| dc.description | This thesis examines temporal and spatial variability in settlement and recruitment of echinoderms in rocky subtidal habitats. A review of the literature revealed that the processes which regulate the transitions from early life stages through to adulthood, and thereby determine the distribution and abundance of echinoderm populations, remain poorly understood. However, a salient feature of most echinoderm populations is a high degree of temporal and spatial variability in settlement and recruitment. In this study, settlement of echinoderm species was measured on artificial collectors placed on and above the bottom in kelp beds and barrens at multiple sites and sampled over a variety of temporal (days to years) and spatial (metres to 100's of kilometres) scales. Settlement of echinoids (Strongylocentrotus droebachiensis) measured in 3 regions of the northwest Atlantic showed order of magnitude differences between regions, where settlement was highest in the Gulf of Maine, lowest in the Bay of Fundy and intermediate in Nova Scotia. Within each region, settlement differed between sites but was within the same order of magnitude. In Nova Scotia, settlement of ophiuroids (Ophiopholis aculeata, Ophiura) sampled over 3 day intervals was compared with concurrent hydrographic and meteorologic measures. A major settlement pulse occurred over one 3 day period and was associated with minor fluctuations in the physical environment. Sampling every 2 weeks over 3 years in kelp beds and barrens at 2 sites (exposed and sheltered) showed settlement pulses of ophiuroids (O. aculeata, Ophiura ), asteroids (Asterias) and echinoids ( S. droebachiensis, Echinarachnius parma) occurred between July and September of each year. Timing of settlement differed consistently among species, the magnitude of each pulse varied between years and species, and the year of maximum settlement differed between species. Settlement of all species was greater at the sheltered site but patterns were not consistent among species between habitats. Sampling settlement concurrently at different frequencies and on different collector types gave different estimates of settlement. This indicates the need for calibration across studies and assessment of sampling artifacts (e.g. changes in collector quality, post-settlement mortality or migration) which can occur over longer deployment intervals. For most species sampled, settlement predicted recruit density in natural populations the following year. However, the strength of the relationship varied between species, probably because of differing post-settlement processes. | en_US |
