Newly settled invertebrates usually are subject to high rates of mortality (Type 111 survivorship). Therefore, knowledge of early post-settlement events is critical in determ~nlng if and when patterns of abundance and distribution of juveniles reflect settlement patterns. Causes of mortality of early juvenile invertebrates include delay of metamorphosis, biological disturbance, physical disturbance and hydrodynamics, physiological stress, predation, and competition. Predation is the best documented cause of early n~ortallty, particularly for mobile species. Other possible causes which have not yet been investigated are developmental abnormalities, insufficient energy reserves, disease and parasitism In most studies of sessile invertebrates, early post-settlement mortality did not obscure the relationship between recruit and settler abundance. This relatlonsh~p appears to be more varlable among mobile species for which migrat~on also can modify the distnbution of settlers. There is still insufficient data to support general conclusions about the conditions under which recruitment rate can be predicted from settlement rate. Studies have found evidence of the effects of both settlement and early post-settlement mortality on the dlstributlon of some sessile species at small spatial scales, but mortality appears to have less influence a t larger scales. Much of the present knowledge of the early postsettlement period has come from studies of barnacles and ascidians and more information is needed for other groups of benthic marine invertebrates, particularly mobile species. The relative importance of mortality during the early post-settlement period compared to other life history stages can only be detel-mined in studies which examlne several stages.

Recently, the effects of ocean acidification (OA) on marine animal behaviour have garnered considerable attention, as they can impact biological interactions and, in turn, eco system structure and functioning. We reviewed current published literature on OA and marine behaviour and synthesize current understanding of how a high CO 2 ocean may impact animal behaviour, elucidate critical unknowns, and provide suggestions for future research. Although studies have focused equally on vertebrates and invertebrates, vertebrate studies have primarily focused on coral reef fishes, in contrast to the broader diversity of invertebrate taxa studied. A quantitative synthesis of the direction and magnitude of change in behaviours from current conditions under OA scenarios suggests primarily negative impacts that vary depending on species, ecosystem, and behaviour. The interactive effects of co-occurring environmental parameters with increasing CO 2 elicit effects different from those observed under elevated CO 2 alone. Although 12% of studies have incorporated multiple factors, only one study has examined the effects of carbonate system variability on the behaviour of a marine animal. Altered GABA A receptor functioning under elevated CO 2 appears responsible for many behavioural responses; however, this mechanism is unlikely to be universal. We recommend a new focus on determining the effects of elevated CO 2 on marine animal behaviour in the context of multiple environmental drivers and future carbonate system variability, and the mechanisms governing the association between acid-base regulation and GABA A receptor functioning. This knowledge could explain observed species-specificity in behavioural responses to OA and lend to a unifying theory of OA effects on marine animal behaviour.

Breaking waves impose large hydrodynamic forces which may dislodge mussels and other organisms living on exposed rocky shores. We examined the effect of variation in attachment strength with size, habitat and season on the predicted probability of wave dislodgment of mussels Mytilus trossulus and M. edulis on an exposed shore on the Atlantic coast of Nova Scotia, Canada. Mussels on this shore are exposed to maximum significant wave heights of at least 7 to 9 m each winter and to maximal water velocities of at least 12 m s -1. We used Denny's (1995) mechanistic approach to predict probabilities of dislodgment from measures of attachment strength of mussels. Predicted probabilities of dislodgment indicated that mussels of 10 to 25 mm shell length are vulnerable to dislodgment by water velocities of > 7 m s -1 . As a result of variation in dislodgment forces, probabilities of dislodgment did not differ consistently between tidepools and emergent rock, or with mussel size. Attachment strength increased from July to February as mussels were exposed to stronger wave action, reducing the probability of dislodgment by a given water velocity. This study indicates that knowledge of patterns of change in attachment strength are necessary for prediction of probabilities of dislodgment of mussels.

We examined larval abundance patterns near deep-sea hydrothermal vents along the East Pacific Rise to investigate how physical transport processes and larval behavior may interact to influence larval dispersal from, and supply to, vent populations. We characterized vertical and lateral distributions and temporal variation of larvae of vent species using high-volume pumps that recovered larvae in good condition (some still alive) and in high numbers (up to 450 individuals sample -1 ).Moorings supported pumps at heights of 1, 20, and 175 m above the seafloor, and were positioned directly above and at 10s to 100s of meters away from vent communities. Sampling was conducted on 4 cruises between November 1998 and May 2000. Larvae of 22 benthic species, including gastropods, a bivalve, polychaetes, and a crab, were identified unequivocally as vent species, and 15 additional species, or species-groups, comprised larvae of probable vent origin. For most taxa, abundances decreased significantly with increasing height above bottom. When vent sites within the confines of the axial valley were considered, larval abundances were significantly higher on-vent than off, suggesting that larvae may be retained within the valley. Abundances of all vent species varied significantly among sample dates; the variation was not synchronized among taxa, except for consistently low abundances during November 1998. Lateral distributions did not vary among major larval groups (gastropods, polychaetes and bivalves), although polychaetes showed anomalously high abundances off-vent at 1 m above bottom. Lateral patterns also did not vary among species of gastropods, indicating that hydrodynamic processes may be transporting diverse species in similar ways. However, the species-level differences in temporal patterns indicate that there is substantial discontinuity in the abundance of individual species at vent communities, possibly due to timing of spawning and/or behavioral interactions with flow.

Physical and biological factors influencing mussel(Mytilus trossulus, M. edulis) settlement on a wave-exposed rocky shore Heather L. Hunt*, Robert E. ScheiblingDepartment of Biology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 451ABSTRACT: Settlement rates of mussels Mytjlus trossulus and M, edulis on artificial collectors (aquar~um filter wool) and natural substrata were measured in tidepools and on emergent rock in recently ice-scoured and non-scoured regions of a rocky shore near Halifax, Nova Scotia, Canada.Patterns of abundance and size distribution of mussel settlers differed markedly between artificial collectors and natural substrata. Settlement rate on artificial collectors was directly related to water flux, and was highest on ice-scoured emergent rock and lowest in non-scoured tidepools. Settlement rate on natural substrata was related to a suite of biological (macroalgal/barnacle cover) and physical factors (water flux, tidal height, flushing time), and was highest in ice-scoured tidepools and lowest on ice-scoured emergent rock. Large postlarval mussels (>S mm shell length) were common on natural substrata but rare on artificial collectors. Recruitment patterns of mussels on natural substrata reflected the distribution of settlers, suggesting that settlement patterns are important in determining the distribution and abundance of mussels In this population.