The marine angiosperms, seagrass

Seagrasses are a group of marine flowering plants. They are under the sub-division of angiosperms classed within a family of the monocotyledonous plants, which also includes the freshwater aquatic macrophytes. Although totally submerged, seagrasses have all the structures of the terrestrial plants with a root system, a shoot system, a vascular system, and vegetative and sexual reproduction, with flowers fertilized by water borne pollen. These structures and functions are unique for plants in the sea. Seagrasses occur in many areas along the coast of Malaysia and although small in area, form a significant component of the coastal ecosystem besides mangroves and coral reefs. Our research group field studies revealed that even though are seagrasses patchy in distribution, they constitute one of the common coastal ecosystem types. Those areas that were studied were those accessible ones. Many more areas, far and wide particularly in the off-shore islands in the territorial waters of Sabah are the most likely environments where extensive seagrasses occur. The structure of seagrass ecosystem can vary from a few or patches of plants to extensive seagrass beds by two or more mixed species. These beds are dynamic and productive, attract diverse grazers and predators, and often these are commercially important species. In some coastal areas, seagrasses are service provider i.e., support livelihood of coastal communities that depend on fisheries which are linked directly or indirectly to the environment and production created by seagrasses. These intrinsic roles of seagrasses although have been recognized have not been afforded the same priority as the mangroves and corals. One reason could be that seagrass ecosystem has historically been neglected and not been well-studied. With the growing concern and interest, this important system is based on what have been studied should be communicated. In this respect, I am glad to have this opportunity to present this lecture personally than my numerous papers published on seagrasses alone could provide. In general, what are known about seagrasses in Malaysia? What differentiates seagrasses from other plants? Seagrasses together with seaweeds and phytoplankton form the important primary producers of a shallow marine environment. Seagrasses and seaweeds in particular share similar habitats e.g., mangroves, coral reef ecosystem, intertidal areas, lagoons and rocky shores. It is important to learn and be able to distinguish between them. “If you take seagrasses away to identify, make sure take the “whole plant” – a complete cluster of shoots with rhizomes, roots and if available the flowering plants. If just a shoot is collected, not only you may miss the flowering materials but you may find that you do not have all the information that you require”. Accurate species identification in the field would be helpful and allow more people to understand and appreciate seagrasses. This is especially true where people now are very much aware on its unique natural values e.g., especially seagrass beds provide habitats and feeding ground for dugongs, green turtles, seahorses and other invertebrates. Are seagrasses merely green vegetation along the coastline? Seagrasses do much more than providing underwater spectacular scenes. The lush vegetation in a seagrass bed (e.g., Sungai Pulai estuary and its adjacent waters) may harbor hundreds of species and each is unique and interconnected in a food web. In this case the heart of a food web is the seagrasses, providing food and oxygen. A food web is strong when intact, yet easily disturbed and each disrupted connection weakening the web. We must recognize the value of all species and the hidden relationship between them. This lecture provides the basis for far more work on the seagrasses and their associates

Changes in macroalgae species composition, assemblage and coverage at an inter-tidal rocky shore.

Samplings of macroalgae were undertaken at an inter-tidal rocky shore of Kuala Similajau (Lat. 3°22′ 13.9′N, Long. 113°17′ 39.1″E), Bintulu, Sarawak during two peaks of wet period; Feb.-Mar. (monthly total rainfall of 514.0 mm, 481.6 mm; average temperature 25.7℃, 26.2℃) and Jul.-Aug.(monthly total rainfall 585.8 mm, 566.2 mm; average temperature 26.3℃, 27.0℃) 2008. This study investigates the changes in macroalgae species composition, assemblage and coverage covering the two peaks of wet period. A total of 23 taxa comprising 7 green, 5 brown and 11 red algae were recorded covering the two peaks of wet period, with red algae being the most diverse division. Comparatively a lower number of macroalgae species occurred during Feb.-Mar. (12 species) compared to the period of Jul.-Aug. (20 species). Several species such as Ulva clathrata (Roth) Greville, Valonia aegagropila C. Agardh and Lobophora variegata (Lamouroux) Womersley ex Oliveira, were absent during the Feb.-Mar. Common species Anadyomene plicata C. Agardh, Sargassum sp., Acanthophora spicifera (Vahl) Borgesen, Amphiroa fragilissima (Linnaeus) Lamouroux, Gelidiella acerosa(Forsskal) Feldmann & Hamel, Gracilaria salicornia(C. Agardh) Dawson, Hydropuntia edulis (S. G. Gmelin) P. C. Silva, Laurencia papillosa (C. Agardh) Greville and Laurencia sp. were present in both periods. Acetabularia major C. Agardh, Cladophora prolifera (Roth) Kutzing, Ulva intestinalis (Linnaeus) Nees, Padina minor Yamada, Ceramium sp. and Pterocladia sp. were only present in the Jul.-Aug. In terms of mean coverage, there is no distinct trend in domination with respect to a particular species between the two peaks of wet period. However, based on the number of mean coverage contributed by the species, categorically this can be represented as Division Rhodophyta>Division Chlorophyta>Division Phaeophyta

Photosynthetic light responses of wild and cultured Halophila ovalis

A laboratory based experiment was performed on leaves of the seagrass Halophila ovalis to elucidate its photosynthesis versus irradiance (P-I) relationships. Plant samples were sourced from a low water level seabed off the Teluk Kemang coast (2° 30′N, 101° 45′E) in Negeri Sembilan, Malaysia. Plants growing naturally from this area as well as those transplanted into indoor culture tanks were studied. The oxygen evolution responses of the leaves based on parameters of leaf fresh weight (FW), leaf surface area (Area) and leaf chlorophyll content (Chl) towards varying degrees of illumination were recorded. A comparison between leaves from cultures with those from the wild showed that the curve plotted for its respective values was lowered for the former based on FW and Area but comparatively lowered based on Chl. The light compensation (Ic,) value did not vary much between leaves from the wild and leaves from the cultures (8-13 μmol m-2 s-1) while light saturation point (Ik) was in the range of 268 - 275 μmol m-2 s-1 for leaves from the wild and increased to 290 - 293 μmol m-2 s-1 for leaves from cultures. Dark respiration values did not differ between wild and cultured leaves based on the measurements calculated from the parameters stated (FW, Area and Chl). Calculations based on FW and Area showed a higher light saturation (Pmax) photosynthetic rate for cultured leaves but comparatively lowered based on Chl. Pmax values between leaves from culture to that from the wild based on the parameters of FW and Area were significantly different (p<0.05) but not based on Chl while the trends of curves fitted between wild and cultured leaves were significantly different based on Area only (p<0.05). The results collated in this study serve to add to the present knowledge of biological traits of H. ovalis from Malaysia to further understand its importance in local waters

Variability of leaf morphology and marker genes of members of the halophila complex collected in Viet Nam

Seagrasses are marine angiosperms and adapted to aquatic life several times independently. In tropical as well as in temperate regions they play an important role in the coastal ecosystem. Classification according to morphology remains difficult due to very similar adaptations to the aquatic lifestyle and small simple flowers which are often not even formed. Especially the Halophila genus (Hydrocharitaceae) forms a complex group with an unresolved taxonomy due to overlapping morphological characters and high plasticity leading to many misidentifications. Hence, this led to the hypothesis that phylogenetic analysis on the molecular level may resolve taxonomic classification. The aim of this study is to identify and unambiguously characterize Halophila species collected in Viet Nam using tree- and character-based analysis of rbcL and matK sequences. Results obtained from molecular data and leaf morphology indicate that there are at least three species found in Viet Nam. Topologies based on single locus or combined datasets were similar but not equal. Analysis of rbcL sequences showed lowest species resolution when only Halophila beccarii Aschers was resolved at the Halophila complex. matK shows better resolution with respect to H. beccarii and H. decipiens Ostenfeld. Combined rbcL and matK consensus trees showed the highest species resolution when all species form three distinct clades representative for three difference species including H. beccarii, H. decipiens, and H. ovalis (R. Br.) Hook. f

Age, growth, mortality and population structure of Strombus canarium (Gastropoda: Strombidae): variations in male and female sub-populations.

The age, growth, mortality and population structure of Strombus canarium Linnaeus, 1758 were examined in the Johor Straits, Malaysia from January to December 2005. A total of 2088 conchs were sampled where females were more abundant than males with monthly sex ratio of 1.72±0.17 (N = 12). The estimated growth parameter showed higher asymptotic length (L∞) and growth coefficient (K) in females (L∞ = 70.20 mm, K = 1.50 year-1) compared with the males (L∞ = 69.30 mm, K = 1.20 year-1). This resulted in better overall growth performance of females (φ’ = 3.81) compared with the males (φ’ = 3.48). The growth pattern of females and males showed positive allometric nature of growth (b>3, p<0.05), with estimated maximum life span of 2.0 and 2.5 year, respectively. The recruitment pattern was continuous, displaying only a single major peak event per year. The estimated natural mortality rate (M) was 0.95 year-1 in females and 0.86 year-1 in males, while the total mortality rate (Z) was 2.56 and 2.72 year-1, respectively. The fishing mortality rate (F) was 1.61 year-1 in females and 1.86 year-1 in males, which were higher than the natural mortality rates, thus indicating an unbalanced position of the stock. In addition, the exploitation rate (E) was higher than the maximum allowable limit of exploitation (EMSY), which was a further indication of overexploitation. For sustainable utilization of the resource, serious efforts should immediately be taken in reducing the exploitation rates of S. canarium in the study area

Sexual maturity and sex determination in Strombus canarium Linnaeus, 1758 (Gastropoda: Strombidae).

The study was conducted at the Merambong Shoal, Johor Straits, Malaysia. Strombus canarium was the most abundant herbivorous mollusc within the study site, highly prized as seafood and contributes to the economics of the locals. Ontogenetic development of sex characters and sexual maturity were determined via logistic curve analysis, using shell-length and/or lip thickness as predictors. The minimum shell-length at which sex characters appeared was at 30 mm in males and 32 mm in females and both sexes can definitely be determined at more than 41 mm shell-length. The SX50 (probability of individuals can be sexed is 0.5) was at 38.33+0.41 mm for male and at 37.15+0.31 mm for female. The SL„ (length at which the probability of individuals are matured is 0.5) was at 54.14+0.86 mm shell-lengths for males and at 58.51+1.02 nun shell-lengths for females. The LIP„ (lip thickness at which the probability of individuals are matured is 0.5) values on the other hand was about 0.69+0.0003 and 0.80+0.014 mm for males and females respectively. The findings indicate that sexual dimorphisms occurred at very early stage in S. canarium life histor

Morphological characteristics, shoot density and biomass variability of Halophila sp. in a coastal lagoon of the east coast of Malaysia.

This study in a coastal lagoon of Merchang Terengganu, east coast of Peninsular Malaysia evaluated the morphological characteristics, shoot density and biomass for Halophila in pure and mixed population with Halodule pinifolia (Miki) den Hartog. Both species inhabited the silt and sand substrates at depth of about 1.9 m to 2.0 m. They are well adapted and tolerated a range of micro-ecology; pH of 6.57–7.32, wide salinity differences of 9.42–34.47 psu, conductivity 16.14–52.27 ms/cm, and light availability of 446.63–624.1 lux. Morphologically, there are two forms for Halophila (a) small-leaved in pure population and those mixed with the short-leaved, (b) big-leaved with the long-leaved Halodule pinifolia. Both forms have variable leaf shapes, a respond to the wide and frequent fluctuation in water salinity. Leaves possessed red or purplish spots or blotches with more spots and blotches in leaves of Halophila in pure population. Shoot density of 79.08�38.02 shoots/100cm2; is comparatively higher in pure Halophila population compared with 26.33�13.20 shoots/100cm2 and 64.00�17.09 shoots/100cm2 for small-leaved and big-leaved Halophila sp. respectively. Halophila biomass (AG and BG) exhibit similar trend as those observed for shoot density. In pure or mixed Halophila population the majority of the biomasses (63–77% of the total) were in the belowground parts (rhizome and roots). Although Halophila sp. is a smaller size seagrass, for propagation they would need extensive rhizome networks buried in the substrates

Morphology of Halophila ovalis (R.Br.) Hook. f. from Peninsular and East Malaysia

Halophila ovalis plants were collected from six locations with different habitat characteristics; Merambong, lohore ofPeninsular Malaysia (sub-tidal shoal), Teluk Sepinong of Sabah (sub-tidal estuary), Pulau Gaya, Sabah (subtidal degraded coral), Merchang, Terengganu (inter-tidal lagoon), Teluk Kemang, Negeri Sembilan (inter-tidal degraded coral platform) and Punang, Sarawak (inter-tidal beach front). Based on the leaf dimensions (length and width) and number of paired cross-veins, three Halophila ovalis variants can be distinguished; big, intermediate and small-leaved. The big-leaved H. ovalis are found at sub-tidal areas e.g. Merambong, Teluk Sepinong, while intermediate- and small-leaved variants are from inter-tidal areas that are exposed to air for 3 to 4 hours during low tides e.g. Punang, Merchang, Teluk Kemang and Pulau Gaya. The salinity and depth in a particular habitat contribute to the variability in shapes and dimension of leaf sizes. Halophila ovahs leaves showed diverse shapes from ovate, obovate, oblong to spathulate. At deeper depths, turbid water and muddy substrate, leaves of H. ovalis are elongated in shape and with longer petiole length. Halophila ovalis in Malaysia exhibit morphological variability particularly in the leaves in response to the different environmental factors in the various habitats

Description and evaluation of imposex in Strombus canarium Linnaeus, 1758 (Gastropoda, Strombidae): A potential bio-indicator of tributyltin pollution.

Strombus canarium Linnaeus, 1758 is an important gastropod species within the study area and was traditionally collected for food by the locals. The objective of the present study is to assess the incidence of imposex and its severity in this species. Adult conchs were sampled during their main reproductive period, from October 2005 to January 2006, at Sungai Pulai estuary, Johor Straits, Malaysia. A total of 32.81% of adult females showed imposex characteristics, with varying degrees of severity though. The relative penis size (RPS) index ranged from 1.74 to 33.29 (mean = 13.40 ± 2.27, n=21), while the relative penis length (RPL) index ranged from 6.28 to 55.19 (mean = 25.83 ± 3.33, n=21). The use of vas deferens sequence (VDS) index was however cannot be applied as the presence of egg groove obscured any vas deferens development in affected females. Sequence of imposex (male penis) development in female conch, from merely a small stump to an advance male penis homologous was therefore carefully analyzed and described, and an alternative imposex classification scheme was proposed. S. canarium can be a good indicator for monitoring of organotin pollution within the study area. However, more studies are needed in order to further develop and test its validity and application, such as its correlation with levels of pollutant within the tissues and the environment, as well as its application on other Strombus species