Diet Assessment And Gut Microbiota Of Intertidal Grazing Gastropods

Rocky shores are narrow seacoasts made from solid rock,whose locations are at the interface of terrestrial(land)and marine ecosystems.As the transitional regions between terrestrial and marine regimes,rocky shores present complex coastlines where intense land-sea and air-sea interactions take place.The tides create a gradient of environmental conditions moving from a terrestrial to a marine ecosystem.The distribution of different species across the rocky shore is influenced by biotic and abiotic factors from above high tide to the sub-tidal zone,such as solar radiation,temperature,tidal movement,salinity and interference from human activity.Although rocky shores are tough and complex habitats with underling mechanisms hard to untangle,yet they enjoy a relatively high primary productivity across marine ecosystems,which make them home for a high diversity of flora and fauna.They also play key roles in material and energy exchange processes between land and ocean ecosystems,supporting and providing crucial ecosystem services.The abundance and distribution of primary producers in rocky shore ecosystems are,to a large extent,related to the amount of food available of diverse intertidal grazers.They can influence and ultimately regulate material cycling and energy flow in the marine food chain.Primary producers also have critical roles in global biogeochemical cycles and dramatically impact on the process of global climate change.Paucity on the research about distribution patterns of primary producers in rocky shores ecosystems along the China coast reflects on the urgent need to address scientific problems,(1)such as the spatial and temporal patterns of primary producers,(2)the impact of food availability on the standing stock of food ingested by herbivorous grazers and(3)the links between gut microbiota of intertidal gastropods and environment.Different patterns were observed between food available and food ingested by E.radiata from the splash zone and C.toreuma from the mid tide zone.For C.toreuma,the amount of pigment contents in the guts tended to be higher where the environment support sufficient food stock.Nevertheless,no such positive patterns were found for E.radiata.This difference might occur due to different feeding behaviours caused by varied zonations on the shore.Analysis of composition of food ingested by E.radiata and C.toreuma along with epilithic and planktonic microalgae by using metabarcoding indicated that gut contents of these grazers had a higher similarity level with microalgae from the seawater compared with microalgae on the rock surfaces.We believe planktonic microalgae deposited on the shore were often loosely attached to the rock and thus became easily scraped off by these grazers.Mucus secreted by gastropods was confirmed to acquire the ability to trap food particles from the seawater and was ingested by these organisms afterwards.Therefore,planktonic microalgae became available food for intertidal gastropods through multiple processes.Investigation into the food availability(both epilithic and planktonic microalgae)on the shore and its ingestion by two species of grazing gastropods(E.radiata and C.toreuma)on three typical rocky shores along Fujian coastline brought new understandings of the seasonal changes in the standing stock of primary producers.June witnessed an abrupt drop in abundance of epilithic and planktonic microalgae,while at the same time,the amount of gut pigment contents were also at their lowest level for both of the grazers.The results highlighted summer time as critical period for the survival of many grazers on the shore,since they were faced with both extreme thermal stress and shortage of food simultaneously.Artificial seawalls and breakwaters harbored different macrobenthic community from adjacent natural rocky shore ecosystems.It was in our nature to ask whether biomass of primary producer on these different types of substrate and surrounding waters showed any differences in summer and winter,and if so,whether food ingested by grazing gastropod were subsequently affected?The results of our preliminary research indicated that the abundance of microalgae on different types of substrate showed no significant difference,however,biomass of planktonic microalgae in the seawater from natural rocky shore ecosystems significantly surpass that from artificial seawalls and breakwaters only in summer.This highlighted the role of primary producers in the surrounding seawater in shaping the varied community structures between natural rocky shores and artificial infrastructures.Recent ecological survey about the distribution of macrobenthos on the Jiangsu coast documented the northward shift in geographic range of a typical rocky shore species,N.yoldii,amid the scenario of global warming and continued shoreline armoring in this region.We sampled N.yoldii from three artificial seawalls and breakwaters north of the Yangtze River Delta,and samples from two southern natural rocky shores were also collected.By analyzing the gut microbiota of N.yoldii and microbial community from seawater and rock samples,different bacterial communities were found between gut and environment samples.Special intestinal structure of the gastropod and functional property in question are likely to account for this difference in bacterial community.This study also identified species-specific bacterial community,Tenericutes,in the gastrointestinal tract of N.yoldii.However,no differences were documented neither in composition nor in predicted function between gut bacterial communities from artificial infrastructures and natural rocky shores.The association with highly diverse,yet very specific gut microbiota might not influence the fitness of this species in the ongoing northward shift in distribution with the facilitation of seawalls and breakwaters as stepping-stones.This also called for thorough investigation into the complex interaction between gut microbial community and fitness of host.