Temporal changes in a demersal fish and cephalopod community of an unexploited coastal area in Northern Australia

Change in oceanographic conditions causes structural alterations in marine fish communities, but this effect may go undetected as most monitoring programs until recently mainly have focused on oceanography and commercial species rather than on whole ecosystems. In this paper, the objective is to describe the spatial and temporal changes in the Barents Sea fish community in the period 1992–2004 while taking into consideration the observed abundance and biodiversity patterns for all 82 observed fish species. We found that the spatial structure of the Barents Sea fish community was determined by abiotic factors such as temperature and depth. The observed species clustered into a deep assemblage, a warm water southern assemblage, both associated with Atlantic water, and a cold water north-eastern assemblage associated with mixed water. The latitude of the cold water NE and warm water S assemblages varied from year to year, but no obvious northward migration was observed over time. In the period 1996–1999 we observed a significant reduction in total fish biomass, abundance, mean fish weight, and a change in community structure including an increase in the pelagic/demersal ratio. This change in community structure is probably due to extremely cold conditions in 1996 impacting on a fish community exposed to historically high fishing rates. After 1999 the fish community variables such as biomass, abundance, mean weight, P/D ratio as well as community composition did not return to levels of the early 90s, although fishing pressure and climatic conditions returned to earlier levels.

Fishery resources are threatened by environmental changes and anthropogenic pressures, particularly in coastal ecosystems. It is crucial to understand the changes of fish communities and their responses to environmental changes and human disturbances to formulate rational fisheries and ecosystem-based management. The Pearl River Estuary (PRE) is a typical sub-tropic coastal ecosystem located in the center of the Guangdong-Hong Kong-Macao Greater Bay Area in the northern South China Sea. The demersal fish in the PRE is traditionally targeted as commercial fishing and severely impacted by overexploitation and hypoxia in the last few decades. In this study, we analyze the fish survey data during the period of 2020~2021 using multivariate statistics to investigate the impacts of human disturbances on the species and functional dynamics of the demersal fish community in the PRE. The results reveal that dissolved oxygen and temperature have significant correlations with the functional traits of the demersal fish community. The impacts of hypoxia on the demersal fish vary with species and locations. We found that the mean functional redundancy of the demersal fish community in the PRE was high across three surveys, but the functional diversity was low in this region. The abundance and richness of the demersal fish community increased during the summer fishing moratorium in the South China Sea in 2021, but the functional diversity did not increase significantly. We conclude that the high functional redundancy in the PRE might not be sufficient to buffer against environmental disturbances because of its low functional diversity. Our study highlights the complicated interactions between the demersal fish community and disturbances in the PRE. Understanding the traits structure and functional diversity of the fish community can help elucidate the factors determining the dynamic responses of the fish community to disturbances.

Nelson Lake, a moderately acidic (pH 5.7), metal-contaminated (Cu 22 μg L−1; Zn 18 ug L−1) lake, 28 km from the smelters at Sudbury, had a degraded fish community in the early 1970's, with lake trout (Salvelinus namaycush) scarce, smallmouth bass (Micropterus dolomieui) extinct, and the littoral zone dominated by the acid-tolerant yellow perch (Perca flavescens). Liming of the lake in 1975–76 increased pH to 6.4, and decreased metal concentrations. Chemical conditions have remained relatively stable in the 10 yr following base addition. Initially, it appeared that neutralization produced dramatic changes in the resident fish community. Yellow perch abundance declined rapidly after neutralization, lake trout abundance increased to the extent that 3.26 kg ha−1 were caught in the winter of 1980, and reintroduced smallmouth bass reproduced and established a large population. However, these changes in the fish community can not be directly attributed to liming, as water quality and the sport fisheries of an unlimed nearby lake also improved. Reduced emissions from Sudbury smelters were responsible for improvements in the untreated lake. Recovery of the lake trout population in Nelson Lake appears to have begun prior to liming. Of the lake trout sampled during the 1980 winter fishery, 65.8% were present prior to the chemical treatment. Predation by lake trout was the likely cause of the perch decline. Our results suggest that chemical conditions producing population level responses in fish have abrupt thresholds and that neutralization of lakes above these thresholds may not produce distinguishable effects.

We describe and explain some of the changes in the fish community as reflected by the catches of the commercial fishery, and evaluate the efforts to restore the trout (Salvelinus spp.) in Georgian Bay. The changes in the fish community were caused in part by excessive fishing for lake trout (S. namaycush), lake whitefish (Coregonus clupcaformis) and deepwater ciscoes (Coregonus spp.), and the introduction of new species such as sea lamprey (Petromyzon marinus), alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax) and salmonids (Oncorhynchus spp.). The most striking changes were the near extinction of the lake trout, reductions in lake herring (Coregonus artedii), deepwater ciscoes and lake whitefish, and the increase in abundance of smelt and alewife. In an effort to replace the low of yield from the cold-water habitat, a fast growing and early maturing hybrid trout (splake [S. namaycush x S. fontinalis]) and its backcross to lake trout were selectively bred for stocking in Georgian Bay. Splake did poorly because of low survival immediately after planting. The survival of backcross after planting was better, but adult mortality was still high. Adult survival of backcross improved considerably after restrictions were placed on the commercial fishery in 1984. The first naturally produced backcross larvae were collected in 1985.

Suo, A.; Cao, K.; Zhao, J., and Lin, Y., 2015. Study on impacts of sea reclamation on fish community in adjacent sea areas: a case in Caofeidian, North China.To reveal the impacts of sea reclamation on fish communities in adjacent areas, Caofeidian in north China was chosen as a case study in this paper. A total of 19 sample points were set in offshore areas reclaimed in 2004, 2008, and 2010, which represents the beginning, middle and ending phase of reclamation works. Species richness, density, biomass, and biodiversity index were analyzed to describe changes of adjacent fish community during the reclamation process. It is found that the fish density declined by 22.66% from 2004 to 2010 due to sea reclamation. The fish biomass decreased from 46.07 kg·m−2·h−1 in 2004 to 25.35 kg·m−2·h−1 in 2010, which was mainly caused by body miniaturization of dominated fish and increased density of other fish species. The sea reclamation also reduced the eggs and fries in adjacent areas. The density of fish eggs decreased from 5.42 ind·m−3·h−1 to 0.13 ind·m−3·h−1and the density of fries decreased from 2.29 ind·m−3·h−1to 0.19 ind·m−3·h−1. These changes of fish community were mainly due to the plenty of suspended sand diffused to adjacent waters. Besides, the impact of reclamation on fish community was bigger in autumn than in spring.

Fine-scale spatial patterns in the demersal fish and invertebrate community in a northwest Atlantic ecosystem

Aquatic vegetation in the relatively pristine coastal wetlands of eastern Georgian Bay provides critical habitat for a diverse fish community. Declining water levels in Lake Huron over the past decade, however, have altered the wetland plant assemblages in favour of terrestrial (emergent and meadow) taxa and have thus reduced or eliminated this important ecosystem service. In this study, we compared IKONOS satellite images for two regions of eastern Georgian Bay (acquired in 2002 and 2008) to determine significant changes in cover of four distinct wetland vegetation groups [meadow (M), emergent (E), high‐density floating (HD) and low‐density floating (LD)] over the 6 years. While LD decreased significantly (mean −2995.4 m2), M and HD increased significantly (mean +2020.9 m2 and +2312.6 m2, respectively) between 2002 and 2008. Small patches of LD had been replaced by larger patches of HD. These results show that sustained low water levels have led to an increasingly homogeneous habitat and an overall net loss of fish habitat. A comparison of the fish communities sampled between 2003 and 2005 with those sampled in 2009 revealed that there was a significant decline in species richness. The remaining fish communities were also more homogeneous. We suggest that the observed changes in the wetland plant community due to prolonged low water levels may have resulted in significant changes in the fish communities of coastal wetlands in eastern Georgian Bay.

Boström, M. K., Östman, Ö., Bergenius, M. A. J., and Lunneryd, S-G. 2012. Cormorant diet in relation to temporal changes in fish communities. – ICES Journal of Marine Science, 69: 175–183. The stomach contents of 229 great cormorants (Phalacrocorax carbo sinensis) shot between March and October 2009 along the Swedish east coast were analysed for differences in diet between gender, age, and breeding phase. Sticklebacks (Gasterosteus aculeatus and Pungitius pungitius) were the most common prey, followed by eelpout (Zoarces viviparus), herring (Clupea harengus membras), and cyprinids (Cyprinidae). Diet did not differ between age and gender, but changed over the breeding season. The different phases explained around 10% of the total variation in stomach content between cormorants, suggesting no major shift in diet over the breeding season. The diet of cormorants in 2009 was compared with the results of a study conducted in the same area in 1992. There were evident changes in the diet between 1992 and 2009, with less perch (Perca fluviatilis) and cyprinids and more eelpout and herring in 2009. This change in diet could partly be related to changes in the fish community. The seasonal changes in diet composition of whole stomachs were less notable than in many previous studies, but long-term changes in the fish communities may induce changes in cormorant diet. It is clearly important to use stomach contents in areas with many small fish species for a comprehensive assessment of cormorant diet.

Long-term changes in fish communities of the Ria Formosa coastal lagoon (southern Portugal) based on two studies made 20 years apart

In freshwater ecosystems, invasive salmonid fishes can have a significant impact on native fish species. Detecting the invasion and its negative effects is critical for the conservation of native fish communities. We examined the species composition and seasonal changes in the freshwater fish community, including salmonids, on the Kamikawa Plain, Hokkaido Island, Japan, using environmental DNA (eDNA) metabarcoding. We detected 23 fish species in 176 samples collected from 16 sites over 12 months (October 2018 – August 2019). Between 11 and 20 species were detected at each site, including five native salmonids (Oncorhynchus masou, Oncorhynchus keta, Parahucho perryi, Salvelinus leucomaenis leucomaenis and Salvelinus malma krascheninnikova). The invasive alien rainbow trout Oncorhynchus mykiss was detected at all 16 sites and it was the most commonly detected salmonid. Although we found no obvious competitive exclusion of native salmonids by rainbow trout in the study area, the invasive species occurred more often and at more sites than any of the natives. We also determined the occurrence and seasonal changes in the fish community, classified as native salmonids, invasive rainbow trout, Cypriniformes and other benthic fishes. There were fewer species overall in winter, but the sites with higher species richness in winter were on the lower reaches of the river. In addition, we detected domestic invaders, such as the topmouth gudgeon, Pseudorasbora parva, although they were less prevalent than rainbow trout. These results show the effectiveness of eDNA metabarcoding, which can be used for surveying species richness at an ecosystem scale. In particular, the detection of the early stages of establishment and spread of invasive species can be achieved by eDNA monitoring.

Coastal marine fish populations are in decline due to overfishing, habitat destruction, climate change and invasive species. Seasonal monitoring is important for detecting temporal changes in the composition of fish communities, but current monitoring is often non-existent or limited to annual or semi-annual surveys. In the present study, we investigate the potential of using environmental DNA (eDNA) metabarcoding of seawater samples to detect the seasonal changes in a coastal marine fish community. Water sampling and snorkelling visual census were performed over 1 year (from 23rd of August 2013 to 11th of August 2014) at a temperate coastal habitat in Denmark (55°45′39″N, 12°35′59″E) and compared to long-term data collected over a 7-year period. We used Illumina sequencing of PCR products to demonstrate that seawater eDNA showed compositional changes in accordance with seasonal changes in the fish community. The vast majority of fish diversity observed in the study area by snorkelling was recovered from sequencing, although the overlap between methods varied widely among sampling events. In total, 24 taxa were detected by both methods, while five taxa were only detected using eDNA and three taxa were only detected by snorkelling. A limitation of the applied primers was the lack of resolution to species level in a few diverse families, and varying sequencing depth between samples represents a potential bias. However, our study demonstrates the utility of eDNA for recovering seasonal variation in marine fish communities, knowledge of which is essential for standardised long-term monitoring of marine biodiversity.

This research is the first to investigate deepwater demersal fish distribution and community structure around South Georgia and Shag Rocks. Analysis of catch data from a trawl survey conducted in 2003 indicated that depth and location have a marked influence over demersal fish community structure in the region. Three distinct, depth-stratified fish assemblages were observed. The demersal fish assemblage found on the shelf to depths of around 400 m was dominated by nototheniids and was comprised largely of species endemic to the Southern Ocean and Scotia Sea. At the greatest depths sampled (>600 m) the demersal fish community was dominated by gadiform fishes including members of the Macrouridae and Moridae, many of which are not endemic to the Southern Ocean. From 400 to 600 m there was a transitional zone with demersal fish representatives of both the shelf and deeper slope communities. Clear geographic differences in the shelf community were apparent with differences observed in community structure between South Georgia and Shag Rocks to depths of around 400 m. These data provide valuable baseline information to aid environmental management decisions and assess potential impacts of rapid ocean warming around South Georgia.

The changes in a tropical demersal fish community in the southeast Gulf of Carpentaria, Australia, were examined by comparing the results of a survey undertaken in 1964 before the area was fished, with two surveys in 1985 and 1986 after 20 yr of commercial trawl fishing. The numerical abundance of 52 of the 82 fish taxa had not changed significantly, but that of 18 had decreased while 12 had increased. One taxon (Paramonacanthus spp.) had decreased by more than 500 times and another (Saurida micropectoralis) had increased substantially in abundance. The changes occurred throughout the area surveyed, but the largest changes were offshore. In the pre-trawling community most taxa were caught mainly during the night, while in the post-trawling community most were caught in the same numbers during day and night. In 10 of the 30 taxa that changed in abundance, changes were within a family and could not be explained. For the remaining 20, the changes could be related to their position in the water column: benthic taxa decreased and bentho-pelagic taxa increased. The changes were assessed in relation to fishing effort, and changes in the mud content of the substrate in the study area. Although the changes did not correlate with the fishing effort among three zones in the study area, it is suggested that fishing effort and discarding of the by-catch caused the change in 18 taxa. The magnitude of the decreases of some species might be related to changes in the sediment or possibly other long-term environmental change. There was also a change in the diel behaviour in the fish community that perhaps may be related to the effects of fishing on a tropical multispecies fish community.

To evaluate fish community changes and the impact of exotic fish between the Nakdong River (lotic) and Upo Wetlands (lentic) using long-term ecological monitoring results, we conducted seasonal surveys of the fish community from 2005 to 2010. A fixed shore net (mesh <TEX>$15{\times}15\;mm$</TEX>), cast net (<TEX>$7{\times}7\;mm$</TEX>), and scoop-net (<TEX>$5{\times}5\;mm$</TEX>) were used to collect fish specimens. Changes in the fish community were not significantly different in the Nakdong River and Upo Wetlands, respectively (<TEX>$R_s$</TEX> > 0.322, N = 44, P < 0.05). Changes in the fish community between the Nakdong River and Upo Wetlands were identified as significant according to the results of cluster analysis. The relative abundance of exotic species increased steadily during the study period, and reached 34.2% and 89.7% in the Nakdong River and Upo Wetlands, respectively, in 2010. The bluegill (Lepomis macrochirus) was used to evaluate the level of health according to prevalence around all study sites. The length-weight relationship for bluegill in the Upo Wetlands was shown to have the highest values, via the formula (W = <TEX>$aL^b$</TEX>), with an average of 3.26 for the 'b' variable. According to the results of this study, lentic and lotic systems differed significantly; exotic species had an impact on both the lentic and lotic systems, but the impact of exotic species in lentic systems was greater than in the lotic systems. Additionally, the exotic species tested herein (bluegill) adapted well in the lentic system.

Context Global and local stressors can drive phase shifts from zooxanthellate scleractinian coral communities to macroalgae-dominated ecosystems. However, our understanding of altered ecosystem functioning, productivity and stability remains limited as pre-shift data are typically lacking for degraded coral-reef sites. Aims Here, we assessed functional changes in fish communities in Nakagusuku Bay, Okinawa, Japan, over 45 years, by comparing pre-disturbance (1975) to post-disturbance (2018–2020) datasets, and identified possible drivers of changes. Methods We analysed data for 393 fish species and 26 coral genera at 13 sites, measured at four-time points (1975, 2018, 2019 and 2020). Analyses were performed using a range of ordination techniques. Key results We found reductions in functional richness and trait space contraction over time for fishes. Changes in coral functional groups over time correlated with changes in the functional diversity of reef-fish communities; a reduction in branching corals reduced habitat availability for coral-reliant fishes. Conclusions Increasing sedimentation and eutrophication as a result of construction along the Nakagusuku Bay coast likely reduced living coral cover and fish diversity, and thermal stress likely facilitated the simplification and shifts of both coral communities and coral specialist fishes away from shore. Implications Both global and local threats need to be considered when assessing functioning of coral-reef ecosystems for coral-reef conservation efforts.