Differences in morphology and habitat use among the native mussel <Emphasis Type="Italic">Mytilus trossulus</Emphasis>, the non-native <Emphasis Type="Italic">M. galloprovincialis,</Emphasis> and their hybrids in Puget Sound,Washington

Mytilus galloprovincialis (Mg), the Mediterranean blue mussel, is sympatric with the native M. trossulus (Mt) throughout much of the north Pacific, likely as the result of human introduction. We investigated the distribution of the two species and their hybrids (Mgt) in Puget Sound, Washington, to determine whether differences occur in habitat preference between the two species and hybrids. In addition, we investigated whether there were consistent size and shape differences between the native and introduced mussels and hybrids. Measurements of over 6,000 mussels from 30 sites, of which 1,460 were genotyped for a species-specific genetic marker, revealed that Mg and Mgt can be found throughout Puget Sound. Mg and Mgt were larger and exhibited a greater height:length ratio than Mt. Frequencies of Mg and Mgt were higher in subtidal habitats, such as docks, than on intertidal rocks, walls or pilings. Within intertidal habitats, Mg and Mgt were more frequent than Mt in the lower reaches of the intertidal. At slightly more than half the sites the frequency of the three genotypes accorded with random mating expectations suggesting no consistent barriers to gene flow between species. The standardized random sampling methods and simple morphometric identification techniques described here can be used to test whether the frequency of invasive mussels changes over time and space in Puget Sound.     

Feeding behavior of adult <Emphasis Type="Italic">Vinciguerria nimbaria</Emphasis> (Phosichthyidae), in the tropical Atlantic (0°–4°N, 15°W)

Adult Vinciguerria nimbaria are the main prey of tuna during the tuna fishing season (late autumn and winter) in the equatorial Atlantic (0–4°N, and ~15°W). V. nimbaria trophic behavior in the fishing grounds was studied in relation to hydrobiological factors to determine its role in the trophic food web. Sampling stations spaced by 20 nautical miles were set up along a 15°W north–south transect from 4°N to 0°40S. At each station, the temperature and vertical fluorescence profiles were recorded. Nitrate and chlorophyll a analyses were performed on water sampled at different levels in the euphotic zone. Vertical plankton hauls were carried out at depths of 0–100 and 0–200 m using a standard WP2 net fitted with a 200-μm mesh gauze. Vinciguerria nimbaria adults were collected using a young-fish mid-water trawl net (10 × 15 m opening mouth, 10 mm cod end mesh). The weight of the stomach contents, the stomach fullness index, the number of prey, the frequency of occurrence and the prey preponderance were recorded for 20 fish from each haul. An oligotrophic typical tropical structure (TTS) was found between 1° and 4°N where small zooplankton was relatively abundant above or near the thermocline. In the TTS, V. nimbaria behaved as an epipelagic fish, feeding on the dominant small prey during the daytime. In turn, it was a prey for tuna. In the equatorial zone, where zooplankton was more abundant than in the north equatorial zone, V. nimbaria behaved as a mesopelagic fish and as an opportunistic mesozooplankton feeder. It consumed a wide range of sizes of food, feeding on the most abundant species of zooplankton as well as the largest zooplankton species, possibly while migrating towards the surface in the late afternoon or in the deep layer.     

Morphological and molecular data suggest a cosmopolitan distribution of the polychaete <Emphasis Type="Italic">Proscoloplos cygnochaetus</Emphasis> Day, 1954 (Annelida,Orbiniidae)

The discovery of a possibly invasive Proscoloplos species on the French Atlantic coast led to a detailed morphological and molecular investigation. Proscoloplos consists of three nominal species, but molecular analyses of the variable ITS1 and ITS2 region revealed no clade support for samples from South Africa, France and Australia, representing at least two of these nominal species. We found no unambiguous diagnostic characters for the three different species even with scanning electron microscopy. Two main characters—first appearance of branchiae and hooks—that were used for species delineation show considerable intrapopulational variation and do not withstand critical evaluation. The obtained data and the observed regenerative capabilities point to a cautious use of the position of branchiae and hooked chaetae as taxonomic marker in Proscoloplos. After experimental bisection of animals, the recovery led to a phenotype without recognizable signs of regeneration, but neither branchiae nor hooked chaetae reoccurred at the same initial segmental position. Summarising the molecular and morphological data we suggest the synonymy of the known Proscoloplos species under the senior synonym Proscoloplos cygnochaetus Day, 1967. The enormous geographic range of this species comprises the temperate waters of the whole southern hemisphere and includes the French population. We discuss a dispersal enabled through the effective anchorage on vessels using mucous glands and chaetae possibly combined with architomic reproduction.     

Strong variability in bacterioplankton abundance and production in central and western Bay of Bengal

With large influx of freshwater that decreases sea-surface salinities, weak wind forcing of <10 m s⁻¹ and almost always warm (>28°C) sea-surface temperature that stratifies and shallows the mixed layer leading to low or no nutrient injections into the surface, primary production in Bay of Bengal is reportedly low. As a consequence, the Bay of Bengal is considered as a region of low biological productivity. Along with many biological parameters, bacterioplankton abundance and production were measured in the Bay of Bengal during post monsoon (September–October 2002) along an open ocean transect, in the central Bay (CB, 88°E) and the other transect in the western Bay (WB). The latter representing the coastal influenced shelf/slope waters. Bacterioplankton abundances (<2 × 10⁹cells l⁻¹) were similar to those reported from the HNLC equatorial Pacific and the highly productive northern Arabian Sea. Yet, the thymidine uptake rates along CB (average of 1.46 pM h⁻¹) and WB (average of 1.40 pM h⁻¹) were less than those from the northwestern Indian Ocean. These abundances and uptake rates were higher than those in the oligotrophic northwestern Sargasso Sea (<7 × 10⁸ cells l⁻¹; av 1.0 pM h⁻¹). Concentrations of chlorophyll a (chl a), primary production rates and total organic carbon (TOC) were also measured for a comparison of heterotrophic and autotrophic production. In the WB, bacterioplankton carbon biomass equaled ∼ 95% of chl a carbon than just 31% in the CB. Average bacterial:primary production (BP:PP) ratios accounted for 29% in the CB and 31% in the WB. This is mainly due to lower primary productivity (PP) in the WB (281 mg C m⁻² d⁻¹) than in the CB (306 mg C m⁻² day⁻¹). This study indicates that bacteria–phytoplankton relationship differs in the open (CB) and coastal waters (WB). Higher abundance and contrastingly low bacterial production (BP) in WB may be because of the riverine bacteria, brought in through discharges, becoming dormant and unable to reproduce in salinities of 28 or more psu. Heterotrophic bacteria appear to utilize in situ DOC rather rapidly and their carbon demand is ∼50% of daily primary production. It is also apparent that allochthonous organic matter, in particular in the western Bay, is important for meeting their carbon demand.     

Trophic variation with length in two ommastrephid squids, <Emphasis Type="Italic">Ommastrephes bartramii</Emphasis> and <Emphasis Type="Italic">Sthenoteuthis oualaniensis</Emphasis>

From 1998 to 2001 a total of 200 Ommastrephes bartramii (27 paralarvae) and 170 Sthenoteuthis oualaniensis (14 paralarvae) were sampled from the Central North Pacific. One group of non-paralarval O. bartramii (n = 30) was sampled from farther northwest in 1996. The δ¹⁵N of mantle muscle of non-paralarval O. bartramii ( = 12.4‰) was significantly greater than that of non-parlarval S. oualaniensis ( = 8.1‰) (P < 0.001). The δ¹⁵N of whole paralarvae of O. bartramii ( = 6.4‰) was not significantly different than parlarvalae of S. oualaniensis ( = 6.1‰) (P = 0.528). There was no significant difference between the mantle muscle δ¹⁵N values of male (n = 95, = 13.3‰) and female (n = 18, = 12.9 ‰) O. bartramii greater than 300 mm mantle length (ML) (P = 0.15). There was also no significant difference between the mantle muscle δ¹⁵N values of male (n = 15, = 7.2‰) and female (n = 26, = 7.3 ‰) S. oualaniensis in the same size range (P = 0.41). Overall there was a distinct logistic increase in δ¹⁵N with mantle length for O. bartramii, whereas S. oualaniensis showed an exponential increase in δ¹⁵N with mantle length that was stronger within individual years than with all samples combined. In general, adult O. bartramii are more than a trophic level above S. oualaniensis (4.3‰, 1.3 TLs). Because of the nature of the sampling protocol, this study could not separate spatial and temporal effects on the δ¹⁵N signals from each squid species. This study demonstrates the ability of stable isotope analyses to differentiate trophic levels between squid species as well as track trophic changes across size ranges from paralarvae to adults. Additional research is needed to validate these trophic changes across size within individuals.     

Animals on marine flowers: does the presence of flowering shoots affect mobile epifaunal assemblage in an eelgrass meadow?

Eelgrass, Zostera marina, produces two types of shoots: morphologically simple vegetative shoots and highly branched flowering (reproductive) shoots, the latter found only in summer months. We examined whether the abundance and diversity of mobile epifaunal assemblage are affected by the presence of flowering shoots in an eelgrass meadow of Otsuchi Bay, northeastern Japan. Comparisons of epifauna in natural vegetation revealed that density and species richness did not differ significantly between sites consisting of both flowering and vegetative shoots, and those only of vegetative shoots. A transplant experiment, conducted to examine the colonization rates of epifauna to defaunated eelgrass planted with different combination of vegetative and flowering shoots, showed no obvious variation in abundance and species richness. At species level, the density of some species such as a tanaid Zeuxo sp. and a polychaete Platynereis sp. was higher at sites and/or treatments with flowering shoots, whereas that of some gastropods, such as Lirularia iridescens and Siphonacmea oblongata was higher at sites without flowering shoots. The species-specific response led to dissimilarity of epifaunal assemblage between sites and among treatments with different densities of vegetative and flowering shoots. Similar patterns observed for natural vegetation and the transplant experiment suggest that the variation in assemblage structure is caused by habitat selection of each species, for example, the utilization of flowering shoots as feeding ground and nursery by Zeuxo sp.     

Annual population development and production by small copepods in Disko Bay,western Greenland

The population of small copepod species (approximately <1 mm) were investigated during an annual cycle in Disko Bay, western Greenland. The small species considered were Acartia longiremis, Pseudocalanus spp., Oithona spp., Oncaea spp., Microsetella spp., and Microcalanus spp. Most of the small species were present in the surface waters year round and numerically dominated the community, and in biomass from late summer and throughout winter. Oithona spp. was numerically the main contributor, while Pseudocalanus spp. dominated in terms of biomass. In the uppermost 50 m, maximum abundance, biomass and secondary production were observed in late September after the phytoplankton production practically had terminated and the winter initiated. The free spawning Acartia longiremis showed a strong seasonal fluctuation in biomass and egg production, in contrast to the egg carrying species Pseudocalanus spp. and Oithona spp. These had a long spawning season and maintained a more stable biomass year round. Secondary production was estimated by three different ways: (1) based on the obtained specific egg production rates, (2) a temperature dependent equation, and (3) a multilinear regression taking temperature, body weight and chlorophyll into consideration. The contribution of the small species was insignificant when compared to the large Calanus species during the spring- and post-bloom. However, during late summer and winter, where Calanus had left the upper water strata for hibernation, the small species played a crucial role in the pelagic carbon cycling.     

Lipid and protein utilisation during early development of yellowtail kingfish (<Emphasis Type="Italic">Seriola lalandi</Emphasis>)

The pelagic yellowtail kingfish Seriola lalandi has become a target species for aquaculture in Asia and Australasia. Australasian production is reliant on larviculture from eggs of captive brood stock; however, knowledge regarding the nutritional requirements of larvae of this species is still scarce, particularly in relation to lipids. As a first step in establishing these requirements, eggs and larvae from captive S. lalandi brood stock were examined for differences in total protein, total lipid and lipid classes between individual spawning events, over the spawning season, and during larval development from fertilisation to 15 days post hatch. Results indicate that total protein egg⁻¹ varied significantly between individual spawning events within a season, but neither total lipid nor total protein egg⁻¹ varied significantly across the spawning season. Brood stock egg lipids were made up of approximately 60% phospholipid, 25% wax and/or sterol esters (WE), 15% triacylglycerol (TAG), and small amounts of sterols and free fatty acids. During the early larval period, both WE and TAG were utilised concurrently for energy. The larvae experienced very high mortality around 5–7 days post hatch, which coincided with very low levels of all neutral lipid classes. Although many other factors may also influence larval mortality, these results indicate that lipid provisioning may be an important factor in larval survival during the critical period around first-feeding in this species. Examination of ratios of TAG:ST, often used as a condition index in fish larvae, suggested that some of the larvae were suffering from starvation. However, as egg-derived WE appears to provide a significant source of energy during the early larval period in S. lalandi, it is suggested that WE should be included in any index of larval nutritional state.     

Transient ontogenetic expression of hermaphroditic gonad morphology within the Gobiosoma group of the Neotropical seven-spined gobies (Teleostei: Gobiidae)

The Neotropical seven-spined gobies (tribe Gobiosomatini), including the Gobiosoma and Microgobius groups, constitute a speciose, monophyletic gobiid taxon. In particular, member species of the Gobiosoma group exhibit a combination of behavioral diversification and microhabitat specialization that may have played a major role in their collective rapid evolution and high rate of speciation. Functional hermaphroditism, which is common among gobiids, can promote exploitation of patchily distributed micro-niches by countering potential reductions in reproductive opportunities. However, the possible role of functional hermaphroditism in the exploitation of microhabitats and rapid speciation in the Gobiosoma group is unknown. One member species, Tigrigobius multifasciatus, is a functional hermaphrodite. Two other Gobiosoma group species are functionally gonochoric (i.e., constant-sexed), but exhibit transient hermaphroditic ovarian structure among immatures. In this study, ovarian morphology among immature and adult females of several Gobiosoma group species was examined to see if hermaphroditic gonadal features are present. Although no evidence of functional hermaphroditism in the form of precursive accessory gonadal structures (pAGS) associated with the adult ovary was found among newly examined species, all species exhibited the transient expression of hermaphroditic gonadal features associated with the immature ovary. In contrast, among six species of non-Gobiosomatini genera having no record of hermaphroditism, none exhibited similar transient hermaphroditic features associated with the immature ovary. These findings suggest that hermaphroditism may have been an ancestral trait which has been secondarily lost within some Gobiosoma group species. This study also shows that ontogenetic and morphogenic processes within the gobiid reproductive system may provide new insights into the evolution of life history traits and significantly further our understanding of the extraordinary evolutionary success of this group.     

Growth and survival differences among native,introduced and hybrid blue mussels (<Emphasis Type="Italic">Mytilus</Emphasis> spp.): genotype,environment and interaction effects

The Mytilus species complex consists of three closely related mussel species: Mytilus trossulus, Mytilus edulis, and Mytilus galloprovincialis, which are found globally in temperate intertidal waters. Introduction of one or more of these species have occurred world-wide via shipping and aquaculture. Stable hybrid zones have developed in areas where these species have come into contact, making the invasion process complex. On the east coast of Vancouver Island (VI), British Columbia (BC), Canada, the native (M. trossulus) and introduced species (M. edulis and M. galloprovincialis), as well as their hybrid offspring, occur sympatrically. This study used a common environment experiment to quantify growth and survival differences among native, introduced, and introgressed mussels on VI. Mussels were collected from an area of known hybridization and reared in cages from May to August 2006. The cages were deployed at a local site as well as a remote site (approximately 150 km apart), and the mussels were genotyped at two species-specific loci. Growth and survival, as fitness measures, were monitored: native, introduced, and introgressed individuals were compared between and within sites to determine whether growth and survival were independent of site and genotype. Overall, mussels reared at Quadra Island performed better than locally-reared mussels at Ladysmith. Specifically, introgressed mussels reared at Quadra Island performed better than all genotypes reared at Ladysmith, as well as better than native mussels reared at Quadra Island. Differences in survival and growth among the native, introduced and introgressed mussels may serve to explain the complex hybridization patterns and dynamics characteristic of the VI introgression zone.