Do man-made habitats affect spatial patterns of mollusk abundance?

XVIII Simposio Ibérico de Estudios de Biología Marina (SIEBM), Gijón (Asturias), 2 al 5 de septiembre de 2014.

The fragmentation of natural habitats, together with its loss, is considered a major threat to biodiversity. Man-made habitats, e.g., seawalls and coastal defence structures, are a common feature causing the fragmentation on the shoreline of many urbanized coastal areas and will become more widespread in response to rising and stormier seas. Fragmentation can alter functional connectivity of habitats and determine the spatial distribution of organisms, since the movement and dispersal of individuals can be interrupted. However, ecological consequences of coastal defence structures have not been extensively studied and we know little about their effects in marine systems. One of the most important factors affecting the connectivity among fragments or patches is the ability of the organisms to disperse despite potential barriers. Spatial patterns of molluscs with planktonic larvae or direct development (non-planktotrophic larvae) has been compared before, but there is a growing interest to understand the role of the man-made habitats in determining the patterns of spatial abundances of marine organisms. This study was aimed at exploring the role of type of larval development (planktotrophic vs non-planktotrophic) on patterns of spatial variation of gastropods on rocky shores, elucidating the possible responsibility of habitat fragmentation in observed patterns (i.e. seawall presence). Strongly aggregated distribution patterns are supposed to be characteristic of organisms with direct development, while the existence of planktotrophic larvae could allow the homogeneous distribution of organisms with indirect development. We examined the distribution patterns of grazing molluscs with both planktotrophic (the gastropods Tectarius striatus and Melaraphe neritoides) and direct (e.g. Omalogyra atomus or Lasaea adansoni) development in continuous rocky shores, natural patches and fragments. Two natural rocky shores of each type (continuous rocky shores, natural patches and fragments), separated from each other by kms, were sampled. At the mid-intertidal level, the gastropods Tectarius striatus and Melaraphe neritoides were identified and quantified in situ in quadrats randomly deployed on the shore. Randomly replicates of seaweed turfs, composed mostly by articulated coralline algae, were collected in the chosen locations and target gastropods were sorted and quantified in the laboratory. We predict that organisms with planktotrophic development will be less affected by fragmentation because they have the ability to disperse among fragments.

FCT