Mike F. Barker

DNA photorepair in echinoid embryos: effects of temperature on repair rate in Antarctic and non-Antarctic species

SUMMARY To determine if an Antarctic species repairs DNA at rates equivalent to warmer water equivalents, we examined repair of UV-damaged DNA in echinoid embryos and larvae. DNA repair by photoreactivation was compared in three species Sterechinus neumayeri (Antarctica), Evechinus chloroticus (New Zealand) and Diadema setosum (Tropical Australia) spanning a latitudinal gradient from polar (77.86°S) to tropical (19.25°S) environments. We compared rates of photoreactivation as a function of ambient and experimental temperature in all three species, and rates of photoreactivation as a function of embryonic developmental stage in Sterechinus. DNA damage was quantified from cyclobutane pyrimidine dimer (CPD) concentrations and rates of abnormal embryonic development. This study established that in the three species and in three developmental stages of Sterechinus, photoreactivation was the primary means of removing CPDs, was effective in repairing all CPDs in less than 24 h, and promoted significantly higher rates of normal development in UV-exposed embryos. CPD photorepair rate constant (k) in echinoid embryos ranged from 0.33 to 1.25 h-1, equating to a time to 50% repair of between 0.6 and 2.1 h and time to 90%repair between 3.6 and 13.6 h. We observed that experimental temperature influenced photoreactivation rate. In Diadema plutei, the photoreactivation rate constant increased from k=0.58 h-1 to 1.25 h-1, with a Q10=2.15 between 22°C and 32°C. When compared among the three species across experimental temperatures (-1.9 to 32°C), photoreactivation rates vary with a Q10=1.39. Photoreactivation rates were examined in three developmental stages of Sterechinus embryos, and while not significantly different, repair rates tended to be higher in the younger blastula and gastrula stages compared with later stage embryos. We concluded that photoreactivation is active in the Antarctic Sterechinus, but at a significantly slower (non-temperature compensated) rate. The low level of temperature compensation in photoreactivation may be one explanation for the relatively high sensitivity of Antarctic embryos to UV-R in comparison with non-Antarctic equivalents.

Reproduction of the sea urchin Evechinus chloroticus (Echinodermata: Echinoidea) in a New Zealand fiord

Abstract The reproductive cycle of Evechinus chloroticus (Val.) was examined at three (outer, mid, and inner) sites in Doubtful Sound, Fiordland over a 3‐year period. We found that sea urchins from all three populations had an annual gametogenic cycle, the timing of which was temporally and spatially consistent. Inter‐individual variation in the gametogenic cycle was noted within each population, however, initiation of gametogenesis was generally synchronous among males and females and among sites, occurring in May/June. Strong asynchrony in gamete maturation was observed in Deep Cove, occurring in males 4–5 months earlier than females. Spawning occurred in December at the inner and mid fiord sites, while occurring in January at the outer fiord site. Reproductive potential (maximum gonad index) and output (weight of gametes released/g of animal/year) varied spatially and temporally, where there was a consistent decreasing trend in reproductive potential and output with increasing distance away from the fiord entrance. Spatial variation in reproductive output may be associated, in part, with the strong ecological gradient found in Doubtful Sound, where there is a reported decrease in macrophyte biomass and cover towards the fiord headwaters. The implications of spatial differences in gonad production with respect to the population biology and fisheries management of E. chloroticus in the fiords are discussed.

Population differences in gonad and pyloric caeca cycles of the New Zealand seastarSclerasterias mollis (Echinodermata: Asteroidea)

Inshore and offshore populations ofSclerasterias mollis (Hutton, 1872) were sampled on the outer continental shelf off the Otago Peninsula, New Zealand, and their nutritional and reproductive cycles are described from 1985–1986. Histological changes in the gonads are generally typical of other asteroids. The gametogenic cycle takes 12 mo. The gonad and pyloric caeca indices in both females and males had an inverse relationship.S. mollis accumulates nutrients in the pyloric caeca during summer and early autumn. The gonads develop in the autumn and winter. Offshore seastars were much larger and had significantly higher gonad and pyloric caeca indices than inshore individuals. These differences in body sizes and organ indices arise from differences in food availability and/or population density.

Expression of the DNA Repair Enzyme, Photolyase, in Developmental Tissues and Larvae, and in Response to Ambient UV-R in the Antarctic Sea Urchin Sterechinus neumayeri

Gene expression of the DNA repair enzyme, photolyase (E.C. 4.1.99.3) was examined in the gonads, eggs, embryos and larval stages of the Antarctic sea urchin, Sterechinus neumayeri. Partial sequencing of the gene revealed two highly conserved regions, including a 300 bp region representing the binding site for the cofactor flavin adenine dinucleotide. The second 1200 bp region, likely representing a second light‐harvesting cofactor binding site, was identified in a second sea urchin species, Strongylocentrotus frascicanus. Probes for photolyase were developed from the shorter sequence, and expression in sea urchin developmental tissue and stages, and in response to in situ exposure to ultraviolet radiation was quantified using PCR and RT‐qPCR, with concentrations of photolyase normalized to actin concentrations. Photolyase was expressed in all tissues and developmental stages examined. In controlled field‐based experiments in McMurdo Sound, Antarctica, we found evidence of both constitutive expression of photolyase and induction in response to in situ exposure of embryos to UV‐R. Induction of photolyase was observed in response to greater ambient UV‐R (such as shallower water depths or sea ice‐free regions).

Laboratory experiments on the effects of diet on the gonad and pyloric caeca indices and biochemical composition of tissues of the New Zealand starfish Sclerasterias mollis (Hutton) (Echinodermata: Asteroidea)

Abstract Four experimental groups of Sclerasterias mollis (Hutton) were fed different diets for four months during the period of active gametogenesis. The gonad and pyloric caeca index of fed animals increased significantly compared to starved starfish which showed a steady decline. There were also some significant differences in indices between the different diets. The level of all biochemical components in the body wall was low compared to gonads and pyloric caeca and, in general, carbohydrate, lipid and protein were all significantly lower in starved than fed starfish. In the gonads carbohydrate level and content increased in fed starfish and decreased in starved animals and females generally had significantly higher carbohydrate levels than males. Although females had higher lipid levels in gonads than males, the only difference in lipids between diet groups was a higher content in fed than starved starfish. Protein showed little difference in level in the gonad between fed and starved groups although the total content was higher in fed starfish. In the pyloric caeca carbohydrate levels and contents were very similar in males and females with significant differences between the diet groups and between fed and starved starfish. Pyloric caeca lipid levels were significantly higher in starved than fed groups, but lipid contents were higher in fed than starved animals. Both pyloric caeca protein level and contents showed some significant differences between diet groups and between fed and starved starfish during the course of the study. Biochemical analysis of the prey species used showed no significant differences in levels of carbohydrate or protein, however, lipids showed significant differences between the three species with snails > mussels > cockles. These results suggest that the body wall, as well as the pyloric caeca, may act as a nutrient reservoir to support reproductive and maintenance activities under nutritional stress. In well fed starfish, gonad and pyloric caeca indices both increased, suggesting that reproductive processes can occur independently of the pyloric caeca under such nutritional conditions. There is clear evidence carbohydrate is transferred from pyloric caeca to ovaries during gametogenesis although carbohydrate transfer does not seem to occur in males. Differences between starved and fed starfish in lipid and protein suggest these components are also metabolised under nutrient stress. Significant differences in lipid levels in pyloric caeca of starfish fed different diets, and differences in the prey lipid composition strongly suggest biochemical composition of prey affects composition of the pyloric caeca of starfish, although this does not seem to occur for carbohydrate. It is likely that biochemical composition of the pyloric caeca in S. mollis is related not only to feeding rate and prey biochemical composition, but to digestibility, absorption and is probably also influenced by reproductive processes. Differences in the biochemical composition in the pyloric caeca between the starved and fed S. mollis suggest that a double mechanism of release of materials from the cells in the pyloric caeca to the gonad and autolysis of pyloric caeca tissue occurred concurrently in starved starfish.

Effect of Season on the Sensory Quality of Sea Urchin (Evechinus chloroticus) Roe

The influence of season, gender, and reproductive maturity on the sensory properties (appearance, odor, taste, flavor, texture/mouth feel, and after taste) of roe from sea urchins (Evechinus chloroticus) was investigated. A trained sensory panel applied descriptive analysis, with a comprehensive sensory vocabulary of 35 descriptors to analyze sea urchin roe obtained from samples collected during the austral autumn, winter, summer, and spring, over a 2-y period. Sensory differences between genders were less pronounced in autumn (March to May) and winter (June to August) when more nutritive cells were present in the roe, and more pronounced over spring (September to November) and summer (December to February) months as the gametogenic cells matured. Roe from female sea urchins were commonly associated with sulfur odor, bitter taste, and metallic flavor, while roe from the male sea urchins were associated with sweet taste. During autumn, female roe were closest in sensory quality to male roe (least bitter and most sweet compared to other seasons), while there were little differences in sweetness and bitterness of male roe over the 4 seasons. Despite the relative size of the roe being lowest in autumn, it appeared to be the optimum season to harvest E. chloroticus sea urchins to obtain high-quality roe.

Variation in sunscreen compounds (mycosporine‐like amino acids) for marine species along a gradient of ultraviolet radiation transmission within doubtful sound, New Zealand

Abstract We examined the response of four species of New Zealand marine algae (Ecklonia radiata, Apophlaea lyallii, Rhodymenia spp., Ulva lactuca) and a sea urchin (Evechinus chloroticus) to spatial variation in ultraviolet radiation (UV‐R) by examining the concentration of UV‐R absorbing compounds known as mycosporine‐like amino acids (MAAs). The purpose was to understand how, and the degree to which, local marine species could potentially respond to any future increases in incident UV‐R in the New Zealand marine environment. The research was undertaken in Doubtful Sound, where we observed a gradient of water column UV‐R transmission along the 40 km length of the fiord. We examined spatial differences in MAAs along the UV‐B gradient in the macrophytes and temporal changes in MAAs in sea urchin gonads. Among the algae, thallus MAA concentrations (nmol mg–1 protein) ranged from 12.5 to 87.8 in E. radiata, from 433.1 to 1446.4 in A. lyallii, 12.7 to 103.4 in Rhodymenia spp., but were not detected in U. lactuca. For E. chloroticus, gonadal MAA concentrations ranged from 83.9 to 224.3 nmol mg–1 protein spatially, and over the year from 1.85 to 14.12 nmol mg–1 dry weight (DW) depending on site and gametogenic cycle. Laboratory manipulations indicated that concentrations of MAAs in E. chloroticus gonads and eggs are influenced by diet. MAA concentration could be correlated with UV‐B intensities in two of the algal species. E. chloroticus MAA concentrations could also be correlated with UV‐B transmission, which we concluded was a reflection of the greater ingestion and accumulation of MAA‐rich macrophytes at those sites where higher ambient UV‐R induced greater MAA concentrations to occur in the algae. Given this, we suggest that one response of marine species to increases in UV‐B would be an increase in the synthesis and/or accumulation of MAAs for photoautotrophs and a dietary accumulation of those MAAs in E. chloroticus, an important herbivore in this system.

Photoperiodic regulation of oogenesis in the starfish Sclerasterias mollis (Hutton 1872) (Echinodermata: Asteroidea)

Female Sclerasterias mollis (Hutton 1872) fed cockles were maintained for 12 months under different photoperiodic regimes that were either in phase (8.65L: 15.35D) or 6 months out of phase (15.58L:8.42D) with natural conditions. The body sizes and the pyloric caeca index of both experimental groups increased continuously, regardless of the different photoperiodic conditions. However, the gonad index, size of oocytes and steroid levels in the 6-month out-of-phase animals showed entirely different patterns from those of the field population or the in-phase laboratory control group. The size of oocytes corresponded with the steroid levels in the ovaries of both experimental groups, suggesting that the environmental regulation of gametogenesis and gonadal growth is likely mediated via the endocrine system.

Seasonal changes in biochemical composition of body walls, gonads and pyloric caeca in two populations ofSclerasterias mollis (Echinodermata: Asteroidea) during the annual reproductive cycle

Seasonal changes in biochemical composition of tissues are compared in a shallow inshore and deeper offshore population of the seastarSclerasterias mollis (Hutton, 1872) on the Otago shelf, New Zealand, from 1985 to 1986. The biochemical composition of the body wall, gonads and pyloric caeca of the two populations did not differ greatly, even though reproductive output and nutrient storage of reserves were consistently higher in the offshore population. The biochemical composition of the ovaries and testes differed. High levels of carbohydrate and lipid were maintained in the ovaries from the commencement of vitellogenesis until spawning occurred. The testes had higher ash levels during spermatogenesis. During the annual reproductive cycle, an inverse relationship in the carbohydrate levels between the ovary and the pyloric caeca suggests nutrient transfer from the pyloric caeca to the gonads during gametogenesis. Annual changes in biochemical composition indicate that the body wall is also used for nutrient storage.

Deep‐basin macrobenthos of Doubtful Sound, Fiordland, New Zealand

Abstract The first quantitative deep‐benthic macrofaunal survey of a New Zealand fjord sampled the macrofaunal communities of 12 deep basins that are spatially subdivided along the two main axes of the Doubtful Sound complex. Within basin communities, there was high between‐sample variability of both abundance and family level alpha diversity. Despite this high variability, basin communities could be separated into high (entrance basins), medium (inner deep basins), and low (inner shallow basins) diversity communities, each having an associated characteristic change in family level beta diversity. Community groupings were comparable to previous qualitative community types described for other fjords in New Zealand. Fiord taxa appeared similar to those found on the continental shelf to the north, although there were some unique elements (Nuculanidae, Neilonellidae, Malletidae, Pronemomeniidae, Trochochaetidae), their presence supporting the notion of “emergent” species in fjord habitats. The observed differences in community composition between basins may represent differences in environmental tolerances or dispersal capabilities.