained from our experiments, in spring, grazing by Neocalanus spp. and the remaining mesozooplankton consumed ∼10% of daily growth of phytoplankton >20 µm in the outer-shelf region, where chlorophyll a concentrations were <0.5 mg m−3, and in PWS. Mesozooplankton consumed a smaller percentage of the >20 µm daily phytoplankton production in the inner- and mid-shelf regions where chlorophyll a concentrations were typically >5 mg m−3 with blooms of large diatoms. In summer, without Neocalanus spp. in the surface layer, mesozooplankton grazing accounted for a very small proportion of phytoplankton production across the whole shelf.