Species richness and diversity across rocky intertidal elevation gradients in Helgoland: testing predictions from an environmental stress model

Abstract

Environmental stress affects species richness and diversity in communities, but the precise form of the relationship is unclear. We tested an environmental stress model (ESM) that predicts a unimodal pattern for total richness and diversity in local communities across the full stress gradient where a regional biota can occur. In 2008, we measured richness and diversity (considering all macrobenthic species) across the entire intertidal range on three rocky shores on Helgoland Island, Germany. Intertidal elevation is known to be positively related to abiotic stress. Since Helgoland is between the northern and southern biogeographic boundaries for the cold-temperate NE Atlantic intertidal biota, it exhibits low stress levels for this biota at low elevations and high stress at high elevations because of long ([6 h) emersion times. Thus, we predicted a unimodal trend for richness and diversity across elevation. On all three shores, richness increased from high to middle elevations, but remained similar between middle and low elevations. Diversity followed the same trend on one shore and different trends (although also nonunimodal) on the other two. Evenness explained the trend differences between richness and diversity. Overall, our study yielded little support for the ESM. Reasons for richness and diversity not decreasing at low elevations may be related to influences of mostly subtidal species, Helgoland's intertidal range, or sampling resolution. Our study also suggests that the ESM must be developed further to differentiate between richness and diversity. We offer recommendations to improve future ESM research using intertidal systems.

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

“…Physical stresses such as wave action are also known to influence community structure at the shore scale [47]. In Helgoland, in situ measurements using dynamometers have revealed that wave exposure is higher at Bunker than at Nord-Ost-Hafen and Kringel, being similar between these last two shores [46]. Thus, wave exposure might explain the horizontal variation at the shore scale to a certain degree.…”

Predator chemical cues affect prey feeding activity differently in juveniles and adults

“…These species commonly occur sympatrically on North Atlantic rocky shores (Scrosati and Heaven 2007;Scrosati et al 2011), with N. lapillus being one of the main predators of S. balanoides (Largen 1967).…”

“…In June 2010, we collected dogwhelks from a wavesheltered section of Helgoland's shoreline (mean (SE) daily maximum water velocity of 2.0 ± 0.2 m·s -1 ; Scrosati et al 2011), kept the organisms in a tank with running seawater at 16°C, and fed them barnacles and mussels for 20 days prior to experimentation. We collected the experimental barnacles by chipping off small pieces of rocks to which barnacles were attached on the same shore, using a hammer and a chisel.…”

Résistance des communautés benthiques aux perturbations multiples /

“…This latter procedure is common (e.g. Scrosati et al 2011) and the same unit among abundances is necessary to assess the community dominance profiles in our treatments. The cover was estimated per species, so the total summed % in a plot often exceeded 100%.…”