Long-term changes in the macrobenthic invertebrate fauna of the Wadden Sea: Are polychaetes about to take over?

Decadal changes of macrofauna community in a semi-enclosed Bay of Yueqing in East China Sea

To reveal the long-term variation of macrofauna community in Yueqing Bay, an aquacultural bay famous for its shellfish culturing in the East China Sea, macrofauna samples were collected in three period from 2002 to 2003 and 2006-2007 to 2020-2021. The results show that macrofaunal community structure in this area has changed significantly (ANOSIM, p < 0.01) in nearly two decades with significant decreases in species number, biodiversity index and average biomass. Meanwhile, the taxa composition also changed significantly as the dominance of annelid increased while that of mollusks, echinoderms and vertebrates decreased. As a consequence of the variation of taxa composition and total biomass, macrofauna community showed a tendency of miniaturization as individuals with smaller body size and lower biomass dominated the community. According to the results of CCA analysis, temperature, salinity and dissolved oxygen content were the main environmental factors that restricted the species composition of macrofauna community. Further studies still needed to reveal the main reasons that cause the variation of macrofauna community. Overall, the results of this study suggest that the present status of Yueqing Bay benthic ecosystem is concerning from a macrobenthos perspective, as the biodiversity index and biomass of macrofauna decreased significantly. Effective measures should be taken in urgently to restrain the safety and function of coastal ecosystems.

Sensitivity of multispecies maximum sustainable yields to trends in the top (marine mammals) and bottom (primary production) compartments of the southern North Sea food-web

In marine ecosystems, maximum sustainable yield considerations are affected by any substantial changes that occur in the top and bottom compartments of the food-web. This study explores how the southern North Sea's fisheries may need to adjust their fishing efforts to maintain optimum yields of sole, plaice, cod and brown shrimps under increased marine mammal populations and a reduced primary productivity. We constructed plausible scenarios of ongoing food-web changes using the results of Bayesian age-structured population models to estimate carrying capacities of harbour porpoises (Phocoena phocoena) and grey seals (Halichoerus grypus). Losses in primary productivity were predicted by lower trophic level ecosystem models. These scenarios were implemented in a food-web model of the southern North Sea. For each scenario, we sought mixed-fleet fishing efforts that would deliver maximum yields of sole, plaice, cod and brown shrimp combined. We also did so for a baseline run with unaltered mammal and primary production, and compared the differences in optimal fishing strategies, predicted yields, and states of the stocks between the scenarios. We found stocks and yields to be far more sensitive to changes in primary productivity than to increased marine mammal predation. The latter predominantly impacted cod, and even benefitted brown shrimps compared to the baseline run. Under 30% reduced primary productivity, fishing efforts had to be reduced by 50% to still provide maximum yields, whereas the marine mammal scenario induced no need to adjust the fishing regime. This draws attention to the potential gains of incorporating bottom-up processes into long-term management considerations, while marine mammal predation may be less of a concern, in particular for flatfish fisheries in the North Sea, and may even benefit shrimp trawlers because of reduced predation on shrimp from fish predators.

The Diversity of Teleost Fish Trematodes in the Bay of Bizerte, Tunisia (Western Mediterranean)

A total of 39 digeneans species allocated to 28 genera in 12 families were recovered from 534 fishes belonging to 14 species in three families (Carangidae, Mullidae and Sparidae) collected in the Bay of Bizerte off the coast of Tunisia. We provide a host-parasite list of records from this locality, including 63 host-parasite combinations. The Opecoelidae Ozaki, 1925 is the most diverse group with 12 species. The species richness of individual digenean genera in the Bay of Bizerte ranges from 1 - 6 species. The mean number of 2.58 species per host indicates a relatively high digenean diversity in the Bay of Bizerte, which is related to its geographical location, its connection with the neighbouring Bizerte Lagoon and the nature of the bottoms of the littoral marine areas off the northern Tunisian coasts. This diversity is significantly higher than that reported off the southern coast of Tunisia and distinctly lower than that observed for teleost hosts in the Scandola Nature Reserve off Corsica. Generally, the levels of infection in teleosts fishes from the Bay of Bizerte are lower than those from the other two localities.

Sex-biases in distribution and resource use at different spatial scales in a migratory shorebird

In migratory species, sexual size dimorphism can mean differing energetic requirements for males and females. Differences in the costs of migration and in the environmental conditions occurring throughout the range may therefore result in sex-biases in distribution and resource use at different spatial scales. In order to identify the scale at which sexual segregation operates, and thus the scale at which environmental changes may have sex-biased impacts, we use range-wide tracking of individually color-ringed Icelandic black-tailed godwits (Limosa limosa islandica) to quantify sexual segregation at scales ranging from the occupation of sites throughout the non-breeding range to within-site differences in distribution and resource use. Throughout the range of this migratory shorebird, there is no evidence of large-scale sex differences in distribution during the non-breeding season. However, the sexes differ in their selection of prey types and sizes, which results in small-scale sexual segregation within estuaries. The scale of sexual segregation therefore depends on the scale of variation in resource distribution, which, in this system, is primarily within estuaries. Sexual segregation in within-site distribution and resource use means that local-scale anthropogenic impacts on estuarine benthic prey communities may disproportionately affect the sexes in these migratory shorebirds.

The use of benthic macroinvertebrates to establish a benchmark for evaluating the environmental quality of microtidal, temperate southern hemisphere estuaries

Establishment of a benchmark against which deleterious changes to an estuary can be evaluated requires validating that it has not been subjected to detrimental anthropogenic perturbations and then identifying the biological features which are indicative of a pristine condition and can thus be employed as indicators for detecting and monitoring departures from the natural state. The characteristics of the benthic macroinvertebrate fauna of an essentially pristine, seasonally-open estuary in Western Australia (Broke Inlet) have been determined and compared with those previously recorded for a nearby eutrophic, seasonally-open estuary (Wilson Inlet). Density was far lower in Broke than Wilson. Compositions differed radically at all taxonomic levels, with polychaetes contributing less, and crustaceans more, to the abundance in Broke. Average taxonomic distinctness was greater for Broke than both Wilson and 16 other temperate southern hemisphere estuaries, whereas the reverse was true for variation in taxonomic distinctness, emphasizing that Broke Inlet is pristine.

Benthic macroinvertebrates as indicators of environmental deterioration in a large microtidal estuary

This study tested the hypothesis that, during recent years, the benthic macroinvertebrate fauna of the large basin of the Swan-Canning Estuary has changed in ways consistent with deteriorating environmental conditions in that estuary. Between 1986/7 and 2003/4, the compositions of that fauna altered markedly at the species and even family levels. Thus, the densities and number of species of molluscs, and especially of crustaceans, which are particularly susceptible to environmental stress, declined, while those of the more tolerant polychaetes increased. However, taxonomic distinctness declined consistently only at one of the four widely-spaced sampling sites and the dispersion of samples did not differ markedly between periods, indicating that the benthic fauna has not undergone such extreme changes as in the nearby Peel-Harvey Estuary. It is thus proposed that benthic macroinvertebrates can act as important indicators of the severity of environmental degradation in microtidal estuaries in regions where such perturbations are increasing.

Changes in the benthic macroinvertebrate fauna of a large microtidal estuary following extreme modifications aimed at reducing eutrophication

An artificial channel was opened in 1994 between the microtidal Peel-Harvey Estuary and the Indian Ocean to increase tidal exchange and thus ameliorate the problems of eutrophication. Although this greatly reduced macroalgal and cyanobacterial growths and the amount of particulate organic matter, our data indicate that, contrary to managerial expectations, the benthic environment has deteriorated. Thus, although macroinvertebrate density has declined as predicted, taxonomic distinctness (Delta( *)) has also declined and species composition has become more variable. Macroinvertebrate composition has also changed markedly at the species, family and even phylum levels. The Crustacea, the most sensitive of the major macrobenthic taxa to environmental stress, has become proportionally less abundant and speciose, whereas the Polychaeta, the least sensitive, was unique in showing the reverse trend. The benthos of the Peel-Harvey Estuary is thus apparently more stressed than previously, probably due to the multiple effects of a great increase in system use.