Variation in Community Structure across Vertical Intertidal Stress Gradients: How Does It Compare with Horizontal Variation at Different Scales?

Abstract

In rocky intertidal habitats, the pronounced increase in environmental stress from low to high elevations greatly affects community structure, that is, the combined measure of species identity and their relative abundance. Recent studies have shown that ecological variation also occurs along the coastline at a variety of spatial scales. Little is known, however, on how vertical variation compares with horizontal variation measured at increasing spatial scales (in terms of sampling interval). Because broad-scale processes can generate geographical patterns in community structure, we tested the hypothesis that vertical ecological variation is higher than fine-scale horizontal variation but lower than broad-scale horizontal variation. To test this prediction, we compared the variation in community structure across intertidal elevations on rocky shores of Helgoland Island with independent estimates of horizontal variation measured at the scale of patches (quadrats separated by 10s of cm), sites (quadrats separated by a few m), and shores (quadrats separated by 100s to 1000s of m). The multivariate analyses done on community structure supported our prediction. Specifically, vertical variation was significantly higher than patch- and site-scale horizontal variation but lower than shore-scale horizontal variation. Similar patterns were found for the variation in abundance of foundation taxa such as Fucus spp. and Mastocarpus stellatus, suggesting that the effects of these canopy-forming algae, known to function as ecosystem engineers, may explain part of the observed variability in community structure. Our findings suggest that broad-scale processes affecting species performance increase ecological variability relative to the pervasive fine-scale patchiness already described for marine coasts and the well known variation caused by vertical stress gradients. Our results also indicate that experimental research aiming to understand community structure on marine shores should benefit from applying a multi-scale approach.

Up, Down, and All Around: Scale-Dependent Spatial Variation in Rocky-Shore Communities of Fildes Peninsula, King George Island, Antarctica

“…The vertical zonation patterns discussed above depended on the spatial scale of observation, which is well in line with studies conducted in temperate [18], [19] and sub-Antarctic shores [54], [55]. In particular, the effects of intertidal height and subtidal depth on diversity and community structure significantly varied among the smallest sampling units in our study.…”

Benthic assemblages of rock pools in northern Portugal: seasonal and between-pool variability

“…Although there is large and widespread evidence that patterns of distribution, abundance and diversity of organisms are heterogeneous over a range of spatial and temporal scales (Underwood et al 2000, Benedetti-Cecchi 2001, Fraschetti et al 2005, Terlizzi et al 2007, Valdivia et al 2011, this concept is still key for a number of basic and applied ecological issues. As abiotic and biological processes are themselves variable in space and time, examining relevant scales of variation of populations and assemblages is essential to enhance the predictive and explanatory value of ecological models (Andrew and Mapstone 1987, Levin 1992, Underwood and Chapman 1996, Benedetti-Cecchi 2000.…”

A multistate dynamic site occupancy model for spatially aggregated sessile communities

“…This result coincides with the known observation that rocky intertidal communities may be more variable along the vertical than the horizontal direction because environments tend to vary more rapidly along the vertical axis (Benedetti‐Cecchi ; Valdivia et al . ). The estimated resampling error rate tended to be higher in the spatial model than in the non‐spatial model (Table ).…”