This work aimed to study the effects of recreational diving and snorkeling on the distribution, diversity, and abundance of surgeonfishes in six northern islands, different in their diving and snorkeling load, at the Hurghada area in the Egyptian Red Sea waters. SCUBA diving survey was conducted in summer 2019 using transect technique in the reef flat and reef slope in the study sites to compare total and single surgeonfish species census among sites and microhabitats. A total of six species of surgeonfish belonging to three genera were recorded during the current survey, including Zebrasoma xanthurum, Zebrasoma desjardinii, Acanthurus gahhm, Acanthurus sohal, Naso lituratus, and Naso unicornis. Z. desjardinii was the most abundant species, recording 41.2% relative abundance, followed by Acanthurus sohal (19%). In all sites, surgeonfish species diversity and average/total abundance in reef flat was always higher than that recorded in the reef slope. Meanwhile, the recreational effect results showed that, in reef flat habitats, surgeonfishes total/average abundance was inversely related to the numbers of divers and snorkelers across survey sites. In contrast, deeper habitat at the opened reef edge exhibited inverse distribution pattern, whereas, the obtained results showed that surgeonfish preferred the reef edge when the diving activities load increased.
Human Impacts on the Environment
Chile has one of the largest coastlines in the world with at least 50% of the world cetacean species occurring within its jurisdictional waters. However, little is known regarding the health status and main causes of death in cetaceans off continental Chile. In this report, we summarize the major pathological findings and most likely causes of death of 15 cetaceans stranded along the Chilean coast between 2010 and 2019. Drowning, due to fishing gear entanglement, was the most likely cause of death in 3 Burmeister’s porpoises (Phocoena spinipinnis), a Risso’s dolphin (Grampus griseus) and a short-beaked common dolphin (Delphinus delphis). Additionally, the 3 Burmeister’s porpoises had mild to moderate eosinophilic and histiocytic pneumonia with pulmonary vasculitis associated with the nematode Pseudalius inflexus. A fourth Burmeister’s porpoise died of drowning after stranding alive at a sandy beach. Two fin whales (Balaenoptera physalus) died most likely of trauma associated with large vessel collision. A long-finned pilot whale (Globicephala melas) and an Orca (Orcinus orca) stranded most likely due to traumatic intra/interspecific interaction with other odontocete although for the pilot whale, osteoporosis with loss of alveolar bone and all teeth could have played a role. For a Strap-toothed beaked whale (Mesoplodon layardi), Dwarf sperm whale (Kogia sima), Southern right-whale dolphin (Lissodelphis peronii), Peale’s dolphin (Lagenorhynchus australis) and a dusky dolphin (Lagenorhynchus obscurus), the cause of stranding could not be determined. This study shows, despite the small number of examined carcasses that in Chile, human related trauma is an important cause of single cetacean stranding events.
Coastal eutrophication caused by anthropogenic nutrient inputs is one of the greatest threats to the health of coastal estuarine and marine ecosystems worldwide. Globally, ∼24% of the anthropogenic N released in coastal watersheds is estimated to reach coastal ecosystems. Seven contrasting coastal ecosystems subject to a range of riverine inputs of freshwater and nutrients are compared to better understand and manage this threat. The following are addressed: (i) impacts of anthropogenic nutrient inputs on ecosystem services; (ii) how ecosystem traits minimize or amplify these impacts; (iii) synergies among pressures (nutrient enrichment, over fishing, coastal development, and climate-driven pressures in particular); and (iv) management of nutrient inputs to coastal ecosystems. This comparative analysis shows that “trophic status,” when defined in terms of the level of primary production, is not useful for relating anthropogenic nutrient loading to impacts. Ranked in terms of the impact of cultural eutrophication, Chesapeake Bay ranks number one followed by the Baltic Sea, Northern Adriatic Sea, Northern Gulf of Mexico, Santa Barbara Channel, East China Sea, and the Great Barrier Reef. The impacts of increases in anthropogenic nutrient loading (e.g., development of “dead zones,” loss of biologically engineered habitats, and toxic phytoplankton events) are, and will continue to be, exacerbated by synergies with other pressures, including over fishing, coastal development and climate-driven increases in sea surface temperature, acidification and rainfall. With respect to management, reductions in point source inputs from sewage treatment plants are increasingly successful. However, controlling inputs from diffuse sources remains a challenging problem. The conclusion from this analysis is that the severity of coastal eutrophication will likely continue to increase in the absence of effectively enforced, ecosystem-based management of both point and diffuse sources of nitrogen and phosphorus. This requires sustained, integrated research and monitoring, as well as repeated assessments of nutrient loading and impacts. These must be informed and guided by ongoing collaborations among scientists, politicians, managers and the public.
Blue whale survival and fitness are highly contingent on successful food intake during an intense feeding season. Factors affecting time spent at the surface or at depth in a prey patch are likely to alter foraging effort, net energy gain, and fitness. We specifically examined the energetic consequences of a demonstrated reduction in dive duration caused by vessel proximity, and of krill density reductions potentially resulting from krill exploitation or climate change. We estimated net energy gain over a simulated 10-h foraging bout under baseline conditions, and three scenarios, reflecting krill density reductions, vessel interactions of different amplitudes, and their combined effects. Generally, the magnitude of the effects increased with that of krill density reductions and duration of vessel proximity. They were also smaller when peak densities were more accessible, i.e., nearer to the surface. Effect size from a reduction in krill density on net energy gain were deemed small to moderate at 5% krill reduction, moderate to large at 10% reduction, and large at 25 and 50% reductions. Vessels reduced cumulated net energy gain by as much as 25% when in proximity for 3 of a 10-h daylight foraging period, and by up to 47–85% when continuously present for 10 h. The impacts of vessel proximity on net energy gain increased with their duration. They were more important when whales were precluded from reaching the most beneficial peak densities, and when these densities were located at deeper depths. When krill densities were decreased by 5% or more, disturbing foraging blue whales for 3 h could reduce their net energy gain by ≥30%. For this endangered western North Atlantic blue whale population, a decrease in net energy gain through an altered krill preyscape or repeated vessel interactions is of particular concern, as this species relies on a relatively short feeding season to accumulate energy reserves and to fuel reproduction. This study highlights the importance of distance limits during whale-watching operations to ensure efficient feeding, as well as the vulnerability of this specialist to fluctuations in krill densities.
Motorboats are a pervasive, growing source of anthropogenic noise in marine environments, with known impacts on fish physiology and behaviour. However, empirical evidence for the disruption of parental care remains scarce and stems predominantly from playback studies. Additionally, there is a paucity of experimental studies examining noise-mitigation strategies. We conducted two field experiments to investigate the effects of noise from real motorboats on the parental-care behaviours of a common coral-reef fish, the Ambon damselfish Pomacentrus amboinensis, which exhibits male-only egg care. When exposed to motorboat noise, we found that males exhibited vigilance behaviour 34% more often and spent 17% more time remaining vigilant, compared to an ambient-sound control. We then investigated nest defence in the presence of an introduced conspecific male intruder, incorporating a third noise treatment of altered motorboat-driving practice that was designed to mitigate noise exposure via speed and distance limitations. The males spent 22% less time interacting with the intruder and 154% more time sheltering during normal motorboat exposure compared to the ambient-sound control, with nest-defence levels in the mitigation treatment equivalent to those in ambient conditions. Our results reveal detrimental impacts of real motorboat noise on some aspects of parental care in fish, and successfully demonstrate the positive effects of an affordable, easily implemented mitigation strategy. We strongly advocate the integration of mitigation strategies into future experiments in this field, and the application of evidence-based policy in our increasingly noisy world.
Anthropogenic contaminants in the marine environment often biodegrade slowly, bioaccumulate in organisms, and can have deleterious effects on wildlife immunity, health, reproduction, and development. In this study, we evaluated tissue toxicant concentrations and pathology data from 83 odontocetes that stranded in the southeastern United States during 2012–2018. Mass spectrometry was used to analyze blubber samples for five organic toxicants (atrazine, bisphenol-A, diethyl phthalates, nonylphenol monoethoxylate [NPE], triclosan), and liver samples were analyzed for five non-essential elements (arsenic, cadmium, lead, mercury, thallium), six essential elements (cobalt, copper, manganese, iron, selenium, zinc) and one toxicant mixture class (Aroclor1268). Resultant data considerably improve upon the existing knowledge base regarding toxicant concentrations in stranded odontocetes. Toxicant and element concentrations varied based on animal demographic factors including species, sex, age, and location. Samples from bottlenose dolphins had significantly higher average concentrations of lead, manganese, mercury, selenium, thallium, and zinc, and lower average concentrations of NPE, arsenic, cadmium, cobalt, and iron than samples from pygmy sperm whales. In adult female bottlenose dolphins, average arsenic concentrations were significantly higher and iron concentrations were significantly lower than in adult males. Adult bottlenose dolphins had significantly higher average concentrations of lead, mercury, and selenium, and significantly lower average manganese concentrations compared to juveniles. Dolphins that stranded in Florida had significantly higher average concentrations of lead, mercury, and selenium, and lower concentrations of iron than dolphins that stranded in North Carolina. Histopathological data are presented for 72 animals, including microscopic evidence of Campula spp. and Sarcocystis spp. infections, and results of Morbillivirus and Brucella spp. molecular diagnostic testing. Sublethal cellular changes related to toxicant exposure in free-ranging odontocetes may lead to health declines and, in combination with other factors, may contribute to stranding.
Diadromous fishes have drastically declined over the last century, especially in Europe. Several authors have highlighted the role of large dams in this decline, but in fact, its causes are potentially multiple and cumulative, including degradation of local environmental conditions and widespread fragmentation of hydrographic networks associated with the pervasive establishment of smaller barriers. Consequently, there is a need to improve the identification and prioritization of the drivers of diadromous species loss in order to identify and apply the most appropriate conservation and restoration measures. In this study, we used both historical sources (from mid-18th to early 20th century) and current data to quantify the long-term loss of diadromous taxa over 555 sites throughout the French river network. Then, we modeled the effects of several anthropogenic pressures (e.g. barriers, water quality, hydrological and river morphological alterations) on diadromous taxon loss. Lastly, we assessed the potential consequences of four different scenarios of anthropogenic pressure reduction. Due to uncertainties in historical sources, some species were grouped into taxa leading to a potential underestimation of actual species extinctions. Despite this limitation, our results showed that the decline in diadromous assemblages is widespread but with contrasting magnitudes depending on site locations. The maximum height and density of barriers appeared as the major factors of taxon loss. Over the scenarios tested, we observed that exclusively improving local conditions have much more limited effects than restoring river continuity. Focusing actions on large dam removal did not show the strongest responses compared to removing medium and small-sized barriers. For effective and sustainable restoration of diadromous fish assemblage, (1) historical occurrences of diadromous fishes should be used as an indicator for assessing recovery, and (2) undertaken measures must be adapted to each basin to target and limit the number of barriers to remove while allowing diadromous fish recovery.
An increasing number of studies have shown that anthropogenic noise can negatively affect aspects of the anti-predator behaviour of reef fishes, potentially affecting fitness and survival. However, it has been suggested that effects could differ among noise sources. The present study compared two common sources of anthropogenic noise and investigated its effects on behavioural traits critical for fish survival. In a tank-based experiment we examined the effects of noise from 4-stroke motorboats and ships (bulk carriers > 50,000 tonnes) on the routine swimming and escape response of a coral reef fish, the whitetail damselfish (Pomacentrus chrysurus). Both 4-stroke boat and ship noise playbacks affected the fast-start response and routine swimming of whitetail damselfish, however the magnitude of the effects differed. Fish exposed to ship noise moved shorter distances and responded more slowly (higher response latency) to the startle stimulus compared to individuals under the 4-stroke noise treatment. Our study suggests that 4-stroke and ship noise can affect activity and escape response of individuals to a simulated predation threat, potentially compromising their anti-predator behaviour.
The composition, spatial structure, diversity and abundance of Antarctic nematode and copepod meiobenthic communities was examined in shallow (5–25 m) marine coastal sediments at Casey Station, East Antarctica. The sampling design incorporated spatial scales ranging from 10 meters to kilometers and included testing for human impacts by comparing polluted (metal and hydrocarbon contaminated sediments adjacent to old waste disposal sites) and control areas. A total of 38 nematode genera and 20 copepod families were recorded with nematodes being dominant, comprising up to 95% of the total abundance. Variation was greatest at the largest scale (km’s) but each location had distinct assemblages. At smaller scales there were different patterns of variation for nematodes and copepods. There were significant differences between communities at control and impacted locations. Community patterns had strong correlations with concentrations of metals introduced by human activity in sediments as well as sediment grain size and total organic content. Given the strong association with environmental patterns, particularly those associated with human impacts, we provide further evidence that meiofauna are very useful indicators of anthropogenic environmental changes in Antarctica.
Approximately one-quarter of the World’s sandy beaches, most of which are interrupted by tidal inlets, are eroding. Understanding the long-term (50–100 year) evolution of inlet-interrupted coasts in a changing climate is, therefore of great importance for coastal zone planners and managers. This study, therefore, focuses on the development and piloting of an innovative model that can simulate the climate-change driven evolution of inlet-interrupted coasts at 50–100 year time scales, while taking into account the contributions from catchment-estuary-coastal systems in a holistic manner. In this new model, the evolution of inlet-interrupted coasts is determined by: (1) computing the variation of total sediment volume exchange between the inlet-estuary system and its adjacent coast, and (2) distributing the computed sediment volume along the inlet-interrupted coast as a spatially and temporally varying quantity. The exchange volume, as computed here, consists of three major components: variation in fluvial sediment supply, basin (or estuarine) infilling due to the sea-level rise-induced increase in accommodation space, and estuarine sediment volume change due to variations in river discharge. To pilot the model, it is here applied to three different catchment-estuary-coastal systems: the Alsea estuary (Oregon, United States), Dyfi estuary (Wales, United Kigdom), and Kalutara inlet (Sri Lanka). Results indicate that all three systems will experience sediment deficits by 2100 (i.e., sediment importing estuaries). However, processes and system characteristics governing the total sediment exchange volume, and thus coastline change, vary markedly among the systems due to differences in geomorphic settings and projected climatic conditions. These results underline the importance of accounting for the different governing processes when assessing the future evolution of inlet-interrupted coastlines.