Marine turf of an invasive alga expels lugworms from the lower shore

Bare sandy flats at and below low tide level of the Wadden Sea (eastern North Sea, European Atlantic) were observed in 2020 to have been invaded by an introduced grass-like alga, Vaucheria cf. velutina (Xanthophyceae). A dense algal turf accumulated and stabilized mud, where resident seniors of the lugworm Arenicola marina had reworked rippled sand. Algae and worms were incompatible. Initially, rising patches with algal turf alternated with bare pits where lugworms crowded. Their bioturbation inhibited young algae, while the felt of established algal rhizoids clogged feeding funnels of worm burrows. Eventually, a mosaic pattern of competitors gave way to a coherent algal turf without lugworms. Concomitantly, a rich small-sized benthic fauna took advantage of the novel algal turf. This exotic Vaucheria may have the potential for drastically altering the ecological web at the lower shore.

Saccharobesus litoralis gen. nov., sp. nov., a novel alginate-degrading bacterium isolated from the surface of intertidal algal turf

A novel rod-shaped, Gram-stain-negative, strictly aerobic and alginate-degrading marine bacterium, designated CCB-QB4T, was isolated from a surface of algal turf collected from a coastal area of Penang, Malaysia. The cells showed motility by a lateral flagellum. The rod-shaped cells formed long chains end-to-end. Phylogenetic analysis based on the 16S rRNA gene sequence of strain CCB-QB4T showed 94.07, 92.69, 91.52 and 90.90 % sequence similarity to Algibacillus agarilyticus RQJ05T, Catenovulum maritimum Q1T, Catenovulum agarivorans YM01T and Catenovulum sediminis D2T, respectively. Strain CCB-QB4T formed a cluster with A. agarilyticus RQJ05T. Strain CCB-QB4T was catalase-negative, oxidase-positive, and degraded agar, alginate, and starch. Cell growth was observed at 15–40 °C, at pH 7.0–10.0 and in the presence of 1–6 % (w/v) NaCl and glucose. The major fatty acids were summed feature 3 (C16 : 1 ω7c/iso-C15 : 0 2-OH), C16 : 0 and C18 : 1 ω7c. The polar lipids were phosphatidylethanolamine, two unidentified aminolipids, two unidentified glycolipids, an unidentified phospholipid and unidentified lipid. The major respiratory quinone was ubiquinone-8. The genomic DNA G+C content was 46.7 mol%. Based on the phenotypic, chemotaxonomic and phylogenetic data, strain CCB-BQ4T represents a novel species in a new genus, for which the name Saccharobesus litoralis gen. nov., sp. nov. is proposed. The type strain is CCB-QB4T (=JCM 33513T=CCB-MBL 5008T).

Marine Turf of an Invasive Alga Ousts Lugworms From Lower Shore

Bare sandy flats at and below low tide level were observed in 2020 to have been invaded by an introduced grass-like alga, Vaucheria cf. velutina (Xanthophyceae). A dense algal turf accumulated and stabilized mud where resident seniors of the lugworm Arenicola marina had reworked rippled sand. Algae and worms were incompatible. Initially, rising patches with algal turf alternated with bare pits where lugworms crowded. Their bioturbation inhibited young algae, while the felt of established algal rhizoids clogged feeding funnels of worm burrows. Eventually, the mosaic pattern of competitors gave way to a coherent algal turf without lugworms. Concomitantly, a rich small-sized benthic fauna took advantage of the novel algal turf. This exotic Vaucheria has the potential for taking over at the lower shore of the Wadden Sea (eastern North Sea, European Atlantic).

6. Reef fish and other major predators

Fish, like corals, have geographical patterns across regions and across individual reefs, being structured in the latter case by wave energy and depth. The thousands of species show a variety of feeding patterns. Detritus feeders are very abundant, feeding on the detritus on the seabed, especially in the fine, filamentous algal turf on apparently bare rock. Plankton feeders are common also, and herbivorous fishes show a large abundance, perhaps a quarter of the total species present, cropping algae that otherwise would grow unchecked and smother coral. Since turf algae also contain many micro-species and detritus, most herbivores also ingest much food other than simple plant material. Carnivores range from extreme specialists, such as polyp-picking butterflyfish, to generalists. Sharks and barracuda only consume other fish and generally are at the top of their food chains. The complicated ecological structure of the food webs can be clarified by analysing nitrogen isotope ratios in their tissues. Other important coral carnivores include the crown of thorns starfish, which can remove almost all living coral on a reef when it develops into plagues. Overfishing by humans greatly disturbs the equilibrium of a reef, and this is increasingly causing reef degradation.

Positive and Negative Species Interactions Shape Recruitment Patterns of a Range Expanding Native Alga

A species’ ability to spread is in part governed by the extent to which recipient habitats either resist, tolerate or promote the species’ recruitment. In disturbed marine environments, there is a general trend for the loss of algal canopies, thought to resist invasion, toward algal turf or rock barrens habitat. This study tested whether the spread of the range-expanding native macroalga Caulerpa filiformis was resisted by algal canopies but facilitated by algal turf or barrens habitats. Large-scale field surveys generally supported the predicted recruitment patterns, with C. filiformis recruits being most abundant on turf (but not barrens) and absent under kelp canopies. However, a discrepancy existed between different structural forms of turf, with the positive association holding true only for geniculate corallines, not filamentous turf. Secondly, a laboratory experiment tested whether the physical structure and/or the sediment-trapping properties of coralline turf influenced the recruitment success of C. filiformis. Whilst the structural complexity of turf aided overall recruitment performance (i.e., increased rhizoid production, attachment speed, success, and strength), a positive influence of turf-derived sediment on recruits’ growth was less obvious, at least over 10 days. The high morphological plasticity of C. filiformis propagules resulted in possible benefits of faster or stronger attachment of more developed propagules being only temporary, and that recruitment may be regulated in accordance with habitat preference. Finally, a field experiment confirmed the observed positive role of turf and the negative influence of algal canopies in the short-term, however, adverse environmental conditions in the longer-term resulted in the loss of most fragments. In conclusion, this study demonstrated the importance of both positive and negative species interactions for the recruitment success of a native alga, suggesting that a shift from kelp to turf algae can initiate further community change.