Seasonal benthic species composition linked to coastal defense structures (CDS) in Kuala Nerus, Terengganu, Malaysia

Background

The natural hydrodynamic process of Kuala Nerus, Terengganu, has changed since the extension of Sultan Mahmud Airport runway in 2008. Consequently, severe coastal erosion has occurred in the area, particularly during the northeast monsoon season (NEM). Numerous types of coastal defense structures (CDS) have been constructed to protect the coastline. Despite the loss of esthetic values, the effect of CDS construction on marine organisms in the area remains unknown. Hence, this study aims to assess the ecological aspects of macrobenthic compositions at the CDS area of Kuala Nerus, Terengganu, based on the differences between the southwest (SWM) and northeast (NEM) monsoon seasons.

Methods

Macrobenthos were collected from the sediment in July (SWM) and December 2021 (NEM) using the Ponar grab at 12 substations from five sampling stations.

Results

The density of macrobenthos was higher in SWM (48,190.82 ind./m2) than in NEM (24,504.83 ind./m2), with phylum Mollusca recording the highest species composition (60-99.3%). The macrobenthos species had a low to moderate level of diversity (H' = 1.4-3.1) with the species were almost evenly distributed (J' = 0.2-0.8). Windward substations exhibited coarser grain sizes (38.56%-86.84%), whereas landward substations exhibited very fine grain sizes (44.26%-86.70%). The SWM season recorded a higher organic matter content (1.6%-6.33%) than the NEM season (0.4%-3.1%). However, metal concentrations in the surface sediment were within the safe range and permissible limits for both seasons, inferring that the macrobenthos composition was unaffected.

Discussion

This study demonstrated that the CDS associated with the monsoon system has controlled the hydrodynamics and nearshore sedimentary processes in the Kuala Nerus coastal zone, thereby affecting the macrobenthos population, in terms of richness and density. The ecological and energetic effects of the coastal structures in different seasons have resulted in a more significant result, with the SWM exhibiting a higher macrobenthos composition than the NEM.

Responses of biological traits of macrobenthic fauna to a eutrophication gradient in a semi-enclosed bay, China

The impacts of eutrophication on benthic ecological functions are of increasing concern in recent years. In order to assess the response of macrobenthic fauna to increasing eutrophication, two field sampling surveys were conducted during the summer (July-August 2020) and autumn (October-November 2020) from offshore, nearshore to estuarine sediments in Bohai Bay, northern China. Biological trait analysis was employed for the assessment of macrofaunal samples. The results indicated that there was an increase in the proportion of benthic burrowering or tube-dwelling sediment feeders and taxa with higher larval dispersal ability, but a decrease in the proportion of taxa showing high motility in areas with higher nutrient levels. Seasonal differences were also noted in the shift in biological traits, with a significantly lower similarity among the sampling areas in summer and a higher proportion of carnivorous taxa in autumn. The findings suggested that long-term disturbance can lead to the dominance of smaller body-sized benthic species and reduced sediment quality, impeding ecological recovery of benthic organisms under such harsh environment.

Survey of the allelopathic potential of Mediterranean macroalgae: production of long-chain polyunsaturated aldehydes (PUAs)

Chemical interactions between macroalgae and other organisms play an important role in determining species compositions and dominance patterns, and can explain the widespread success of some species in establishing their predominant populations in a specific coastal area. Allelopathy could act as a self-regulatory strategy of the algal community, being not only a succession regulator but also an active mechanism maintaining the species diversity especially in a delimited environment, such as the benthic ecosystem. Polyunsaturated aldehydes (PUAs) are among the most studied allelopathic compounds and are commonly released into the aquatic environment by different phytoplankton species in response to environmental stressors (e.g. wounding, grazing, or competition for nutrients). Diatom-released PUAs were observed to affect phytoplankton community dynamics and structure, and showed inhibitory effects on the reproduction and development of marine invertebrates. As for macroalgae, there are only a few reports that attest to the production of PUAs, and mostly refer to Ulva spp. In this study, the production of PUAs by several Mediterranean macroalgae was investigated at different sampling times, aiming at providing the first evidence of potential allelochemical activity. Results highlighted the potential production by macroalgae of a variety of aldehydes, among which some have never reported so far. Some species (i.e. D. polypodioides and U. cf. rigida) were found to produce higher PUAs amounts than others, and even a wider variety of structures (e.g. length of the carbon chain); these species might exert strong effects on epiphytic species or other organisms of the benthic community, especially considering the differential sensitivities of the various taxa. A high dPUA concentration (order of μM) potentially due to the release of PUAs by algal species was found, and might affect the population dynamics of the epiphytic organisms (e.g. microalgae, meiofauna), of grazers, as well as of the microbial community.

Impact of derelict fishing gear on the seafloor integrity and benthic communities in the macrotidal flats from northern Gyeonggi Bay, west coast of Korea

Derelict fishing gear (DFG) is increasingly common in the Korean tidal flats due to intensive fishing activity and the lack of monitoring system to remove the DFG from the tidal flats. Despite the widespread occurrence of DFG in the tidal flats, little is known about DFG in terms of quantity, types, distribution, and the impact on the benthic ecosystem. Unmanned aviation vehicle (UAV)-assisted photogrammetry and high-precision leveling were conducted to characterize DFG in the macrotidal flat, south of Gangwha Island, west coast of Korea. High concentration of DFG occurs preferentially in the channel where nets with stakes were installed for catching fishes. Topographic relief around DFG is more rugged and pronounced in the lower intertidal zone than in the middle intertidal zone, suggesting more dynamic sedimentary processes related to DFG in the lower intertidal zone. The density of benthic species is nearly identical in the middle intertidal zone regardless of the presence of DFG. In contrast, the density of macrofauna in the lower intertidal zone nearly doubles at the area free of DFG compared to the area affected by DFG. The biomass and primary production of the microphytobenthos (MPB) are smaller in the lower intertidal zone than the middle intertidal zone but show no discernible trend related to the presence of DFG. Strong tidal currents in the lower intertidal zone induce larger vortices over DFG and promote rapid deposition and erosion around DFG, resulting in a more hostile condition for the benthic ecosystem. The present study showcased that UAV-assisted mapping provides an effective tool to characterize the distribution and physical disturbance caused by DFG in the macrotidal flats, which will be a breakthrough for the sustainable management of rapidly deteriorating tidal flats with poor accessibility.

Long-distance influence of the Rhône River plume on the marine benthic ecosystem: Integrating descriptive ecology and predictive modelling

The Gulf of Lions (GoL) is among the most productive areas of the Mediterranean Sea, with the Rhône River contributing with as much as 90% of the liquid and solid materials (including anthropogenic chemicals) reaching the area. In this paper, we assessed whether classical descriptive ecology and MaxEnt predictive species distribution modelling were able to provide complementary information when analysing the long-distance influence of the river discharges on the GoL benthic ecosystem. Samples were collected in August 2014 from 12 stations covering the sedimentary plain of the deep submarine delta, from the Gulf of Fos to Gruissan. Sediments were mostly muddy with a high organic carbon and low P and N contents first decreasing and then increasing from east to west. The same pattern occurred for chlorophyll-a, particulate organic carbon and sea surface temperature, and was overall correlated with metal and pollutant contents derived from agricultural, port, urban and industrial sources driven by Rhône outputs. We observed a typical deltaic succession in the benthos, showing a relatively low diversity and including polychaetes (Sternaspis scutata) and holothurians (Oestergrenia digitata) known to be indicators of high sedimentation rates. Overall, benthos showed an inversed pattern regarding environmental variables, an evident consequence of the Rhône River influence. The suitability of some species was either positively or negatively correlated with some of the environmental variables, producing species-specific predicted distribution patterns, with the highest amount of information allowing to predict distributions being mainly provided by organic pollutants. Even with a limited number of available samples, our integrated approach reveals to be a very robust tool to highlight hidden patterns and contributes to improve our knowledge on how river-mediated anthropogenic discharges may influence biodiversity distribution and functional patterns in marine benthic ecosystems.

The Biology of Seamounts: 25 Years on

Seamounts are one of the major biomes of the global ocean. The last 25 years of research has seen considerable advances in the understanding of these ecosystems. The interactions between seamounts and steady and variable flows have now been characterised providing a better mechanistic understanding of processes influencing biology. Processes leading to upwelling, including Taylor column formation and tidal rectification, have now been defined as well as those leading to draw down of organic matter from the ocean surface to seamount summit and flanks. There is also an improved understanding of the interactions between seamounts, zooplankton and micronekton communities especially with respect to increased predation pressure in the vicinity of seamounts. Evidence has accumulated of the role of seamounts as hot spots for ocean predators including large pelagic fish, sharks, pinnipeds, cetaceans and seabirds. The complexity of benthic communities associated with seamounts is high and drivers of biodiversity are now being resolved. Claims of high endemism resulting from isolation of seamounts as islands of habitat and speciation have not been supported. However, for species characterised by low dispersal capability, such as some groups of benthic sessile or low-mobility invertebrates, low connectivity between seamount populations has been found with evidence of endemism at a local level. Threats to seamounts have increased in the last 25 years and include overfishing, destructive fishing, marine litter, direct and indirect impacts of climate change and potentially marine mining in the near future. Issues around these threats and their management are discussed.