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Although many marine invertebrates reproduce by releasing gametes into the water, major spawning events have rarely been observed for cold-water invertebrates. We documented mass spawnings by the sea star Asterias vulgaris and the ophiuroid Ophiopholis aculeata on 6 July 1996 and 2 July 1998, and by these 2 species plus a second ophiuroid Ophiura robusta and the sea urchin Strongylocentrotus droebachiensis on 3 July 2003. In each year, the abrupt spawning events coincided with the first major intrusion of warm surface water into a region normally dominated by cold upwelling. The behaviours of the ophiuroids and sea stars favoured fertilization success. First, they spawned from elevated surfaces, with the central disc raised, to increase suspension and mixing of gametes. Second, many individuals pseudocopulated, which involved crawling over one another in the case of the sea star, and individuals holding their central discs together in the case of the 2 ophiuroids. Models of fertilization success need to incorporate such behaviours to better understand fertilization in the sea.KEY WORDS: Ophiopholis aculeata · Ophiura robusta · Asterias vulgaris · Strongylocentrotus droebachiensis · Mass spawning · Behaviour · Pseudocopulation · External fertilization · Northern Gulf of St. Lawrence Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 361: [161][162][163][164][165][166][167][168] 2008 Japan (Kubota 1980) and for the palolo worm Eunice viridis in the Samoan Islands (Caspers 1984). Subsequently, multi-species mass spawnings have been documented for many sessile tropical species (corals, anemones and sponges) that spawn at a predictable time in coordination with environmental rhythms (Harrison et al. 1984, Babcock et al. 1992). In contrast, there are surprisingly few reports of major spawning events for temperate and cold-water invertebrates. The reports most clearly indicating synchronous spawning by large numbers of individuals are probably those of Minchin (1987Minchin ( , 1992, Breen & Adkins (1980), Sewell & Levitan (1992) and Hamel & Mercier (1996). The scarcity of such observations, due to their short duration and unpredictable timing, greatly limits our understanding of fertilization dynamics. In particular, we know little about how animals behave during major spawnings. Strong selective pressure to adopt behaviours that enhance fertilization success would be expected. Most reports of spawning behaviours are based on incidental spawnings of a few individuals.The aim of the present paper is 3-fold: (1) to report rare spawning events involving mass multi-species spawnings of cold-water echinoderms; (2) to consider environmental factors that potentially triggered these highly synchronized events; and (3) to describe behaviours during spawning, including rapid aggregation and pseudocopulation, which likely enhanced fertilization success. MATERIALS AND METHODSOur observations were made during the course of ecological studies of sea stars (Gaymer et al. 2001...

The increasing number and diversity of anthropogenic stressors in marine habitats have multiple negative impacts on biological systems, biodiversity and ecosystem functions. Methods to assess cumulative effects include experimental manipulations, which may identify non-linear responses (i.e. synergies, antagonisms). However, experiments designed to test these ideas are uncommon, generally focusing on single biological responses. We conducted a manipulative experiment to investigate the isolated and combined effects of warming (+ 6 °C), salinity variation (freshwater pulses or presses), and nutrient enrichment (natural or enriched) following one and three month’s exposure, on responses measured at multiple levels of biological complexity in a simple bivalve assemblage. More specifically, we determined effects on bivalve mortality, growth, shell mineralization, and energy content, as well as microphytobenthos biomass. Salinity variation and nutrient enrichment, individually and combined, caused strong impacts on some of the measured variables and their effect varied through time. In contrast, warming had no effect. Our work highlights the prevalence of antagonistic interactions, the importance of examining effects of single and multiple stressors through time, and of considering multiple responses to understand the complexity behind stressor interactions.

Top-down, bottom-up, middle-out and abiotic factors are usually viewed as main forces structuring biological communities, although assessment of their relative importance, in a single study, is rarely done. We quantified, using multivariate methods, associations between abiotic and biotic (top-down, bottom-up and middle-out) variables and infaunal population/community variation on intertidal mudflats in the Bay of Fundy, Canada, over two years. Our analysis indicated that spatial structural factors like site and plot accounted for most of the community and population variation. Although we observed a significant relationship between the community/populations and the biotic and abiotic variables, most were of minor importance relative to the structural factors. We suggest that community and population structure were relatively uncoupled from the structuring influences of biotic and abiotic factors in this system because of high concentrations of resources that sustain high densities of infauna and limit exploitative competition. Furthermore, we hypothesize that the infaunal community primarily reflects stochastic spatial events, namely a “first come, first served” process.