MEPS 541:105-122 (2015)  -  DOI: https://doi.org/10.3354/meps11537

ABSTRACT: Predation is considered a major source of mortality during the planktonic larval phase of most species of benthic marine invertebrates; however, direct estimates of predation are scarce. We estimated predation rates (d^-1) on nauplii of 3 species of barnacles (Balanus balanus, Balanus crenatus, Semibalanus balanoides) by the ctenophore Pleurobrachia pileus in the Northwest Arm, Halifax, in winter and early spring 2014. Ingestion rates (prey d^-1) were predicted from the number and digestion time of barnacle nauplii in the pharynx of P. pileus. Predation rates were estimated by multiplying the ingestion rate by the ratio of the predator to prey concentration. The digestion time (mean ± SE) of barnacle nauplii was significantly longer at 2°C (7.1 ± 0.4 h, n = 5 to 8.6 ± 0.3 h, n = 9) than at 6°C (4.9 ± 0.4, n = 6 to 6.6 ± 0.3 h, n = 8), in 3 laboratory experiments. The digestion time of cyprid larvae could not be reliably estimated because they were egested alive as freely swimming individuals or trapped within a prey bolus. Nauplii of B. crenatus were positively ‘selected for’ by P. pileus, and estimates of predation rate were generally highest for this species. The predation rates of each species were frequently <0.005 d^-1, indicating that predation by P. pileus was negligible. Concentrations of P. pileus were within the normal range for this area (on the order of 0.1 ind. m^-3) and probably would need to be sustained at anomalously high levels (1 to 10 ind. m^-3) to have an ecologically significant impact on populations of larval barnacles.

KEY WORDS: Digestion time · Larval ecology · Larval invertebrates · Larval mortality · Predation impact · Larval predation