Supply side ecology: supply and settlement of marine invertebrate larvae
The majority of marine benthic invertebrates exhibit a complex life cycle, that includes separate planktonic and bottom dwelling phases, linked by a settlement event. The analysis of mechanisms which control settlement and recruitment in marine organisms and determination of the conditions under which recruitment variation affects adult distribution and abundance is fundamental to advancing our understanding of population and community variability and hence our ability to manage natural systems. Our research uses intertidal barnacles as convenient model organisms to address these questions.
Role of larval supply in dictating adult distribution
The transport, dispersal and ultimately supply of planktonic larvae to the adult habitat is fundamentally important in determining adult abundance and dynamics but at small spatial scales behaviour at settlement or complex early post-settlement processes may modify the relationship between the number of larvae arriving at a site and juvenile/adult abundance. Work on the Isle of Man showed that biotic interactions at settlement (Jenkins et al 1999) (ID 978) not larval supply (Jenkins and Hawkins 2003) (ID 965) were responsible for dictating adult distribution of Semibalanus balanoides over the wave exposure gradient of the shore and in SW England work to understand the differential distribution of two barnacles Chthamalus stellatus and C. Montagui showed that larval behaviour at settlement modified the distribution of adults expected on the basis of larval supply (Jenkins 2005) (ID 957).
Larval supply and settlement may be measured directly in taxa such as barnacles where larvae are large, abundant and easy to identify but for many taxa this is very challenging. Also large scale dispersal patterns and supply of larvae to multiple sites can only be addressed through hydrodynamic modelling studies. Recent collaborative work at SOS between ecologists and hydrodynamic modellers has led to increased understanding of the levels of connectivity and larval supply across the Irish sea (Robins et al 2013) (ID 2081). This work highlights the role of larval behaviour during larval transport in determining dispersal patterns.
Incorporating larval/ juvenile traits into recruitment modelling
The role of variation in levels of supply, settlement and recruitment to the adult habitat in dictating the dynamics of benthic invertebrate populations and wider effects at the community level have been debated for many years. Our work has examined how strong density dependent mortality as a result of competition for limiting resources, can strongly modify patterns established at settlement; work on Semibalanus balanoides has shown that settlement density can have positive, neutral and negative effects on adult density owing to processes operating soon after settlement (Jenkins et al 2008) (ID 1626). These approaches view settling larvae as equivalent. However in recent years the importance of larval and juvenile traits has been recognised in determining post-settlement success. Through funding from NERC and collaborations with Prof Michael Burrows of the Scottish Association for Marine Science we are currently exploring how we can integrate traits of larvae and of juveniles to better predict consequences of settlement variation to the dynamics of adult populations. One approach has been through developing recruitment models which integrate, rather than ignore, juvenile traits (Gimenez and Jenkins 2013 (ID 2092). Through doing so we believe we can gain greater predictive power in understanding the role of recruitment variation in determining adult dynamics.
Giménez L, Jenkins SR (2013)
Combining Traits and Density to Model Recruitment of Sessile Organisms. PLoS ONE 8(3): e57849. doi:10.1371/journal.pone.0057849
Robins, P.E., Neill, S.P., Giménez, L., Jenkins, S.R. and Malham, S.K. (2013)
Physical and biological controls on larval dispersal and connectivity in a highly energetic shelf sea. Limnology and Oceanography, 58, 505-524
Jenkins SR, Murua J, Burrows MT, 2008
Temporal changes in the strength of density-dependent mortality and growth in intertidal barnacles Journal of Animal Ecology 77: 573-584
Jenkins SR 2005
Larval habitat selection not larval supply determines settlement patterns and adult distribution in two chthamalid barnacles. Journal of Animal Ecology 74:893-904
Jenkins SR, Hawkins SJ. 2003
Barnacle larval supply to sheltered rocky shores: a limiting factor? Hydrobiologia 503: 143-151
Jenkins SR, Norton TA, Hawkins SJ. 1999
Settlement and post-settlement interactions between Semibalanus balanoides (L.) (Crustacea: Cirripedia) and three species of fucoid canopy algae. Journal of Experimental Marine Biology and Ecology 236:49-67