The observed rates and deleterious impacts of biological invasions have caused significant alarm in recent years, driving efforts to reduce the risk (establishment) of new introductions. Characterizing the supply of propagules is key to understanding invasion risk and developing effective management strategies. In coastal ecosystems, ships' ballast water is an important transfer mechanism (vector) for marine and freshwater species. Commercial ships exhibit a high degree of variation in ballast water operations that affect both the quantity and quality of propagule supply, and thereby invasion risk. The per-ship inoculation size from ballast water depends upon both the volume discharged and the organism density. Moreover, propagule quality will vary among source regions (ports) and voyage routes, due to differences in species composition and transport conditions, respectively. We show that significant differences exist in (i) the frequency and volume of ballast water discharge among vessel types, (ii) the frequency of vessel types and routes (source regions) among recipient ports, and (iii) the transit success (survivorship) of zooplankton in ballast tanks among voyage routes. Thus, propagule supply is not a simple function of total ship arrivals. For ships, as well as other vectors, variation in propagule quantity and quality must be explicitly considered to estimate invasion risk and advance predictive ability.

Ships' ballast water is a leading mechanism for the transport and introduction of nonindigenous species to ports worldwide. Two management strategies are being advanced to reduce propagule supply and invasions from overseas shipping. Ballast water exchange (BWE) is now required by several nations and is expected to be replaced by discharge standards (maximum organismal concentrations), negotiated as a treaty within the International Maritime Organization (IMO). Here, we provide the first forecast and comparison of changes to propagule supply at a national scale, resulting from these alternate management strategies. For unmanaged ballast water, sampled ships (n = 354) arriving to the US typically contained zooplankton concentrations < 3000 organisms m−3, but some ships (1.1%) contained > 50 000 organisms m−3. Only 3.8% of these arrivals meet the IMO standards. BWE substantially reduces zooplankton concentrations, but we estimate that ≤ 17.2% of BWE ships will meet IMO standards. Although most overseas arrivals discharged < 1500 m3 of ballast water, discharges are reported as high as 103 000 m3, and total inocula ≥ 106 remain possible, even under the more stringent IMO strategy.

The dynamics and feeding biology of a population of Marthasterias glacialis (Echinodermata: Asteroidea) was examined over a two-year period from 2000^2002 at Lough Hyne Marine Nature Reserve, Co. Cork, Ireland. A multivariate approach was used and both multiple factors and multiple interactions between factors were found to in£uence population structure. These included time of year, site, individual sea-star size, depth, and predator density. Individuals belonging to the smallest size-classes (0^50 mm and 51^100 mm) were most abundant amongst boulders in shallow water (0^1m), while larger individuals were primarily found in water below 1m in depth on ¢ner grade substratum and shell debris. Dietary composition was also found to di¡er with depth; sea-stars in the immediate subtidal had an opportunistic diet, and fed on a variety of taxa, whilst those M. glacialis from 1^6 m were more selective and restrictive, feeding chie£y on bivalve prey. We propose that spatial partitioning of di¡erent size-classes and a generalist feeding strategy may account for the success of M. glacialis at Lough Hyne.

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Abiotic and biotic aspects of the covering behaviour of the purple sea urchin, Paracentrotus lividus (Echinodermata: Echinoidea) were systematically examined in situ and in the laboratory to analyse potential intra-population differences in the nature of this behaviour. In the field, significant differences in the occurrence of covering behaviour were found between age groups. Smaller P. lividus covered at higher frequencies than larger individuals. Higher proportions of individuals were also observed to cover during afternoon sampling periods. Significant differences in the types of covering material used were found between P. lividus observed in the laboratory and in the field. These findings suggest that the benefits and/or opportunities of covering behaviour may change with size and habitat.