Influence Of Seagrasses Research Articles

Influence of seagrass on juvenile Pacific oyster growth in two US west coast estuaries with different environmental gradients

Ocean acidification threatens many marine organisms, including oysters. Seagrass habitat has been suggested as a potential refuge for oysters because it may ameliorate stressful carbonate chemistry and augment food availability. We conducted an in situ study to investigate whether eelgrass Zostera marina habitat affects the growth of juvenile Pacific oysters Crassostrea gigas and influences local carbonate chemistry or food quantity at sites where we expected contrasting conditions in two US west coast estuaries. Juvenile oysters were out-planted in typical intertidal on-bottom (just above sediment) and off-bottom (45 cm above sediment) culture positions and in adjacent eelgrass and unvegetated habitats from June to September 2019. Water quality was measured with sondes for 24 h periods each month, and discrete water samples were collected in conjuncture. Results show that eelgrass habitat did not alter average local carbonate chemistry (pH, pCO2, Ωcalcite), but consistently reduced available food (relative chlorophyll a). Eelgrass habitat had little to no effect on the shell or tissue growth of juvenile oysters but may have influenced their energy allocation; oysters displayed a 16% higher ratio of shell to tissue growth in eelgrass compared to unvegetated habitat when cultured on-bottom. At the seascape scale, average site-level pH was negatively correlated with shell to tissue growth but not with shell growth alone. Overall, these findings suggest that juvenile oysters may display a compensatory response and allocate more energy to shell than tissue growth under stressful conditions like acidic water and/or altered food supply due to reduced immersion or eelgrass presence.

Effects of the Zostera noltei meadows on benthic macrofauna in North Atlantic coastal ecosystems of Morocco: spatial and seasonal patterns

The influence of seagrass on benthic macroinvertebrates was investigated in four semi-enclosed coastal systems in Morocco. Biological and environmental variables were examined in vegetated and bare habitats at four selected sites in two seasons (winter and summer). A total of 28,687 individuals were reported as belonging to 69 taxa. Species richness increased significantly with latitudinal gradient. Macrofaunal biomass varied significantly across sites and had a significant positive relationship with the presence of seagrass in both summer and winter. The DIMO model indicated that the variations in macrobenthic faunal structure were mainly due to the existence of the Zostera noltei; PERMANOVA analysis detected that faunal assemblages shifted within the site and that their variation was enhanced with latitude, in both seasons. A seasonal cause for the spread of macrofauna at all the study sites may be the type of habitat. Distance-based linear models (DistLM) revealed that sediment characteristics (carbon and calcium carbonate concentrations and clay percentage) are the main predictor variables that explain the composition of the macrobenthic faunal assemblage. This study proposes a general model for evaluating spatial distribution patterns at various levels within seagrass-dominated coastal lagoons.

Porewater Carbonate Chemistry Dynamics in a Temperate and a Subtropical Seagrass System

Seagrass systems are integral components of both local and global carbon cycles and can substantially modify seawater biogeochemistry, which has ecological ramifications. However, the influence of seagrass on porewater biogeochemistry has not been fully described, and the exact role of this marine macrophyte and associated microbial communities in the modification of porewater chemistry remains equivocal. In the present study, carbonate chemistry in the water column and porewater was investigated over diel timescales in contrasting, tidally influenced seagrass systems in Southern California and Bermuda, including vegetated (Zostera marina) and unvegetated biomes (0–16 cm) in Mission Bay, San Diego, USA and a vegetated system (Thallasia testudinium) in Mangrove Bay, Ferry Reach, Bermuda. In Mission Bay, dissolved inorganic carbon (DIC) and total alkalinity (TA) exhibited strong increasing gradients with sediment depth. Vertical porewater profiles differed between the sites, with almost twice as high concentrations of DIC and TA observed in the vegetated compared to the unvegetated sediments. In Mangrove Bay, both the range and vertical profiles of porewater carbonate parameters such as DIC and TA were much lower and, in contrast to Mission Bay where no distinct temporal signal was observed, biogeochemical parameters followed the semi-diurnal tidal signal in the water column. The observed differences between the study sites most likely reflect a differential influence of biological (biomass, detritus and infauna) and physical processes (e.g., sediment permeability, residence time and mixing) on porewater carbonate chemistry in the different settings.

Benthic macrofaunal assemblages in multispecific seagrass meadows of the southern Philippines: Variation among vegetation dominated by different seagrass species

Although the influence of seagrasses on the diversity and abundance of associated fauna is generally well understood, the effects of seagrass specific identity are not. To determine whether benthic epifaunal and infaunal assemblage patterns vary by the identity of dominant seagrass species in shallow water meadows, we compared quantitative measures of faunal species richness, abundance, and assemblage structure among beds dominated by Cymodocea rotundata, Enhalus acoroides, and Thalassia hemprichii; the study site was at Lopez Jaena, Misamis Occidental Province in the southern Philippines. The Cymodocea-dominated vegetation had higher seagrass shoot density and lower seagrass biomass than those dominated by Enhalus and Thalassia. Across vegetation types, we encountered 30 and 15 species of epifauna and infauna at average densities of 1.73 and 0.82 animals/core (0.0314m2), respectively. Neither densities and species richnesses of epifauna and infauna nor species composition varied significantly by vegetation type. Multivariate analyses of macrofaunal assemblage structure and abiotic/biotic environmental factors demonstrated that seagrass aboveground biomass explained a significant proportion of the multivariate variation in epifaunal species composition (39%); none of the potential explanatory variables was related to variation in ecological parameters of the infauna. Thus, seagrass specific identity is not a good predictor of either macrofaunal abundance or diversity patterns. Although the ecological parameters of the benthic macrofauna may be influenced by seagrass biomass and structure, responses differ between epifauna and infauna.

Influence of Seagrasses on Water Quality in Shallow Regions of the Lower Chesapeake Bay

The influence of seagrasses on water quality was investigated seasonally from permanent stations located along transects across vegetated and formerly vegetated sites in shoal regions of the Chesapeake Bay National Estuarine Research Reserve in Virginia. The effect of the seagrass bed on conditions inside compared to outside the bed varied seasonally and could be related to bed biomass and development. During spring (April to June), the rapidly growing seagrass bed was a sink for nutrients, suspended inorganic particles, and phytoplankton, whereas during the summer, as bed dieback progressed, resuspension and release of nutrients were observed. Reductions in suspended particle concentrations and light attenuation were generally not measurable until bed biomass exceeded 50–100 gdm/m2 or 25–50% vegetative cover. During April, when nitrate levels in adjacent channel waters were observed to be highest (>10 μM), rapid uptake, equivalent to 48% of nitrogen requirements for seagrass growth, reduced inorganic nitrogen standing stocks by 73% within the bed compared to outside of it. An unvegetated site that previously supported seagrass demonstrated little capacity to reduce measurable levels of suspended particles or nutrients, and resuspension of bottom sediments contributed to higher levels of suspended particle concentrations and turbidity in the unvegetated shallows compared to adjacent waters. The capacity of seagrass beds to improve local water-quality conditions, such as turbidity and nutrients, during the spring when suspended particle concentrations are highest may be key to their continued long-term survival in this lower bay region. High levels of spring turbidity, which have been related to seagrass declines in this area, can be mediated by dense seagrass structure, but largely unvegetated areas are unlikely to modify conditions to permit survival of first-year recruits or transplants through the summer. Therefore, water-quality conditions that are suitable for recovery are likely greater than those required for continued survival of existing seagrass beds. Given this, statistically derived estimates of water-quality conditions or habitat requirements that are usually obtained from measurements in areas adjacent to existing seagrass beds should be used with caution. Although suitable for predicting the maintenance of existing beds with adequate biomass and structure, they may underestimate the levels needed for restoration and recovery of many currently unvegetated sites.

Investigation of the Influence of Seagrass on Fisheries Catch Level Using Isotonic Regression

The relationship between seagrass area and the commercial catch of some economically important South Australian fish species is not known in any quantitative sense. However, there is evidence in the literature to suggest that seagrass decline will detrimentally impact on species abundance and composition, and consequently that the presence or absence of seagrass will compromise the commercial and recreational fishery. In this paper we describe the construction of models based on order restricted (isotonic) regression and discuss the role of seagrass area, in terms of its influence on the level of commercial catch through modifying the effect of fishing 'effort'.

A preliminary evaluation of wave attenuation by four species of seagrass

Seagrasses are able to modify current flow and sediment composition, yet little information exists describing their effect on waves. Four species of seagrass, Halodule wrightii, Syringodium filiforme, Thalassia testudinum and Zostera marina were evaluated for their ability to reduce wave energy under various combinations of shoot density and water depths over a 1 m test section in a wave tank. Percent wave energy reduction per meter of seagrass bed equaled 40% when the length of these seagrasses was similar to the water depth. Seagrasses are approximately equal to saltmarshes in reducing wave energy on a unit distance basis, but only when water depth is scaled to plant size. When seagrass beds occur as broad, shallow meadows, the influence of seagrasses on wave energy will be substantial.