Understanding the variability of macrobenthic communities and larval availability associated with subtidal kelp forest habitats

Kelp forests are highly productive, structurally complex and dominate the subtidal rocky shores in many temperate regions such as those present in Chile. Through the provision of shelter and food, they support rich benthic communities, living on or in the shade of the canopy forming macroalgae. Although many reef fish use the forest as a nursery or settlement area, benthic communities associated with kelp forests mainly consist of invertebrates. Most of these organisms have low mobility and therefore depend on a larval phase for dispersal. Processes affecting larval availability and settlement are highly variable on spatial and temporal scales. These variations impede our ability to predict recruitment of natural populations. On a small scale, for instance, the complex structure of kelp forest can interfere with hydrodynamic currents by retaining and trapping propagules, forcing them to settle down. However, large-scale oceanographic processes and geographical features such as coastal topography will most likely drive spatiotemporal variation in larval availability and settlement along the shore. To understand the variability of macrobenthic communities and larval availability associated with subtidal kelp forests of the brown macroalgae Lessonia trabeculata, fieldworks were carried out during a 30-day period in four sites in northern-central Chile, spanning from 30° to 33 °S. Temporal and spatial variations in upwelling dynamics have been well documented along these latitudes and we spanned the sampling effort to include the influence of upwelling regime. In each site, the water column (i.e. larval availability and emerging macrobenthos) and bottom (i.e. recruits and young of the year) associated with the kelp forest were sampled simultaneously, using standardized methods for each (light trapping and bottom suctions respectively). Light trap collections consisted of emerging macrobenthos and early-life history stages of mainly decapod crustaceans and gastropod mollusks and fish. Within the larval assemblage, megalopa of Paraxanthus barbiger were most abundant and representative in all study sites. In order to explain spatiotemporal patterns of emerging macrobenthos and larval availability, sites with different upwelling regimes were compared. The relationship between larval availability and benthic recruits was assessed through spatial scale variation analysis. Lastly, to examine the influence of the moon cycle on the structure of emerging macrobenthos and early-life history assemblages, a field experiment was conducted in a local site under the effect of the lunar cycle. Results indicate that four decapod species (i.e. Paraxanthus barbiger, Romaleon polyodon, Taliepus spp., and Pagurus spp.) were represented in both the water column and benthic sampling, suggesting a coupling between pelagic and benthic subsequent stages. Moreover, CPUE as a proxy for abundance of emerging macrobenthos and larval availability is influenced by lunar cycle (or ambient light intensity) as emerging macrobenthos abundance was higher with new moon (0,9 % illumination) in comparison to full moon (99,8 % illumination), whereas for early-life history stages a higher species richness was found with new moon. The effect of the lunar cycle seemed to be imposed on the effect of upwelling, which is why no differences between sites with high and low upwelling regimes could be observed. The results of this study aims to provide information about the influence of larval availability to complex benthic community structure.

ISCED Categories

The highlighted icons, represent the fields of education (in compliance with ISCED Classification) engaged during this course/programme.

0511 - Biology", "0521 - Ecology", "0532 - Physical and chemical oceanography", "0588 - Scientific modelling