We investigated the nonconsumptive effects (NCEs) of predatory dogwhelks (Nucella lapillus) on intertidal barnacle (Semibalanus balanoides) recruitment through field experiments on the Gulf of St. Lawrence coast and the Atlantic coast of Nova Scotia, Canada. We studied the recruitment seasons (May-June) of 2011 and 2013. In 2011, the Gulf coast had five times more nearshore phytoplankton (food for barnacle larvae and recruits) during the recruitment season and yielded a 58% higher barnacle recruit density than the Atlantic coast at the end of the recruitment season. In 2013, phytoplankton levels and barnacle recruit density were similar on both coasts and also lower than for the Gulf coast in 2011. Using the comparative-experimental method, the manipulation of dogwhelk presence (without allowing physical contact with prey) revealed that dogwhelk cues limited barnacle recruitment under moderate recruit densities (Atlantic 2011/2013 and Gulf 2013) but had no effect under a high recruit density (Gulf 2011). Barnacle recruits attract settling larvae through chemical cues. Thus, the highest recruit density appears to have neutralized dogwhelk effects. This study suggests that the predation risk perceived by settling larvae may decrease with increasing recruit density and that prey food supply may indirectly influence predator NCEs on prey recruitment.

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Recent studies have shown that predator chemical cues can limit prey demographic rates such as recruitment. For instance, barnacle pelagic larvae reduce settlement where predatory dogwhelk cues are detected, thereby limiting benthic recruitment. However, adult barnacles attract conspecific larvae through chemical and visual cues, aiding larvae to find suitable habitat for development. Thus, we tested the hypothesis that the presence of adult barnacles (Semibalanus balanoides) can neutralize dogwhelk (Nucella lapillus) nonconsumptive effects on barnacle recruitment. We did a field experiment in Atlantic Canada during the 2012 and 2013 barnacle recruitment seasons (May–June). We manipulated the presence of dogwhelks (without allowing them to physically contact barnacles) and adult barnacles in cages established in rocky intertidal habitats. At the end of both recruitment seasons, we measured barnacle recruit density on tiles kept inside the cages. Without adult barnacles, the nearby presence of dogwhelks limited barnacle recruitment by 51%. However, the presence of adult barnacles increased barnacle recruitment by 44% and neutralized dogwhelk nonconsumptive effects on barnacle recruitment, as recruit density was unaffected by dogwhelk presence. For species from several invertebrate phyla, benthic adult organisms attract conspecific pelagic larvae. Thus, adult prey might commonly constitute a key factor preventing negative predator nonconsumptive effects on prey recruitment.

Benthic species from rocky intertidal systems are irregularly distributed along marine coastlines. Nearshore pelagic conditions often help to explain such variation, but most such studies have been done on eastern ocean boundary coasts. We investigated possible benthic–pelagic coupling along the Atlantic coast of Nova Scotia, a western ocean boundary coast. In 2014, we surveyed high‐intertidal habitats from nine wave‐exposed bedrock locations spanning 415 km of coastline. At each location in the spring, we measured the recruitment of barnacles and mussels, the two main filter‐feeders. Recruitment varied irregularly along the coast. Satellite data on coastal phytoplankton and particulate organic carbon (food for intertidal filter‐feeders and their pelagic larvae) and in‐situ data on sea surface temperature explained, to varying degrees, the geographic structure of recruitment. In turn, the summer abundance of barnacles and mussels was positively related to their spring recruitment. Ultimately, intertidal predator (dogwhelk) abundance was positively related to the recruitment and/or abundance of barnacles and mussels (the main prey of dogwhelks). Sea ice may also have influenced this predator–prey interaction. Drift ice leaving the Gulf of St. Lawrence in late winter strongly disturbed the northern surveyed locations, making barnacles (through high spring recruitment) the only food source for dogwhelks (which survived ice scour in crevices) in such places. Overall, this study supports the occurrence of benthic–pelagic coupling and bottom‐up forcing on this coast. Investigating the oceanographic drivers of pelagic food supply and seawater temperature should help to further understand how this large metacommunity is organized.

On the Gulf of St. Lawrence coast of Nova Scotia (Canada), recruitment of the barnacle Semibalanus balanoides occurs in May and June. Every year in June between 2005 and 2016, we recorded recruit density for this barnacle at the same wave-exposed rocky intertidal location on this coast. During these 12 years, mean recruit density was lowest in 2015 (198 recruits dm−2) and highest in 2007 (969 recruits dm−2). The highest recruit density observed in a single quadrat was 1,457 recruits dm−2 (in 2011) and the lowest was 34 recruits dm−2 (in 2015). Most barnacle recruits appear during May, which suggests that most pelagic larvae (which develop over 5–6 weeks before benthic settlement) are in the water column in April. An AICc-based model selection approach identified sea surface temperature (SST) in April and the abundance of phytoplankton (food for barnacle larvae, measured as chlorophyll-a concentration –Chl-a–) in April as good explanatory variables. Together, April SST and April Chl-a explained 51% of the observed interannual variation in recruit density, with an overall positive influence. April SST was positively related to March–April air temperature (AT). April Chl-a was negatively related to the April ratio between the number of days with onshore winds (which blow from phytoplankton-limited offshore waters) and the number of days with alongshore winds (phytoplankton is more abundant on coastal waters). Therefore, this study suggests that climatic processes affecting April SST and April Chl-a indirectly influence intertidal barnacle recruitment by influencing larval performance.

Citation: Ellrich, J. A., and R. A. Scrosati. 2016. Water motion modulates predator nonconsumptive limitation of prey recruitment. Ecosphere 7(7):e01402. 10.1002/ecs2.1402Abstract. Predator chemical cues can elicit behavioral changes in prey to minimize predation risk. Recent field studies have shown that such predator nonconsumptive effects (NCEs) can ultimately affect prey demography. The environment is known to modulate predator consumptive effects on prey demography, but the environmental modulation of predator NCEs on prey demography remains unstudied. We investigated this knowledge gap using an intertidal predator-prey system. Dogwhelk (Nucella lapillus) chemical cues can limit barnacle (Semibalanus balanoides) recruitment by limiting larval settlement. As waves disperse chemicals in coastal environments, we experimentally tested the hypothesis that wave exposure limits dogwhelk NCEs on barnacle recruitment. Shortly before the barnacle recruitment season of 2013 (May-June), we established cages in rocky intertidal habitats in Atlantic Canada under two levels of wave exposure. The cages were used to manipulate the presence and absence of dogwhelks. At the center of each cage, we installed a tile where barnacle pelagic larvae could settle and develop into recruits. Mesh prevented caged dogwhelks from accessing the tiles, but allowed their waterborne cues to reach the tiles. Data collected at the end of the recruitment season indicated that dogwhelk cues limited barnacle recruitment in wave-sheltered habitats but had no effect on recruitment in wave-exposed habitats. These findings suggest that predicting predator NCEs on prey demography may require environmental information related to the ability of prey to locate predators.

We report the presence of 'plasticrusts' and 'pyroplastic' from coastal habitats in Giglio island, Tyrrhenian Sea, Italy. These novel plastic debris types have only recently been described for the first time from Madeira island (NE Atlantic Ocean) and the United Kingdom, respectively. While 'plasticrusts' are generated by sea waves smashing plastic debris against intertidal rocks, 'pyroplastic' derives from (un)deliberately burnt plastic waste. Using Fourier-transform infrared (FTIR) spectroscopy, we identified the 'plasticrust' material as polyethylene (PE) and the 'pyroplastic' material as polyethylene terephthalate (PET). These polymers are widely used in everyday products and, therefore, contribute heavily to plastic pollution in aquatic and terrestrial environments worldwide. Furthermore, our field surveys suggest that 'plasticrust' abundance is related to wave-exposure and that the 'pyroplastic' derived from beverage bottles which we frequently found along the Giglio coast. Overall, our findings corroborate the notion that 'plasticrusts' and 'pyroplastic' are common debris types in marine coastal habitats.