Settlement of <Emphasis Type="Italic">Macoma balthica</Emphasis> larvae in response to benthic diatom films

The role of multi-species benthic diatom films (BDF) in the settlement of late pediveliger larvae of the bivalve Macoma balthica was investigated in still-water bioassays and multiple choice flume experiments. Axenic diatom cultures that were isolated from a tidal mudflat inhabited by M. balthica were selected to develop BDF sediment treatments characterized by a different community structure, biomass, and amount of extracellular polymeric substances (EPS). Control sediments had no added diatoms. Although all larvae settled and initiated burrowing within the first minute after their addition in still water, regardless of treatment, only 48–52% had completely penetrated the high diatom biomass treatments after 5 min, while on average 80 and 69% of the larvae had settled and burrowed into the control sediments and BDF with a low diatom biomass (<3.5 μg Chl a g⁻¹ dry sediment), respectively. The percentage of larvae settling and burrowing into the sediment was negatively correlated with the concentration of Chl a and EPS of the BDF. This suggests higher physical resistance to bivalve penetration by the BDF with higher diatom biomass and more associated sugar and protein compounds. The larval settlement rate in annular flume experiments at flow velocities of 5 and 15 cm s⁻¹ was distinctly lower compared to the still-water assays. Only 4.6–5.8% of the larvae were recovered from BDF and control sediments after 3 h. Nonetheless, a clear settlement preference was observed for BDF in the flume experiments; i.e., larvae settled significantly more in BDF compared to control sediments irrespective of flow speed. Comparison with the settlement of polystyrene mimics and freeze-killed larvae led to the conclusion that active selection, active secondary dispersal and, at low flow velocities (5 cm s⁻¹), passive adhesion to the sediment are important mechanisms determining the settlement of M. balthica larvae in estuarine biofilms.     

Effect of sub-lethal damage to juvenile colonies of massive Porites spp. under contrasting regimes of temperature and water flow

In this study, juvenile colonies of massive Porites spp. (a combination of P. lutea and P. lobata) from the lagoon of Moorea (W 149°50′, S 17°30′) were damaged and exposed to contrasting conditions of temperature and flow to evaluate how damage and abiotic conditions interact to affect growth, physiological performance, and recovery. The experiment was conducted in April and May 2008 and consisted of two treatments in which corals were either undamaged (controls) or damaged through gouging of tissue and skeleton in a discrete spot mimicking the effects of corallivorous fishes that utilize an excavating feeding mode. The two groups of corals were incubated for 10 days in microcosms that crossed levels of temperature (26.7 and 29.6°C) and flow (6 and 21 cm s⁻¹), and the response assessed as overall colony growth (change in weight), dark-adapted quantum yield of PSII (F _v/F _m), and healing of the gouged areas. The influence of damage on growth was affected by temperature, but not by flow. When averaged across flow treatments, damage promoted growth by 25% at 26.7°C, but caused a 25% inhibition at 29.6°C. The damage also affected F _v/F _m in a pattern that differed between flow speeds, with a 10% reduction at 6 cm s⁻¹, but a 4% increase at 21 cm s⁻¹. Regardless of damage, F _v/F _m at 21 cm s⁻¹ was 11% lower at 26.7°C than at 29.6°C, but was unaffected by temperature at 6 cm s⁻¹. The lesions declined in area at similar rates (4–5% day⁻¹) under all conditions, although the tissue within them regained a normal appearance most rapidly at 26.7°C and 6 cm s⁻¹. These findings show that the response of poritid corals to sub-lethal damage is dependent partly on abiotic conditions, and they are consistent with the hypothesis that following damage, calcification and photosynthesis can compete for metabolites necessary for repair, with the outcome affected by flow-mediated mass transfer. These results may shed light upon the ways in which poritid corals respond to biting by certain corallivorous fishes.     

Modification of light utilization for skeletal growth by water flow in the scleractinian coral <Emphasis Type="Italic">Galaxea fascicularis</Emphasis>

In this study, we tested the hypothesis that the importance of water flow for skeletal growth (rate) becomes higher with increasing irradiance levels (i.e. a synergistic effect) and that such effect is mediated by a water flow modulated effect on net photosynthesis. Four series of nine nubbins of G. fascicularis were grown at either high (600 μE m⁻² s⁻¹) or intermediate (300 μE m⁻² s⁻¹) irradiance in combination with either high (15–25 cm s⁻¹) or low (5–10 cm s⁻¹) flow. Growth was measured as buoyant weight and surface area. Photosynthetic rates were measured at each coral’s specific experimental irradiance and flow speed. Additionally, the instantaneous effect of water flow on net photosynthetic rate was determined in short-term incubations in a respirometric flowcell. A significant interaction was found between irradiance and water flow for the increase in buoyant weight, the increase in surface area, and specific skeletal growth rate, indicating that flow velocity becomes more important for coral growth with increasing irradiance levels. Enhancement of coral growth with increasing water flow can be explained by increased net photosynthetic rates. Additionally, the need for costly photo-protective mechanisms at low flow regimes could explain the differences in growth with flow.     

Macroalgal morphology mediates particle capture by the corallimorpharian <Emphasis Type="Italic">Corynactis californica</Emphasis>

The shallow kelp forest at Santa Catalina Island, California (33.45 N, −118.49 W) is distinguished by several canopy guilds ranging from a floating canopy (Macrocystis pyrifera), to a stipitate, erect understory canopy (Eisenia arborea), to a short prostrate canopy just above the substratum (Dictyopteris, Gelidium, Laminaria, Plocamium spp.), followed by algal turfs and encrusting coralline algae. The prostrate macroalgae found beneath E. arborea canopies are primarily branching red algae, while those in open habitats are foliose brown algae. Densities of Corynactis californica, are significantly greater under E. arborea canopies than outside (approximately 1,200 versus 300 polyps m⁻² respectively). Morphological differences in macroalgae between these habitats may affect the rate of C. californica particle capture and serve as a mechanism for determining polyp distribution and abundance. Laboratory experiments in a unidirectional flume under low (9.5 cm s⁻¹) and high (21 cm s⁻¹) flow speeds examined the effect of two morphologically distinct macroalgae on the capture rate of Artemia sp. cysts by C. californica polyps. These experiments (January–March 2006) tested the hypothesis that a foliose macroalga, D. undulata, would inhibit particle capture more than a branching alga, G. robustum. G. robustum, found predominantly under the E. arborea canopy did not affect particle capture. However, D. undulata, found predominantly outside of the canopy, inhibited particle capture rates by 40% by redirecting particles around C. californica polyps and causing contraction of the feeding tentacles. These results suggest that the morphology of flexible marine organisms may affect the distribution and abundance of adjacent passive suspension feeders.     

Swimming ability and its rapid decrease at settlement in wrasse larvae (Teleostei: Labridae)

Wrasses are abundant reef fishes and the second most speciose marine fish family, yet little is known of their larval swimming abilities. In August 2010 at Moorea, Society Islands, we measured swimming ability (critical speed, Ucrit) of 80 settlement-stage larvae (11–17 mm) of 5 labrid species (Thalassoma quinquevittatum [n = 67], Novaculichthys taeniourus [n = 6], Coris aygula [n = 5], Halichoeres trimaculatus [n = 1] and H. hortulanus [n = 1]) and 33 new recruits of T. quinquevittatum. Median (mdn) larval Ucrit was 7.6–12.5 cm s⁻¹. In T. quinquevittatum (n = 67), larvae of 12.5–14.5 mm swam faster (mdn 16.9 cm s⁻¹) than smaller or larger larvae (mdn 3.9 and 3.2 cm s⁻¹, respectively). Labrid larvae Ucrit is similar to that of other similar-sized tropical larvae, so labrids and species with comparable settlement sizes should have similar abilities to influence dispersal. Ucrit of T. quinquevittatum recruits decreased to 47–56% of larval Ucrit in 2 days, implying rapid physiological changes at settlement.     

Swimming ability of eels (<Emphasis Type="Italic">Anguilla rostrata,Conger oceanicus</Emphasis>) at estuarine ingress: contrasting patterns of cross-shelf transport?

The transport of eel early life stages may be critical to their population dynamics. This transport from ocean spawning to freshwater, estuarine and coastal nursery areas is a combination of physical and biological processes (including swimming behavior). In New Jersey, USA, the American eel (Anguilla rostrata) enters estuaries as glass eels (48.7–68.1 mm TL) in contrast to the Conger eel (Conger oceanicus) that enters as larger (metamorphosing) leptocephali (68.3–117.8 mm TL). To begin to understand the mechanisms of cross-shelf transport for these species, we measured the potential swimming capability (critical swimming speed, U _crit) under ambient conditions throughout the ingress season. A. rostrata glass eels were collected over many months (January–June) at a range of temperatures (4–21°C), with relative condition declining over the course of the ingress period as temperatures warmed. C. oceanicus occurred later in the season (April–June) and at warmer temperatures (14–24.5°C). Mean U _crit values for A. rostrata (11.7–13.3 cm s⁻¹) and C. oceanicus (14.7–18.6 cm s⁻¹) were comparable, but variable, with portions of the variability explained by water temperature, relative condition, ontogenetic stage, and fish length. Travel times to Little Egg Inlet, New Jersey, estimated using 50% U _crit values, indicate it would take A. rostrata ~30 and ~60 days to swim from the shelf edge and Gulf Stream, respectively. Travel times for C. oceanicus were shorter, ~20 days from the shelf edge, and ~45 days from the Gulf Stream. Despite differences in life stage, our results indicate both species are competent swimmers, and suggest they are capable of swimming from the Gulf Stream and/or edge of the continental shelf to estuarine inlets.     

Potential of bivalves' secondary settlement differs with species: a comparison between cockle (Cerastoderma edule) and clam (Ruditapes philippinarum) juvenile resuspension

Juvenile bivalves may be dispersed by entering a bysso-pelagic phase where they drift through the water mass aided by a long thread. The ability to resuspend and control the specific weight in two bivalve species, the cockle Cerastoderma edule (L.) and the Japanese clam Ruditapes philippinarum (Adams and Reeves), was documented with juveniles through flume and still-water experiments. Cockle juveniles initially placed on an unsuitable substratum were exposed to two shear velocities (u _*). At the end of the experiment, 42 (±15)% (for u _*=0.51 cm s⁻¹) and 79 (±9)% (for u _*=0.99 cm s⁻¹) of individuals were retrieved from the sand area which represents only 8% of the total flume surface. Most juveniles (70.5%) with shell lengths <2.5 mm migrated from the unsuitable Plexiglas substratum to the sand array by resuspension in the water column. The percentage was lower (21.5%) for larger individuals. The same experimental design was applied to clams, which immediately adhered to the Plexiglas substratum and remained attach to it. Sinking rates of live and dead specimens of both species were measured in a 1 m long transparent PVC tube. Cockle fall velocities showed severe deceleration, probably due to byssus secretion (up to 15-fold slower than dead cockles), sometimes interrupted by brutal acceleration probably due to byssal rupture. Cockles were able to reduce their sinking rate for shell lengths up to 4.25 mm. By contrast, clam sinking rates were constant, and similar to dead clam sinking rates. Specific weights of all experimental juveniles were calculated in relation to their lengths, and their passive motion into the boundary layer was theoretically assessed with Shields curve. In short, C. edule and R. philippinarum can both exhibit dense populations in the field with a good capacity to colonize, although juveniles display different abilities to resuspend in the water column. Received: 27 January 1997 / Accepted: 13 February 1997     

Habitat-induced morphological variation influences photosynthesis and drag on the marine macroalga <Emphasis Type="Italic">Pachydictyon coriaceum</Emphasis>

Photosynthesis, growth, distribution, and persistence of macroalgae are determined in part by the physical environment in which they live. Therefore, discerning how macroalgae interact with their physical environment is necessary to better understand their physiological performance. The purpose of this study was to examine what photosynthetic and hydrodynamic costs and benefits the morphology of Pachydictyon coriaceum (Phaeophyta) confers on the thallus in a given environment. Principal components analysis of morphometric measurements of Pachydictyon coriaceum from different flow habitats and depths separated thalli into three distinct morphs: shallow wave-exposed, shallow wave-protected, and deep. To test the hypothesis that thallus morphology affects net photosynthesis (NP), thalli of three morphotypes of P. coriaceum were incubated in an enclosed recirculating flume under three simulated light/water flow environments representing conditions from which the three morphotypes were collected. The wave-protected and deep morphs had significantly higher rates of photosynthesis than the wave-exposed morph for all three simulated environments. The dense, compact shape of the wave-exposed morph readily streamlines with flow and in doing so, potentially shades many of its internal blades likely accounting for its lower biomass-specific NP. Drag coefficients (C _d) were estimated for the three morphotypes over a range of flow velocities between 0.08 and 0.47 m s⁻¹. At lower water flow velocities (0.08–0.21 m s⁻¹), wave-exposed morphs had the lowest C _d among the three morphotypes. But drag coefficients of the three morphotypes converged with increasing flow velocities, and at velocities >0.31 m s⁻¹ there were no differences in C _d among the three morphotypes. The results of this study indicate that the environmentally-shaped morphs influence photosynthesis and, to a lesser degree, hydrodynamic forces acting on P. coriaceum.     

Ontogenetic habitat shift,population growth,and burrowing behavior of the Indo-Pacific beach star, <Emphasis Type="Italic">Archaster typicus</Emphasis> (Echinodermata; Asteroidea)

Archaster typicus, a common sea star in Indo-Pacific regions, has been a target for the ornamental trade, even though little is known about its population biology. Spatial and temporal patterns of abundance and size structure of A. typicus were studied in the Davao Gulf, the Philippines (125°42.7′E, 7°0.6′N), from February 2008 to December 2009. Specimens of A. typicus were associated with intertidal mangrove prop roots, seagrass meadows, sandy beaches, and shoals. Among prop roots, specimens were significantly smaller and had highest densities (131 ind. m⁻²) between November and March. High organic matter in sediment and a relatively low predation rate seemed to support juvenile life among mangroves. Size and density analyses provided evidence that individuals gradually move to seagrass, sandy habitats, and shoals as they age. Specimens were significantly larger at a shoal (maximum radius R = 81 mm). New recruits were found between August and November in both 2008 and 2009. Timing of recruitment and population size frequencies confirmed a seasonal reproductive cycle. Juveniles had relatively high growth rates (2–7 mm month⁻¹) and may reach an R of 20–25 mm after 1 year. Growth rates of larger specimens (R > 30 mm) were generally <2 mm month⁻¹. The activity pattern of A. typicus was related to the tidal phase and not to time of day: Specimens moved over the sediment surface during low tides and were burrowed during high tides possibly avoiding predation. This is one of the first studies to document an ontogenetic habitat shift for sea stars and provides new biological information as a basis for management of harvested A. typicus populations.     

Assessment of total and organic vanadium levels and their bioaccumulation in edible sea cucumbers: tissues distribution,inter-species-specific,locational differences and seasonal variations

The objective of this study is to investigate the levels, inter-species-specific, locational differences and seasonal variations of vanadium in sea cucumbers and to validate further several potential factors controlling the distribution of metals in sea cucumbers. Vanadium levels were evaluated in samples of edible sea cucumbers and were demonstrated exhibit differences in different seasons, species and sampling sites. High vanadium concentrations were measured in the sea cucumbers, and all of the vanadium detected was in an organic form. Mean vanadium concentrations were considerably higher in the blood (sea cucumber) than in the other studied tissues. The highest concentration of vanadium (2.56 μg g⁻¹), as well as a higher degree of organic vanadium (85.5 %), was observed in the Holothuria scabra samples compared with all other samples. Vanadium levels in Apostichopus japonicus from Bohai Bay and Yellow Sea have marked seasonal variations. Average values of 1.09 μg g⁻¹ of total vanadium and 0.79 μg g⁻¹ of organic vanadium were obtained in various species of sea cucumbers. Significant positive correlations between vanadium in the seawater and V _org in the sea cucumber (r = 81.67 %, p = 0.00), as well as between vanadium in the sediment and V _org in the sea cucumber (r = 77.98 %, p = 0.00), were observed. Vanadium concentrations depend on the seasons (salinity, temperature), species, sampling sites and seawater environment (seawater, sediment). Given the adverse toxicological effects of inorganic vanadium and positive roles in controlling the development of diabetes in humans, a regular monitoring programme of vanadium content in edible sea cucumbers can be recommended.

     

Migration,distribution, and diving behavior of adult male loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) following dispersal from a major breeding aggregation in the Western North Atlantic

Sixteen satellite-tagged adult male loggerhead sea turtles (Caretta caretta) dispersed widely from an aggregation near Port Canaveral, Florida, USA (28°23′N, −80°32′W) after breeding. Northbound males migrated further (990 ± 303 km) than southbound males (577 ± 168 km) and transited more rapidly (median initial dive duration = 6 (IQR = 4–16) versus 19 (IQR = 10–31) min, respectively).. Migration occurred along a depth corridor (20–40 m) except where constricted by a narrow continental shelf width. Males foraged in areas 27 ± 41 km² day⁻¹ at locations <1–80 km from shore for 100.1 ± 60.6 days, with variability in foraging patterns not explained by turtle size or geography. Post-breeding dispersal patterns were similar to patterns reported for adult female loggerhead sea turtles in this region and adult male loggerhead sea turtles elsewhere in the northern hemisphere; however, foraging ground distributions were most similar to adult female loggerhead sea turtles in this region.     

Effects of ultraviolet radiation and water motion on the reef coral Porites compressa Dana: a flume experiment

The effects of water flow and ultraviolet radiation (UVR, 280–400 nm) on the reef coral Porites compressa Dana were explored in a manipulative flume experiment. The aim of this study was to determine whether this coral responds to changes in the UVR environment by adjusting the tissue concentration of UV-absorbing compounds (mycosporine-like amino acids, MAAs), and to see whether such an acclimation is affected by water flow. Also, calcification rate and chlorophyll-a concentration were measured during the experiment to estimate the potential costs (in the form of slowed growth and/or reduced photosynthetic capacity) to the coral–alga symbiosis of being exposed to UVR and producing MAAs. Branches of P. compressa from a single male colony were exposed to high or low flow (15 cm s⁻¹ and 3 cm s⁻¹, respectively) and ambient or no UVR in an outdoor, continuous-flow seawater system. Chlorophyll-a and MAA concentrations were determined after zero, 3 and 6 weeks of exposure to the experimental conditions. Increase in buoyant weight during the two 3-week periods was used to calculate calcification rate. The presence of UVR had a significant positive effect on total MAA concentration in the P. compressa colonies; however, there were significant interactions present. In colonies exposed to UVR, MAA concentration increased and then decreased to initial levels in high water flow, and increased steadily in low water flow. In colonies receiving no UVR, MAA concentration decreased steadily, declining 23% in 6 weeks. The absence of UVR did not result in higher chlorophyll-a concentrations, but the calcification rate was slightly affected by UVR. This study supports the putative photoprotective role of MAAs in P. compressa, and suggests that the costs of mitigating the effects of ambient UVR are detectable, but they are very small. Received: 29 February 2000 / Accepted: 20 September 2000     

Genetic population structure in a commercial marine invertebrate with long-lived lecithotrophic larvae: <Emphasis Type="Italic">Cucumaria</Emphasis><Emphasis Type="Italic">frondosa</Emphasis> (Echinodermata: Holothuroidea)

The patterns of genetic diversity and connectivity were investigated in Cucumaria frondosa, the most abundant sea cucumber in the North Atlantic, to assist in the management and conservation of this ecologically important marine invertebrate, which is the target of an emerging fishery. Mitochondrial DNA COI sequences of 334 C. frondosa were obtained and analyzed, mainly from its western North Atlantic range, where the commercial fishery is being developed, with complementary sampling in the mid- and eastern North Atlantic. Analysis of molecular variance showed no significant (P > 0.05) differences among subpopulations in the western region suggesting that it constitutes one panmictic population. The same analysis showed low, but significant differences between eastern and western Atlantic populations. Coalescent analyses using isolation with migration models and a Bayesian skyline plot indicated historical divergence and a general increase in population size prior to the last glacial maximum and highly asymmetric gene flow (nearly 100 times lower from west to east) between sea cucumbers from North America and Norway. Results suggest that subpopulations of C. frondosa within the western North Atlantic have been highly connected. We propose that aided by the high-connectivity local subpopulations can recover rapidly from natural (i.e., ice ages) or anthropogenic (i.e., overfishing) population declines through recruitment from deep refugia.     

In situ net primary productivity and photosynthesis of Antarctic sea ice algal, phytoplankton and benthic algal communities

Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica. Maximum oxygen export from sea ice was 0.95 mmol O₂ m⁻² h⁻¹ (~11.7 mg C m⁻² h⁻¹) while from the sediment it was 6.08 mmol O₂ m⁻² h⁻¹ (~70.8 mg C m⁻² h⁻¹). When the ice was present O₂ export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3.77 mg C (mg Chl-a)⁻¹ h⁻¹ while those from the benthos were up to 1.53 mg C (mg Chl-a)⁻¹ h⁻¹. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice was present approximately 55–65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production.     

Effect of acclimatization to low temperature and reduced light on the response of reef corals to elevated temperature

This study tested the effects of acclimatization on the response of corals to elevated temperature, using juvenile massive Porites spp. and branching P. irregularis from Moorea (W149°50′, S17°30′). During April and May 2006, corals were acclimatized for 15 days to cool (25.7°C) or ambient (27.7°C) temperature, under shaded (352 μmol photons m⁻² s⁻¹) or ambient (554 μmol photons m⁻² s⁻¹) natural light, and then incubated for 7 days at ambient or high temperature (31.1°C), under ambient light (659 μmol photons m⁻² s⁻¹). The response to acclimatization was assessed as biomass, maximum dark-adapted quantum yield of PSII (F _v/F _m), and growth, and the effect of the subsequent treatment was assessed as F _v/F _m and growth. Relative to the controls (i.e., ambient temperature/ambient light), massive Porites spp. responded to acclimatization through increases in biomass under ambient temperature/shade, and low temperature/ambient light, whereas P. irregularis responded through reduced growth under ambient temperature/shade, and low temperature/ambient light. Acclimatization affected the response to thermal stress for massive Porites spp. (but not P. irregularis), with an interaction between the acclimatization and subsequent treatments for growth. This interaction resulted from a lessening of the negative effects of high temperature after acclimatizing to ambient temperature/shade, but an accentuation of the effect after acclimatizing to low temperature/shade. It is possible that changes in biomass for massive Porites spp. are important in modulating the response to high temperature, with the taxonomic variation in this effect potentially resulting from differences in morphology. These results demonstrate that corals can acclimatize during short exposures to downward excursions in temperature and light, which subsequently affects their response to thermal stress. Moreover, even con-generic taxa differ in this capacity, which could affect coral community structure. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Growth and grazing responses of Chrysochromulina ericina (Prymnesiophyceae): the role of irradiance, prey concentration and pH

The effect of irradiance, prey concentration and pH on the growth and grazing responses of the mixotrophic prymnesiophyte Chrysochromulina ericina under N-and P-replete conditions was studied using the pedinophyte Marsupiomonas pelliculata as prey. The two organisms were inoculated in monocultures and in mixed cultures at different predator: prey ratios at three irradiances and allowed to grow for 4–7 days. All cultures were non-axenic. Algal densities and pH were monitored throughout the experiments and growth and grazing rates were measured. An increase in growth of C. ericina cultures at irradiances of 25 and 70 μmol photons m⁻² s⁻¹ was observed after the addition of prey, while growth of C. ericina cultures at the high irradiance (150 μmol photons m⁻² s⁻¹) was unaffected by the addition of prey. However, although the growth of C. ericina increased at low irradiance (25 μmol photons m⁻² s⁻¹), it did not reach the same level as monocultures at the high irradiance (150 μmol photons m⁻² s⁻¹), suggesting that phagotrophy can only partly replace photosynthesis in C. ericina. Maximum growth rates of C. ericina at irradiances of 25 and 70 μmol photons m⁻² s⁻¹ were obtained at concentrations of > 0.15–0.3×10⁵ M. pelliculata ml⁻¹, corresponding to 50–100 μg C 1⁻¹. Ingestion of M. pelliculata cells by C. ericina did not generally follow Michaelis—Menten kinetics. Deviation from the expected saturation kinetics was especially pronounced at irradiances of 70 and 150 μmol photons m⁻² s⁻¹. At these irradiances ingestion of M. pelliculata cells by C. ericina decreased at high concentrations of M. pelliculata, indicating an increased uptake of bacterial prey in these cultures. The growth rate of C. ericina was affected in both monocultures and in mixed cultures when pH increased above 8.6, and growth stopped around pH 9. The prey alga M. pelliculata tolerated high pH better and, consequently, took over in the mixed cultures when pH exceeded 9. The ecological significance of mixotrophy in the genus Chrysochromulina is discussed. Published online: 4 July 2002     

Vertical movement and habitat of opah (Lampris guttatus) in the central North Pacific recorded with pop-up archival tags

Data from 11 pop-up archival transmitting tags attached to opah (Lampris guttatus, F. Lampridae) in the central North Pacific between November 2003 and March 2005 were used to describe their vertical movement and habitat. In the subtropical gyre northwest of the Hawaiian Islands, opah generally inhabited a 50–400 m depth range and 8–22°C temperatures. They were frequently found in depths of 50–150 m at night and in greater depths (100–400 m) during the day, but were constantly moving vertically within this broad range. At night, excursions below 200 m were not uncommon and during the day they were very likely to spend some time at depths <175 m. Their vertical speeds were generally <25 cm s⁻¹ but on one occasion an opah descended at a burst speed of 4 m s⁻¹. Vertical habitat use by individual opah apparently varied with local oceanographic conditions, but over a 24-h period the average temperature experienced was always in the narrow range of 14.7 to 16.5°C.

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Population dynamics,reproduction and growth of the Indo-Pacific horned sea star, <Emphasis Type="Italic">Protoreaster nodosus</Emphasis> (Echinodermata; Asteroidea)

The horned sea star (Protoreaster nodosus) is relatively common in the Indo-Pacific region, but there is little information about its biology. This study of the population biology of P. nodosus was carried out in Davao Gulf, The Philippines (7°5′N, 125°45′E) between September 2006 and May 2008. Protoreaster nodosus was found in sand and seagrass dominated habitats at a mean density of 29 specimens per 100 m² and a mean biomass of 7.4 kg per 100 m², whereas a significantly lower density and biomass was found in coral and rock dominated habitats. Adult specimens (mean radius R = 10.0 cm) were found at depths of 0–37 m, whereas juveniles (R < 8 cm) were only found in shallow sandy habitats with abundant seagrass (water depth ≤2 m). Increased gonad weights were found from March to May (spawning period), which coincided with an increasing water temperature and a decreasing salinity. Density and biomass did not change significantly during reproduction, but sea stars avoided intertidal habitats. All specimens with R > 8 cm had well developed gonads and their sex ratio was 1:1. Protoreaster nodosus grew relatively slowly in an enclosure as described by the exponential function G = 7.433 e^{−0.257 × R} . Maturing specimens (R = 6–8 cm) were estimated to have an age of 2–3 years. Specimens with a radius of 10 cm (population mean) were calculated to have an age of 5–6 years, while the maximum age (R = 14 cm) was estimated as 17 years. Potential effects of ornamental collection on the sea star populations are discussed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Aerobic metabolic rates of swimming juvenile mako sharks, <Emphasis Type="Italic">Isurus oxyrinchus</Emphasis>

The shortfin mako shark, Isurus oxyrinchus, is a highly streamlined epipelagic predator that has several anatomical and physiological specializations hypothesized to increase aerobic swimming performance. A large swim-tunnel respirometer was used to measure oxygen consumption (MO₂) in juvenile mako sharks (swimming under controlled temperature and flow conditions) to test the hypothesis that the mako shark has an elevated maintenance metabolism when compared to other sharks of similar size swimming at the same water temperature. Specimen collections were conducted off the coast of southern California, USA (32.94°N and 117.37°W) in 2001-2002 at sea-surface temperatures of 16.0–21.0°C. Swimming MO₂ and tail beat frequency (TBF) were measured for nine mako sharks [77–107 cm in total length (TL) and 4.4 to 9.5 kg body mass] at speeds from 28 to 54 cm s⁻¹ (0.27–0.65 TL s⁻¹) and water temperatures of 16.5–19.5°C. Standard metabolic rate (SMR) was estimated from the extrapolation to 0-velocity of the linear regression through the LogMO₂ and swimming speed data. The estimated LogSMR (±SE) for the pooled data was 2.0937 ± 0.058 or 124 mg O₂ kg⁻¹ h⁻¹. The routine metabolic rate (RMR) calculated from seventeen MO₂ measurements from all specimens, at all test speeds was (mean ± SE) 344 ± 22 mg O₂ kg⁻¹h⁻¹ at 0.44 ± 0.03 TL s⁻¹. The maximum metabolic rate (MMR) measured for any one shark in this study was 541 mg O₂ kg⁻¹h⁻¹ at 54 cm s⁻¹ (0.65 TL s⁻¹). The mean (±SE) TBF for 39 observations of steady swimming at all test speeds was 1.00 ± 0.01 Hz, which agrees with field observations of 1.03 ± 0.03 Hz in four undisturbed free-swimming mako sharks observed during the same time period. These findings suggest that the estimate of SMR for juvenile makos is comparable to that recorded for other similar-sized, ram-ventilating shark species (when corrected for differences in experimental temperature). However, the mako RMR and MMR are apparently among the highest measured for any shark species.     

The oxygen microenvironment adjacent to the tissue of the scleractinian Dichocoenia stokesii and its effects on symbiont metabolism

The biology of symbiotic scleractinians is profoundly influenced by their intracellular zooxanthellae, and many studies have focused on the mechanistic basis of this influence. This has usually been accomplished by examining the metabolism of zooxanthellae under physical conditions measured in the open reef and assumed to be similar to conditions in hospite. Recent advances in the measurement of conditions near and within coral tissue suggests that this assumption may result in substantial errors. To address this possibility, the role of water flow in determining oxygen saturation adjacent to the tissue of Dichocoenia stokesii was investigated, and the effect of these measured oxygen saturations on the respiration and photosynthesis of zooxanthellae isolated from the same species was quantified. Using a microelectrode (700 μm diam), we measured oxygen saturations above (≤4 mm) the tissue in two flow speeds over 24 h periods in a flume receiving sunlight at in situ levels. The results were used as a proxy for ecologically relevant intracellular oxygen saturations, which were applied to zooxanthellae in vitro to assess their effect on symbiont metabolism. Microenvironment oxygen saturations (% air saturation) ranged from 74–159% in slow flow (2.7 cm s⁻¹) to 88–110% in faster flow (7.5 cm s⁻¹) over day–night cycles. Therefore, the metabolic rates of zooxanthellae were measured at 50 to 54% (hypoxia), 98 to 102% (normoxia) and 146 to 150% (hyperoxia) oxygen saturation. Oxygen saturation significantly affected the metabolism of zooxanthellae, with gross photosynthesis increasing 1.2-fold and dark respiration increasing 2-fold under hyperoxia compared to hypoxia. These results suggest that the metabolism of zooxanthellae in hospite is affected markedly by their microenvironment which, in turn, is influenced by flow-mediated mass transfer. Received: 13 July 1998 / Accepted: 30 April 1999