Nutrient transfer in a marine mutualism: patterns of ammonia excretion by anemonefish and uptake by giant sea anemones

Many symbioses involve multiple partners in complex, multi-level associations, yet little is known concerning patterns of nutrient transfer in multi-level marine mutualisms. We used the anemonefish symbiosis as a model system to create a balance sheet for nitrogen production and transfer within a three-way symbiotic system. We quantified diel patterns in excretion of ammonia by anemonefish and subsequent absorption by host sea anemones and zooxanthellae under laboratory conditions. Rates of ammonia excretion by the anemonefish Amphiprion bicinctus varied from a high of 1.84 μmole g⁻¹ h⁻¹ at 2 h after feeding, to a basal rate of 0.50 μmole g⁻¹ h⁻¹ at 24–36 h since the last meal. Conversely, host sea anemones Entacmaea quadricolor absorbed ammonia at a rate of 0.10 μmole g⁻¹ h⁻¹ during the daytime in ammonia-enriched seawater, but during the night reduced their absorption rate to near zero, indicating that ammonia uptake was driven by zooxanthella photosynthesis. When incubated together, net ammonia excretion was virturally zero, indicating that host anemones absorbed most of the ammonia produced by resident fish. Adult anemonefish weighed about 11 g under laboratory conditions, but on the coral reef may reach up to 64 g, resulting in a maximal potential ammonia load of >200 μmole h⁻¹ produced by two adult fish during daylight hours. In contrast, host sea anemones weighed about 47 g in the laboratory, but under field conditions, large individuals may reach 680 g, so their maximal ammonia clearance rates may reach about 70 μmole h⁻¹ during the daytime. As such, the ammonia load produced by adult anemonefish far exceeds the clearance rate of host anemones and zooxanthellae. Ammonia transfer likely occurs mainly during the daytime, when anemonefish consume zooplankton and excrete rapidly, and in turn the zooxanthellae are photosynthetically active and drive rapid ammonia uptake. We conclude that zooplanktivorous fishes that form mutualisms with coral reef cnidarians may serve as an important link between open water and benthic ecosystems, through the transfer of large quantities of nutrients to zooxanthellate hosts, thus enhancing coral reef productivity.     

Distribution of a marginal population of <Emphasis Type="Italic">Mytilus edulis</Emphasis>: responses to biotic and abiotic processes at different spatial scales

Physical and biological processes interact to produce pattern in nature. Pattern is scale dependent as processes generating pattern are heterogeneous in time and space. We tested some causes of variation in abundance and distribution of three marginal populations of sublittoral blue mussels, Mytilus edulis, in the non-tidal northeastern Baltic Sea. We studied the role of substrate inclination, perennial algae and siltation along local wave exposure gradients on mussel distribution over a regional salinity gradient. We found marked differences on regional scales (p < 0.001) with lower densities and biomasses of mussels with declining salinity. Along local gradients, mussel densities increased with increasing exposure (p < 0.001) and declining slope and sedimentation (p < 0.01). Site specifically, densities of blue mussels and the perennial red algae, Furcellaria lumbricalis, were positively related, results supported by a colonisation experiment. Also, young post-recruits showed significant relations to adult biomass, wave exposure, algal biomass, bottom slope and sediment cover. Findings showed that the relative importance of the determinants affecting blue mussels at the edge of their range vary with scale and are affected by the density and size structure of mussel populations. The study provides an indication of the types of factors that may be invoked as causes of spatial variation in marginal blue mussel populations and reinforces the need to consider multiple aspects when distributional patterns are assessed.     

Red bioluminescence in fishes: on the suborbital photophores of Malacosteus,Pachystomias and Aristostomias

Many deep-sea animals produce blue bioluminescence, but species of three genera of midwater dragonfishes also produce red light. In addition to numerous small body photophores, species of these genera (Malacosteus, Pachystomias and Aristostomias) have large suborbital photophores that emit red light and postorbital ones that emit blue light. Pachystomias microdon additionally has a red-emitting preorbital photophore. Fluorescence measurements from the intact suborbital photophores, and from their exposed cores, confirm the previous hypothesis that the red light emitted by Malacosteus is spectrally altered by a superficial shortwave cutoff brown filter. No such filter is present in the other two genera. Studies of the anatomy of the photophores show that the suborbital photophore of Malacosteus is similar in general organisation to other photophores, including the postorbital photophore. The red-emitting photophores of Pachystomias and Aristostomias, however, have a unique organisation, in which the bulk of the photophore comprises a gland that lies outside the thick reflector. Strands of tissue run from the gland into the photogenic core of the photophore through numerous pores in the reflector. The production and use of red light by these fishes is discussed in the context of these results.Electronic Supplementary Material Supplementary material is available for this article at     

On reducing the windfall profits in environmental subsidy programs

Investment subsidies are widely used to induce adoption of new technologies that can lower the (marginal) cost of reducing emissions. To economize on these subsidies, governments would like to distinguish between firms that need to receive a subsidy to adopt a new technology, and firms that would adopt that technology even without subsidies. We show that policies consisting of a menu of emission taxes and investment subsidies can potentially induce firms to self-select.     

Accumulation of cadmium and zinc in <Emphasis Type="Italic">Evodiopanax innovans</Emphasis>

The use of tree species for phytoremediation of contaminated soil offers the advantage of a large biomass in which to store contaminants. We investigated the cadmium (Cd) and zinc (Zn) accumulation ability of Evodiopanax innovans, a common deciduous tree species belonging to the Araliaceae family and widely found in secondary forests in Japan. Sampling was conducted at an old silver mine. Leaf samples were collected from nine tree species, including E. innovans. The seasonal variation of metal concentrations in the leaves and the detailed distribution of metals in the leaves and twigs of E. innovans were measured. We also analyzed the contents of organic acids in the leaves. The highest concentration of Cd in the leaves of E. innovans was 118 μg/g, which exceeds the threshold level for being considered a Cd hyperaccumulator (100 μg/g). For Zn, the highest value was 1040 μg/g in leaves, which is less than required to qualify as a Zn hyperaccumulator. Both Cd and Zn were found to accumulate in the petioles and veins of leaves and the bark of twigs. Since the oxalic acid content of leaves showed a weak correlation with Cd concentration, oxalic acid may play an important role in the accumulation of Cd. Taking both the Cd concentration level and the biomass of this woody plant into consideration, it may be possible to use E. innovans for the phytoremediation of Cd-contaminated soils.     

Risk to humans of consuming metals in anchovy (<Emphasis Type="Italic">Coilia</Emphasis> sp.) from the Yangtze River Delta

Concentrations of metals were determined in four species of anchovy (Coilia sp.) from the Yangtze River, Taihu Lake, and Hongze Lake in Jiangsu Province, China. Concentrations of Cr in anchovy fish muscle ranged from 2.6 × 10⁻² to 5.0 mg/kg ww, and Coilia nasus taihuensis in Jiaoshan, Taihu Lake contained the highest concentrations of Cr, which was almost 111-fold higher than the mean value at other locations. Concentrations of Pb ranged from 1.5 × 10⁻² to 1.3 × 10⁻¹ mg/kg ww. Comparisons of concentrations of lead (Pb) among the four species indicated that anadromous species contained higher concentrations of Pb than did freshwater species. However, concentrations of Pb in C. nasus from the Nanjing and Haimen locations in the Yangtze River were not significant higher than those of two freshwater species: C. nasus taihuensis from Taihu Lake and C. brachygnathus from Hongze Lake (Duncan’s test, α = 0.05). While concentrations of Cd and Zn ranged from 7.0 × 10⁻⁴ to 3.6 × 10⁻³ mg/kg ww and 3.4 to 4.8 mg/kg ww, respectively, there were no significant differences in concentrations among the eight locations. The only concentration of the metals studied that exceeded the Chinese National Standard was Cr in Coilia from Jiaoshan, Taihu Lake, which was 2.5-fold higher than the standard. These results indicate that people who consume the genus Coilia are not at risk due to concentrations of metals, except Cr in C. nasus taihuensis from Jiaoshan in Taihu Lake. Concentrations of all of the metals studied except for Cr were similar to or less than those of metals in most other areas in the world.     

Fiddler crab burrowing affects growth and production of the white mangrove (<Emphasis Type="Italic">Laguncularia racemosa</Emphasis>) in a restored Florida coastal marsh

Positive plant–animal interactions are important in community ecology, but relatively little attention has been paid to their effect on the production of mangroves, dominant halophytic trees in tropical coastal marshes. Here, the role of fiddler crab (Uca spp.) burrowing on the growth and production of the white mangrove, Laguncularia racemosa (<2 years old), was examined in a restored marsh in Tampa Bay, Florida (27°41.65 N, 82°30.34 W) with manipulative experiments from June 2006 to May 2007. Fiddler crab burrowing significantly increased mangrove height by 27%, trunk diameter by 25%, and leaf production by 15%, compared to mangroves in crab exclusion enclosures. Additionally, the exclusion of fiddler crabs significantly increased interstitial water salinity from 32.4 to 44.2, and decreased the oxidation–reduction potential of the low organic sediments, but did not affect soil pH or sulfide concentration. Mangrove height, trunk diameter, and leaf production along a transect that varied in crab burrow density were positively associated with the number of crab burrows. Further, the density of sympatric Spartina alterniflora shoots was positively correlated with crab burrow density along the transect. As in temperate marshes, fiddler crabs can have significant ecological effects on mangrove communities, serving as ecological engineers by modulating the amount of resources available to marsh plants, and by altering the physical, chemical, and biological state of these soft sediment communities. In restored coastal systems that typically have very poor sediment quality, techniques such as soil amendment could be used to facilitate a more natural interaction between crabs and mangroves in ecosystem development.     

Love bites: male fang use during coercive mating in wolf spiders

Evolutionary conflicts of interest between the sexes are common, as mating tactics and strategies that increase fitness benefits for one sex may incur costs for the other. As a consequence, antagonistic coevolution between the sexes often results in a complex arms race between male persistence and female resistance. Coercive mating (e.g., forced copulation) likely benefits males by increasing the probability of mating; however, costs to females may be high, including injury or even death. Here, we report on a study of the use of fangs by males of the wolf spider Schizocosa ocreata (Hentz) during forcible mating with resistant females, which results in hemolymph loss and scar tissue formation in females. Microscopic inspection revealed that fang wounds (evidenced by scar tissue) were absent on unmated (virgin) females but were found on mated females and were significantly more frequent in coercively mated females. Experimental fang immobilization studies found no difference in copulation success between experimental (fangs immobilized) and control (sham manipulation) males. However, males that had use of their fangs had significantly longer copulation duration. These findings represent a previously unknown male mating tactic in spiders and an unrecognized potential cost of mating for female spiders.     

Re-orientation in clock-shifted homing pigeons subjected to a magnetic disturbance: a study with GPS data loggers

Some authors have proposed that homing pigeons are able to correct the error in orientation following a phase-shift treatment by using the magnetic compass reference. They reported that clock-shifted pigeons bearing magnets display a greater deflection compared to magnetically unmanipulated clock-shifted birds. However, this hypothesis tested by recording pigeons’ vanishing bearings has led to contradictory results. The present study reports pigeons’ tracks recorded with a GPS and shows that clock-shifted pigeons bearing magnets displayed a greater deviation through the whole route compared to the magnetically unmanipulated shifted pigeons. Moreover, the analysis of the tracks shows that the birds belonging to both experimental groups stop in coincidence with their subjective night. When re-starting their journey, the birds corrected the clock-shift induced error in orientation, but the magnetically manipulated pigeons were less efficient in doing so. Our results are consistent with the hypothesis that homing pigeons released from unfamiliar location re-orient after clock shift by using the magnetic compass.