Background Coastal land development has deteriorated the habitat and water quality for seagrass growth and causes the proliferation of opportunist macroalgae that can potentially affect them physically and biochemically. The present study investigates the morphological and biochemical responses of seagrass from the Hydrocharitaceae family under the macroalgal bloom of Ulva reticulata, induced by land reclamation activities for constructing artificial islands. Methods Five seagrass species, Enhalus acoroides, Thalassia hemprichii, Halophila ovalis, Halophila major, and Halophila spinulosa were collected at an Ulva reticulata-colonized site (MA) shoal and a non-Ulva reticulata-colonized site (MC) shoal at Sungai Pulai estuary, Johor, Malaysia. Morphometry of shoots comprising leaf length (LL), leaf width (LW), leaf sheath length (LSL), leaflet length (LTL), leaflet width (LTW), petiole length (PL), space between intra-marginal veins (IV) of leaf, cross vein angle (CVA) of leaf, number of the cross vein (NOC), number of the leaf (NOL) and number of the leaflet (NOLT) were measured on fresh seagrass specimens. Moreover, in-situ water quality and water nutrient content were also recorded. Seagrass extracts in methanol were assessed for total phenolic content (TPC), total flavonoid content (TFC), 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity (DPPH), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid radical cation scavenging activity (ABTS), and ferric reducing antioxidant power (FRAP). Results Seagrasses in the U. reticulata-colonized site (MA) had significantly higher (t-test, p < 0.05) leaf dimensions compared to those at the non-U. reticulata colonized site (MC). Simple broad-leaved seagrass of H. major and H. ovalis were highly sensitive to the colonization of U. reticulata, which resulted in higher morphometric variation (t-test, p < 0.05) including LL, PL, LW, and IV. Concerning the biochemical properties, all the seagrasses at MA recorded significantly higher (t-test, p < 0.05) TPC, TFC, and ABTS and lower DPPH and FRAP activities compared to those at MC. Hydrocharitaceae seagrass experience positive changes in leaf morphology features and metabolite contents when shaded by U. reticulata. Researching the synergistic effect of anthropogenic nutrient loads on the interaction between seagrasses and macroalgae can provide valuable information to decrease the negative effect of macroalgae blooms on seagrasses in the tropical meadow.

Increasing global paper consumption has fostered the search for new alternative non-wood fiber sources. The aquatic weeds Cyperus digitatus, Cyperus iria, and Scirpus grossus were analysed for their fiber characteristics and chemical composition, and the processed fibers were transformed into handmade paper. The selected species yielded medium-length fibers (0.92 mm to 1.03 mm), which were thin-walled with a lumen diameter (3.37 µm to 5.26 µm) wider than cell wall thickness (2.73 µm to 2.97 µm). In terms of fiber derived values, the selected species possessed a slenderness ratio of 86.5 to 113.1 (favourable, > 30) and flexibility coefficient of 35.2 to 47.6 (favourable, within the range 50 to 70), which was classified as rigid fiber. The species also contained high cellulose, 42.1% to 44.8% (favourable, > 40%) and hemicellulose content, 42.8% to 45.6% (favourable, within the range of 30% to 50%), and low lignin content, 10.6% to 11.8% (favourable, < 12%). Handmade paper of Cyperus digitatus possessed relatively high tensile strength (2.61 ± 0.15 kN/m) and breaking length (1.20 ± 0.07 km) among studied species. Comparison with other non-wood fibers indicated that the studied plants fibers can be used for production of paper plates, paperboard, and decorative paper.