Anna Fricke

Drivers of colonization and succession in polar benthic macro- and microalgal communities

Information on succession in marine benthic primary producers in polar regions is very scarce, particularly with regard to effects of abiotic and biotic drivers of community structure. Primary succession begins with rapid colonizers, such as diatoms and ephemeral macroalgae, whereas slow, highly seasonal recruitment and growth are characteristic of annual or perennial seaweed species. Colonization of intertidal and subtidal assemblages on polar rocky shores is severely affected by physical disturbance and by seasonal changes in abiotic conditions. Biotic factors, such as grazing, can strongly affect colonization patterns and also alter competitive interactions among benthic algae. Ambient UV radiation affects the diversity of macroalgal communities during early and later stages of succession. In contrast, microalgal assemblages have high tolerance to UV stress. Climate warming could alter algal latitudinal distribution and favor invasion of polar regions by cold-temperate species. Reduced sea ice cover and retreating glaciers could expand colonization areas but alter light, salinity, sedimentation and disturbance processes. Although the key role of macroalgae in coastal systems and, to a much reduced extent, the importance of microphytobenthos have been documented for polar regions, information on the successional process is incomplete and will benefit from further ecological studies.

Succession patterns in algal turf vegetation on a Caribbean coral reef

Abstract Over the past three decades, Caribbean coral reefs have drastically changed in structure and organization due to anthropogenically driven environmental changes. The prognostic trend indicates a shift from coral- to more algal-dominated reefs coupled with a loss in biodiversity and destabilization of reef structure. This study focuses on the composition of the most common algal growth form, the turf, and investigates turf succession within a fringing Caribbean coral reef. In a field study starting October 2007, we followed succession of turf algal assemblages grown on artificial substrata for periods of 15 up to 333 days at different water depths (5, 15 and 25 m). Species composition and abundance,biodiversity, total cover, and biomass were investigated and compared in uni- and multivariate analyses. Despite the pronounced change in coral reef structure over the past years, we found little difference from primary succession patterns described 30 years earlier. Succession patterns revealed a high diversity, mainly driven by the filamentous brown algal order Ectocarpales, the crustose green alga Pringsheimiella scutata at early stage, and diverse filamentous Cyanobacteria at later stages. Overall, the study provides insight into the early successional stages of coral reef vegetation by identifying the key species and discussing possible factors determining reef development in relation to environmental change.

Mega-epibenthos at Bouvet Island (South Atlantic): a spatially isolated biodiversity hot spot on a tiny geological spot

Mega-epibenthic diversity was analysed using a seabed photography at four stations off Bouvet Island and one station at the Spiess Seamount in the South Atlantic. Surprisingly, the intermediate-scale diversity within the area of investigation was not lower compared to that on the Patagonian shelf and only moderately lower than that on the Antarctic continental shelf. This result is incompatible with Mac Arthur and Wilson’s Island Biogeography Theory describing species richness as a function of immigration of new species into an area and its extension. The relatively high species number and the very small extension of the Bouvet shelf compared to the much larger continental shelves of the other two areas can be explained by long-range dispersal of marine benthic animals in the Antarctic Circumpolar Current and high habitat heterogeneity. The observed uncoupling of intermediate-scale from large-scale background species diversity on the Antarctic shelf raises the question whether in these benthic systems an upper capacity limit for diversity exists.

Studying mesoalgal structures: a non-destructive approach based on confocal laser scanning microscopy

Abstract Mesoalgae play a key role in shallow coastal ecosystems. Composed of small macroalgae, intermixed with filamentous cyanobacteria and colonial diatoms, these multi-specific, but minute (μm–cm) assemblages form complex three-dimensional structures, providing shelter for different unicellular (e.g. bacteria, diatoms, dinoflagellates) and multicellular (e.g. fishes, invertebrates) organisms. Characterized by a high colonization potential, these primary producers are observed to bloom and overgrow disturbed areas (e.g. damaged coral reefs, urchin barrens), and play a crucial role in terms of invasion and colonizing new habitats. Driven by anthropogenic environmental changes, mesoalgae are receiving considerable attention in current marine research. So far, most studies approach mesoalgae at the functional group level (e.g. turf algae, microphytobenthos), whereas only few studies tackle the importance of species-specific interactions, which play an important role in benthic ecology (e.g. coral-algal competition and disease spreading). To facilitate the study of not only the presence but also the composition and the structure of these habitat formers, we provide a new approach combining inexpensive fixation methodology with modern confocal laser scanning microscopy (CLSM), to study minute macroalgal structures (e.g. germlings, reproductive structures), and investigate their relation to microphytobenthic components (e.g. diatom colonies). Detailed procedures for mounting, staining and imaging phytobenthic communities are provided.

The Chlorophytes of Curaçao (Caribbean): a revised checklist for the south-west coast

Abstract The global trend of unprecedented losses in coral reefs is particularly striking in the Caribbean, where dense algal assemblages are commonly replacing corals. So far, hardly anything is known about the ecology of the dominant algal groups. The present study compiled records of Chlorophytes from nine studies in the shallow reefs of Curaçao in the years preceding the onset of coral reef decline (1908–1978) and compared them with records from three recent (2007–2009) expeditions conducted at the same and nearby study locations along the south-west coast of the island. A total of 107 species were encountered, including seven new records for Curaçao (Anadyomene saldanhae, Bryopsis hypnoides, Chaetomorpha minima, Derbesia fastigiata, Ulva flexuosa subsp. paradoxa, Ulvella scutata and Ulvella lens). Sampled material revealed a higher species number during the dry seasons than during the wet seasons, indicating a seasonal variation in algal growth. Most species grew on hard substratum or were epibiotic, and 13 species were found growing on more than one substratum. Comparisons with earlier studies suggest an extension in depth range for nine species. The present work provides a comprehensive overview of the distribution of Chlorophytes of the island and can serve as an important baseline for further research on coral reef ecosystem changes.