Metrics matter: Multiple diversity metrics at different spatial scales are needed to understand species diversity in urban environments

Soil resource heterogeneity promotes species richness only at a fine scale at the early restoration of karst abandoned farmland

The relationship between heterogeneity and plant diversity remains unclear in low-resource karst. We made in situ observations at different spatial scales within a fixed plot on abandoned farmland that had been enclosed for 4 years. Species richness was spatially scale dependent, while species evenness remained consistently low across all scales. Species diversity was positively related to resource heterogeneity only at a fine scale (1 m × 1 m), mainly driven by an increase in the species richness of non-dominant groups. Resource heterogeneity reduced overall plant growth at a large scale. However, it reduced the growth of the dominant families (Asteraceae and Poaceae) at a fine scale, but promoted it at a large scale. Our results suggest that soil resource heterogeneity exerts a scale-dependent positive impact on species richness during the early restoration of abandoned farmland by low resource availability and highlight the importance of fine-scale ecological information in karst areas.

Kelp forests collapse reduces understorey seaweed β-diversity

BACKGROUND AND AIMS

Kelps are the primary foundation species in temperate subtidal rocky shores worldwide. However, global change is causing their decline with consequences for the organisms that rely on them. An accurate assessment of these consequences may depend on which attributes of the associated community are considered. This study shows that conventional α-diversity approaches may overlook some of these consequences compared to spatially explicit approaches such as with β-diversity.

METHODS

A 1-year seasonal study was conducted to compare the macroalgal understorey between healthy reefs with a Laminaria ochroleuca canopy and degraded reefs where the canopy collapsed years ago due to excessive fish herbivory. At each reef, the understorey seaweed assemblage was recorded in five replicate quadrats to estimate α-diversity (total richness, species density, Shannon index) and β-diversity (intra- and inter-reef scale).

KEY RESULTS

The understorey assemblage exhibited a distinct seasonal dynamic in both healthy and degraded reefs. α-Diversity attributes increased in spring and summer; turf-forming algae were particularly dominant in degraded reefs during summer. β-Diversity also showed seasonal variability, but mostly due to the changes in degraded reefs. None of the α-diversity estimates differed significantly between healthy and degraded reefs. In contrast, spatial β-diversity was significantly lower in degraded reefs.

CONCLUSIONS

Although the loss of the kelp canopy affected the composition of the macroalgal understorey, none of the conventional indicators of α-diversity detected significant differences between healthy and degraded reefs. In contrast, small-scale spatial β-diversity decreased significantly as a result of deforestation, suggesting that the loss of kelp canopy may not significantly affect the number of species but still have an effect on their spatial arrangement. Our results suggest that small-scale β-diversity may be a good proxy for a more comprehensive assessment of the consequences of kelp forest decline.

Victim of changes? Marine macroalgae in a changing world

BACKGROUND

Marine macroalgae ('seaweeds') are a diverse and globally distributed group of photosynthetic organisms that together generate considerable primary productivity, provide an array of different habitats for other organisms, and contribute many important ecosystem functions and services. As a result of continued anthropogenic stress on marine systems, many macroalgal species and habitats face an uncertain future, risking their vital contribution to global productivity and ecosystem service provision.

SCOPE

After briefly considering the remarkable taxonomy and ecological distribution of marine macroalgae, we review how the threats posed by a combination of anthropogenically induced stressors affect seaweed species and communities. From there we highlight five critical avenues for further research to explore (long-term monitoring, use of functional traits, focus on early ontogeny, biotic interactions and impact of marine litter on coastal vegetation).

CONCLUSIONS

Although there are considerable parallels with terrestrial vascular plant responses to the many threats posed by anthropogenic stressors, we note that the impacts of some (e.g. habitat loss) are much less keenly felt in the oceans than on land. Nevertheless, and in common with terrestrial plant communities, the impact of climate change will inevitably be the most pernicious threat to the future persistence of seaweed species, communities and service provision. While understanding macroalgal responses to simultaneous environmental stressors is inevitably a complex exercise, our attempt to highlight synergies with terrestrial systems, and provide five future research priorities to elucidate some of the important trends and mechanisms of response, may yet offer some small contribution to this goal.