2 Bullard et al. AbstractDidemnum sp. A is a colonial ascidian with rapidly expanding populations on the east and west coasts of North America. The origin of Didemum sp. A is unknown.Populations were first observed on the northeast coast of the U.S. in the late 1980s and on the west coast during the 1990s. It is currently undergoing a massive population explosion and is now a dominant member of many subtidal communities on both coasts. 3 Bullard et al.

No abstract

No abstract

Chemical defenses against consumers have been hypothesized to be common among marine macro-holoplankton, but few studies have assessed macro-holoplankton susceptibility to predators or the traits affecting palatability. We used generalist fishes to determine the palatability of fresh tissues, freeze-dried homogenates, and chemical extracts from 19 species of macro-holoplankton. Fishes rejected fresh tissues of all the cnidarians, ctenophores, and cyanobacteria we examined but consumed salp and chaetognath tissues. In contrast, fishes consumed homogenates and chemical extracts of all macro-holoplankton except for the cyanobacterium Trichodesmium sp. We examined nematocysts and low nutritional quality as mechanisms causing rejection of fresh tissues. Once nematocysts were deactivated, fishes consumed cnidarian tentacles, indicating that nematocysts served as defenses. The nutritional quality of macro-holoplankton varied almost 500-fold among species and was strongly bimodal, with most macroholoplankton species having Յ0.7 mg soluble protein ml Ϫ1 or Ն7 mg ml Ϫ1 . In laboratory assays, there was a significant positive relationship between the nutritional quality of artificial foods and their acceptability to fishes. In field assays, reef fishes avoided experimental foods that had a protein content similar to low-quality macroholoplankton but fed rapidly on higher quality foods. Furthermore, macro-holoplankton that were high in protein content possessed defensive traits that low-protein species lacked. Although fresh tissues of most macro-holoplankton were rejected by generalist fishes, we found evidence of chemical defense only in a cyanobacterium. Thus, chemical defenses were rare among macro-holoplankton, and rejection for Ͼ90% of the species we assessed was due to nematocysts or low nutritional quality.There are conflicting notions regarding the role of predation in shaping the population and community structure of pelagic marine systems. In trying to explain why so many marine invertebrates have evolved complex life cycles with long-lived planktonic larval stages, Strathmann (1985) and Wray (1995) argued that high nearshore predation had selected for larvae that develop offshore in the plankton where the risk of predation was lower. Using ecological data, Morgan (1990Morgan ( , 1997 also concluded that offshore environments

It has been hypothesized that larvae of benthic marine invertebrates may reduce their risk of post-settlement competition by avoiding superior competitors during settlement. Few studies, however, have directly compared the levels of larval settlement close to and away from established competitors. We conducted experiments in the New England subtidal to determine whether larvae of fouling organisms would avoid substrata (100 cm 2 PVC panels) with established adult colonies of the tunicates Botryllus schlosseri, Botrylloides violaceus, and Diplosoma listerianum compared to control substrata without tunicates. After panels had been exposed for 1 wk in the field, we assessed larval settlement on the entire surface of panels and within 1 cm of established tunicate colonies. We also monitored the fate of larvae that settled near established tunicates to determine if different tunicate species posed different risks of overgrowth to newly settled juveniles. Pair-wise comparisons revealed only 1 significant difference (out of 48 total analyses) when we examined levels of settlement on panels with tunicates relative to bare controls. We also found no significant differences in the number of settlers overgrown by different tunicate species. Thus, our results suggest that invertebrate larvae do not avoid settling near established dominant competitors (i.e. colonial tunicates). These results are in contrast to a previous study which had shown that larvae of competitively inferior species avoided settling near B. schlosseri.