The epiphytic bryozoan Membranipora membranacea encrusts the surface of kelp blades, causing recurrent large-scale defoliation events in kelp beds off the Atlantic coast of Nova Scotia, Canada. The gastropod Lacuna vincta grazes kelp, creating perforations that weaken blade tissues and increase the fragmentation rate. We assess the interaction between M. membranacea and L. vincta by measuring the grazing rate of snails on bryozoan-encrusted and non-encrusted kelp (Saccharina latissima) in no-choice and choice experiments in the laboratory conducted in November and December 2010. There was no effect of diet on grazing rate in no-choice experiments. In choice experiments, however, L. vincta grazed significantly more non-encrusted than encrusted kelp (7.1 versus 1.1 mg snail−1 d−1), and grazing rate of non-encrusted kelp was almost twice that in the no-choice experiment (3.8 mg snail−1 d−1), indicating that snails may avoid colonies of M. membranacea on partially encrusted kelp blades. We found no effect of diet on growth, reproduction and survival of snails maintained for four weeks on encrusted or non-encrusted kelp. By concentrating grazing damage on non-encrusted areas of blades, L. vincta may act synergistically with M. membranacea to increase the likelihood of blade breakage and canopy loss. This indirect effect of the invasive bryozoan could augment its direct effect on the standing biomass of native kelp beds and detrital export to adjacent communities.
Single diet feeding experiment data from: Invasive bryozoan alters interaction between a native grazer and its algal food. A Canadian Healthy Oceans Network Ecosystem Function Project, EF-11.
Rate of mass change (mg/day) of kelp tissue disks (Saccharina latissima) in experimental feeding arenas in the laboratory containing snails (Lacuna vincta) offered one dietary item and autogenic control arenas with no snails. Data for each replicate container includes herbivore absence/presence, diet (kelp encrusted by invasive bryozoan M. membranacea or non-encrusted kelp), and rate of mass change of kelp disk.
single_diet_exp_data.csv
Mixed diet feeding experiment data from: Invasive bryozoan alters interaction between a native grazer and its algal food. A Canadian Healthy Oceans Network Ecosystem Function Project, EF-11.
Rate of mass change (mg/day) of kelp tissue half disks (Saccharina latissima) in feeding arenas in the laboratory with snails (Lacuna vincta) offered dietary choice of kelp encrusted by invasive bryozoan M. membranacea or non-encrusted kelp simultaneously and in autogenic control arenas with no snails. Data include arena identity, herbivore absence/presence, dietary item (encrusted/non-encrusted), rate of mass change of kelp tissue.
mixed_diet_exp_data.csv
Snail growth data from: Invasive bryozoan alters interaction between a native grazer and its algal food. A Canadian Healthy Oceans Network Ecosystem Function Project, EF-11.
Weekly measures of shell height (mm) of individual snails (Lacuna vincta) maintained in feeding arenas in the laboratory over 4 weeks on single diets of either kelp (Saccharina latissima) encrusted by the invasive bryozoan M. membranacea, non-encrusted kelp, or starved. Data include arena identifier, individual identifier (nested within arena), diet, initial shell height (mm), and shell heights at the end of weeks 1-4 (mm).
growth_data_lacuna.csv
Snail egg mass production data from: Invasive bryozoan alters interaction between a native grazer and its algal food. A Canadian Healthy Oceans Network Ecosystem Function Project, EF-11.
Egg mass production between weeks 3 and 4 of snails (Lacuna vincta) maintained in feeding arenas over 4 weeks on single diets of either kelp (Saccharina latissima) encrusted by the invasive bryozoan M. membranacea, non-encrusted kelp, or starved. Data for each replicate container include diet, egg mass count, and number of snails per container.
egg_production_data_lacuna.csv
Snail survival data from: Invasive bryozoan alters interaction between a native grazer and its algal food. A Canadian Healthy Oceans Network Ecosystem Function Project, EF-11.
Survival of snails (Lacuna vincta) maintained in feeding arenas in the laboratory over 4 weeks on single diets of either kelp (Saccharina latissima) encrusted by the invasive bryozoan M. membranacea, non-encrusted kelp, or starved. Data for each replicate container include diet and proportion of snails surviving at start of experiment and by the end of weeks 1-4.
survival_data_lacuna.csv