Centrostephanus Rodgersii Research Articles

Overfishing reduces resilience of kelp beds to climate-driven catastrophic phase shift.

A key consideration in assessing impacts of climate change is the possibility of synergistic effects with other human-induced stressors. In the ocean realm, climate change and overfishing pose two of the greatest challenges to the structure and functioning of marine ecosystems. In eastern Tasmania, temperate coastal waters are warming at approximately four times the global ocean warming average, representing the fastest rate of warming in the Southern Hemisphere. This has driven range extension of the ecologically important long-spined sea urchin (Centrostephanus rodgersii), which has now commenced catastrophic overgrazing of productive Tasmanian kelp beds leading to loss of biodiversity and important rocky reef ecosystem services. Coincident with the overgrazing is heavy fishing of reef-based predators including the spiny lobster Jasus edwardsii. By conducting experiments inside and outside Marine Protected Areas we show that fishing, by removing large predatory lobsters, has reduced the resilience of kelp beds against the climate-driven threat of the sea urchin and thus increased risk of catastrophic shift to widespread sea urchin barrens. This shows that interactions between multiple human-induced stressors can exacerbate nonlinear responses of ecosystems to climate change and limit the adaptive capacity of these systems. Management actions focused on reducing the risk of catastrophic phase shift in ecosystems are particularly urgent in the face of ongoing warming and unprecedented levels of predator removal from the world's oceans.

Overview of phenotypic plasticity in echinoid larvae, ‘Echinopluteus transversus’ type vs. typical echinoplutei

Many sea urchin echinoplutei exhibit phenotypic plasticity, increasing arm length to enhance food capture in nutrient poor conditions. We tested this phenomenon in species with contrasting larval forms reared in similar feeding conditions. Heliocidaris tuberculata has a typical echinopluteus larva with 4 pairs of arms while Centrostephanus rodgersii larvae have only 1 pair of arms (‘Echinopluteus transversus ’ type larva). Larvae were exposed to high, medium and no food treatments. The ratio ‘postoral arm length’ to ‘midline body length’ (PO:MBL) was used to document phenotypic plasticity. Fed H. tuberculata larvae developed short postoral arms and low PO:MBL, while starved larvae developed long postoral arms and high PO:MBL, indicative of plastic arm growth. In contrast, well fed C. rodgersii larvae had the longest arms and high PO:MBL, indicating the absence of plastic arm growth. Taking MBL into account, ANCOVA revealed that differences among treatments were due to PO. The hypothesis that starved C. rodgersii larvae would develop long arms was not supported. Principal component analysis confirmed that larvae in different food treatments had distinct morphologies and that H. tuberculata and C. rodgersii had opposite growth patterns with respect to food treatment. We suggest that ‘Echinopluteus transversus ’ type larvae are adapted for long distance dispersal, and with only 2 arms for feeding and swimming, there may be an imperative to maintain arm length irrespective of food conditions. Phenotypic plasticity in echinopluteal arm growth is not universal and may be influenced by phylogeny, latitude and the hydromechanics of larval form.

Competition between an invasive urchin and commercially fished abalone: effect on body condition, reproduction and survivorship

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 377:169-182 (2009) - DOI: https://doi.org/10.3354/meps07816 Competition between an invasive urchin and commercially fished abalone: effect on body condition, reproduction and survivorship Elisabeth M. A. Strain*, Craig R. Johnson University of Tasmania, Department of Zoology, Private Bag 05, Hobart 7005, Australia *Email: estrain@utas.edu.au ABSTRACT: Incursion of the urchin Centrostephanus rodgersii into Tasmania, Australia, and its establishment at high densities raises questions about its potential interactions with another large herbivore on subtidal rocky reefs, the commercially fished abalone Haliotis rubra. Surveys on the southeast coast of Australia show a negative relationship between densities of C. rodgersii and H. rubra at several spatial scales, suggesting negative interactions. In intact algal beds, we used enclosures to estimate the effects and relative magnitude of intra- and interspecific competition on the body condition, gonad development and survival of C. rodgersii and H. rubra. An increased density of conspecifics led to declines in the dry gonad weight of C. rodgersii and in the dry foot and stomach content weights of H. rubra. The effects of interspecific competition were asymmetrical. Manipulations of H. rubra densities had no detectable effect on C. rodgersii. In contrast, in enclosures with added C. rodgersii, H. rubra showed reduced total and dry weights of stomach contents and increased mortality relative to controls without urchins. The effects of C. rodgersii on H. rubra could be linked to differences in feeding habits and morphology. C. rodgersii is a generalist herbivore, which, even at low densities, reduced the cover and standing biomass of total, brown and red algae relative to controls without urchins. In contrast, H. rubra is a specialist herbivore, which, even at high densities, had little effect on the cover and standing biomass of algae relative to the effect of C. rodgersii. This study suggests that the invader C. rodgersii is the superior competitor in interactions with H. rubra, and that its presence, even at low densities, affects the abalone fishery. KEY WORDS: Invasion · Fishing · Competition · Centrostephanus rodgersii · Haliotis rubra Full text in pdf format PreviousNextCite this article as: Strain EMA, Johnson CR (2009) Competition between an invasive urchin and commercially fished abalone: effect on body condition, reproduction and survivorship. Mar Ecol Prog Ser 377:169-182. https://doi.org/10.3354/meps07816 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 377. Online publication date: February 26, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Climate‐driven range extension of a sea urchin: inferring future trends by analysis of recent population dynamics

AbstractPatterns of climate‐forced range shift in the marine environment are informed by investigating the population dynamics of an ecologically important sea urchin (Centrostephanus rodgersii– Diadematidae) across its newly extended range in Tasmania (southeastern Australia). A growth model of C. rodgersii is developed allowing estimation of a sea urchin age profile and, in combination with abundance data, we correlate the sea urchin population dynamic with respect to environmental signals across the range extension region. Growth patterns did not vary across the extension region; however, there was a strong pattern of decreasing sea urchin age with increasing distance from the historic range. The sequential poleward discovery of the sea urchin, a pattern of declining age and a general poleward reduction in abundance along the eastern Tasmanian coastline are consistent with a model of range extension driven by recent change in patterns of larval dispersal. We explore this hypothesis by correlating C. rodgersii population characteristics with respect to the East Australian Current (EAC), i.e. the chief vector for poleward larval dispersal, and reveal patterns of declining sea urchin age and abundance with increasing distance from this oceanic feature. Furthermore, C. rodgersii is generally limited to sites where average winter temperatures are warmer than the cold threshold for its larval development. Potential dispersal and physiological mechanisms defining the range extension appear to be strongly coupled to the EAC which has undergone recent poleward advance and resulted in coastal warming in eastern Tasmania. Predicted climate change conditions for this region will favour continued population expansion of C. rodgersii not only via atmospheric‐forced ocean warming, but also via ongoing intensification of the EAC driving continued poleward supply of larvae and heat.

Population dynamics of an ecologically important range-extender: kelp beds versus sea urchin barrens

The barrens-forming sea urchin Centrostephanus rodgersii (Diadematidae) has recently undergone poleward range-extension to Tasmania where grazing of diverse and economically important macroalgal beds has occurred. We compared growth, biometric, dietary and morphometric characteristics of C. rodgersii between macroalgal habitat and adjacent barrens to inform population dynamics of the sea urchin within the newly extended range. The age structure of C. rodgersii in macroalgal habitat and adjacent barrens is similar, suggesting that both habitats have been influenced by similar recruitment events. However, there are clear differences in body size, body mass, spine length and diet of sea urchins in the 2 habitat types. We identified 2 broad morphologies of C. rodgersii. The first is of relatively large size with thick test, rapid growth and short spines, that grazes macroalgal beds (macroalgal eco-morph). The second ecomorph persists on the barrens habitat and demonstrates smaller body size, slower growth and thinner test, with gut contents dominated by closely cropped filamentous and/or coralline algae; but occurs at higher density, possesses longer spines and appears to enhance the persistence stability of barrens habitat once it is formed (barrens ecomorph). Invading dense, swell-prone macroalgal habitat of eastern Tasmania, the phenotypic plasticity displayed by this sea urchin appears to be an important mechanism facilitating colonisation of reef habitats within the extension region. Importantly, habitat-specific patterns in population dynamics are broadly consistent with those observed from within the historical range, suggesting that patterns in macroalgal–sea urchin dynamics and the ecological importance of this species will be similar across the newly extended range.

Heart of glass: spicule armament and physical defense in temperate reef sponges

Siliceous inclusions play an important role in deterring terrestrial herbivores, but their role in marine systems remains controversial. Sponges are ubiquitous members of marine benthic communities and represent a potentially valuable food source for many predatory species, yet they have few natural predators. An in situ method was used to assess the deterrent effects of siliceous spicules or whole sponge skeleton, which were hypothesised to act as a physical defense in temper- ate reef sponges. Natural concentrations of spicules from 5 species of sponge and the spongin skele- ton from a sixth species were incorporated into artificial diets, which were similar in nutritional qual- ity to the sponge tissues. These were offered to the sea urchin Centrostephanus rodgersii in feeding choice experiments including control discs containing no spicules or spongin skeleton. Spicules from 4 species, Tedania anhelans, Clathria pyramida, Chondrilla australiensis and Chondrilla sp., deterred feeding by C. rodgersii. Spicules from a fifth species, Callyspongia sp., and intact skeleton isolated from Cacospongia sp., failed to deter C. rodgersii. This is the first demonstration of antifeedant activ- ity associated with skeletal elements against sea urchins. Importantly, unlike previous work in the tropics, very small spicules (microscleres) measuring <100 µm were effective feeding deterrents.

Range expansion of a habitat-modifying species leads to loss of taxonomic diversity: a new and impoverished reef state

Global climate change is predicted to have major negative impacts on biodiversity, particularly if important habitat-modifying species undergo range shifts. The sea urchin Centrostephanus rodgersii (Diadematidae) has recently undergone poleward range expansion to relatively cool, macroalgal dominated rocky reefs of eastern Tasmania (southeast Australia). As in its historic environment, C. rodgersii in the extended range is now found in association with a simplified 'barrens' habitat grazed free of macroalgae. The new and important role of this habitat-modifier on reef structure and associated biodiversity was clearly demonstrated by completely removing C. rodgersii from incipient barrens patches at an eastern Tasmanian site and monitoring the macroalgal response relative to unmanipulated barrens patches. In barrens patches from which C. rodgersii was removed, there was a rapid proliferation of canopy-forming macroalgae (Ecklonia radiata and Phyllospora comosa), and within 24 months the algal community structure had converged with that of adjacent macroalgal beds where C. rodgersii grazing was absent. A notable scarcity of limpets on C. rodgersii barrens in eastern Tasmania (relative to the historic range) likely promotes rapid macroalgal recovery upon removal of the sea urchin. In the recovered macroalgal habitat, faunal composition redeveloped similar to that from adjacent intact macroalgal beds in terms of total numbers of taxa, total individuals and Shannon diversity. In contrast, the faunal community of the barrens habitat is overwhelmingly impoverished. Of 296 individual floral/faunal taxa recorded, only 72 were present within incipient barrens, 253 were present in the recovered patches, and 221 were present within intact macroalgal beds. Grazing activity of C. rodgersii results in an estimated minimum net loss of approximately 150 taxa typically associated with Tasmanian macroalgal beds in this region. Such a disproportionate effect by a single range-expanding species demonstrates that climate change may lead to unexpectedly large impacts on marine biodiversity as key habitat-modifying species undergo range modification.

A molecular approach to identify prey of the southern rock lobster

We demonstrate the use of molecular techniques to detect specific prey consumed by the southern rock lobster (Jasus edwardsii). A quick and non-lethal method was used to collect rock lobster faecal material and a molecular protocol was employed to isolate prey DNA from faecal samples. The isolated DNA was amplified using the polymerase chain reaction (PCR) with PCR primers designed to target specific prey items. Feeding experiments determined that DNA from black-lipped abalone (Haliotis rubra) and sea urchins (Centrostephanus rodgersii and Heliocidaris erythrogramma) can be detected in rock lobster faecal samples within seven hours and remains present for up to 60 h after ingestion.

Reproductive potential of a marine ecosystem engineer at the edge of a newly expanded range

AbstractGlobal climate change is leading to redistribution of marine species and altering ecosystem dynamics. Given recent poleward range extension of the barrens‐forming sea urchin Centrostephanus rodgersii (Diadematidae) from mainland Australia to Tasmania, there is a need to understand the population dynamics of this ecologically important species in the Tasmanian environment. This paper informs possible population dynamics of C. rodgersii in Tasmania by examining its reproductive ecology in this new environment. Reproductive periodicity (gonad index and propensity to spawn) was assessed bimonthly over 18 months at four sites in eastern Tasmania spanning ∼2° in latitude. At all sites, C. rodgersii displayed a strong seasonal cycle in gonad production with major spawning occurring in winter (∼August) at minimum annual water temperature. Gametes from Tasmanian C. rodgersii were viable as determined by fertilization and early development trials. However, development to the two‐arm stage at ∼3 weeks was strongly dependent on water temperature across the 8–20 °C temperature range, with poor development occurring below 12 °C. The range of temperatures tolerated by Tasmanian C. rodgersii larvae was similar to that of larvae from its native New South Wales range, indicating that this species has not undergone an adaptive shift to the cooler Tasmanian environment. There was also no evidence for an adaptive shift in reproductive phenology. Importantly, coastal water temperatures in eastern Tasmania during the peak spawning in August fluctuate about the 12 °C larval development threshold. Recent warming of the eastern Tasmanian coast and further warming predicted by global climate change will result in an environment increasingly favourable for the reproduction and development of C. rodgersii.

OCEANIC VARIABILITY AND COASTAL TOPOGRAPHY SHAPE GENETIC STRUCTURE IN A LONG-DISPERSING SEA URCHIN

Understanding the scale of marine population connectivity is critical for the conservation and sustainable management of marine resources. For many marine species adults are benthic and relatively immobile, so patterns of larval dispersal and recruitment provide the key to understanding marine population connectivity. Contrary to previous expectations, recent studies have often detected unexpectedly low dispersal and fine-scale population structure in the sea, leading to a paradigm shift in how marine systems are viewed. Nonetheless, the link between fine-scale marine population structure and the underlying physical and biological processes has not been made. Here we show that patterns of genetic structure and population connectivity in the broadcast-spawning and long-distance dispersing sea urchin Centrostephanus rodgersii are influenced by physical oceanographic and geographic variables. Despite weak genetic differentiation and no isolation-by-distance over thousands of kilometers among samples from eastern Australia and northern New Zealand, fine-scale genetic structure was associated with sea surface temperature (SST) variability and geography along the southeastern Australian coast. The zone of high SST variability is characterized by periodic shedding of eddies from the East Australian Current, and we suggest that ocean current circulation may, through its influence on larval transport and recruitment, interact with the genetic consequences of large variance in individual reproductive success to generate patterns of fine-scale patchy genetic structure. If proven consistent across species, our findings suggest that the optimal scale for fisheries management and reserve design should vary among localities in relation to regional oceanographic variability and coastal geography.

Microsatellite DNA markers for analysis of population structure in the sea urchin Centrostephanus rodgersii

AbstractWe describe the development of 13 variable microsatellites developed to investigate population structure and dispersal in the sea urchin Centrostephanus rodgersii. This species is the dominant grazing herbivore in southeast Australian coastal waters and has the ability to modify benthic community structure. The microsatellites we identified showed a range of allele numbers (4–21) and expected heterozygosity (0.32–0.91) in two sampled populations. Contrary to previous findings in free‐spawning marine invertebrates, genotype proportions in neither population deviated significantly from Hardy–Weinberg expectations.

Seeding small numbers of cultured black-lip abalone (Haliotis rubra Leach) to match natural densities of wild populations

Haliotis rubra Leach, the black-lip abalone, is a valuable, commercially harvested species, but populations have declined since the onset of commercial fishing. Seeding juvenile cultured abalone into natural habitats can enhance and/or re-establish populations. This is often done in numbers well above natural densities of both unfished and fished populations, but is usually unsuccessful (probably because of increased mortality from predation or other density-dependent factors) and is potentially problematic for the ecology of the habitat. A major aim was, therefore, to assess survival of H. rubra when seeded in small numbers. The current study is one of a few experimental investigations to improve understanding of the potential of re-seeding. We test: (1) the importance of the spatial and temporal configuration of seed; (2) the usefulness of the urchins, Centroste phanus rodgersii, to act as a potential shelter from predators; and (3) differences in survival when using the deployment devices versus urchins. After a few days, total recovery among treatments ranged between 3 and 31%. The configuration of abalone or their proximity to urchins did not affect long-term survival. Survival in devices may be greater than with urchins, but these results were spatially variable. Recovery dropped to 0.2–3% from 1–2 months, and 0.05–2% after 6 months. Nevertheless, these results show that seeding fewer abalone (rather than previous attempts at mass out-planting) can sustain populations close to average natural densities of adults previously observed in Australia (1–3 abalone per m2). It may be more productive and ecologically conservative to release fewer and therefore larger abalone, which are known to survive better in the wild.

Arsenic Occurrence and Species in Near-Shore Macroalgae-Feeding Marine Animals

This study was undertaken to improve the understanding of arsenic species and their pathways of formation in marine animals: fish (Odax cyanomelas), abalone (Haliotis rubra), and sea urchins (Heliocidaris erythrogramma and Centrostephanus rodgersii) that are directly exposed through their diets to dimethyl arsenoriboses in macroalgae (Phyllospora comosa and Halopteris platycena). The identification of dimethyl arsenoriboses (phosphate, sulfonate, and glycerol) in both dominant macroalgae species, and especially digestive tissues of marine animals that consume them, suggests these arsenic species, are to some degree accumulated directly from their diets without degradation or conversion. An unknown arsenic species in H. rubra intestinal tissue was identified using tandem mass spectrometry as 2',3'-dihydroxypropyl 5-deoxy-5-trimethyl arsonioriboside (trimethyl glycerol arsenoribose). The concentration of trimethyl glycerol arsenoribose in H. rubra intestinal tissue was estimated to account for 28% (5.0 microg g(-1) dry mass) of the methanol-water-soluble arsenic fraction. The presence of a trimethyl glycerol arsenoribose in marine animal tissues may be due to microbial-mediated processes that promote the reduction and methylation of dimethyl arsenoriboses released during the breakdown of macroalgae in their diets. Arsenobetaine formation may then occur in the lumen of the digestive tract (i.e., mediated by microorganisms) or in the liver catalyzed by enzymes. The identification of a large amount of trimethyl glycerol arsenoribose in H. rubra intestinal tissue suggests this species is a main constituent in the pathway for arsenic in this marine animal.

Responses of common SE Australian herbivores to three suspected invasive Caulerpa spp.

We sought to determine whether common intertidal and shallow subtidal zone grazers would consume extracts or fronds of three invasive Caulerpa spp., all of which are now resident in southern New South Wales, Australia. We examined the responses of herbivorous fishes, echinoderms and molluscs to C. filiformis. A subset of these organisms was tested with extracts of C. scalpelliformis and C. taxifolia. Polar (seawater) extracts of C. filiformis deterred a single herbivore, Aplysia sydneyensis, but confirmed that the biological activity reported from some Caulerpa spp. is not restricted to the lipophilic fractions. The large turbinid Turbo torquatus was deterred by an ethanol extract of C. filiformis, while the small congener T. undulatus demonstrated a significant preference for palatable agar discs containing ethanol extracts of C. filiformis. However, when T. undulatus were offered a choice of fronds from five algal species in the laboratory, they readily consumed Ulva spp. and Sargassum sp., showing the lowest preference for C. filiformis. Solvent extracts of C. scalpelliformis and C. taxifolia did not significantly deter any grazers. However, the overall trend was for reduced consumption of discs containing solvent extracts of these seaweeds. Indeed, for the large urchin Centrostephanus rodgersii and in the fish trials these effects were very near significant (P<0.06). We conclude that common herbivores associated with hard substrata are highly unlikely to intercede in the spread or control of these invasive algae.

Larval development and metamorphosis of the Australian diadematid sea urchin Centrostephanus rodgersii

Summary The complete larval development through to metamorphosis of the sea urchin Centrostephanus rodgersii is described for the first time. Embryos developed from small eggs (113 μm) to large echinopluteus larvae (3250 μm arm length) over a period of approximately 4 months. Fully developed larvae are two-armed echinoplutei with densely pigmented postoral and anterolateral arms and oral hood. The posterodorsal and the preoral arms do not appear to form. The skeletal body rods form a basket-like structure posteriorally, and fenestrated skeletal rods support the postoral arms. Five primary podia emerge from the vestibule, at around 100 days old, and attach to the substrate at settlement. The larval epidermis recedes from the arm rods and collects on the aboral surface of the juvenile, and the adult rudiment emerges as the larva metamorphoses to the juvenile stage.

Size matters sometimes: wall height and the structure of subtidal benthic invertebrate assemblages in south‐eastern Australia and Mediterranean Spain

AbstractAim Variation in the structure of shallow subtidal invertebrate assemblages was examined over three spatial scales; within reef, between reef and between continents. We sought to provide a context from which to examine and interpret ecological processes between continents. In addition, we predicted that variation in pattern would increase as the scale of examination increased.Location Reefs near Wollongong and within Jervis Bay in south‐eastern Australia and Mediterranean reefs on the Costa Brava (Catalonia), north‐eastern Spain.Methods We compared assemblages on vertical rock walls of two heights – short (&lt; 2 m) and tall (&gt; 3 m) in two temperate regions over the same depth range. Specifically we examined the diversity and cover of invertebrates, the cover and biomass of foliose and crustose algae, the size of invertebrate colonies and the biomass of urchins on short and tall walls (n = 3) at each of two locations in each country.Results Foliose algae dominated rock walls in Spain and although invertebrate cover was high, colonies were generally very small. Two urchin species were commonly encountered on rock walls in Spain, Arbacia lixula and Paracentrotus lividus; their biomass was relatively low and did not differ significantly between short and tall walls. These findings contrasted strongly with south‐eastern Australia, where foliose algae were almost completely absent. A single urchin species, Centrostephanus rodgersii occurred with extremely high biomass on short walls, which were dominated by grazer‐resistant crustose calcareous algae. In contrast, the biomass of this urchin was low on tall walls, which were dominated by invertebrates, usually exceeding 95% in cover. Invertebrate colonies were significantly larger on both short and tall walls in south‐eastern Australia relative to the Mediterranean. Findings within a country were consistent between the replicate rock walls and between locations. In contrast to our prediction, however, there was significant variation among walls within a location, but not among locations within a continent. Temporal variation in the structure of these assemblages was not examined, but appears limited.Main conclusions We conclude that submarine topography, i.e. the presence of short or tall rock walls, as a function of rock type and structure, has a marked impact on community structure in south‐eastern Australia, but made little difference to the structure of the assemblage in Mediterranean Spain. The differences in structure we observed between walls of different heights in Australia were correlated with differences in the biomass of urchins and they appear to be major determinants of assemblage structure. Interactions among species are often reported from disparate parts of the globe with little or no reference to the structure of the assemblage of which they are a part; we contend that this will hinder interpretation. Our data are consistent with the organisms in these two regions experiencing distinct selection pressures; for example high levels of urchin grazing activity in south‐eastern Australia, and shading and whiplash associated with an algal canopy in the Mediterranean. It may not be appropriate to contrast processes operating at very large (intercontinental) scales unless context can be established with a clear understanding of ecological pattern.

Grazing effects of the sea urchin Centrostephanus rodgersii in two contrasting rocky reef habitats: effects of urchin density and its implications for the fishery

The sea urchin Centrostephanus rodgersii plays an important role in determining the abundance and composition of benthic macroalgae in New South Wales. Centrostephanus rodgersii is commonly found in areas devoid of foliose algae (termed 'barrens habitat'), which abruptly change into areas rich in foliose algae (termed 'fringe habitat'). Complementary experiments were used to investigate the impact of C. rodgersii grazing on algal assemblages at a range of densities in the barrens and fringe habitats. Although 33% of the natural density of C.�rodgersii maintained barrens areas relatively free of foliose algae, only densities exceeding natural densities within barrens habitat cleared areas dominated by macroalgae. The impact of grazing was not linearly related to density in either habitat, which suggests that both the barrens and fringe habitats are stable and will persist unless there is a dramatic decrease in urchin densities in barrens areas or a large influx into fringe areas. These findings have significant implications for the commercial harvesting of C. rodgersii. They imply that reducing urchin densities in barrens habitats, or translocating urchins from barrens to fringe habitats in order to improve roe quality, will not significantly alter the algal assemblage of either habitat in the short term (less than 3 months).

Identifying individuals of the sea urchin Centrostephanus rodgersii with high-quality roe in New South Wales, Australia

The quality of sea urchin roe determines its value at market, but it is not visible to commercial divers during harvest. To aid efficiency of harvesting, the relationship between three important attributes of the quality of roe (colour, texture and granularity) and several covariates was investigated for Centrostephanus rodgersii in New South Wales, Australia. The covariates included three physical attributes of the sea urchin (roe weight, test diameter and total weight), as well as the habitat, location and reproductive period. There were significant relationships among the measures of roe quality and among the covariates. The preferred colour of roe was associated with poor granularity and texture, and roe weight was strongly associated with test diameter, reproductive period and habitat. Generalised linear models were used to estimate the probability of selecting each category of roe quality for a sea urchin with a given set of covariates. In combination, roe weight and test diameter accounted for most variation in roe quality explained by the covariates. Sea urchins with smaller test diameters and heavier roe were more likely to contain roe of a preferred colour, but less likely to contain roe of a preferred granularity and texture. Despite this contrast, physical characteristics of sea urchins and their local habitat can be used by commercial divers to enable the selection of individuals with a greater probability of containing high-quality roe.

Spatial and temporal variation in fish assemblages exposed to sewage and implications for management

Underwater visual surveys, involving a Before/After/Control/Impact (BACI) experimental design, were used to investigate the abundance and species richness of temperate rocky reef fishes and the abundance of a sea urchin following the discharge of sewage effluent from a deepwater outfall. Multivariate analyses indicated that fish assemblages were significantly different at the outfall and control locations, and these differences were largely attributed to the declines in relative abundance of several common, resident species of reef fish, such as the eastern hulafish, Trachinops taeniatus and yellowtail Trachurus novaezelandiae and the sea urchin Centrostephanus rodgersii. Univariate analysis indicated that the abundance and richness of groups of fish and individual species varied over times, periods and locations. The abundance and species richness of fish from the outfall location were generally less than for fish assemblages at the control locations. We detected decreases of 33% in the species richness of fish and 50% in the abundance of Centrostephanus rodgersii at the outfall location and, conversely, the abundances of some cryptic (small, cave dwelling or camoflagued) fishes increased over time at the outfall. This study indicates that the discharge of sewage effluent resulted in an environmental impact affecting fish assemblages, some fish species and a sea urchin, and it was concluded that the outfall was not complying with current pollution management guidelines.

Reproduction in the diadematoid sea urchin Centrostephanus rodgersii in contrasting habitats along the coast of New South Wales, Australia

Reproduction in the sea urchin Centrostephanus rodgersii was examined in two types of habitats (“barrens”, i.e. habitats characterised by the high crustose coralline algal cover typical of urchin-barren grounds, and by the absence of macroalgae; and “fringe”, i.e. habitats characterised by a high macroalgal biomass and few C. rodgersii) at four locations in New South Wales. The four locations: the Solitary Islands, Sydney, Ulladulla and Eden, span the distribution of C.␣rodgersii from the subtropics at its northern limit to temperate waters near its southern limit. Histology and estimates of gonad retrieval rate (GRR) from January 1994 to October 1995 indicated that reproduction was synchronous at all locations. An increase in the tempo of gametogenesis in May and onset of spawning in June at all locations is consistent with entrainment in response to exogenous factors. Over the range studied, C. rodgersii experienced relatively similar daylength cycles and contrasting sea-temperature cycles. Short days and lunar conditions coinciding with the solstice appear likely proximate cues for the onset of spawning. The major difference in reproduction among locations was in the duration of spawning. In the southern parts of its range breeding occurred over a 5 to 6 mo period, whereas at the Solitary Islands it lasted ≃1 mo. At most locations the GRRs were significantly higher in the fringe habitat than in the barrens habitat. The lower reproductive output of urchins in the barrens habitat was attributed to the food-poor conditions typical of this habitat. The developing fishery for C. rodgersii is likely to be most effective from March to early May. Urchins from barrens areas may not provide sufficient yield to warrant harvesting.