The influence of marine sand extraction on benthic copepod communities

More than 95% of the sand extraction on the Belgian Continental Shelf occurs on the Kwintebank and is concentrated at the north-western tip and in the centre of the bank. The extraction activities impact bottom habitat structure and diversity by coarsening and homogenising the sediment and cause a strong erosion process. Density, diversity and community structure of harpacticoid copepods on the Kwintebank were determined and related to sediment characteristics and sand extraction intensity. Samples were taken in 1997 with a Reineck box corer and included 10 stations on the bank and 2 in the channels next to the bank. Eighty copepod species were recorded, of which 38% were new to science. Three maior copepod communities were distinguished on the bank. Their occurrence was related to a linear gradient from fine sands in the south to coarser sands in the north. This gradient is a result of local tidal current patterns. A fourth community was found in the gullies next to the bank and in one station positioned in the centre of the bank. The sediment composition of this station however was comparable to the other bank stations. Analogies could be found in the occurrence of erosion and extraction areas and the occurrence of communities on the sandbank. The results of 1997 were compared with copepod species distribution data collected in 1978 prior to intensive sand extraction. The harpacticoid community structure of the southern part of the bank was still comparable after 20 years and hence stable in time. In the northern part the species composition altered in favour of interstitial species. In the centre of the bank a community shift was recorded due to changes in sediment characteristics, adjacent to an area with very low density and diversity. The harpacticoid cammuhities of areas with a high amount of exposure, like on the Kwintebank, are adapted to continuously changing conditions. Nevertheless human-induced physical disturbances may decrease community complexity in the centre of the bank, where the extension of a present depression can become quite problematic. This depression may grow due to sand extraction. The presence of some harpacticoids that are adapted to physical stress and the significantly higher density of juveniles in the most intensively exploited stations, suggest the existence of a frequently disturbed environment. Spreading the extraction activities over the different sandbanks in the concession zone will help decreasing the disturbance frequency and intensity

The impact of primary production in the water column on benthic copepods

A phytoplankton bloom was followed from 9 March till 12 July 1999 at a subtidal station in the Southern Bight of the North Sea. Chla (in surface-, bottom- and interstitial water) and nutrient concentrations (interstitial water) as well as diatom biomass were measured in order to detect any deposition of organic material originating from the bloom on the bottom. The response of the benthic copepods to the sedimentation of the spring phytoplankton bloom was described in terms of changes in density, diversity and community structure. In March the bottom was already organically enriched, probably due to lateral transport. May and June were characterised by organic enrichment derived from the diatom and Phaeocystis spring bloom. In April and July no organic enrichment was observed. The changes in copepod density, diversity and community structure have been attributed to organic enrichment. Over the whole time series copepods were most abundant in the upper two centimetres of the sediment. Nevertheless, a migration of the copepods to the surface was observed during the organic enrichment. Individual species reacted differently to the spring bloom. Some species disappeared, others took advantage of the situation for reproduction. Most pronounced was the reaction of Apodopsyllus n. sp. 1 which was defined as an opportunistic species. The species composition along the sediment depth profile was very diverse in the months devoid of organic enrichment, in contrast with the months with organic enrichment, the community structure over the depth layers then being homogeneous

Using Bioenergetics and Radar-Derived Bird Abundance to Assess the Impact of a Blackbird Roost on Seasonal Sunflower Damage

Methods aimed at reducing avian damage to agricultural crops are routinely implemented in situations where efficacy can be assessed by quantifying blackbird (Icteridae) abundance relative to environmental variables and extrapolating to ensuing crop damage. Concomitantly, Weather Surveillance Radar (WSR) data may have potential to enhance crop damage mitigation through improved monitoring of nuisance wildlife populations. We used WSR to derive daily abundance estimates of blackbirds at a fall roost in North Dakota, USA from 2012 to 2019. We integrated these estimates with previously developed bioenergetics-economic models to estimate local sunflower (Helianthus annuus) damage. The greatest losses usually occurred during a brief period in October, when peak blackbird abundance coincided with large percentages (\u3e50%) of mature but unharvested sunflower fields. Most sunflower fields were harvested later than peak blackbird abundance (360,000–1,120,000 birds) and maximum daily damages ($900–$2,000 USD per day). This seasonal trend suggests advancing harvest time as a strategy to avoid the greatest losses in yield (up to $1,800 in savings at this 1 roost), which may be attainable by earlier planting of early-maturing crop varieties or crop desiccation

Morphological evolution of the Kwinte Bank central depression before and after the cessation of aggregate extraction

Analyses of the records of ships registers and Electronic Monitoring Systems, of the trailer suction hopper dredgers, operating on the Belgian Continental Shelf, reveal that since the beginning of extraction in 1976, 75% of the total extracted volume originates from only one sandbank, the Kwinte Bank. At present, two morphologically-distinguished depressions are observed along the two most dredged areas of this sandbank: one in the central; and one in the northern part of the bank. In order to limit the impact of sand extraction on the bathymetry, the central depression of the Kwinte Bank was closed for exploitation, in February 2003. An understanding of the morphological evolution of this central depression is based upon data obtained: (a) from November 1999, until the closure for extraction in February 2003; and (b) on the subsequent post-dredging evolution, until June 2005. During this 5-year period, a total of 17 surveys were carried out with a multibeam echosounder over the area of the central depression (KBMA) and over a reference zone on an adjacent non-exploited sandbank. The resulting time-series of bathymetrical digital terrain models, together with backscatter strength maps, permit a detailed comparison of the bathy-morphological and sedimentary evolution of both of the monitored areas. Since the commencement of multibeam monitoring in 1999, an overall deepening (by 0.5m) of the entire KBMA monitoring zone is observed, until the cessation of dredging, in February 2003. Subsequently, the deepening slowed down and the variation in sediment volumes became similar to that of the adjacent non-exploited sandbank. From this, marine aggregate extraction appears to have only a local impact