中国温带海域新发现较大面积(大于50 ha)海草床:Ⅳ烟台沿海海草分布现状及生态特征

海草床是珍贵的“海底草原”,具有十分重要的生态服务功能。上世纪90年代,烟台曾分布有4种海草,尚不明确海草的分布现状。本研究结合了现场调查、声呐探测等手段,查清了烟台市莱州市至莱山区沿海海草的分布现状,发现了一处位于烟台市套子湾的面积为51.90 ha的鳗草-日本鳗草混合草床,并对鳗草、日本鳗草的生态特征进行了调查。调查发现烟台现存海草仅有2种,部分草床严重退化,亟需对现存海草进行保护与监测,以遏制海草的退化速度。     

中国温带海域新发现较大面积(大于0.5km2)海草床:Ⅱ声呐探 测技术在渤海唐山沿海海域发现中国面积最大的鳗草海草床

近些年来随着生境的破坏其分布面积急遽下降,较大面积连续分布的海草床已经非常少见。本研究首次将声呐探测技术应用到海草床时空分布特征的相关研究中,在河北唐山乐亭-曹妃甸沿海发现目前中国面积最大的鳗草(Zostera marina)海草床,海草床面积高达29.17 km~2,绘制了鳗草分布图和水深分布图,并对鳗草生物量和茎枝高度等基本生物学指标进行了调查。该发现极大丰富了中国海草数据库,并为鳗草的深入研究及保护提供了得天独厚的实验基地,也为周边海洋牧场的构建打下良好的基础。     

中国温带海域新发现较大面积(大于50ha)海草床:Ⅲ渤海兴城-觉华岛海域大面积海草床鳗草种群动力学及补充机制

鳗草(ZosteramarinaL.)广布于北半球温带浅海海域,其形成的鳗草床具有重要的生态价值。近些年来,我国黄渤海海域鳗草退化严重,较大面积、连续分布的海草床已经非常少见。在渤海兴城-觉华岛海域发现较大面积的海草床,可以作为渤海沿海海草床的典型代表。基于此,2018年5月、9月、11月和2019年3月对该海草床进行了初步调查,探究了渤海兴城-觉华岛海草床鳗草种群补充等生态特征,分析了海草床生境的主要威胁,并提出了对海草床进行有效保护和科学管理的相关建议。结果表明:渤海兴城-觉华岛海草床总面积为791.61ha,海草种类为鳗草和日本鳗草(Z.japonica),以鳗草为优势种,日本鳗草极少且呈斑块状分布;鳗草生物量在2018年5月达到最大值(1241.22—1632.64g/m2);鳗草叶片碳、氮、磷元素含量分别为35.35%—36.57%、1.89%—3.35%、0.14%—0.48%;鳗草海草床以无性繁殖为主要补充方式,有性繁殖补充比例平均仅为1.92%,明显低于国内其他鳗草草床,具有鲜明的独特性;该海草床主要受围填海、捕蛤、围网捕鱼等人类活动的严重影响,并致使海草床边缘区域呈现斑块化趋势。建议对这片珍贵的海草床加以保护和修复。     

日本大叶藻（Zostera japonica）根状茎和不同发育阶段叶片的热值动态

对广西沿岸海草优势种日本大叶藻（Zostera japonica）根状茎、幼叶、成熟叶和老叶的灰分含量、干质量热值和去灰分热值进行了初步研究。结果表明, （1） 日本大叶藻叶片从幼叶到成熟叶再到老叶的生长发育过程中, 灰分含量升高, 而干质量热值和去灰分热值下降; （2） 日本大叶藻根状茎的灰分含量和去灰分热值大于叶片...     

富营养化和海水盐度对日本鳗草生物量和碳氮含量的协同影响

营养盐和盐度对海草的生长和生理都具有重要影响,但二者对海草的协同作用还未见报道。本研究以日本鳗草(Zosterajaponica)为对象,在室内可控条件下进行营养盐和盐度对日本鳗草的协同影响研究。实验结果显示,营养盐和盐度对日本鳗草地上生物量、地上部分C含量、地下部分C含量均有显著的协同影响。日本鳗草组织中的营养盐含量(Nt)与盐度有显著相关性,但并未受到营养盐和盐度的协同影响。营养盐和盐度会协同影响海草的固碳能力,并同时影响其对硝酸盐的吸收。     

Habitat characteristics and spatial arrangement affecting the diversity of fish and decapod assemblages of seagrass (Zostera marina) beds around the coast of Jersey (English Channel)

Recent research and management plans for seagrass habitats have called for landscape level approaches. The present study examines the spatial utilisation of subtidal seagrass beds by fish and decapods around the coast of Jersey (49°N 02° W). A hierarchical scale of landscape configuration and the plant characteristics of eight seagrass beds were measured and the contributions of these variables as predictors of the properties of the fish and decapod assemblages were evaluated using multiple linear regression models. The results indicated that total diversity had a negative relationship with transect heterogeneity and total species number had a weak negative association with increasing fragmentation. Both total diversity and total species number showed a positive relationship with depth. In fact, in all models of species number and densities, values were higher in deeper seagrass beds. Total decapod density increased with aggregation of seagrass patches within a landscape. In addition to landscape configuration, smaller-scale structural changes in both canopy height and epiphyte load appeared to influence densities of decapod crustaceans. At night, fewer patterns could be explained by the independent variables in the model.     

Effects of current exposure on habitat preference of mobile 0-group epibenthos for intertidal seagrass beds (Zostera noltii) in the northern Wadden Sea

In the northern Wadden Sea, the extent of intertidal seagrass beds, their plant biomass and shoot density highly depends on local current regimes. This study deals with the role of intertidal Zostera noltii beds as nursery for mobile epibenthic macrofauna and the impact of seagrass bed characteristics on their abundance and distribution patterns. According to their exposure to the main tidal gullies, sampling sites were separated into exposed, semi-exposed and sheltered. Dominant species of crustaceans and demersal fish were studied in respect of their abundances within seagrass beds and adjacent unvegetated areas. Quantitative sampling was performed at day and night high tide using a portable drop trap. In general, species composition varied little between seagrass beds and bare sand. However, the presence of vegetation had a quantitative effect increasing individual numbers of common epifaunal species. Abundances of 0-group shore crabs (Carcinus maenas), common gobies (Pomatoschistus microps) and brown shrimps (Crangon crangon) were highest within sheltered seagrass beds. With decreasing plant density habitat preference of epibenthos changed on species level. By regulating the habitat complexity the currents regime is profoundly influencing the nursery function of intertidal seagrass beds in the Wadden Sea.     

Molecular diversity and biogeography of benthic microeukaryotes in temperate seagrass (Zostera japonica) systems of northern China

The productivity and health of seagrass depend on the combined inputs of nutrients from the water and sediments in which they grow and the microbiota with which they live intimately. However, little is known about the composition and diversity pattern of single-celled benthic eukaryotes in seagrass meadows. Here, we investigated how the structure and diversity of the benthic microeukaryotic community vary with respect to season, location, and seagrass colonization, by applying 18S rRNA gene amplicon sequencing for 96 surface sediment samples that were collected from three different seagrass habitats through four seasons. We found that benthic microeukaryotic communities associated with seagrass Zostera japonica exhibited remarkable spatial and seasonal variations, as well as differences between vegetated and unvegetated sediments. Diatoms and dinoflagellates predominated in the benthic microeukaryotic communities, but they were inversely correlated and displaced each other as the dominant microbial group in different seasons or habitats. Mucoromycota was more prevalent in vegetated sediments, whereas Lobulomycetales and Chytridiales had higher proportions in unvegetated sites. Total organic carbon and total organic nitrogen were the most important environmental factors in driving the microeukaryotic assemblages and diversity. Our study expands the available knowledge on the biogeographic distribution patterns and niche preferences for benthic microeukaryotes in seagrass systems.     

Architectural characteristics of two bed types of the seagrass Posidonia oceanica over different spatial scales

Seagrass beds occur in various morphological forms, ranging from small patches to continuous meadows. The endemic Mediterranean seagrass Posidonia oceanica forms dense and extensive stands that occur in several different morphotypes, including reticulate (seagrass interspersed with a different habitat type, such as bare sand) and continuous beds. This study, undertaken in the Maltese Islands, examined whether reticulate and continuous P. oceanica beds, located adjacent to each other and at similar depths, had different within-bed architectural characteristics. Five commonly used architectural measures (shoot density, number of leaves per shoot, mean leaf length, mean leaf width and shoot biomass) were measured from P. oceanica shoots collected from the two bed types at three different spatial scales: (1) tens of metres (‘small’ scale); (2) hundreds of metres (‘medium’ scale); and (3) kilometres (‘large’ scale). Results of 2-factor ANOVA (factor 1=bed type; factor 2=sampling locality) carried out at the three spatial scales indicated significant differences between the two bed types in shoot density (P<0.01) and leaf length (P<0.05) at the small scale, and in leaf number (P<0.05) at the large scale. Significant interactions were also apparent for shoot density (at the large scale) and for shoot biomass (at the medium scale). However, the results obtained did not indicate consistent architectural differences between the two P. oceanica bed types over the spatial scales considered. Spatial variations in within-bed architectural characteristics observed were therefore thought to be attributable mainly to the influence of local environmental factors. The findings are discussed with reference to the conservation and management of P. oceanica habitat.     

Small is beautiful: An inverted view of habitat fragmentation in seagrass beds

An intertidal Zostera marina landscape in Torbay, Devon, UK, was sampled to investigate the relationship between patch size, diversity and infaunal assemblage composition with the intention of defining a minimum Zostera patch size where the infaunal seagrass assemblage becomes distinct from the bare sand assemblage. All Zostera patches were found to support a higher level of biodiversity than the surrounding bare sand. However, the size of the Zostera patch had no impact on the level of diversity; it was just the presence or absence of seagrass that made a difference. The sediment and seagrass variables were not significantly different across the range of Zostera patch sizes, indicating that the environment characteristics were homogeneous within the Zostera patches at the patch scale. Multivariate analysis revealed that assemblage composition did vary between the patch types, although the opportunistic polychaete Capitella capitata was present in all patch types and was the most abundant species overall. The presence of opportunistic species and the homogeneity of the Zostera patch variables may be due to the location of this intertidal seagrass bed, which is relatively exposed compared to the locations of other seagrass beds along the south coast of Devon, resulting in a more dynamic and disturbed environment. Nevertheless, our results demonstrate that even small patches of seagrass comprising a few plants support a higher abundance and diversity of infaunal invertebrates than bare sand, indicating that Zostera patches have conservation value whatever their size.     

Horizontal distribution and population dynamics of the dominant mysid Hyperacanthomysis longirostris along a temperate macrotidal estuary (Chikugo River estuary, Japan)

The estuarine turbidity maximum (ETM) that develops in the lower salinity areas of macrotidal estuaries has been considered as an important nursery for many fish species. Mysids are one of the dominant organisms in the ETM, serving as a key food source for juvenile fish. To investigate the horizontal distribution and population dynamics of dominant mysids in relation to the fluctuation of physical conditions (temperature, salinity, turbidity, and freshwater discharge), we conducted monthly sampling (hauls of a ring net in the surface water) along the macrotidal Chikugo River estuary in Japan from May 2005 to December 2006. Hyperacanthomysis longirostris was the dominant mysid in the estuary, usually showing peaks of density and biomass in or close to the ETM (salinity 1–10). In addition, intra-specific differences (life-cycle stage, sex, and size) in horizontal distribution were found along the estuary. Larger males and females, particularly gravid females, were distributed upstream from the center of distribution where juveniles were overwhelmingly dominant. Juveniles increased in size toward the sea in marked contrast with males and females. The findings suggest a possible system of population maintenance within the estuary; gravid females release juveniles in the upper estuary, juveniles grow during downstream transport, young males and females mature during the upstream migration. Density and biomass were primarily controlled by seasonal changes of temperature, being high at intermediate temperatures (ca. 15–25 °C in late spring and fall) and being low at the extreme temperatures (ca. 10 °C in midwinter and 30 °C in midsummer). High density (up to 666 ind. m⁻³) and biomass (up to 168 mg dry weight m⁻³) of H. longirostris were considered to be comparable with those of copepods in the estuary.     

Influences of diel and tidal cycles on fish assemblage in eelgrass (Zostera marina) bed of southern Korea during autumn

Short-term tidal and diel variations of autumn fish assemblage in a Zostera marina bed were investigated using 3 h interval samplings for 24 h in both spring and neap tide using a small beam trawl. A total of 1 346 fishes belonging to 19 species were collected at spring tide, whereas 1 115 fishes belonging to 17 species were at neap tide. The common fish species were Nuchequula nuchalis, Acanthogobius flavimanus, Takifugu niphobles, Acentrogobius pflaumii, and Pholis nebulosa with the former three species dominating at spring tide, while the latter two species being abundant at neap tide. Diel variation in abundance was significant with higher abundance at night than day, but there were no significant differences between spring and neap tides, and between ebb and flood tides (three-way ANOVAs). Diel variation in the abundance of fishes may be influenced by tidal range and cycle, and day-night differences of food availability and behaviors of fishes indirectly. Non-metric multidimensional scaling (nMDS) ordination and analysis of similarity (ANOSIM) results revealed significant differences in species compositions both between day and night, and between spring and neap tide. Eelgrass beds are highly productive marine ecosystem, and thus, our results will contribute to conservation of seagrass ecosystem in the study area.