The intertidal zone is finely partitioned in species distributions and abundances. The demographies of key species over varying spatial and temporal scales are fundamental to understanding the population structure and overall dynamics of habitats and assemblages. In this thesis, settlement, dispersal and early life stage survival and growth were examined in several habitat-forming intertidal fucoid algae in New Zealand and Oregon, U.S.A. Natural settlement patterns of Hormosira banksii, Cystophora torulosa and Cystophora scalaris were quantified for over three years at a semi-protected shore in southern New Zealand. Settlement was monitored in four tidal zones, within bare rock and algal habitats. Settlement was synchronous between tidal zones but the density of settlement varied spatially and temporally. There were significant differences between tidal zones, habitats and times of the year. For H. banksii, small pulses of settlement occurred year-round with greatest densities during spring and early summer. Greatest settlement occurred at low tidal zones and under adult canopies. Both Cystophora species also reproduced year-round, but had much lower settlement densities than H. banksii. Most settlement occurred during spring and summer, while only small pulses occurred in autumn and winter months. Most settlement was in the lowest tidal zone (0.4 m above chart datum), with only a few zygotes settling at higher shore zones. Canopy cover had no significant effect on settlement densities. Dispersal was examined in Durvillaea spp., H. banksii, C. torulosa and Fucus gardneri. For all species, settlement densities declined with distance from the source populations, but densities were variable between species. Durvillaea spp. dispersal was more extensive than expected, with significant settlement occurring 32 m from the source population, the maximum sample range of the study. However, settlement densities were much higher within 8 m from the source. The extensive dispersal of Durvillaea spp. is a result of the combination of small, slowly sinking eggs and the presence of buoyant mucilage. The other species studied showed far more restrictive dispersal, and much lower settlement densities. Settlement occurred 2 m from the source, but most settlement occurred under or near the canopy. The eggs of these species are much larger and sink faster than the eggs of Durvillaea spp. The consequences of settling at different shore heights and seasons were examined in H. banksii and D. antarctica in New Zealand, and F. gardneri and Pelvetiopsis limitata in Oregon. Transplant experiments tested the effects of grazing and heat/desiccation stress on survival and growth of germlings at different shore heights, during different seasons. High germling mortality was a feature of all species, but rate of mortality depended on conditions and species. There is a trade-off for settling at different times of the year; overall, growth was faster in warmer seasons, but survival was better in cooler seasons. During cooler seasons, germlings are exposed to less heat/desiccation stress, but their slow growth exposes them to grazing and competitive interactions for longer periods. For New Zealand species, shore height had large effects, with better survival and growth in the low shore. Grazers were very effective in the low shore, and heat/desiccation stress had strong effects in the mid and high shores. For Oregon species, effects of grazing and heat/desiccation stress were generally weaker than for New Zealand species. Shore height had weak effects, but ultimately low shore germlings had poor survival, primarily because of overgrowth by ephemeral algae. This is in contrast to the generalisation that survival and growth in the low shore should be better due to a more benign environment. In this study, species had specific demographies that related to their life history characteristics and responses to the local environment. Differences in settlement, dispersal abilities, survival and growth over small spatial and temporal scales clearly underpinned large scale differences in recruitment and adult distribution and abundances.

Fucoid algae live in the intertidal region where they experience daily fluctuations in light and external osmotic environment. High light, especially in combination with ultraviolet (UV) radiation and hyper-osmotic stress affected the cellular physiology of Fucus embryos. Two photoinhibition responses were recognised. Firstly, a rapid decline of the photosystem II (PSII) efficiency, linked with the operation of the xanthophyl cycle, followed by a slower decline correlated with reactive oxygen species (ROS) production. As a result of enhanced ROS production, a slower repair of the PSII efficiency was observed, particularly with increased UV-B doses. Development of the embryos was transiently affected by UV-B. The cellular signal transduction pathway during hyper-osmotic stress was investigated. ROS production in response to hyperosmotic stress comprised two distinct components. The first ROS component coincided closely with the origin of a Ca2+ wave in the peripheral cytosol at the growing cell apex, had an extracellular origin, and was necessary for the Ca2+ wave. Patch clamp experiments showed that a non-selective cation channel was stimulated by H2O2, and may underlie the initial cytosolic Ca2+ elevation. The spatio-temporal pattern of the Ca2+ wave was thus determined by peripheral ROS production. The second, later ROS component localised to the mitochondria and was a direct consequence of the Ca2+ wave. The first, but not the second component was required for short-term adaptation to osmotic stress, probably through the activity of cell wall bromoperoxidases. Mitogen-activated protein kinases may be involved in the hyper-osmotic stress response downstream or independently of the mitochondrial ROS production.

The intertidal zone is finely partitioned in species distributions and abundances. The demographies of key species over varying spatial and temporal scales are fundamental to understanding the population structure and overall dynamics of habitats and assemblages. In this thesis, settlement, dispersal and early life stage survival and growth were examined in several habitat-forming intertidal fucoid algae in New Zealand and Oregon, U.S.A. Natural settlement patterns of Hormosira banksii, Cystophora torulosa and Cystophora scalaris were quantified for over three years at a semi-protected shore in southern New Zealand. Settlement was monitored in four tidal zones, within bare rock and algal habitats. Settlement was synchronous between tidal zones but the density of settlement varied spatially and temporally. There were significant differences between tidal zones, habitats and times of the year. For H. banksii, small pulses of settlement occurred year-round with greatest densities during spring and early summer. Greatest settlement occurred at low tidal zones and under adult canopies. Both Cystophora species also reproduced year-round, but had much lower settlement densities than H. banksii. Most settlement occurred during spring and summer, while only small pulses occurred in autumn and winter months. Most settlement was in the lowest tidal zone (0.4 m above chart datum), with only a few zygotes settling at higher shore zones. Canopy cover had no significant effect on settlement densities. Dispersal was examined in Durvillaea spp., H. banksii, C. torulosa and Fucus gardneri. For all species, settlement densities declined with distance from the source populations, but densities were variable between species. Durvillaea spp. dispersal was more extensive than expected, with significant settlement occurring 32 m from the source population, the maximum sample range of the study. However, settlement densities were much higher within 8 m from the source. The extensive dispersal of Durvillaea spp. is a result of the combination of small, slowly sinking eggs and the presence of buoyant mucilage. The other species studied showed far more restrictive dispersal, and much lower settlement densities. Settlement occurred 2 m from the source, but most settlement occurred under or near the canopy. The eggs of these species are much larger and sink faster than the eggs of Durvillaea spp. The consequences of settling at different shore heights and seasons were examined in H. banksii and D. antarctica in New Zealand, and F. gardneri and Pelvetiopsis limitata in Oregon. Transplant experiments tested the effects of grazing and heat/desiccation stress on survival and growth of germlings at different shore heights, during different seasons. High germling mortality was a feature of all species, but rate of mortality depended on conditions and species. There is a trade-off for settling at different times of the year; overall, growth was faster in warmer seasons, but survival was better in cooler seasons. During cooler seasons, germlings are exposed to less heat/desiccation stress, but their slow growth exposes them to grazing and competitive interactions for longer periods. For New Zealand species, shore height had large effects, with better survival and growth in the low shore. Grazers were very effective in the low shore, and heat/desiccation stress had strong effects in the mid and high shores. For Oregon species, effects of grazing and heat/desiccation stress were generally weaker than for New Zealand species. Shore height had weak effects, but ultimately low shore germlings had poor survival, primarily because of overgrowth by ephemeral algae. This is in contrast to the generalisation that survival and growth in the low shore should be better due to a more benign environment. In this study, species had specific demographies that related to their life history characteristics and responses to the local environment. Differences in settlement, dispersal abilities, survival and growth over small spatial and temporal scales clearly underpinned large scale differences in recruitment and adult distribution and abundances.

Macroalgae are a dominant feature of many rocky intertidal habitats worldwide. An understanding of the processes affecting their growth and survival, especially at early life history stages, is therefore important to an understanding of the structure of rocky intertidal communities. This thesis examines the role that the sediment environment has on habitat-dominating fucoid algae and intertidal community structure. Measurements of sediment flux showed considerable spatial and seasonal variation, while the benthic sediment environment remained relatively stable. Experimental disturbances over 13 months, showed two distinct effects. First, direct effects of sedimentation favoured ephemeral algae and also those with tough thalli. Secondary to this was an alteration of species interactions due to the shifts in community composition. The effect sedimentation has on habitat dominating fucoid algae was also examined with laboratory experiments and outplants of cultured algae. The presence of sediment had a negative effect on the ability of Cystophora torulosa and Hormosira banksii zygotes to attach to the substratum, with even sparse coverings of sediment preventing at least 37% of zygotes attaching to the substratum, and almost a complete recruitment failure with dense coverings of both sand and silt. Sediment and disturbance of turfing communities also influenced early post-settlement survival especially of C. torulosa. Manipulations of the sediment load, nutrient levels and grazer abundance showed the resilience of rocky intertidal communities to the predicted increase in nutrient leaves in coastal waters due to increases anthropogenic intrusion. Most research into the effects of sedimentation have been observational studies and much of the experimental work has been carried out subtidally. My experiments have extended research into the intertidal zone, finding that if sedimentation increases as predicted there will be a consequential loss of habitat dominating fucoid algae and its replacement with sediment tolerant species

Macroalgae are a dominant feature of many rocky intertidal habitats worldwide. An understanding of the processes affecting their growth and survival, especially at early life history stages, is therefore important to an understanding of the structure of rocky intertidal communities. This thesis examines the role that the sediment environment has on habitat-dominating fucoid algae and intertidal community structure. Measurements of sediment flux showed considerable spatial and seasonal variation, while the benthic sediment environment remained relatively stable. Experimental disturbances over 13 months, showed two distinct effects. First, direct effects of sedimentation favoured ephemeral algae and also those with tough thalli. Secondary to this was an alteration of species interactions due to the shifts in community composition. The effect sedimentation has on habitat dominating fucoid algae was also examined with laboratory experiments and outplants of cultured algae. The presence of sediment had a negative effect on the ability of Cystophora torulosa and Hormosira banksii zygotes to attach to the substratum, with even sparse coverings of sediment preventing at least 37% of zygotes attaching to the substratum, and almost a complete recruitment failure with dense coverings of both sand and silt. Sediment and disturbance of turfing communities also influenced early post-settlement survival especially of C. torulosa. Manipulations of the sediment load, nutrient levels and grazer abundance showed the resilience of rocky intertidal communities to the predicted increase in nutrient leaves in coastal waters due to increases anthropogenic intrusion. Most research into the effects of sedimentation have been observational studies and much of the experimental work has been carried out subtidally. My experiments have extended research into the intertidal zone, finding that if sedimentation increases as predicted there will be a consequential loss of habitat dominating fucoid algae and its replacement with sediment tolerant species

The ecological importance of drifting will depend on the abundance of drifting algae and whether it is reproductively viable. However, the ability of adult plants to successfully disperse long-distances by drifting is largely unknown, particularly for fucoids. The abundance, species composition, and reproductive status of drifting algae was examined by transect surveys around Kaikoura and Banks Peninsula. Abundance and species composition varied between sites, but all drifting algae that were in reproductive season, and had reproductive structures intact, were reproductively active. The reproductive longevity and viability of drifting and beach-cast Hormosira banksii, Durvillaea antarctica and Cytophora torulosa was compared with attached populations. Drifting algae remained reproductively viable, and fecundity did not differ from that of attached algae. Viable propagules were released from drifting algae for the duration of the experiments (H. banksii 57 days, D. antarctica 62 days, and C. torulosa 43 days). In contrast, beach-cast algae ceased to release propagules after 14 days. Dispersal by drifting relies on offshore transport after detachment. To determine the influence of wind and tidal currents on the nearshore transport of drifting algae, tagged H. banksii, D. antarctica, C. torulosa and GPS-tracked drifters were released from shore. Drifters generally moved in the direction of the prevailing wind, but some influence of tidal direction and bathymetry was detected. Offshore winds and outgoing tides were favourable for the offshore transport of surface drifting algae. Following dispersal and arrival at new locations, the distance between gametes may be important in determining the fertilisation success of dioecious species. Experiments testing the fertilisation success of H. banksii and D. antarctica, over increasing distances, showed that fertilisation success decreased with increasing distance between male and female gametes. Despite this, eggs were fertilised when male and female gametes were up to 2m apart, and sperm remained viable for 2 hours.

The ecological importance of drifting will depend on the abundance of drifting algae and whether it is reproductively viable. However, the ability of adult plants to successfully disperse long-distances by drifting is largely unknown, particularly for fucoids. The abundance, species composition, and reproductive status of drifting algae was examined by transect surveys around Kaikoura and Banks Peninsula. Abundance and species composition varied between sites, but all drifting algae that were in reproductive season, and had reproductive structures intact, were reproductively active. The reproductive longevity and viability of drifting and beach-cast Hormosira banksii, Durvillaea antarctica and Cytophora torulosa was compared with attached populations. Drifting algae remained reproductively viable, and fecundity did not differ from that of attached algae. Viable propagules were released from drifting algae for the duration of the experiments (H. banksii 57 days, D. antarctica 62 days, and C. torulosa 43 days). In contrast, beach-cast algae ceased to release propagules after 14 days. Dispersal by drifting relies on offshore transport after detachment. To determine the influence of wind and tidal currents on the nearshore transport of drifting algae, tagged H. banksii, D. antarctica, C. torulosa and GPS-tracked drifters were released from shore. Drifters generally moved in the direction of the prevailing wind, but some influence of tidal direction and bathymetry was detected. Offshore winds and outgoing tides were favourable for the offshore transport of surface drifting algae. Following dispersal and arrival at new locations, the distance between gametes may be important in determining the fertilisation success of dioecious species. Experiments testing the fertilisation success of H. banksii and D. antarctica, over increasing distances, showed that fertilisation success decreased with increasing distance between male and female gametes. Despite this, eggs were fertilised when male and female gametes were up to 2m apart, and sperm remained viable for 2 hours.