NUTRIENTS DO NOT INFLUENCE SWIMMING BEHAVIOR OR SETTLEMENT RATES OF ECTOCARPUS SILICULOSUS (PHAEOPHYCEAE) SPORES

Spores newly released from plurilocular sporangia of Ectocarpus siliculosus (Dillw.) Lyngb. sporophytes were assayed for chemotaxis to nutrients and for settlement stimulation by nutrients. To enable these measurements with relatively small volumes and numbers of released spores, we developed a computer-assisted motion-analysis assay for spore chemotaxis and verified the results with a more standard, capillary tube chemotaxis assay. The presence of a nutrient gradient did not influence the swimming behavior of E. siliculosus spores in the motion-analysis assay, and likewise no chemotactic effect was measured in the capillary tube assay. Microplate settlement assays previously utilized with bacteria and invertebrates were adapted for use with algal spores. E. siliculosus spores settled at higher rates on a hydrophobic plastic surface than on surfaces with either positively or negatively charged hydrophilic coatings. Nutrient mixtures had no effect on the rate of spore settlement on hydrophobic surfaces.     

Time-courses of size-fractionated phosphate uptake: are larger cells better competitors for pulses of phosphate than smaller cells?

Summary Time-course experiments of phosphate uptake by size-fractionated phytoplankton were conducted in oligotrophic Kennedy and Sproat Lakes. The objective was to determine if large phytoplankton obtained more phosphate than smaller cells, when the nutrient was present at higher concentrations. Studies at Kennedy Lake revealed that uptake rates in the 0.2–3.0 m fraction were very sensitive to the time they were exposed to elevated concentrations; rates determined over the 60–120 min interval were less than 30% of those recorded over the 0–60 min interval. In contrast, there was little difference in uptake rates over these intervals for cells>3.0 m. At Sproat Lake phosphate incorporation into the two size fractions was followed after the aerial fertilization of the lake with inorganic nutrients. Following nutrient addition the proportion of phosphate entering the>3.0 m size fraction increased from ca. 35% to ca. 85%. Despite these observations, it is doubtful that larger cells are able to sequester enough phosphate from pulses to realize the same specific growth rates as their smaller counterparts.     

Pacific Coral-reef Fishes: The Implications of Behaviour and Ecology of Larvae for Biodiversity and Conservation, and a Reassessment of the Open Population Paradigm

The two-phase life history of most marine fishes and invertebrates has enormous implications for dispersal, population connectivity, and resource management. Pelagic dispersal larvae of marine animals traditionally thought to ensure that populations are widespread, that chances of local extinction are low, and that marine protected areas (MPA) can easily function to replenish both their own populations and those of unprotected areas. Traditionally, dispersal is considered to depend primarily on two variables: pelagic larva duration and far-field currents. These conclusions arise from the open population paradigm and are usually accompanied by a simplifying assumption: larvae are distributed passively by far-field currents. Unfortunately, they ignore the complex reality of circulation and hydrological connectivity of reefs, and do not consider newly-demonstrated behavioural capabilities of coral-reef fish larvae. Far-field circulation varies with depth and often excludes water bodies where propagules are released, and this has important implications for predicting trajectories of even passive larvae. However, larvae are not passive: late-stage larvae of coral-reef fishes can swim faster than currents for long periods, can probably detect reefs at some distance, and can actively find them. This behaviour is flexible, which greatly complicates modelling of larval fish trajectories. Populations at ecological (as opposed to evolutionary) scales are probably less open and more subdivided than previously assumed. All this means that dispersal predictions based solely on far-field water circulation are probably wrong. An emerging view of larval-fish dispersal is articulated that takes these new data and perspectives into account. This emerging view shows that re-evaluation of traditional views in several areas is required, including the contribution of larval-fish biology and dispersal to biodiversity patterns, the way reef fishes are managed, and the way in which MPA are thought to operate. At evolutionary and zoogeographic scales, reef-fish populations are best considered to be open.     

Persistent maternal effects on juvenile survival in North American red squirrels

Maternal effects can have lasting fitness consequences for offspring, but these effects are often difficult to disentangle from associated responses in offspring traits. We studied persistent maternal effects on offspring survival in North American red squirrels (Tamiasciurus hudsonicus) by manipulating maternal nutrition without altering the post-emergent nutritional environment experienced by offspring. This was accomplished by providing supplemental food to reproductive females over winter and during reproduction, but removing the supplemental food from the system prior to juvenile emergence. We then monitored juvenile dispersal, settlement and survival from birth to 1 year of age. Juveniles from supplemented mothers experienced persistent and magnifying survival advantages over juveniles from control mothers long after supplemental food was removed. These maternal effects on survival persisted, despite no observable effect on traits normally associated with high offspring quality, such as body size, dispersal distance or territory quality. However, supplemented mothers did provide their juveniles an early start by breeding an average of 18 days earlier than control mothers, which may explain the persistent survival advantages their juveniles experienced.     

The complex barnacle perfume: identification of waterborne pheromone homologues in Balanus improvisus and their differential expression during settlement

A key question in barnacle biology is the nature of cues that induce gregarious settlement. One of the characterised cues is the waterborne settlement pheromone (WSP). This study aimed to identify WSP homologues in Balanus improvisus and to investigate their expression during settlement. Six WSP homologues were identified, all containing an N-terminal signal peptide, a conserved core region, and a variable C-terminus comprising several -GR- and -HDDH- motifs. The B. improvisus WSP homologues were expressed in all settlement stages but showed different expression patterns. The homologue most similar to the B. amphitrite WSP was the most abundant and was constantly expressed during settlement. In contrast, several of the other WSP homologues showed the greatest expression in the juvenile stage. The presence of several WSP homologues suggests the existence of a pheromone mix, where con-specificity might be determined by a combination of sequence characteristics and the concentration of the individual components.     

Effects of live coral,epilithic algal communities and substrate type on algal recruitment

The recruitment of algae is a critical process during algal colonization and invasions, including coral-to-algal phase shifts. Although algae are widely assumed to colonize and kill corals, there is very little known about the recruitment dynamics of coral reef algae. This study tested the ability of two dominant macroalgae (Fucales including Sargassum spp. and Lobophora variegata) to settle and grow on healthy coral tissue. The study also explored the effects of interactions with prior occupants, and of abiotic substrate properties (texture, and ceramic and carbonate material). The results indicate that healthy corals were able to prevent attachment or survival of recruits of these macroalgae. This is a significant point, since it suggests that the replacement of corals by algae may often require prior stress or death in the coral tissue. Pre-conditioning of plates at different sites had some effects, but these were relatively minor, whereas there was considerable variation within sites. Some of this variation appeared to be related to the amount of turf algae or crustose coralline algae on the plates. Recruitment was generally, but not always, higher on plates with rougher texture. Overall, this preliminary exploration indicates considerable potential for variability in outcomes of algal colonization, with implications for the dynamics of algal invasions. In particular, the results do not support suggestions that planktonic algal propagules can directly settle on and colonize healthy coral tissue.Communicated by Topic Editor D. Barnes