Evolution of Holdfast Diversity and Attachment Strategies of Ediacaran Benthic Macroalgae

Holdfast morphologies and attachment strategies of benthic macroalgae are somewhat flexible and controlled by both the substrate condition and species. Six forms (tapered base, globose holdfast, composite globose holdfast, discoidal holdfast, rhizoids and horizontal rhizomes) of attachment structures of Ediacaran benthic macroalgae are recognized from the early Ediacaran Lantian biota and late Ediacaran Miaohe biota in South China based on functional morphology. Each form is considered either adapted to firm substrates that dominate the Precambrian seafloor, or soft substrates that are more common in the Phanerozoic. The results show a diversification in both holdfast morphology and attachment strategies of macroalgae during the Ediacaran Period. In the early Ediacaran Lantian biota, none of the benthic macroalgae is adapted to soft substrates, while in the late Ediacaran Miaohe biota, a considerable number (41%) of species are adapted to relatively soft substrates. This shift might be an adaptive response to the diversification of macroalgae and a changing substrate condition during the Ediacaran Period: the decline of microbial mats and increase of water content in the sediments in the Ediacaran.

COLEÇÃO FICOLÓGICA E A IMPORTÂNCIA DO REGISTRO HISTÓRICO DE MACROALGAS PARA A BIODIVERSIDADE MARANHENSE = PHICOLOGICAL COLLECTION AND THE IMPORTANCE OF HISTORICAL RECORD OF BENTHIC MARINE ALGAE FOR THE BIODIVERSITY OF MARANHAO STATE

Os acervos biológicos destacam-se por ser uma fonte de dados sobre os diferentes organismos, apresentando um grande e inestimado valor histórico e cultural. Diante disso, o presente estudo teve o objetivo de registrar a importância histórica do acervo de macroalgas existente no Herbário do Maranhão (MAR) devido à necessidade de conservação desse acervo. A coleção ficológica foi organizada pela Profa. Maria Marlúcia, e teve seu início com a coleta da alga marinha Catenella caespitosa (Florideophyceae) em 1985. A partir de então, foi iniciado o levantamento de macroalgas marinhas bentônicas do Maranhão, sendo doada para o Herbário MAR, em 2013. Apesar do litoral maranhense ser o segundo maior litoral do Brasil, os estudos sobre as algas não são proporcionais à extensão litorânea do Estado. Assim, o presente estudo buscou evidenciar a importância histórica do registro das macroalgas e a necessidade de mais estudos para ampliar o conhecimento sobre as macroalgas que compõem o Maranhão.ABSTRACTBiological collections stand out for being a source of data on different organisms, presenting a great and inestimated historical and cultural value. In addition, the present study aimed to record he historical importance of the existing macroalgae collection in the Herbarium of Maranhão (MAR) due to the need to preserve this collection. The ficological collection was organized by the professor Maria Marlúcia, and started with the collection of seaweed Catenella caespitosa (Florideophyceae) in 1985. From that period, it started the survey of marine benthic macroalgae in the state of Maranhão, being donated to Herbarium MAR in 2013. Although the coast of the state of Maranhão is the second largest coast in Brazil, the algae studies are not proportional to the coastal extension of Maranhão state. Thus, the present study sought to highlight the historical importance from the record of macroalgae and the need for further studies to expand knowledge about the macro algae that compound Maranhão state.

Seaweed farming pressure affects seagrass and benthic macroalgae dynamics in Chwaka Bay (Zanzibar, Tanzania)

Farming of Eucheuma denticulatum is a major activity in Zanzibar affecting seagrass ecosystems primarily through shading and trampling. The aim of this study was to test the impacts of shading and trampling during seaweed farming on seagrass meadows composed by Halophila stipulacea and Thalassia hemprichii and their associated benthic macroalgae. Areas covered by these species were selected for the building of seaweed farms in three treatments: seaweed farm plots (with shading and trampling effects), trampling plots (with trampling effects only), and control plots (with no shading or trampling effects). Reduction of light within the plots was recorded over 9 weeks. Percentage cover of seagrasses and macroalgae and shoot density of seagrasses were measured over 12 weeks to assess the impact of shading and trampling by seaweed farming activities. Light was significantly reduced in the seaweed farm plots by 75 to 90% by the end of a seaweed growth cycle. H. stipulacea, despite its capacity for rapid growth, was significantly affected by the combination of shading and trampling under the seaweed farm treatment, while the climax seagrass species T. hemprichii was unaffected. Due to the decline in H. stipulacea, benthic macroalgae cover increased in the seaweed farm treatment, suggesting a change in seagrass community dynamics. In contrast, trampling had a negative effect on the benthic macroalgae as an isolated disturbance, which suggests that seagrasses are more resistant to trampling than macroalgae and would likely dominate the benthic macrophyte community under these conditions.

Coexistence of the reef-building coral Cladocora caespitosa and the canopy-forming alga Treptacantha ballesterosii: Description of a new Mediterranean habitat

Shallow Mediterranean rocky environments are usually dominated by macroalgae, but the stony colonial zooxan­thellate coral Cladocora caespitosa is able to build extensive banks in some particular areas. Although zooxanthellate corals and benthic macroalgae are expected to compete for light and space when overlapping in the same habitat, there is previous evidence that C. Caespitosa and Mediterranean macroalgae do not suffer from competitive exclusion when living together. Here we characterize a new and unique Mediterranean habitat where the reef-building coral C. Caespitosa and erect seaweeds of the order Fucales (Cystoseira s.l.) coexist. In this new habitat C. Caespitosa reaches 34% cover and densities of Cystoseira s.l. (mainly Treptacantha ballesterosii) are much higher than values reported from other sites. Interestingly, abundances of T. Ballesterosii and C. Caespitosa show a positive relationship, suggesting that some kind of facilitation mechanism is taking place. These findings challenge the theory of competitive exclusion between corals and macroalgae and launch a wide array of possible open discussions on coral-macroalgae interactions.