Effects of habitat modification on coastal fish assemblages

Acute noise is harmful on the anti-predator behaviour of commercially important juvenile coral reef fishes

Fish stock enhancement has been utilised in Taiwan for more than 30 years, yet the impacts of anthropogenic noise on the enhancement programs remain unknown. Anthropogenic noise can induce physiological and behavioural changes in many marine fishes. Therefore, we investigated the effects of acute boat noise (from stock enhancement release sites) and chronic noise (from aquaculture processes) on the anti-predator behaviour in three juvenile reef fishes: Epinephelus coioides, Amphiprion ocellaris and Neoglyphidodon melas. We exposed fish to aquaculture noise, boat noise and a combination of both, followed by a predator scare and documented kinematic variables (response latency, response distance, response speed and response duration). For the grouper E. coioides, their response latency decreased in the presence of acute noise, while their response duration increased in the presence of both chronic and acute noise. Among the anemonefish A. ocellaris, all variables remained unaffected by chronic noise, whereas acute noise increased the response distance and response speed. In the case of the black damselfish N. melas, chronic noise decreased the response speed, while acute noise decreased the response latency and response duration. Our results indicate that acute noise had a stronger influence on anti-predator behaviour than chronic noise. This study suggests that acute noise levels at restocking release sites can impact anti-predator behaviour in fishes, potentially altering fitness and likelihood of survival. Such negative effects and interspecific differences must be considered when restocking fish populations.

Seahorse Hotels: Use of artificial habitats to support populations of the endangered White's seahorse Hippocampus whitei

The provision of temporary, specially designed artificial habitat may help support populations of the Endangered Whites' seahorse Hippocampus whitei in the face of rapid coastal urbanisation and declining natural habitats. Three designs of artificial habitat (Seahorse Hotels) were installed in Port Stephens, New South Wales, Australia, where natural habitats had significantly declined. Mark recapture surveys were used to assess seahorse site fidelity and population parameters, and the effect of Seahorse Hotel design on seahorse abundance, epibiotic growth and mobile epifaunal seahorse prey was determined. The Seahorse Hotels sustained a substantial population of seahorses (64; 57-72 95% confidence intervals) in comparison to recent local population estimates. There were no significant differences in seahorse abundance, mobile epifauna or epibiotic growth among the three different hotel designs. This research demonstrated that H. whitei will inhabit Seahorse Hotels in absence of natural habitat, and additional complexity in these artificial structures was not necessary to support seahorse populations. Temporary structures such as Seahorse Hotels will be a valuable tool in supporting H. whitei and other Syngnathid populations through infrastructure maintenance or habitat modification.

Increasing habitat complexity on seawalls: Investigating large- and small-scale effects on fish assemblages

The construction of artificial structures in the marine environment is increasing globally. Eco-engineering aims to mitigate the negative ecological impacts of built infrastructure through designing structures to be multifunctional, benefiting both humans and nature. To date, the focus of eco-engineering has largely been on benefits for benthic invertebrates and algae. Here, the potential effect of eco-engineered habitats designed for benthic species on fish was investigated. Eco-engineered habitats ("flowerpots") were added to an intertidal seawall in Sydney Harbour, Australia. Responses of fish assemblages to the added habitats were quantified at two spatial scales; large (among seawalls) and small (within a seawall). Data were collected during high tide using cameras attached to the seawall to observe pelagic and benthic fish. At the larger spatial scale, herbivores, planktivores, and invertebrate predators were generally more abundant at the seawall with the added flowerpots, although results were temporally variable. At the smaller spatial scale, certain benthic species were more abundant around flowerpots than at the adjacent control areas of seawall, although there was no general pattern of differences in species density and trophic group abundance of pelagic fish between areas of the seawall with or without added habitats. Although we did not find consistent, statistically significant findings throughout our study, the field of research to improve fish habitat within human-use constraints is promising and important, although it is in its early stages (it is experimental and requires a lot of trial and error). To advance this field, it is important to document when effects were detected, and when they were not, so that others can refine the designs or scale of habitat enhancements or their study approaches (e.g., sampling protocols).

Assessing the natural and anthropogenic influences on basin-wide fish species richness

Theory predicts that the number of fish species increases with river size in natural free-flowing rivers, but the relationship is lost under intensive exploitation of water resources associated with dams and/or landscape developments. In this paper, we aim to identify orthomorphic issues that disrupt theoretical species patterns based on a multi-year, basin-wide assessment in the Danshuei River Watershed of Taiwan. We hypothesize that multiple human-induced modifications fragment habitat areas leading to decreases of local fish species richness. We integrally relate natural and anthropogenic influences on fish species richness by a multiple linear regression model that is driven by a combination of factors including river network structure controls, water quality alterations of habitat, and disruption of channel connectivity with major discontinuities in habitat caused by dams. We found that stream order is a major forcing factor representing natural influence on fish species richness. In addition to stream order, we identified dams, dissolved oxygen deficiency (DO), and excessive total phosphorus (TP) as major anthropogenic influences on the richness of fish species. Our results showed that anthropogenic influences were operating at various spatial scales that inherently regulate the physical, chemical, and biological condition of fish habitats. Moreover, our probability-based risk assessment revealed causes of species richness reduction and opportunities for mitigation. Risks of species richness reduction caused by dams were determined by the position of dams and the contribution of tributaries in the drainage network. Risks associated with TP and DO were higher in human-activity-intensified downstream reaches. Our methodology provides a structural framework for assessing changes in basin-wide fish species richness under the mixed natural and human-modified river network and habitat conditions. Based on our analysis results, we recommend that a focus on landscape and riverine habitats and maintaining long-term monitoring programs are crucial for effective watershed management and river conservation plans.

Coral reef fish assemblages along a disturbance gradient in the northern Persian Gulf: A seasonal perspective

Seasonal dynamics of coral reef fish assemblages were assessed along a gradient of potential anthropogenic disturbance in the Northern Persian Gulf. Overall, the attributes of coral reef fish assemblages showed seasonality at two different levels: seasonal changes irrespective of the magnitude of disturbance level (e.g. species richness), and seasonal changes in response to disturbance level (e.g. total abundance and assemblage composition). The examined parameters mostly belonged to the second group, but the interpretation of the relationship between patterns of seasonal changes and the disturbance level was not straightforward. The abundance of carnivorous fishes did not vary among seasons. SIMPER identified the family Nemipteridae as the major contributor to the observed spatiotemporal variations in the composition of coral reef fish assemblages in the study area.

Seasonal dynamics of fish assemblages on breakwaters and natural rocky reefs in a temperate estuary: consistent assemblage differences driven by sub-adults

Development of infrastructure around cities is rapidly increasing the amount of artificial substrate (termed artificial reef, ‘AR’) in coastal marine habitats. However, effects of ARs on marine communities remain unknown, because it is unclear whether ARs can maintain similar communities to natural reefs. We investigated whether well-established (> 30 years old) breakwaters could consistently approximate fish assemblages on interspersed rocky reefs in a temperate estuary over 6 consecutive seasons using regular visual surveys between June 2009 (winter) and November 2010 (spring). We examined whether assemblage differences between reef types were driven by differences in juvenile recruitment, or were related to differences in older life-stages. Assemblages on both reef types were dominated by juveniles (61% of individuals) and sub-adults (34% of individuals). Seasonal fluctuations in assemblage parameters (species richness, diversity, sub-adult abundance) were similar between reef types, and levels of species diversity and assemblage composition were generally comparable. However, abundance and species richness were consistently higher (1.9-7.6 and 1.3-2.6 times, respectively) on breakwaters. These assemblage differences could not be explained by differences in juvenile recruitment, with seasonal patterns of recruitment and juvenile species found to be similar between reef types. In contrast, abundances of sub-adults were consistently higher (1.1-12 times) at breakwaters, and assemblage differences appeared to be driven by this life-stage. Our results indicate that breakwaters in temperate estuaries are capable of supporting abundant and diverse fish assemblages with similar recruitment process to natural reefs. However, breakwaters may not approximate all aspects of natural assemblage structure, with differences maintained by a single-life stage in some cases.

High coral cover and subsequent high fish richness on mature breakwaters in Taiwan

Breakwaters are widely used in coastal development. Breakwaters can alter habitats by undermining shallow coastal ecosystems, especially coral reefs. However, recent studies indicate that mature breakwaters can have well-developed corals and coral-associated fishes. Breakwaters with colonized corals may act as surrogates of natural coral reefs against the global coral crisis. Here, we examined the composition of corals, fishes, and benthic biota/abiota between natural reefs and mature breakwaters to evaluate the possibility of breakwaters supplementing natural reefs. We found equal or higher coral cover, fish abundance, and species richness on breakwaters. Conversely, differential coral growth forms and fish assemblages on mature breakwaters suggested the irreplaceability of natural reefs. Corals and coral reef fishes on mature man-made structures, however, may improve the resistance and resilience of coral reefs. Conclusively, despite high coral cover on mature man-made structures appropriate management (e.g., marine reserves) is still necessary to sustain the coral reefs.