No abstract

Although sea-ice represents a harsh physicochemical environment with steep gradients in temperature, light, and salinity, diverse microbial communities are present within the ice matrix. We describe here the photosynthetic responses of sea-ice microalgae to varying irradiances. Rapid light curves (RLCs) were generated using pulse amplitude fluorometry and used to derive photosynthetic yield (ΦPSII ), photosynthetic efficiency (α), and the irradiance (Ek ) at which relative electron transport rate (rETR) saturates. Surface brine algae from near the surface and bottom-ice algae were exposed to a range of irradiances from 7 to 262 μmol photons · m(-2)  · s(-1) . In surface brine algae, ΦPSII and α remained constant at all irradiances, and rETRmax peaked at 151 μmol photons · m(-2)  · s(-1) , indicating these algae are well acclimated to the irradiances to which they are normally exposed. In contrast, ΦPSII , α, and rETRmax in bottom-ice algae reduced when exposed to irradiances >26 μmol photons · m(-2)  · s(-1) , indicating a high degree of shade acclimation. In addition, the previous light history had no significant effect on the photosynthetic capacity of bottom-ice algae whether cells were gradually exposed to target irradiances over a 12 h period or were exposed immediately (light shocked). These findings indicate that bottom-ice algae are photoinhibited in a dose-dependent manner, while surface brine algae tolerate higher irradiances. Our study shows that sea-ice algae are able to adjust to changes in irradiance rapidly, and this ability to acclimate may facilitate survival and subsequent long-term acclimation to the postmelt light regime of the Southern Ocean.

colony morphology. Given that structural complexity of coral colonies is an important determinant of "habitat quality" for many other species (fishes and invertebrates), these results suggest that the vermetid gastropod, C. maximum (with a widespread distribution and reported increases in density in some portions of its range), may have important indirect effects on many coral-associated organisms.

<p>The brown alga Colpomenia bullosa was first observed in New Zealand more than 20 years ago, yet very little is known about its current intertidal distribution or possible effects it may be having on native communities. This study addresses some of these issues. Surveys indicate little spatial variation in abundance around the Wellington region, however, the sporophytic crustose phase is restricted to pools high in the littoral zone while the gametophytic upright has a low- to sub-littoral distribution. Physiology experiments indicate that C. bullosa can tolerate a wide range of environmental conditions, but the crustose phase has a poor desiccation tolerance. A series of tranplant and competition experiments confirmed this and suggested that the crustose phase requires some level of facilitation by molluscan herbivores in order to become established. These experiments also revealed that crustose C. bullosa does not compete well against more upright macroalgal species. The effects of this introduced algae on native communities are likely to be minimal given its restricted intertidal distribution and its inability to compete against more upright species.</p>

<p><b>Many marine reef fishes have a bipartite life cycle, with reef-based adults that produce pelagic larvae. Pelagic larval development is characteristically risky; intrinsic and extrinsic factors often lead to high spatial and temporal variability in demographic rates. Pelagic larval development may also facilitate dispersal, and this — in combination with variable demographic rates during the larval stage — is likely to drive variation in local population replenishment (i.e., “recruitment”). Long-standing paradigms in benthic marine ecology rest on a belief that pelagic larvae are largely passive, and widely dispersed by ocean currents. However, recent work suggests that many reef organisms (particularly fishes) exhibit complex behavioural patterns, possess well-developed sensory systems, and have strong swimming abilities. These traits raise the possibility that dispersal may be the anomaly and near-shore larval retention (and potentially even reef-based larval development) may be relatively commonplace. If true, this could challenge fundamental ideas that underlie current management of many fisheries and alter our perceptions of the resilience of reef fishes to changing environmental conditions. At present, we continue to have a poor understanding of the early life histories of most reef organisms.</b></p> <p>Here, I evaluate the early life history of the common triplefin (Forsterygion lapillum), a small-bodied reef fish found on rocky reefs throughout New Zealand. I sampled larvae during their development and transition back to the reef. I explored fine-scale spatio-temporal variation in abundance and individual traits, and otolith microchemistry, to infer some key developmental attributes and potential migratory patterns. </p> <p>In chapter 2, I evaluated the near-shore distribution, abundance, and phenotypes of larval triplefin sampled by light traps deployed across the shelf (i.e., a gradient perpendicular to shore), and across depth. I found that late-stage larvae are concentrated in shallow surface waters, very close to the reef. Larval phenotype (e.g., body condition, and other metrics of body size) varied among sampling locations. Immediately above the reef, larvae sampled near the sea surface were in better condition than larvae sampled at depth. At offshore locations, this pattern was reversed. Spatial variation in abundance, condition and morphological traits of larval fish sampled across the shelf suggest one of two likely possibilities: (1) larval fish are highly mobile and may display an onshore movement pattern, forming shoals near the reef, which persist for a period of time prior to settlement, or (2) dispersal is relatively limited, and condition-dependent (i.e., many larvae of a wide range of sizes remain close to the reef, and only those in poor physiological condition are advected offshore).</p> <p>In chapter 3, I used otolith microstructure to reconstruct age and growth patterns of these same larvae. I evaluated spatial variation in larval age and growth, in an attempt to differentiate between the two alternative hypotheses posed in the previous chapter. I found that larvae sampled above the reef were ~5d older than larvae sampled offshore, consistent with a hypothesis of ontogenetic onshore migration. Larvae sampled above the reef also had reduced daily growth rates relative to larvae sampled offshore. Finally, the ages of larvae sampled above the reef were substantially less than the reported settlement age and suggest that these larvae may be shoaling on the reef for up to two weeks prior to their eventual settlement. </p> <p>In chapter 4, I developed and tested a method to infer movement patterns of larval fish based on the environmental fingerprints contained within their otoliths. Specifically, I reared larvae in water collected from different locations (e.g., offshore, near-shore, harbour, etc) and maintained at two different temperatures. I used laser ablation inductively coupled plasma mass spectroscopy (LA-ICPMS) to quantify the resulting concentrations of a set of elements within larval otoliths. I used multivariate statistical approaches to evaluate the ability to chemical signatures within otoliths discriminate among larvae that developed in different water masses. These approaches had some success in differentiating between individuals that developed offshore versus in nearshore/harbour water. In chapter 5, I again used LA-ICPMS to quantify the concentrations of a set of elements within otoliths of larvae sampled above reefs and offshore. I applied the multivariate statistical approaches that I developed in the previous chapter and used them to evaluate variation in chemical signatures recorded within (1) the core of the otolith (i.e., a putative natal signature), and (2) across the growing axis of the otolith (i.e., putative developmental histories). I did not detect significant variation in otolith core signatures, but patterns of variation in otolith microchemistry across the growth axis suggest that larvae collected offshore had significantly different developmental histories than larvae collected above the reef. I also observed significant temporal variation in otolith microchemistry. </p> <p>Collectively, my results indicate a complex set of processes that may occur in the lead-up to settlement. Dispersal may be more limited that is widely assumed. Larvae of the common triplefin may move onshore and form shoals for several weeks prior to settlement. These movements may depend upon larval traits, and in particular, on body condition.</p>