Geography and juveniles in the marine environment: how do they interact?

Submitted by editor on 31 January 2014.

Adams et al. is now on Early View. Read their blog post below.

Understanding the structure and dynamics of biological populations is a central aim of ecology. In the case of marine organisms, a feature uniting diverse taxa has been the evolution of a life cycle entailing two or more stages; a sessile adult stage, and a pelagic larval stage. Populations may be limited by space, environmental conditions or recruitment. However, larvae may settle great distances from their parent populations, meaning that reproduction and recruitment at a given location are disconnected.

Our inability to track larvae directly in the field has meant that simulation modelling has always been a central component of the evaluation of larval dispersal and its impact on population dynamics. Such approaches involve a coupling of hydrodynamic and biological models. These allow representation of specific topography, freshwater influx, prevailing meteorological conditions and so on. We made use of the latest advances in coastal hydrodynamic modelling (which use unstructured triangular grids to allow computation efficiency in conjunction withwith detailed representation of complex areas) to study potential larval dispersal on the west coast of Scotland.

Our principal goal was to identify whether there was a connection between a site’s location within the broader coastline, and i) its potential larval output to other sites; ii) input from other sites; and iii) expected dispersal distance.

Particles released from regions of high current velocity, open coastline and low local habitat availability travelled furthest but were less likely to disperse successfully to other coastal sites. Extensive natal habitat in the vicinity of a site generally had a positive impact on the number of arriving particles, as did low current velocities. However, relationships between numbers of arriving particles and local geographical indices were complex, particularly at longer larval durations. Local geography alone explained up to 50% of the variance in success of particles released and closer to 10% of the variation in the number of particles arriving at each site. Despite these general patterns, coastline properties fall short of directly predicting dispersal measures for particular locations. The study shows that meteorological variation and broad scale current patterns interact strongly with local geography to determine connectivity in coastal areas.

Figure 1: Relative values of the metrics (a) openness, (b) coast length and (c) velocity, plotted at each coastal habitat site, which were used as predictors for larval dispersal.

Figure 2: Two stages of planktonic barnacle larvae (not to scale). Source