Reef Fish Populations Research Articles

A trophic modelling framework: Key metrics for the ecological assessment of artificial structures

As the global population expands, marine coastal ecosystems face mounting pressures from human activities, that have led to habitat deterioration and dwindling fishery resources. In this context, Artificial Reefs (ARs) have emerged as one of the promising solutions. They are generally implemented to provide habitat, to create a protective, physical boundary, to support sustainable fisheries and to facilitate ecosystem rehabilitation. Evaluating their ecological performance is crucial to ensuring they meet their objectives. Initially, assessment relied on comparing ARs to natural reefs using mainly ecological metrics which focused on fish assemblage and dynamics. Despite there being more research and documentation on effectiveness today, assessing ARs remains challenging due to the number of environmental factors that can affect the ecological systems. Moreover, ecological studies mainly used metrics that investigated the reef fish populations or ecological metrics such as fish assemblages or trophic structure that are often overlooked in studies that primarily focus on commercial fishery dynamics. Therefore, new ways of assessing artificial reef performance and the set-up of comprehensive metrics which integrate this level of complexity are needed. In this study, we focused on the "Rade de Cherbourg" in the English Channel, employing a trophic modeling approach using Ecopath with Ecosim (EwE). The study emphasizes the importance of Ecological Network Analysis (ENA) metrics for evaluating changes in the systems’ properties—such as complexity, flow diversity, and recycling capacity— which result from AR implementation. Furthermore, we identified which metrics are suitable for assessing specific AR objectives. The proposed metrics serve as a command-and-control tool for AR site managers, enabling them to evaluate the performance of each AR objective effectively. With the anticipated increase in AR projects, especially those which compensate for human impact like the Cherbourg ARs, this research offers valuable insights and future perspectives to continuously improve the ecological performance of ARs.

Modeling the interactive effects of sea surface temperature, fishing effort, and spatial closures on reef fish populations

Climate change can affect reef fish both directly (e.g., mortality, growth, fecundity) and indirectly (e.g., habitat degradation). The extent to which the effects of rising water temperature could drive changes in fish populations and if and how these effects may interact with potential management interventions remain unclear. The objective of this study was to test various hypothesized mechanisms by which sea surface temperature (SST) could affect reef fish population dynamics and explore these effects in combination with fishing effort restrictions and spatial closures. To do this, we modeled hypothesized relationships between SST and two governing parameters of the fish populations: intrinsic growth rate (r) and carrying capacity (K). We coupled these temperature-dependent fish population models with a fisheries harvest model and explored interactions between thermal effects, fishing effort level, and spatial closures. Under small closure scenarios, we found that the thermal effects models predicted substantially lower fish population biomass and harvest compared to the baseline (constant r and K) model. Under large closure scenarios, the thermal effects models more closely resembled the baseline. Generally, incorporating spatial closures mitigated some of the detrimental thermal effects on fish biomass and allowed for increased harvest under certain fishing effort levels. Whether intrinsic growth or carrying capacity most affected fish population levels also depended on the fishing effort and the spatial closure area. Overall, we described how fishing effort and spatial closures can influence the relative importance of key processes and the extent to which rising water temperatures affect fish populations and harvest.

Impact of invasive seagrass Halophila stipulacea on life history characteristics of juvenile yellowtail snapper (Ocyurus chrysurus)

Seagrass ecosystems provide essential nursery habitat to numerous coral reef fishes. Native Caribbean seagrasses Syringodium filiforme and Thalassia testudinum provide several juvenile fish species with foraging habitat and protection during this vulnerable stage of life. In 2002, an invasive seagrass Halophila stipulacea was discovered off the coast of Grenada and has since rapidly spread throughout the Caribbean. Halophila stipulacea has been shown to displace native seagrass species and may pose additional threats to juvenile reef fish populations that depend on native seagrass habitats as nurseries. The purpose of this study was to determine the effects of H. stipulacea on the early life history of yellowtail snapper (Ocyurus chrysurus). Settlement, mortality, and condition of juvenile yellowtail snapper were compared among native and invasive seagrass habitats around southern St. Thomas, United States Virgin Islands. From May 2020 to June 2021, monthly surveys within fixed plots during new moon periods provided information on settlement rates and survivorship among seagrass types. Length and weight of 260 juvenile yellowtail snapper were measured to derive condition factor among seagrass species. Significantly higher settlement and similar trends in mortality were seen in H. stipulacea when compared to native seagrasses. No significant difference was observed in condition factor of juvenile yellowtail snapper among seagrass species, although trends demonstrated a higher condition in individuals from native seagrass species. This study is the first of its kind to identify the direct effects of H. stipulacea during the early life history stages of a commercially important fish species in the Caribbean.

Dynamic interplay: disentangling the temporal variability of fish effects on coral recruitment

Ecosystems around the world are continuously undergoing recovery from anthropogenic disturbances like climate change, overexploitation, and habitat destruction. Coral reefs are a prime example of a threatened ecosystem and coral recruitment is a critical component of reef recovery from disturbances. Reef fishes structure this recruitment by directly consuming macroalgae and coral recruits or by indirectly altering the substrate to facilitate coral settlement (e.g., grazing scars). However, how these direct and indirect mechanisms vary through time remains largely unknown. Here, we quantified coral recruitment on settlement tiles with divots that mimic grazing scars and caging treatments to exclude or allow fish feeding over 3 years at Palmyra Atoll in the Pacific Ocean. We found that the positive and negative effects of fishes on coral recruitment varies through time. After 3 years, both grazing scars and fish grazing no longer predicted coral recruitment, suggesting that the role of fishes decreases over time. Our results emphasize that reef fish populations are important in promoting initial coral recovery after disturbances. However, over time, factors like the environment may become more important. Future work should continue to explore how the strength and direction of top-down control by consumers varies through time across multiple ecosystems.

Fluctuations of Galapagos mid-water and benthic reef fish populations during the 2015–16 ENSO

El Niño Southern Oscillation (ENSO) events have impacted the marine environment of the Galapagos, causing massive die-offs of corals and megafauna, and benthic habitat shifts. With ENSO events predicted to intensify under climate change scenarios it is important for managers to have an evidence-based understanding of how these events may affect fish assemblages in the Galapagos. We assess the abundance and size fluctuations of benthic and mid-water shore fishes during the 2015–16 “Godzilla” ENSO using data from baited remote underwater stereo-video surveys collected on four occasions over 2015–16. We found significant differences in the assemblage structure between the pre-El Niño, El Niño onset, El Niño receding, and La Niña onset sampling periods. Mackerels (i.e. Trachurus murphyi and Decapterus spp.) had a ∼480% greater relative biomass, 229% greater relative abundance, and 20.6% greater size during La Niña onset compared to El Niño. With the onset of La Niña we observed a severalfold increase in the abundance of mid-water species including large Carangids, medium-size Scombrids, elasmobranchs (i.e. Sphyrna lewini, Carcharhinus galapagensis) and several other bentho-pelagic taxa. We also found evidence of seasonal abundance fluctuations across years, independent of seasonal effects, in Scarids, Haemulids, Labrids, Chaetodontids, and Carangids. Although the 2015–16 ENSO appears to have had a lesser impact on the Tropical Eastern Pacific than past El Niño events, it was linked to changes in the abundance of several species of key ecological and economic importance. This information furthers our understanding of the influence of large-scale climatic events on fish populations and improves our ability to predict how these populations may change under future climate scenarios.

Assessment of habitat and reef fish population characteristics in Pari Island cluster waters Seribu Archipelago Indonesia

The Pari Island Cluster, located on the Southside of the Seribu Archipelago, is bordered by Jakarta and Tangerang Regency is covered Pari, Kudus, and Tikus Islands. The Pari Island cluster has potential ecosystems, such as coral reefs, seagrass, and mangrove. The presentation of this article is an overview of the results of research conducted by the Research Institute for Marine Fisheries and the Research Institute for Fisheries Enhancement, The Agency for Marine and Fisheries Research and Human Resources. This study aims to present and describe habitat and reef fish populations. The assessment result shows that the criteria for the coral reefs’ health were poor to good, mostly moderate, the best in the southeast and northeast waters, which had been designated MPAs. Reef fish population density on the criteria was very rare or low at all observation sites. The dominant group was Caesio cuning, Cephalopholis boenak, Scarus ghobban (target group), and Chaetodon octofasciatus (indicator group). The implementation hopes Pari Island Cluster waters would expand to be designated MPAs due to the large number of care areas used for fishing territories.

Rapid physiological and transcriptomic changes associated with oxygen delivery in larval anemonefish suggest a role in adaptation to life on hypoxic coral reefs.

Connectivity of coral reef fish populations relies on successful dispersal of a pelagic larval phase. Pelagic larvae must exhibit high swimming abilities to overcome ocean and reef currents, but once settling onto the reef, larvae transition to endure habitats that become hypoxic at night. Therefore, coral reef fish larvae must rapidly and dramatically shift their physiology over a short period of time. Taking an integrative, physiological approach, using swimming respirometry, and examining hypoxia tolerance and transcriptomics, we show that larvae of cinnamon anemonefish (Amphiprion melanopus) rapidly transition between "physiological extremes" at the end of their larval phase. Daily measurements of swimming larval anemonefish over their entire early development show that they initially have very high mass-specific oxygen uptake rates. However, oxygen uptake rates decrease midway through the larval phase. This occurs in conjunction with a switch in haemoglobin gene expression and increased expression of myoglobin, cytoglobin, and neuroglobin, which may all contribute to the observed increase in hypoxia tolerance. Our findings indicate that critical ontogenetic changes in the gene expression of oxygen-binding proteins may underpin the physiological mechanisms needed for successful larval recruitment to reefs.

A Habitat‐Based, Fishery‐Independent Survey Using Actively Fished Hooked Gear Successfully Characterizes Reef Fish Populations in the Eastern Gulf of Mexico

AbstractRecognized limitations of fishery‐dependent data under rapidly changing management regimes have resulted in significant effort during recent years to improve the availability of fishery‐independent data in the southeastern United States. These fishery‐independent surveys target numerous species and habitats with various sampling methods, including the use of trawls, longlines, gill nets, traps, and visual surveys. Although passively fished hooked gear (e.g., longlines) are often used to assess the abundance and life history of managed reef fishes, such types of gear are often limited by the habitats they can fish effectively and are species selective. To address these shortcomings, we developed and implemented an actively fished approach to provide fishery‐independent data: the repetitive timed‐drop hooked‐gear method (RTD method). Despite the high degree of standardization applied to the RTD method, important questions remain as to whether active fishing imparts strong angler variability that may reduce the utility of survey data. Accordingly, we analyzed data from 2014 to 2018 to evaluate potential angler bias and how angler‐associated variability compares to other factors often thought to be important predictors of reef fish abundance and community structure. During this study, 962 stations were sampled, representing a variety of artificial and natural reef habitats. In total, 5,770 fish were caught, representing 92 taxa. Sampling was conducted by 103 unique anglers, including 42 commercial or charter fishers and 61 scientists. Results from both population‐ and assemblage‐level analyses found that most of the variability in the catch could be explained by hook size, habitat, water depth, and year. Angler type was rarely correlated with reef fish abundance or assemblages. Our analyses suggest that the RTD method is effective in gathering fishery‐independent abundance and life history data for reef fishes in the eastern Gulf of Mexico and that the resulting data are not strongly biased by an angler effect.

Effects of habitat fragmentation on the recruitment and early post-settlement survival of coral reef fishes

The combined effects of global climate change and local anthropogenic stressors are leading to increasing loss and fragmentation of habitats. On coral reefs, habitat loss has been shown to influence the abundance and composition of associated fish assemblages, yet few studies have considered how habitat fragmentation may influence reef fish populations and assemblages. Herein, we compared survival, growth and recruitment of reef fish among experimental patches composed of six similar sized colonies of finely branching Pocillopora spp. but with different degrees of fragmentation: coral colonies were clumped (unfragmented), divided into two groups (low fragmentation), three groups (moderate fragmentation) or six groups (high fragmentation). Thirty settlement-stage Pomacentrus amboinensis were tagged, released onto each of the experimental patches, and their survival monitored daily for 11 days. Abundance and species richness of all reef fishes that subsequently recruited to the patches were also recorded, and used to analyse recruitment and community composition. There were no detectable differences among fragmentation treatments in the abundance or composition of reef fish assemblages that recruited to the patches, however, fragmentation influenced the survivorship of P. amboinensis. Highest survival of P. amboinensis was recorded on the unfragmented patches (61%.11 days−1) and highly fragmented habitat patches (54%.11 days−1) and lowest survival on low and moderate fragmentation treatments (47% and 48%.11 days−1, respectively). This suggests that there may be multiple competing processes that moderate mortality (e.g., predation) in unfragmented versus highly fragmented habitats, with moderate levels of habitat fragmentation having the greatest influence on the early post-settlement survival of corsal reef fish.

COVID-19 lockdown highlights impact of recreational activities on the behaviour of coral reef fishes.

In 2020, the COVID-19 pandemic led to a reduction in human activities and restriction of all but essential movement for much of the world's population. A large, but temporary, increase in air and water quality followed, and there have been several reports of animal populations moving into new areas. Extending on long-term monitoring efforts, we examined how coral reef fish populations were affected by the government-mandated lockdown across a series of Marine Protected Area (MPA) and non-Marine Protected Area (nMPA) sites around Moorea, French Polynesia. During the first six-week lockdown that Moorea experienced between March and May 2020, increases (approx. two-fold) in both harvested and non-harvested fishes were observed across the MPA and nMPA inner barrier reef sites, while no differences were observed across the outer barrier sites. Interviews with local amateur and professional fishers indicated that while rules regarding MPA boundaries were generally followed, some subsistence fishing continued in spite of the lockdown, including within MPAs. As most recreational activities occur along the inner reef, our data suggest that the lockdown-induced reduction in recreational activities resulted in the recolonization of these areas by fishes, highlighting how fish behaviour and space use can rapidly change in our absence.

Energy use, growth and survival of coral reef snapper larvae reared at elevated temperatures

The success of individuals during the pelagic larval phase is critical to maintaining healthy and viable populations of coral reef fishes; however, it is also the most environmentally sensitive and energetically demanding life stage. Climate change is increasing the frequency and intensity of marine heatwaves, which could have significant effects on the development and survival of larval coral reef fishes. However, little is known about how the larvae of pelagic-spawning coral reef fishes will be affected due to the difficulty of spawning and rearing these species in captivity. In this study, we tested how elevated temperatures, similar to those occurring during a marine heatwave, affected the yolk utilization, growth, and survival of larval, Lutjanus carponotatus, a common mesopredatory fish on Indo-west Pacific coral reefs. Eggs and larvae were reared at a current-day average summer temperature (28.5 °C) and two elevated temperatures (30 °C and 31.5 °C) until 14 d post-hatch (dph). Larvae in the elevated temperatures depleted their yolk reserves 39% faster than at the control temperature. The standard length of larvae was 55% (30 °C) and 92% (31.5 °C) longer in the elevated temperature treatments than the control temperature at 14 dph. Conversely, survival of larvae was 54% (30 °C) and 68% (31.5 °C) lower at elevated temperatures compared with the control temperature. This study provides new insights as to how the early life stages of coral reef fishes could be affected by ocean warming and marine heatwaves, with implications for their population dynamics.

Environmental DNA biomonitoring reveals seasonal patterns in coral reef fish community structure

Coral reef fish populations are declining due to multiple factors including habitat destruction, overfishing, and climate change. While these can include seasonal impact, seasonal changes can also be a confounding factor, so that seasonal monitoring is essential for detecting true temporal changes in fish community abundance and composition. However, seasonal monitoring is rarely implemented. The aim of this study was to detect the seasonal patterns of coral reef fish community structure around Tidung Kecil Island, Indonesia, using eDNA metabarcoding (eDNA) and underwater visual census (UVC). The UVC identified 32 species belonging to 10 families in the rainy season and 29 species belonging to 7 families in the dry seasons. The eDNA metabarcoding identified 209 species belonging to 56 families and 27 species belonging to 17 families in the rainy and dry seasons, respectively. Based on eDNA metabarcoding data, coral reef fish abundance and community composition differed significantly between seasons (Mann Whitney, p < 0.01), while the UVC method did not detect these seasonal differences (Mann Whitney, p > 0.05). UVC and eDNA data both showed a predominance of omnivorous fishes in the rainy season and carnivorous fishes in the dry season. Ecological indices did not differ significantly between seasons for the two used methods, although the species making the highest contributions to the similarity (SIMPER) analysis differed between methods. Overall, this study confirms the premise that eDNA metabarcoding can be an effective tool for monitoring seasonal variation in coral reef fish communities.

Demographic Recovery of a Reef Fish Population Over 30 Years of Spawning Aggregation Site Protection

Over 200 species of reef fish around the world form spawning aggregations to reproduce at specific times and locations. The locations of many reef fish spawning aggregations in the Caribbean have been known and fished for decades. Red Hind (Epinephelus guttatus), a species of grouper important in Caribbean fisheries, migrate to form spawning aggregations which have historically experienced intense fishing pressure. The Red Hind Bank Marine Conservation District (MCD) was established in the United States Virgin Islands to protect a known Red Hind spawning aggregation site. The MCD was closed seasonally to fishing in 1990 and then permanently in 1999. Our goal was to evaluate the success of this marine conservation effort by assessing how the Red Hind population at the spawning aggregation responded to changing levels of protection. We documented Red Hind population demographics at the spawning aggregation site in the MCD during peak spawning events from 2018 to 2020. After 30 years of protection, the mean size of Red Hind at the spawning aggregation increased by &amp;gt;35% and the population sex ratio of females to males was less skewed compared to population characteristics at the spawning aggregation prior to protection. To evaluate stock status relative to management benchmarks, we used length-based stock assessment models that includedin situsize distribution data spanning 1988 to 2020 to estimate population spawning potential ratio (SPR) over time. We found that the SPR of the Red Hind population at the spawning aggregation prior to protection was 0.32 (95% CI: 0.25, 0.39) and under seasonal protection, The SPR increased slightly to 0.35 (95% CI: 0.28, 0.42). Under permanent protection, The SPR increased to its highest value yet at 0.49 (95% CI: 0.42, 0.56), which is above the benchmark value considered sustainable for many fish species. Our work demonstrates demographic recovery of the protected Red Hind spawning population and highlights the value of using size distribution data to evaluate the response of data-limited reef fish populations to seasonal and permanent protection at spawning aggregation sites.

Local Overfishing Patterns Have Regional Effects on Health of Coral, and Economic Transitions Can Promote Its Recovery.

Overfishing has the potential to severely disrupt coral reef ecosystems worldwide, while harvesting at more sustainable levels instead can boost fish yield without damaging reefs. The dispersal abilities of reef species mean that coral reefs form highly connected environments, and the viability of reef fish populations depends on spatially explicit processes such as the spillover effect and unauthorized harvesting inside marine protected areas. However, much of the literature on coral conservation and management has only examined overfishing on a local scale, without considering how different spatial patterns of fishing levels can affect reef health both locally and regionally. Here, we simulate a coupled human-environment model to determine how coral and herbivorous reef fish respond to overfishing across multiple spatial scales. We find that coral and reef fish react in opposite ways to habitat fragmentation driven by overfishing, and that a potential spillover effect from marine protected areas into overfished patches helps coral populations far less than it does reef fish. We also show that ongoing economic transitions from fishing to tourism have the potential to revive fish and coral populations over a relatively short timescale, and that large-scale reef recovery is possible even if these transitions only occur locally. Our results show the importance of considering spatial dynamics in marine conservation efforts and demonstrate the ability of economic factors to cause regime shifts in human-environment systems.

A National Status Report on United States Coral Reefs Based on 2012–2018 Data From National Oceanic and Atmospheric Administration’s National Coral Reef Monitoring Program

National Oceanic and Atmospheric Administration’s Coral Reef Conservation Program supports the National Coral Reef Monitoring Program (NCRMP) in the United States Pacific, Atlantic, Caribbean, and Gulf of Mexico. NCRMP conducts standardized observations of biological, climatic, and socioeconomic indicators across American Samoa, Guam, the Main Hawaiian Islands, the Northwestern Hawaiian Islands, the Northern Mariana Islands, the Pacific Remote Islands, Florida, the Flower Garden Banks, Puerto Rico, and the United States Virgin Islands. NCRMP provides periodic, national-level assessments of the status of United States coral reef ecosystems and communities connected to them. In 2014, NCRMP partnered with the University of Maryland Center for Environmental Science on an unprecedented collaboration between federal and jurisdictional/state agencies, academia, and non-governmental organizations to synthesize NCRMP data into a reporting format designed to be accessible and relevant to the public and policy makers. The process involved multi-year data analyses of key benthic, fish, and climate indicators. In populated jurisdictions, socioeconomic data were integrated to assess public support for management actions, participation in pro-environmental behaviors, and awareness of threats to coral reefs. Jurisdictions were scored using a report-card scale (0–100%) by establishing references for each indicator using best-available historical data or expert opinion where historical data did not exist or were not statistically comparable. Despite overall ecosystem scores of Fair for all combined Atlantic (70%) and Pacific (74%) jurisdictions, the current trend is downward with a majority of United States coral reefs declining and vulnerable to further degradation. Remote, uninhabited reefs had an advantage with respect to reef fish population scores, i.e., Flower Garden Banks (85%) and Pacific Remote Islands (93%), when compared to populated location scores, i.e., Puerto Rico (63%) and Main Hawaiian Islands (66%). All coral reefs are highly impacted by climate change, and climate impacts were more pronounced than expected on remote reefs, i.e., the Northwestern Hawaiian Islands (58%). Presenting results in a report-card style facilitates communication to the public and policy makers, and provides a useful mechanism to garner support for management actions such as expanding protected areas; enforcing existing regulations; increasing climate change education; reducing land-based sources of pollution; and other actions to improve the trajectory of coral reef ecosystem conditions.

Assessment of reef fish and benthic cover of the North and South Dar es Salaam Marine Reserves system before the 2016 El Niño

The status of reef fish density, diversity, species richness, biomass and coral cover was evaluated by comparing the conditions in two Dar es Salaam Marine Reserves (DMRs); the North Dar es Salaam Marine Reserve (NDMR; gazetted in 1975), and the South Dar es Salaam Marine Reserves (SDMRs; gazetted in 2007), before the 2016 El Niño. A 10 m line-intercept transect was used to characterize benthic cover and a 50 m belt transect was used to assess reef fish population status. Sampling occurred between August 2014 and April 2015. The results showed that fish biomass in the (NDMRs) was 2.7 times higher than that in the (SDMRs) and live hard coral cover was 3 times higher. Higher reef fish density, biomass, diversity, species richness and live hard coral cover were revealed before 2016 El Niño in NDMRs as compared to the SDMRs. Differences in status are linked to differences in time of gazetting and level of effective management in the marine protected areas (MPAs), where NDMRs has a General Management Plan (GMP) while SDMRs does not, and the differences in management are likely to have contributed to the differences in fish biomass and coral cover.

Use of acoustic telemetry to evaluate fish movement, habitat use, and protection effectiveness of a coral reef no-take zone (NTZ) in Brazil

Movement is a key factor that shapes the distribution and structure of fish populations and influences the extent of the benefits provided by conservation and management measures, such as the implementation of marine no-take zones (NTZs). We used visual surveys and acoustic telemetry to investigate density and movement of 2 Brazilian endemic and highly targeted reef fish species inside and outside a coral reef NTZ, and subsequently inferred the effectiveness of the NTZ for protecting these species. To do so, visual surveys were performed on protected and unprotected reefs between 2016 and 2017. Moreover, 20 gray parrotfish Sparisoma axillare and 9 Brazilian snapper Lutjanus alexandrei were tagged with acoustic transmitters and passively monitored from December 2016 to October 2017. For both species, fish densities were significantly higher within the NTZ. Also, both species presented a high residence index over the short term, indicating they were full-time residents of the monitored area until detections were permanently lost. The absence of detections may indicate relocation to deeper reefs, predation, or fishing mortality when fish left the NTZ. Home ranges were small (0.10 to 0.45 km2), and both species presented spatially segregated subgroups within the populations. On average, the percentage of the home ranges within the NTZ was 88% for S. axillare and 95% for L. alexandrei. The results showed that small NTZs that are important to part of the life cycle of a target species are an effective measure to conserve reef fish populations, and also highlight the importance of fisheries management outside NTZs.

Habitat associations and impacts on a juvenile fish host by a temperate gnathiid isopod.

The distribution and abundance of organisms is typically shaped by multiple biotic and abiotic processes. Micropredators are parasite-like organisms that are smaller than their hosts and/or prey and feed on multiple hosts during a given life stage. Unlike typical parasites, however, they spend much or most of their time free-living, associating only temporarily with hosts. In the ocean, micropredators can impact multiple fish species, and in particular can have significant lethal and sub-lethal effects on newly settled fish. Although gnathiid isopods are abundant and primary micropredators in coral reef ecosystems, their impacts are relatively unexplored within sub-tidal temperate rocky reefs. We investigated the distribution of juvenile gnathiid isopods along sub-tidal temperate rocky reefs and tested trap methodology. We also quantified both the sub-lethal and lethal impacts of feeding-stage juvenile gnathiid isopods on juvenile, post-settlement reef fish, Heterostichus rostratus (giant kelpfish). We were most interested in determining the relationship between gnathiid infestation level and fish swimming performance, in particular swimming metrics relevant to predator avoidance maneuvers. We found that Gnathia tridens was present in rocky reefs rather than embayments along the Southern California coastline and that within rocky reefs, gnathiids occurred in the highest densities in lighted traps. Surprisingly, we observed almost no influence of fish size or gnathiid sub-lethal infestation level on ambient or burst swimming performance metrics. However, burst duration was reduced by gnathiid infestation, which is important in predator avoidance. There were significant differences in survivorship among small fish compared to large fish as a result of gnathiid infestation. Larger fish survived higher numbers of gnathiids than smaller fish, indicating that parasite-induced mortality is greater for smaller fish. Investigations of the effects of micropredators on subsequent predator-mediated mortality, including the susceptibility of fishes and their individual responses to micropredators, can further contribute to our understanding of processes affecting recruitment in resident reef fish populations. Further research, especially within temperate sub-tidal ecosystems, is needed to understand and highlight the overlooked importance of micropredation in shaping fish populations within a reefscape.

Evaluating the Effects of a Deep-Water Marine Protected Area a Decade After Closure: A Multifaceted Approach Reveals Equivocal Benefits to Reef Fish Populations

Marine protected areas (MPAs) are increasingly used to rebuild fish populations. In 2009, eight MPAs were designated off the southeast United States with the goal of rebuilding populations of long-lived deep-water reef fishes. We tested whether reef fish within the largest of these MPAs, the Snowy Wreck Marine Protected Area (SWMPA), have increased in size and abundance relative to a nearby control area and compared to pre-closure. Hurdle models fitted through Bayesian inference on echosounder data collected in 2007–2009 and 2018–2020 yielded no evidence of an MPA effect. Comparisons of catch-per-unit-effort (CPUE) of all reef fishes yielded similar null results. However, CPUE of reef species with formal stock assessments increased 47% in the SWMPA and decreased 50% in the control area. We found significant increases in mean length of red porgy (Pagrus pagrus) inside the SWMPA but not in the control area. We also found community composition changes, including shifts away from groupers (Serranidae; Epinephelinae) and toward snappers (Lutjanidae) and tilefish (Malacanthidae) in both areas, though we did not detect an MPA effect with this analysis. Our equivocal results indicate that more time and stricter enforcement may be necessary before more biological effects of the SWMPA can be detected.

Spatial and temporal variation in the genetic structure of Dascyllus trimaculatus (Pomacentridae) in the Bohol Sea

The potential of microsatellite markers to detect the spatial and temporal genetic structure of reef fish populations within a linear distance of 300 km in the absence of geographic barriers was tested in the Bohol Sea, central Philippines, using the three-spot damselfish Dascyllus trimaculatus. A total of 672 samples from 7 populations in the Bohol Sea were processed to determine temporal and spatial patterns of genetic variability using ten previously developed and tested microsatellite markers. The extent of differentiation was determined based on a variance-based measure of population structure FST and RST, and genetic distances Ds , DA, and dm2, each of which makes different assumptions on the process of migration, mutation, selection, and genetic drift. Patterns of temporal and spatial variation were consistent among 36 possible pairs of populations. Reef groups are defined as (1) the Mantigue-Dinagat on the northeast edge of the Bohol Sea; (2) the Selinog and Dapitan islands, to the southwest and central Bohol sea populations (3) Apo and (4) Sumilon to the west, and (5) Balicasag group to the northwest. The presence of structure in the absence of geographic barriers suggests the influence of strong surface circulation patterns that differ from the east to the west side of the region. The consistency of a population’s genetic signatures over multiple temporal sampling dates implies strong habitat selection for genotypes. Genetic breaks were detected at a distance 4x greater than the marine protected area’s average size, suggesting a minimum linear distance for networking of MPAs should be expanded to this scale. KEYWORDS: Conservation, Hardy-Weinberg equilibrium, marine protected area, microsatellite markers, population genetics, reef fish