The population biology and ecology of scallops in Greater Omaha Bay (a semi-oceanic bay) and Kawau Bay (a estuarine bay) was quantified by observation and experiment. Information was collected to extend the knowledge base on northern New Zealand scallop population dynamics, and for application to potential scallop enhancement in the region. Contagious scallop population organisation was found at all spatial scales examined, ranging from bay wide through to individual bed patchiness, down to the scale of inter-animal distances. Such clumping has strong implications for a range of population processes, including fishing susceptibility and fertilisation success. Monitoring of adults found two main spawning events to occur; in late October and in mid January. Changes in the gonado-somatic index (GSI) were well synchronised between individuals within populations. Subsequent monitoring of spat-fall in artificial collectors documented two main recruitment events, probably the outcomes of the two local spawning events. These spat-fall events occurred on collectors separated by 1Os of km. However, substantial density variations occurred between sites, indicating that local hydrodynamics may have played a significant role in modifying local spat-fall intensities. Smaller spat-fall events were also present between the two major events. The number of spat collected at a number of combinations of site and time were sufficient to support commercial spat catching operations, although problems were encountered with spat detaching at sizes too small to be retained by the collectors. In the 1993/94 summer a large algal bloom event completely eliminated scallop recruitment to collectors for the first three months of that season. Mass mortality events were a major contributor to overall benthic scallop population mortality. Probable causes included intensive scallop harvesting (commercial and recreational), a major storm episode, and a large algal bloom. These effectively eliminated scallop populations from Greater Omaha Bay. The adjacent Kawau Bay was not affected by any of these particular events, but populations there did not survive long after reaching adult sizes. Estimates of M (natural mortality) were higher for all scallop populations than have been previously documented in New Zealand studies. Growth trajectories were reasonably consistent in waters shallower than 19 m, but a progressive decline occurred in both maximal size reached and average growth rates with increasing depth after this point. Food limitation may have been the mechanism involved, which is likely to vary significantly for other locations depending on local environmental conditions. Average time to recruitment to the fishery (100 mm shell width) was three years for the shallower populations. A slight reduction in average size of adults at higher densities was found for some populations, indicating a possible density-dependent effect. Examination of a high density scallop bed found animals to display distinctive substratum preferences over small spatial scales, with higher abundances occurring on coarser materials such as shell gravel, marl and grit. Mud was not favoured as a habitat type. Movements of tagged animals at this location were spatially limited to within the particular habitat patch in which an individual was tagged and released, i.e. at a scale of 1s to 1Os of metres. No animals moved between adjacent patches of similar habitat (100 m scale). A B.A.C.I type experiment was undertaken to assess incidental mortality effects of commercial scallop dredging on undersize scallops, at the spatial scale of beds. Significant negative effects were quantified, with the number of undersize animals killed per legal animal harvested estimated at 1.7 and 2.8 : 1, depending on the size frequency structure of the fished bed. Modelling of likely improvements in the number of animals surviving at the end of fishing, given a reduction in the minimum legal size from 100 to 90 mm, indicated improvements of 20 to 41% of the original population remaining after fishing, depending on animal size and assumed dredge efficiencies, A 90 mm MLS has subsequently been adopted by the Coromandel Scallop Fishery. The results from this work provide detailed population based estimates of parameters required for successful management and optimal harvesting strategies of Hauraki Gulf scallop populations. The large variability in parameters such as mortality, and strong abundance correlations with habitat type, has strong implications for such activities. This work also provides essential information for the undertaking of locally based enhancement operations, such as the spatial and temporal magnitude and variability of spat-fall events, and growth rates with respect to habitat features (i.e. depth).

The research presented in this thesis was undertaken in order to develop an understanding of the biology of Perna canaliculus sufficient to allow for commercial hatchery based production of Greenshell™ mussel spat. Hatchery production is an alternative to unreliable and inconsistent wild spat collection. In a Perna canaliculus population followed for one year spawning occurred in early spring and late summer. Three quantitative histological measures of gonad maturity utilising image analysis technology and a qualitative classification system were compared. Measuring the relative surface area comprised of gametes on histological sections was found to be the most reliable method. A practical gonad visual index to determine the reproductive condition of adults for the selection of broodstock was developed and found to be highly effective as a means of predicting induced spawning success. Serotonin was not effective for inducing spawning of Perna canaliculus. Temperature shock and the use of stripped gametes was however found to be a reliable spawning induction method. Relative gamete concentration, gamete age, temperature, sperm half life and gamete contact times were all found to have effects on fertilisation success for Perna canaliculus. Sperm concentration and the conditions of sperm aging were particularly important. Fertilisation kinetics of Perna canaliculus gametes modelled using the Vogel-Czihak-Chang-Wolf method suggested that 5% of sperm-egg contacts lead to successful fertilisation. Broodstock management protocols that could be used to condition the adult of Perna canaliculus were investigated in order to enhance and prolong the natural reproductive season. Research suggested that for successful broodstock conditioning animals should already have begun gametogenesis at the time conditioning is commenced. Successful conditioning of Perna canaliculus was achieved at temperatures between l0 and 16°C over a period of about 50 days. A diet ration above 2-3% of the dry meat mass per day is suggested. A trial examining non-algal diet supplements suggest a mixture of yeast and lipid emulsion may have some potential value. Photoperiod manipulation did not effect the reproductive condition of Perna canaliculus. The yield of veliger larvae was significantly enhanced if embryo culture water was treated with 1.0 mg/l EDTA. Veliger yield was not significantly affected at densities below 50 embryos/ml. Perna canaliculus larvae grew most rapidly and survived well at the salinity of 35 ppt. Larvae grew most rapidly when cultured at low densities. Experiments suggest that early larvae can be cultured at 5-10/ml, however late stage larvae grew most rapidly when cultured at l/ml. Perna canaliculus larvae displayed best growth and good survival if fed a mixed flagellate-diatom diet comprising Isochrysis galbana (T-Iso) and Chaetoceros calcitrans. The optimal diet ration, as a function of larval size, increased from about 20 cells/μl Isochrysis galbana (T-Iso) to around 150 cells/μl through the larval development period. Thyroxine between the concentrations of l0-5 and l0-8 M did not have an observable effect on larval developmental rate or eye spot development. Down welling settlement systems were found to be generally successful for Perna canaliculus lanrae. L-DOPA was also demonstrated to enhance the settlement and metamorphosis of Perna canaliculus pediveligers.

The marine pulmonate limpet Siphonaria Zelandica is commonly found in the mid-eulittoral zone in shallow pans or rock pools with dense algal growth. Though it resembles a true limpet externally, it is active when emersed during the ebbing of the tide browsing on small succulent algae, rather than grazing the surface film. The structure and function of the digestive and respiratory systems of Siphonaria were studied, particularly in relation to its adaptations to the intertidal mode of life. The digestive system is relatively simple consisting of a large buccal mass with paired salivary glands, a spacious esophageal crop, a slightly muscular stomach with two digestive diverticula and a simple intestine-rectum. The arrangement of the 28 muscles of the buccal mass and the odontophore is typical of patelliform pulmonates. The radula is a broad sheet with 144 ± 31 rows of teeth, each row having a tooth formula of (18±4) + (18±3) + (1) + (18±3) + (18±4). The radular teeth are continuously produced at a rate of 4.9 rows per day similar to those of active feeding herbivorous gastropods. The characteristics of the teeth and the movement of the mouth and the feeding traces showed that the feeding processes do not involve rasping of a hard substratum but browsing and scooping of soft lush algal growth. The whole alimentary tract is lined by ciliated columnar cells of a basic form but with slight structural variations in different region. Those in the oesophagus and stomach contain apical vesicles and lysosome-like bodies indicating involvement in intracellular digestion, while those in the intestine contain various amounts of lipid and glycogen, functioning in active absorption and storage. The ciliated cells of the post-intestine, having a much folded basal plasma membrane are apparently involved in osmoregulation. The proteinaceous secretory cells in the crop and mid-intestine and the glycoprotein cells in the pro-intestine are either producing enzymes for extracellular digestion or secreting the faecal-binding sheath. Mucous cells interspersed among the ciliated cells of the oesophagus intestine and rectum produce mucoid material for lubrication and transport of food particles. The cuticular strip in the anterior chamber of the stomach, probably a vestigial gastric shield consists of tall non-ciliated cells with thick microvilli embedded in a dense fibrous matrix. The salivary gland contains six cell types: grain cells, duct mucocytes, mucocytes I and mucocytes II, duct ciliated cells and undifferentiated cells. The first four are secretory, the grain cell being serous secretory and the other three muciparous, with varying amounts of mucopolysaccharides. The tubules of the digestive gland are made up of five cell types, acinous digestive cells, neck digestive cells, crypt cells, vacuolated cells and undifferentiated cells. Both types of digestive cells participate in absorption and digestion. The high lipofuscin content in the neck digestive cell suggests its possible role in lipid digestion. The crypt cell with elaborate GER whorls and proteinaceous globules is apparently secretory, producing enzymes for extracellular digestion. Apocrinal secretion of the globules from the crypt cells was observed for the first time. The vacuolated cells appear to be degenerated crypt cells with an excretory function. The digestive gland tubule was found to undergo cyclic changes, correlated with the feeding activity which is related with the tides. Enzyme assays showed the presence of various carbohydrases, proteolytic and lipolytic enzymes in the different region of the digestive system. The digestive gland is the main site of enzyme production. The pH optima of amylase, laminarinase and sucrase from various regions of the digestive tract were found to be within the pH range of the alimentary tract. The activities of various enzymes in the salivary gland and the oesophagus but not digestive gland were synchronous and correlated with feeding. When emersed, Siphonaria respires atmospherically with the pneumostome wide open, and the mantle cavity functioning as a lung without any active ventilatory movements. When submerged, the mantle cavity is filled with water, a strong water current through the gill being created by the ciliated dorsal and ventral raphe behind the gill. The available respiratory surfaces include the sides of the foot, the anterior mantle roof and the single plicate gill. All these are lined by a thin epidermis with large blood spaces beneath it the non-ciliated epidermal cells in different regions carry different lengths of microvilli, apparently related to the degree of their protective role. The respiratory physiology of Siphonaria was also studied. No tidal or diurnal rhythm in oxygen consumption was revealed. In unagitated conditions the aerial respiratory rate was much higher than the aquatic rate but with agitation, the aquatic rate increased to near the aerial rate. Cutaneous respiration constituted about 25% of the total. The respiratory rate varied with body weight, the coefficient b being temperature-independent (0.791 ± 0.122). Both aerial and aquatic respiratory rates increased with temperature. The highest temperature-sensitive range was 10-25°C in winter and 15-30°C in summer which coincided with the normal environmental temperature. No seasonal temperature acclimation was found within the normal thermal range. Respiratory pigments haemocyanin and myoglobin were detected in the blood and buccal mass respectively. Their characteristics were studied and their role in oxygen transfer system was postulated. The reverse Bohr shift of the haemocyanin may facilitate oxygen uptake in the lung during burses of activity at low tide. A high oxygen-combining capacity of the buccal mass myoglobin (21.2 vol%) indicated a role of oxygen storage during bursts of feeding activity. The distribution of carbonic anhydrase in various tissues was consistent with a transfer system facilitating the release of metabolic CO2 from the buccal mass. Finally the phylogenetic relationships of Siphonariidae with other groups of marine pulmonates were discussed. The unspecialised digestive system, the advanced form of nervous system and the possession of a secondary gill suggest that Siphonariidae, as a family, may not be an advanced derivative of any of the more primitive living basommatophoran groups, but could represent, along with the Gadiniidae, a specialized group which has originated directly from a primitive pulmonate stock and are adapted to life on exposed rock shores.

Two subtidal reef communities characterised by sponges were examined to assess two distinct aspects of marine benthic community ecology which have not previously received much attention. The first study focused on the role of settlement events in the origin and maintenance of community structure and involved investigation of factors affecting dispersion, settlement and recruitment of sponge propagules. The second examined how natural gradients in ambient physical conditions, in the absence of disturbance, affected size structure and species interactions within the community. Settlement events were examined on a reef flat which was covered by a shallow sediment overlayer. The distribution and abundance of established sponges was found to be highly correlated with sediment regimes. The sponge community was shown to be stable over time and able to resist disturbance by storms because of the presence of turfing algae. Sponge settlement was inhibited by the sediment overlayer. Established sponges were found clumped into oblong groups orientated east-west and there were many instances where sponges were found closely associated. Adjacent areas were characterised by deeper unstable sediments and fewer sponges. Storms contoured sediments into ripples and scoured oblong east-west orientated patches of basal rock. Sediments were also sorted during storms such that particles of large grain size were left around the edges of ripples and over the scoured rock patches. The basal reef of both the stable and unstable areas was covered in a mosaic of encrusting algal and sponge species which tolerated the sediment overlayer. This assemblage was also exposed during storms. Sponges reproduced in a number of ways, but asexual propagules were the most successful. Sponges from several orders produced buds which developed in a complex manner. Buds adhered to rock and shell fragments of large size which acted as anchors, or attached to other buds irrespective of genotype. The change in weight and shape increased the likelihood that buds would gravitate into the scoured patches of basal rock. Bud loss off the reef was minimal. Buds were able to settle onto the basal rock patches and did so almost exclusively onto bare rock. A high degree of 'selectivity' of settlement site by buds was imparted by altering developmental rate during the settlement process in response to the substrate type. Polymastia granulosa buds exhibited an additional developmental sequence not previously reported for any colonial organism. Buds either settled directly in suitable conditions, or developed further along a different pathway. Buds which did not come into contact with basal rock elongated and appeared to be capable of digging into sediments. The elongated bud then broke up along its length into smaller particles, termed 'beads', which were capable of movement and invariably settled onto gravel fragments. Sponges were shown to settle onto scoured rock patches during storms and were eventually covered by sediments. Subsequent survivorship and recruitment depended species specifically on sediment depth and quality. Settlement patterns matched the observed dispersion patterns of established sponges and suggested a mechanism whereby the community had originated and how structure was maintained. These hypotheses were tested experimentally in situ and in the laboratory. The importance of asexual modes of reproduction, and settlement mediated by physical disturbance appears to be a common formula for recruitment by colonial marine organisms. Recruitment events were found to explain the distributional patterns of the established population. The structure of populations of thin encrusting species on vertical reef walls was examined in a novel manner whereby the mean size and density of individuals was quantified and related to gradients in the ambient physical environment. This was achieved by examining the benthic communities on a range of subtidal reef walls of uniform slope and aspect, but which were subject to natural gradients in physical conditions. The species composition of each of the six reefs studied was similar but the size structure of communties changed within each reef system in response to gradients in light intensity and water movement. Fish and urchin disturbance was shown to be unimportant and there was no indication that storms disrupted communities. The implications of changes in size structure of populations on interactions between component species in different ambient conditions were examined. The eastern wall of two cave, archway and open reef systems was surveyed according to a stratified sampling design where each reef was divided by depth and distance along the wall. Different taxonomic/morphological groups were found at particular positions on reef walls. Thin encrusting algal species were found to be one of the most abundant groups. It was assumed that the individual size of encrusting species at each wall position reflected long term ambient environmental conditions as well as the ability of each species to maintain itself against overgrowth by neighbours. By relating the population size structure of different taxa with indices for light intensity and water movement recorded at each wall position within each reef, it was shown that community structure varied markedly on the same reef wall as a function of ambient physical conditions. Changes in proportional species composition, notably from thin encrusting algal dominated assemblages to sponge characterised assemblages, with decreasing light intensity were accompanied by changes in the individual size structure of populations. At each wall position all species exhibited similar individual size. Individual size decreased and density of individuals of all species increased with decreasing light intensity. In conditions where light levels were not sufficient to support algae, individual size of encrusting fauna increased with increasing water movement. The implications of these observations on competitive interactions between encrusting species was examined. The outcome of competitive interactions between the same species was found to vary depending on wall position.

‘Infaunal haloes’ of either decreasing or increasing abundances of individual soft-sediment species with distance from reefs have been suggested to be caused by reef-associated predators. A large-scale mensurative experiment was used to investigate the distribution of two size classes of macrofauna with distance from the reef edge across three locations in northeastern New Zealand. The role of reef-associated predators, the snapper (Pagrus auratus Sparidae) and rock lobster (Jasus edwardsii Palinuridae), was investigated using established marine reserves at each location. Consistent patterns were found in a few large-bodied fauna. The hermit crab Pagurus novizelandiae occurred more frequently near the reef edge, whilst the heart urchin Echinocardium cordatum and bivalve Dosinia subrosea were more abundant further away from the reef. Dosinia subrosea and another bivalve, Myadora striata, exhibited lower biomass at sites with higher densities of snapper and rock lobster. In contrast, small-bodied macrofauna showed no consistent patterns with distance from the reef or among sites with different predator populations. It was hypothesised that predation was driving the distribution of large bivalves. An experiment was done to investigate this model using D. subrosea. Equal densities of this bivalve were established in plots either with or without cages at sites either inside or outside of reserves. Significant predation was detected, but only inside reserves. Much of this mortality could be specifically attributed to predation by large rock lobsters, given the distinctive marks on the valves of dead D. subrosea. Inside reserves, predators are not only more abundant but also larger. It was hypothesised that different size classes of predators would result in different levels of predation. Laboratory feeding experiments were used to investigate this model. Lobsters of all sizes chose D. subrosea over the heavier shelled D. anus. Small lobsters chose to prey on small D. subrosea and large lobsters more frequently chose larger prey. The distributions of these two bivalve species at protected (large predators) and fished sites (small predators) reflected the feeding choices observed in the laboratory. Results suggested that rock lobster populations are capable, where their size structure is not truncated by fishing pressure, of controlling population-level dynamics of bivalve communities adjacent to reefs.

This thesis presents a descriptive and a functional analysis of the ecology of an island host-parasite system consisting of the Polynesian rat, Rattus exulans (Peale) and its gut helminths. The results, which include an historical perspective, are presented in the form of 7 papers or sections. Each of these examines a particular aspect of this host-parasite relationship. A review of the origin and an update of the theorised dispersal of this rat from Southeast Asia to New Zealand is given in the first section of chapter one. Previous theories have derived the New Zealand populations from a line which passed through Micronesia. In accordance with new information from the Lapita cultural assemblage, this rat is now theorised to have accompanied these "Lapita" peoples through the Bismarck Archipelago and Solomon Islands, arriving in the Tonga- Samoa region about 3600-3000 Before Present (B.P.). From here, the Proto- Polynesians then dispersed further east, taking with them the commensal R. exulans, pig, dog, and chicken. This rat is thus thought to have arrived in New Zealand, the most southern and last-settled landmass in Polynesia, in the canoes of the Maori about 1000 years ago. Information on the ecto- and endoparasites of the Polynesian rat from throughout its geographical range is collated and presented in section two. This includes the results of the two surveys (one being part of this thesis) done on the parasites of this rat in New Zealand. All populations of R. exulans sampled in these two surveys came from offshore islands, to which this rat is almost totally confined, and where, on many, it is the only rodent species present. In contrast, most of the populations sampled beyond New Zealand are now sympatric with other rodent species. For the New Zealand populations only, it was also possible to identify those parasites only accidentally associated with this host; these are listed as "transients". In section three, an attempt is made to determine the probable biogeographical origins of parasites recorded from populations of this rat on "exulans only" offshore islands of New Zealand. Such a study was possible only because of the archaeologically documented commensal relationship between rat and Polynesian man. This information, detailed in section one, together with the parasitological data base assembled in section two, provided the material for this analysis. Several "heirloom" species are identified, theorised to have been inherited by this rat during speciation somewhere in Island Southeast Asia. Parasites acquired during dispersal are divided into "old" and "new souvenirs"; the former are thought to have been acquired from sympatric rodent species in Near Oceania sometime prior to 3000 B.P., and the latter from R. rattus, R. norvegicus or Mus musculus introduced in the last 200 years during European settlement in New Zealand. The conclusions further suggest that some at least of the "new souvenir" species have been acquired by R. exulans on "exulans only" offshore islands of New Zealand by cross-transfer from other rodent species which have temporarily gained access to these islands. This theory is examined in more detail in the fourth section, and reports of such accidental colonizations of offshore islands are presented as supporting evidence. In Chapter two, the influence of habitat on the population demography of the host is investigated. Nearly 1000 rats were trapped and necropsied over a 17 month period in three different habitats on Tiritiri Matangi, an "exulans only" island at the entrance to the Auckland harbour. Rank grassland which covers most of this island formed one habitat; a second consisted of forest remnants confined to gullies, and the third consisted of the small, inhabitated, lighthouse station and farmed area at one end of the island. Between-habitat differences were observed in diet, adult longevity, mean weight of immatures, the time of onset of sexual maturation, and annual reproductive output. These results suggested several modifications to existing models of this host's demography in New Zealand. Shelter in particular appears to play an important role in the demography of this species in temperate latitudes. The effects of parasitism on potential fitness parameters e.g. reproduction, and adult mortality/survival, are examined in chapter three. Based on the results obtained in chapter two, a number of hypotheses were developed, and the predictions arising from these were tested. Few significant results were obtained; these revealed habitat and some sexual interactions with the level of infection, at certain times of the year. However, no causal relationship could be established between these effects and host reproduction or mortality. It is concluded that the helminth parasites of this rat on this island have little or no effect on these host parameters, and support the suggestion that these species constitute a depauperate and well-adapted rodent parasite fauna. The last chapter presents the results of an analysis of the effects of habitat, season, host age, and sex on the distribution and abundance of the helminths of this rat on this island. Together, the graphs and the statistical analyses demonstrate that habitat has the most important influence, significantly affecting all 7 species; this effect is of greater magnitude than the other 3 variables on 5/7 of these species. Season and age also have important effects, while sex had no apparent influence. Explanations for the observed patterns are sought in known aspects of the biology of the host in the three habitats described in chapter two, and in the life cycles of the parasites. In total, this thesis provides a comprehensive account of the ecology of the Polynesian rat and its helminth parasites on Tiritiri Matangi Island. It also identifies gaps in the existing data base, formulates certain hypotheses, and makes a number of predictions all of which will hopefully stimulate further interest in this rat and its parasites.

Interactions among large brown macroalgae, sea urchins, and fishes were investigated in northeastern New Zealand during the period 1988 - 1993. The Cape Rodney to Okakari Point Marine Reserve was the site of many of these investigations. The patterns of abundance of large brown macroalgae and urchins down depth gradients over a wide geographic range were compared with those reported from earlier studies, and 3 major trends were identified. First, the fucoid alga Carpophyllum flexuosum now occurs at many sites which are exposed to wave action, in contrast to earlier studies. This alga occurred most abundantly on urchin-grazed coralline flat areas. Second, at four sites in the Marine Reserve, the densities of the echinometrid urchin Evechinus chloroticus decreased with increasing depth, rather than reaching maximal densities at mid-depths, as had previously been described. Finally, at sites of decreased exposure to wave action, the coralline flats habitat did not occur at all, and dense stands of. C. flexuosum occurred, in conjunction with the ubiquitous laminarian alga, Ecklonia radiata. Following the discovery of this new algal component to exposed rocky reefs, a more detailed study of its population characteristics was initiated. The population size structure of C. flexuosum on coralline flat areas was markedly different from that of the same species in sites sheltered from wave action. These differences occurred at both offshore islands and sites near Leigh, suggesting that it was a general pattern. C. flexuosum plants on coralline flats were smaller than those from sheltered sites, and had a greater number of smaller laminae, heavier stipes, and a greater degree of branching. There was some evidence of temporal change in the morphology of C. flexuosum from coralline flats. Comparisons between a site with C. flexuosum and a site with coralline flats suggested that the activity of fish was 75% lower in the vegetated than in the unvegetated site, and the feeding rate in the vegetated site was less than 50% that in the unvegetated site. I speculate that future effects on fish activity of the invasion of C. flexuosum into a habitat which previously lacked macroalgal vegetation may depend on changes in the morphology of plants. An investigation of many aspects of the biology of E. chloroticus in different habitats was undertaken. Analysis of the body dimensions of E. chloroticus suggested that this species was relatively tall compared to other echinometrids (average ratio of test height: test diameter = 0.54), Comparisons among habitats with differing amounts of vegetation revealed only small differences in the relationship between test diameter and test height. Small E. chloroticus (<40 mm test diameter) lived in crevices, while larger individuals grazed freely over the substratum. In vegetated habitats, the crevice-dwelling habit was maintained at test diameters about l0 mm greater than in unvegetated habitats. Very small (<20 mm test diameter) E. chloroticus frequently covered themselves with shell. Population size structures of E. chloroticus within the Cape Rodney to Okakari Point Marine Reserve were bimodal; other localities had unimodal populations. Modal sizes varied among localities, with smallest modes (50-60 mm TD) being found at Inner Hauraki Gulf sites, and largest modes at the offshore Mokohinau Islands (70-80 mm TD). Habitat did not predictably affect population size structure. A bimodal population structure was maintained at Waterfall Reef rock flats throughout the 5-year study period. Gonad size showed seasonal fluctuations at several sites, being greatest in summer. There were few consistent differences in gonad size between biological habitats. Gonad colour varied among sites and habitats, with orange gonads generally being more prevalent in vegetated habitats, and black gonads being represented more in unvegetated habitats. Smaller urchins had greater proportions of orange gonads, while larger urchins had greater proportions of brown and black gonads. Although highly variable among individual urchins, movement of E. chloroticus was greater at unvegetated sites (0.7 m per 5 days) than at vegetated sites (0.4 m per 5 days), in the Marine Reserve. Feeding of E. chloroticus was studied at a number of sites in the Marine Reserve. Urchins frequently consumed drift algae, particularly E. radiata. C. flexuosum was consumed at less than half the rate of other macroalgae in several laboratory feeding experiments, and was chosen least frequently in a field assay of feeding preferences among 8 species of macroalgae. Boosting densities of E. chloroticus in stands of E. radiata to 60 m-2 led to destructive grazing of plants over a 2 month period - at lower densities, the urchins dispersed. Densities of C. flexuosum were effectively unchanged when urchin densities were increased to these elevated levels. As a result of these observations I speculate that feeding preferences of E. chloroticus may have a role in allowing C. flexuosum to survive on coralline flats. In a laboratory experiment, urchins from a feeding aggregation did not graze algae at higher rates than individuals from outside aggregations. Diets of both E. radiata and C. flexuosum consistently produced similar gonad volumes in urchins held in the laboratory, although gonad volumes produced were low. A preliminary experiment suggested that C. flexuosum from exposed sites was consumed at lower rates than C. flexuosum from sites which were sheltered from wave action. These differences in palatability are mirrored in the formation of stable borders between coralline flats and C. flexuosum of the sheltered morphology, and the ability of C. flexuosum of the exposed morphology to survive in the coralline flats habitat. The fish fauna of the Cape Rodney to Okakari Point Marine Reserve was shown to be different from that of a nearby area. A number of species were more abundant within the Marine Reserve. Subsequent surveys showed that there were differences in abundances of 3 large carnivorous fishes among sites within the Marine Reserve, and that population size structure and the distance within which divers could approach one species, (Pagrus auratus), clearly varied between areas within the Marine Reserve. Mean standard length of P. auratus in the central marine reserve was 40% larger than that of P. auratus outside the central marine reserve, and the average minimum approach distance was 70% less in the central marine reserve. Feeding of fish by humans in the central part of the Marine Reserve was suggested to be the main cause of the differences in responses to divers. Population size structure of, and crevice occupancy by, E. chloroticus, clearly differed between the Marine Reserve and an adjacent area, with bimodal population size structures and a 10 mm greater size of crevice occupancy occurring in the Marine Reserve. The implications of these findings for extrapolating from experiments done in one area to other areas are discussed. The major biological components of rocky reef habitats identified in this study were broadly similar to those identified in previous studies in northeastern New Zealand, and have parallels in overseas studies. Long term changes to the flora of rocky reefs in northeastern New Zealand have occurred, and appear to persist by a mechanism which had previously been discounted. Similar processes to those observed in overseas studies appear to maintain habitats (consistent recruitment of algae or urchins to habitats which they dominate), or cause them to change from one habitat state to another (e.g. grazing outbreaks by urchins). However, the predictability of the persistence of these habitats at a particular site appears to be low. Further, the precise mechanisms whereby habitats may change from one to another may also be unpredictable. I argue that there is little scope for general statements concerning the spatial and temporal occurrence, or mode, of habitat transitions on temperate subtidal reefs. This study emphasises the value of repeated descriptions of patterns of abundance, and highlights problems of extrapolation and generalisation in marine ecology. Insufficient information exists at present to comment adequately on the persistence of subtidal habitat types. This may in part stem from the types of information which have been collected in the past. Methodological problems with the use of quadrats to sample densities of organisms in areas of differing topography are therefore addressed. In conclusion, it is suggested that sampling protocols which incorporate a variety of information, gathered over as wide an area, and as intensively as possible, should be used in future research of this type.

The New Zealand green-lipped mussel, Perna canaliculus, is farmed by an aquaculture industry (> NZ$ 150 million/year) that is dependent on mussel juveniles (spat) collected from unpredictable and unreliable wild sources for more than 80% of its mussel seed requirements. Most wild-caught spat is collected from the surf zone at Ninety Mile Beach, northern New Zealand, where unique environmental conditions cause the accumulation and transport of spat attached to drift algae, which arrive to the shore in great quantities (up to 100 tonnes at once). This study is the first to investigate the ecology of mussels at Ninety Mile Beach throughout their life history, including reproductive behavior, micro-scale settlement patterns on filamentous macroalgae, accumulation and transport of mussel spat to the shore, colonization of the rocky intertidal, and adult population dynamics. Histologic investigation of 4 intertidal and 2 subtidal populations revealed that females and males were well-synchronized throughout their reproductive cycles, with a prolonged spawning season from June to December, when temperatures were lowest and rising. Comparisons of gonad indices and maximum shell length indicated high productivity in certain populations, which likely contribute to the high larval availability of the area. Experiments showed that mussel spat preferentially settled on fine-branching natural and artificial substrata, with correlation evident between mussel shell size and degree of branching. Furthermore, greater numbers of mussels settled on node versus internode areas within natural and artificial substrata. Chemical cues for mussel settlement also were studied using phytogel plates spiked with algal extracts, which were preferred over control plates by mussel larvae/post-larvae in the field, and by hatchery-reared larvae in the laboratory. Three intertidal populations were investigated at different temporal and spatial scales. Mussel concentrations in seawater were higher after spawning for both small mussels (< 0.25 mm) in August, and for larger mussels (> 0.5 mm) in March. Settlement patterns within quadrats cleared of mussels in 2 habitats (adult mussel bed and adjacent areas covered with algae) were studied from July 1999-March 2001. Primary settlement (mussels < 0.5 mm) was found to dominate the algal habitats at the beginning of the spawning season in August, while secondary settlement (mussels > 2.0 mm) was higher in the adult mussel bed late in the spawning season (November-March). Monthly surveys of undisturbed quadrats indicated that a peak in new recruitment coincided with a peak in adult mortality in August. At Scott Point, massive mortality for 2 years in August was followed by a dramatic re-colonization of the empty spaces by juveniles. Settlement patterns of mussels on suspended ropes in the water column were investigated at 3 water depths inside and outside Ahipara Bay during 2 spawning seasons (1999-2000). Mussel settlement was higher for small mussels (< 0.49 mm) in shallower water (2 m water depth) in August, and higher for larger mussels (> 1.0 mm) at greater depths (18 m water depth) in September-December. Mussels found on shallow-water ropes may have settled directly from the plankton, whereas mussels on ropes near the bottom (18 m) may have transferred from macroalgae tumbling on the seafloor. Environmental conditions associated with mussel spat arrival to the beach (spatfall events) were studied by statistical analysis (1990-1998; daily, monthly, inter-annually) of wind speed/direction, tidal range, water temperature, swell height/direction, and records of spatfall events/amounts. Spatfall events/amounts were more abundant during days of strong offshore winds. Swell height in the onshore direction was significantly correlated with spatfall events/amounts. Storm events (wind speeds > 20 m/s) were most frequent between May-August; spatfall events/amounts were more numerous 4 months later (September-October). Years with more storm events (El Niño/La Niña episodes) were associated with significantly higher spatfall events/amounts.

This thesis examines sublethal stress responses in the common New Zealand estuarine bivalve, Austrovenus stutchburyi (cockle). The approach used throughout this thesis is a refinement of the biological indicator approach of Adams (1990), in which biomarker data are collected primarily at the individual and sub-organismal levels, but with additional measurements at the population and community levels. In this research several biochemical and physiological biomarkers are used to assess effects of contaminants on energetics, fecundity and growth of cockles. Adenylate energy charge (AEC) and total adenylate nucleotide pool (TANP) are biomarkers that have previously not been used with A. stutchburyi, and provide new information on energy cycling for this species. RNA concentration has also not previously been used with cockles, and this biomarker is correlated with growth. Glycogen concentration and condition indices are used to indicate reproductive potential and overall health. In order to fully investigate the utility of this comprehensive suite of biomarkers, their performance in laboratory and field situations was tested. Temporal variability in AEC, TANP and glycogen was analysed over two years for two populations of cockles in a northern harbour. The results indicated seasonal patterns for all biomarkers, with AEC reaching a maximum value in spring, TANP being lowest in winter, and glycogen concentration being high over spring and summer. Variability in biomarker response between cockles sampled at low tide and high tide was analysed in a laboratory experiment simulating exposure to air during low tide. Adenylate energy charge was found to be significantly lower in cockles after exposure to air for 4 hours, highlighting the importance of standardised collection protocols. These initial patterns, as well as spatial variability in biomarker response, were further investigated at several sites within a second harbour south of Auckland. There was little among site difference in glycogen concentration, and the data suggested that differences in site characteristics, such as sediment quality and type, were driving the mixed response patterns of AEC, TANP and condition. Because of inherent variability in field conditions, a series of laboratory experiments was then undertaken to assess responses under carefully controlled conditions. Cockles were challenged with PAHs, chlordane and tributyltin at two different doses, and biomarker response (AEC, TANP, glycogen and RNA) measured. One trial examined the effects of a one-off pulse of contaminant, in which sediment containing cockles was dosed at the outset of a 14-day experiment with a high concentration of contaminant. A daily dose of this same concentration of contaminant was supplied to the sediment for 14 days in a second trial to assess effects of a more continuous discharge. There were virtually no significant differences in biomarker response between treatments and controls for either trial, suggesting that the experimental setup may have been causing sublethal stress in some way. Finally, in order to maximise experimental control whilst maintaining environmental realism, a manipulative field experiment was undertaken in which cockles were transplanted from an uncontaminated site to a series of uncontaminated and contaminated sites in one of Auckland's major harbours. Biomarker response (AEC, TANP, glycogen and RNA) was measured in the transplanted and the autochthonous populations two weeks and eight weeks after transplantation. An ability to regulate adenylate nucleotides was detected, as cockles transplanted to contaminated sites had reduced TANP but maintained AEC levels. There were significant differences in glycogen and RNA among sites, with highest levels detected in cockles transplanted to an uncontaminated site. This suite of biomarkers showed great utility for use in environmental quality assessment. It is recommended that an approach such as that used in the Mussel Watch programme in the United States be employed for cockles, in order to monitor estuarine ecosystem health in New Zealand. The transplantation of cockles to estuaries where there are concerns about environmental quality, and the use of TANP, glycogen and RNA concentration to assess sublethal stress, has potential as a sensitive and cost-effective environmental monitoring technique for estuaries in New Zealand.

The eggs and larvae of the New Zealand snapper Pagrus auratus are pelagic with early buoyancy provided by dilute body fluids. The swimbladder begins to develop on the third day after hatch from a dorsal evagination of the gut tube. Communication w1h the gut is lost on about the tenth day following pneumatic inflation at around day eight. At this age the gas gland system appears fully functional and capable of secreting gas. By the age of settlement at around 30 days the swimbladder is a fully functional replica of the adult form except for the lack of a resorbent capillary system which does not develop until later in juvenile life. The swimbladder of the adult is of the euphysoclist form with a dorsally located resorbent oval area and sits high in the pleural cavity. The ventral tunica externa is firmly attached to the connective tissue lining the pleural space. The adult swimbladder displaces 5.6% of the volume of the body and its volume is regulated to provide near neutral buoyancy. The connective tissue integument provides almost no restriction to volume changes brought about by vertical movements of the fish and the swimbladder obeys Boyle's Law for physiological pressure changes. The ability of the connective tissue of the tunica externa to accommodate large tissue strains is due to massive regular crimping of otherwise straight collagen fibrils allowing reversible extensions up to 130%. In all other respects however the tissue structure of the tunica externa is consistent with a tissue providing an active mechanical role. The fibrillar morphology and physicochemical properties of swimbladder collagen is consistent with the vertebrate type I form however there are interesting variations in collagen form distributed throughout the swimbladder. Fibrillar morphology of the highly extensible tunica interna is significantly different to that of the tunica externa and appears to play very little mechanical rote. The extensibilty of the tunica externa appears to be regulated by physiological stress and related to the past history of tissue strain.