Rocky Reef Habitats Research Articles

Kelp forests versus urchin barrens: a comparison of ecosystem functions and services provided by two alternative stable marine habitats.

Kelp forests and urchin barrens are two stable states in rocky reef ecosystems, each providing unique ecosystem functions like habitat for marine species and primary production. While studies frequently show that kelp forests support higher levels of some ecosystem functions than urchin barren habitats, no research has yet compared average differences. To address this gap, we first conducted a meta-analysis of studies that directly compared the ecosystem functions, services and general attributes provided by each habitat. We also compiled individual studies on ecosystem properties from both habitats and qualitatively assessed the benefits provided. The meta-analysis included 388 observations from 55 studies across 14 countries. We found that kelp forests consistently delivered higher levels of ecosystem properties such as biodiversity, species richness, abalone abundance and sea urchin roe quality. Urchin barrens supported higher urchin density and crustose coralline algae cover. The qualitative review further supported these findings, showing that kelp forests ranked higher in 11 out of 15 ecosystem properties. These findings can help guide decisions on managing rocky reef habitats and demonstrate the benefits of preserving or expanding kelp forests.

Development and use of a novel diver-operated ski for surveying nearshore rocky reef habitats.

The use of camera and video technologies for conducting underwater surveys has rapidly expanded over the past several decades. However, the utility of these systems can be significantly hampered by numerous logistical factors, including limited underwater visibility, rough bottom topography, and ease of use for the operator. Video studies can be difficult to compare when methods and terminologies differ. Here, we describe the development of a cost-effective diver-propelled underwater ski-based video system for rapidly acquiring videos in challenging shallow high-energy rocky benthic habitats for quantifying fish, macroalgae, and invertebrates in a coastal temperate system. The ski held the camera at a (relatively) fixed distance from the seafloor, we used parallel lasers to quantify our observations, and we used the standardized language and definitions in the Coastal and Marine Ecological Classification Standard (CMECS) to acquire consistent quantitative data to serve as an ecological baseline, also including archived images. Our results indicate that the ski proved to be an effective tool for capturing insightful data that would otherwise be very difficult and time consuming to collect. Our baseline and repeatable methods can be used by other investigators at this or other locations for monitoring, re-evaluation, or comparisons to other sites.

Fish community composition in the tropical archipelago of São Tomé and Príncipe.

Understanding species distribution across habitats and environmental variables is important to inform area-based management. However, observational data are often lacking, particularly from developing countries, hindering effective conservation design. One such data-poor area is the Gulf of Guinea, an understudied and biodiverse region where coastal waters play a critical role in coastal livelihoods. Here, we describe the results of the largest national-scale Baited Remote Underwater Video Systems (BRUVS) survey in the region, aiming to understand the effects of several environmental variables on fish community composition and diversity. From 2018 to 2020, we successfully deployed 417 benthic BRUVS in the coastal waters of the São Tomé and Príncipe (STP) archipelago. Species richness and relative abundance were higher in deeper waters, on steeper slopes, and in rocky reef habitats. Nevertheless, maerl and sand habitats also hosted unique, and economically important species. Our results potentially indicate historical impacts of fishing in the archipelago, especially in São Tomé Island, where observed fishing effort is higher. Indeed, abundance of large predatory fish was low in both islands and abundance of species targeted by artisanal fisheries was lower in São Tomé than in Príncipe. Our results provide crucial information supporting the designation and future monitoring of marine protected areas in STP.

Evaluating the long term effectiveness of a Mediterranean marine protected area to tackle the effects of invasive and range expanding herbivorous fish on rocky reefs

Here we provide evidence, along an 8-year period time-series based on multifaceted data from a Mediterranean marine protected area (MPA), whether protection can tackle invasive and range expanding herbivore fishes, and their effects on the algal resource availability, taking into account the population trends of predatory fishes, fisheries catches of herbivore fishes and sea surface temperature (SST) through time. Our findings pointed out that an ineffective in restoring top-down control process MPA may facilitate, rather than alleviate, the sudden and enduring population burst of invasive and range-expanding herbivorous fishes at tipping points of abrupt change. This subsequently results in the deterioration of rocky reef habitats and the depletion of algal resources, with the tipping points of abrupt change for algal and herbivore fish species not overlapping chronologically. As sea temperature increases, ineffective or recently established MPAs may inadvertently facilitate the proliferation of invasive and range-expanding species, posing a significant challenge to management effectiveness and conservation objectives.

Correspondence among multiple methods provides confidence when measuring marine protected area effects for species and assemblages

Abstract Marine protected areas (MPAs) have become a popular tool utilised across global oceans to achieve a variety of conservation goals. Because the reasons for MPA implementation can differ, it is imperative that resource managers design and execute management strategies that allow them to effectively assess MPA performance relative to the goals they set. We compared three MPA monitoring techniques commonly utilised to survey groundfish populations across different depth strata of temperate rocky reef habitat: underwater visual census (0–20 m), scientific hook and line fishing (10–50 m) and baited remote underwater video (30–100 m). We compared the strength and direction of standardised metrics, including response ratios, diversity indices and community structure, examining results through the lens of MPA performance. While each of our monitoring techniques detected similar MPA effects on groundfish biomass and density aggregated across species, MPA effects for individual species varied across methods. Each technique was shown to survey distinct groundfish community assemblages with varying levels of species diversity and richness. Synthesis and applications. While each technique was found to measure similar general trends in marine protected area (MPA) performance over time, we found compelling evidence that the utilization of multiple techniques allows managers to create the most comprehensive, effective and inclusive MPA monitoring regimes.

Wave damping by giant kelp, Macrocystis pyrifera.

The increased likelihood and severity of storm events has brought into focus the role of coastal ecosystems in provision of shoreline protection by attenuating wave energy. Canopy-forming kelps, including giant kelp (Macrocystis pyrifera), are thought to provide this ecosystem service, but supporting data are extremely limited. Previous in situ examinations relied mostly on comparisons between nominally similar sites with and without kelp. Given that other factors (especially seafloor bathymetry and topographic features) often differ across sites, efforts to isolate the effects of kelp on wave energy propagation confront challenges. In particular, it can be difficult to distinguish wave energy dissipation attributable to kelp from frictional processes at the seabed that often covary with the presence of kelp. Here, we use an ecological transition from no kelp to a full forest, at a single site with static bathymetry, to resolve unambiguously the capacity of giant kelp to damp waves. We measured waves within and outside rocky reef habitat, in both the absence and the presence of giant kelp, at Marguerite Reef, Palos Verdes, CA, USA. Nested within a broader kelp restoration project, this site transitioned from a bare state to one supporting a fully formed forest (density of 8 stipes m-2). We quantified, as a function of incident wave conditions, the decline in wave energy flux attributable to the presence of kelp, as waves propagated from outside and into reef habitat. The kelp forest damped wave energy detectably, but to a modest extent. Interactions with the seabed alone reduced wave energy flux, on average, by 12 ± 1.4 % over 180 m of travel. The kelp forest induced an additional 7 ± 1.2 % decrease. Kelp-associated declines in wave energy flux were slightly greater for waves of longer periods and smaller wave heights. Macrocystis pyrifera forests have a limited, albeit measurable, capacity to enhance shoreline protection from nearshore waves. Expectations that giant kelp forests, whether extant or enhanced through restoration, have substantial impacts on wave-induced coastal erosion might require re-evaluation.

Urchin Gonad Response to Kelp Forest Restoration on the Palos Verdes Peninsula, California

Along the Palos Verdes Peninsula in southern California, high densities of Strongylocentrotus purpuratus (purple sea urchin) have consumed almost all macroalgae on large expanses (61 ha) of rocky reef habitat, creating “urchin barrens.” Mesocentrotus franciscanus (red sea urchin) harvesting comprises an important fishery in the region, as their gonads are sold as a high-value sushi product called “uni.” However, with a lack of macroalgal food resources, urchins in barrens are smaller and exist in a starved state, meaning little, if any, gonad product is available to the fishery. To restore local kelp forests and increase gonad biomass available to the M. franciscanus fishery, beginning in October 2013, S. purpuratus were culled in barrens to a target density of 2 per m2 across 5.2 ha of rocky reef on the Palos Verdes Peninsula. Mesocentrotus franciscanus were collected from urchin barren, restoration, and kelp reference sites from April to November 2014 to compare differences in gonad production among the three site types. Culling S. purpuratus resulted in the recovery of normal seasonal M. franciscanus gonad production throughout the 8-month study. Mesocentrotus franciscanus gonad weights at a given test diameter length in restoration sites were equivalent to, and sometimes exceeded, the gonad production of those from the kelp reference sites. The urchin test length distributions of collected M. franciscanus were consistently smaller at urchin barren sites than at kelp reference sites, while those in restoration sites generally fell in between.

Settlement and recruitment of fish in mussel farms

. Fish are thought to settle and recruit to shellfish and seaweed farms; however, there is little published evidence to support this assumption. Shellfish and seaweed farms increase structural complexity and epibiota productivity, which may attract settling fish larvae. In this study, fish settlement and recruitment patterns into 2 aquaculture habitats, mussel-kelp co-culture and mussel farm monoculture, were compared to 2 adjacent natural habitats, soft-sediment seafloor and rocky reef, within a settlement season. Standard monitoring units for the recruitment of fish (SMURFs) were used, as they are a common and reliable method for measuring temporal and spatial variability in fish settlement and recruitment among habitat types. The communities of fish species settling and recruiting to both sets of aquaculture and natural habitats were equivalent. This was most likely due to the artificial 3D structure of the mussel farm habitats functioning in a similar manner to the structural complexity of a rocky reef habitat. Further, there was indication that for at least the most abundant fish species, Fosterygion lapillum, the 2 aquaculture habitats were of sufficient quality to support growth from settlement to juvenile size classes (i.e. in mussel monoculture habitat 65% were newly settled in December, and 86% were of juvenile size class by February). Overall, these findings provide foundational quantitative evidence of the interactions that fish have with mussel farms and increases the understanding of restorative opportunities for aquaculture operations.

Rebirth of a reef: As-built description and rapid returns from the Palos Verdes Reef Restoration Project

Palos Verdes Reef (PVR) is an artificial reef designed to restore rocky-reef associated marine species by directly restoring rocky-reef habitat that has been impacted by scour, sedimentation, and burial in the shallow subtidal portion of the Palos Verdes Peninsula in Los Angeles County, California, USA. The restoration reef provides high-quality habitat that is contiguous with the natural reef and allows for rapid succession. This project is a unique endeavor as restoring lost habitat in situ and has not been attempted in a temperate rocky reef and kelp forest community. While the primary design criteria for PVR is fish production in an area where already-limited hard substrate had been lost, it is also designed to be resilient to ongoing sedimentation and turbidity challenges on the peninsula. Following over a decade of design, planning, outreach, site surveying, and permitting, PVR was built in 2020 as 18 discrete modules using 52,729 tons of quarry rock placed approximately 8–80 m from existing, unburied rocky-reef habitat. There was no significant accumulation or scouring of sediment due to the placement of the reef and temperature data shows that internal tides regularly inundate the reef with cool, nutrient rich water. Rocky-reef associated taxa rapidly recruited to the restoration site, with visible changes occurring within just a few months post-construction. PVR modules showed rapid, significantly positive responses in fish density, fish biomass, kelp density, and biotic benthic cover less than 18 months after reef placement with a general pattern of succession in giant kelp growth from nearshore to offshore resulting in an established, thick canopy, in the nearshore, shallow modules. The newly available, high-quality habitat was quickly colonized and already shows late successional patterns with respect to fish and benthic communities. This restoration reef will produce large amounts of biomass over the long-term, though future surveys of multiple restored, adjacent, and reference sites will determine if high biomass at PVR is a result of new secondary production or attraction from nearby reefs.

Observation of juvenile Eastern Blue Groper (Achoerodus viridis) on remnant oyster reefs in New South Wales, Australia.

Observation of juvenile Eastern Blue Groper (Achoerodus viridis) on remnant oyster reefs in New South Wales, Australia.

Movements of Hatchery-Reared Dusky Groupers Released in a Northeast Atlantic Coastal Marine Protected Area

No-take areas are key instruments to promote the effectiveness of Marine Protected Areas (MPAs), particularly concerning the protection of endangered species such as the dusky grouper (Epinephelus marginatus). However, despite the establishment of no-take areas and the prohibition of catching this species in a southwestern Portuguese MPA (SACVMP—‘Sudoeste Alentejano’ and ‘Costa Vicentina’ Marine Park) since 2011, there is still no evidence of population recovery. By using acoustic biotelemetry, this work aimed to evaluate the feasibility of restocking hatchery-reared adult dusky groupers in two no-take areas within the SACVMP. In 2019 and 2021, thirty groupers were tagged with acoustic transmitters and the site attachment and movements of the groupers were assessed in the releasing sites (no-take areas). None of the tagged fish settled down in either of the areas, leaving the no-take areas mainly at dusk and night. Some individuals displayed extended movements of more than a hundred kilometers along the Portuguese coast which was rarely reported for this species. At least in some coastal stretches, those movements were performed close to the shore, which may evidence the importance of coastal MPAs to protect and promote the connectivity of species more associated with rocky reef habitats. Following studies should focus on the conditions that promote site attachment and fidelity by hatchery-reared dusky groupers so that future large-scale restocking programs can be successful in MPAs with appropriate habitats.

Phylogeography and evolutionary history of the Panamic Clingfish Gobiesox adustus in the Tropical Eastern Pacific

The Panamic Clingfish Gobiesox adustus is widely distributed in the Tropical Eastern Pacific (TEP), from the central Gulf of California, Mexico to Ecuador, including the oceanic Revillagigedo Archipelago, and Isla del Coco. This cryptobenthic species is restricted to very shallow rocky-reef habitats. Here, we used one mitochondrial and three nuclear DNA markers from 155 individuals collected across the distribution range of the species in order to evaluate if geographically structured populations exist and to elucidate its evolutionary history. Phylogenetic analyses recovered a monophyletic group, with four well-supported, allopatric subgroups. Each subgroup corresponded to one of the following well-known biogeographic regions/provinces: 1) the Revillagigedo Archipelago, 2) the Cortez + Mexican provinces (Mexico), 3) the Panamic province (from El Salvador to Ecuador), and 4) Isla del Coco. A molecular-clock analysis showed a mean date for the divergence between clade I (the Revillagigedos and Cortez + Mexican provinces) and clade II (Panamic province and Isla del Coco) in the Pliocene, at ca. 5.33 Mya. Within clade I, the segregation between the Revillagigedos and Cortez + Mexican province populations was dated at ca. 1.18 Mya, during the Pleistocene. Within clade II, the segregation between samples of Isla del Coco and the Panamic province samples was dated at ca. 0.77 Mya, during the Pleistocene. The species tree, Bayesian species delimitation tests (BPP and STACEY), the ΦST, AMOVA, and the substantial genetic distances that exist between those four subgroups, indicate that they are independent evolutionary units. These cladogenetic events seem to be related to habitat discontinuities, and oceanographic and geological processes that produce barriers to gene flow for G. adustus, effects of which are enhanced by the intrinsic ecological characteristics of this species.

Multiannual Seafloor Dynamics around a Subtidal Rocky Reef Habitat in the North Sea

Rocky reefs provide complex structures in the otherwise largely sand-dominated coastal North Sea. Therefore, these reefs are highly important natural habitats for the functioning of coastal ecosystems, as they provide shelter, refuge and nursery grounds for various mobile and sessile species. In the North Sea, the spatial distribution of these habitats has been intensively investigated over recent years. However, these studies generally provide static accounts of the current state of these reef systems, but limited data exist on the temporal variations in sediment dynamics at and around natural rocky reefs. In this study, we provide observations from a multiannual time series of hydroacoustic seafloor surveys conducted at an isolated rocky reef in the North Sea. We use multibeam bathymetry and side-scan sonar backscatter data in combination with video observations, sediment sampling, and sub-bottom profiler data to assess the long-term variations of the rocky reef system. The reef is located in water depths between 11 and 17 m with an areal extent of ~0.5 km2 and is surrounded by mobile sands. The topography of the rocky reef appears to create a distinct hydrodynamic system that permits mobile sands to settle or move into bathymetrical deeper parts of the reef. Our results suggest a very dynamic system surrounding the reef with large scale scouring, sediment reworking and transport, while the shallower central part of the reef remains stable over time. We demonstrate the importance of hydrodynamics and current scouring around reefs for the local variability in seafloor properties over time. These small-scale dynamics are likewise reflected in the spatial distribution of sessile species, which are less abundant in proximity to mobile sands. The hydroacoustic mapping and monitoring of seafloor dynamics at higher spatial and temporal resolutions presents an important future direction in the study of valuable coastal habitats.

A Comparison of Fish Diversity in Rocky Reef Habitats by Multi-Mesh Gillnets and Environmental DNA Metabarcoding

This study was undertaken in order to explore the practical effectiveness of the environmental DNA (eDNA) metabarcoding approach in evaluating fish composition and diversity in a high heterogeneous rocky reef habitat. We assessed the fish composition and diversity characteristics of the rocky reef habitat at Dachen Islands, Taizhou and the Zhejiang Province in China in November 2020 by comparing two methods: multi-mesh gillnets and eDNA. A comparative analysis was carried out on the fish composition and diversity characteristics gained under the two methods by using taxonomy, ecotypes and diversity indices. The results showed that there were 28 species of fish collected through gillnets, distributed under 24 genera, 19 families, 6 orders and one class. Among them, 4, 18, and 6 species of near-surface, near groundfish and groundfish were found, respectively, with Thryssa mystax, Johnius belangerii, and Sebastiscus marmoratus being the dominant species in each water layer. A total of 81 species of fish detected by eDNA metabarcoding belonging to 67 genera, 46 families, 15 orders and 2 classes. The near-surface, near groundfish and groundfish species were 17, 42, and 22, with Thryssa vitrirostris, Benthosema pterotum, Harpadon nehereus, and Dasyatis akajei being the dominant species in each water layer. Twenty species (71.4%) and 41 species (50.6%) of reef fish were counted by gillnets and eDNA, respectively. The results showed that multi-mesh gillnets can accurately obtain information on fish composition in rocky reef habitats, but with some selectivity. The eDNA technology can detect species not collected by gillnets, but the number of species detected in areas with fast water velocity is significantly less than other eDNA stations where the water velocity is slow. In summary, the combination of traditional nets and eDNA will provide more information on taxonomic diversity and population biomass, transforming natural resource management and ecological studies of fish communities on a larger spatial and temporal scale.

Habitat-specific performance of high-frequency acoustic telemetry tags in a tropical marine environment

High-frequency (>175 kHz) acoustic telemetry transmitters are increasingly being used to track the movements of small fishes and other aquatic organisms. These transmitters, which are often smaller than conventional types, have primarily been used in freshwater, yet limited information is available on their efficacy in estuarine or marine environments. This study quantified detection ranges (DR) of 180-kHz tags and potential environmental factors influencing detection probability in three different habitats within a large embayment in Costa Rica. Mangrove (DR at 50% detection efficiency; DR50 = 121.0 m ± 8.1 s.e.) and transitional estuarine (DR50 = 145.6 m ± 12.2) habitats had relatively high detection ranges, albeit smaller than similar studies in freshwater, highlighting the effectiveness of using this frequency in tropical marine environments. By contrast, performance within rocky reef habitat was poor (DR50 consistently <0 m), which may have been caused by the heterogeneous bottom structure or close proximity detection interference (CPDI) due to ambient noise. This study provides novel information on the performance of high-frequency acoustic tags in a tropical marine environment serving as an important case study as investigations of the spatial ecology of small fishes in both marine and freshwater become more common.

Comparison of video and traps for detecting reef fishes and quantifying species richness in the continental shelf waters of the southeast USA

The management of reef-associated fish species is challenging due to their life history characteristics and occurrence in rocky reef habitats that are difficult to sample using traditional sampling gears. We compared 2 common sampling gears for reef fish species, chevron traps and underwater video, using 5 yr of comprehensive paired sampling data (N = 7034) collected at reef habitats between North Carolina and Florida along the southeast United States Atlantic continental shelf. Most fish families (80%) and species (85%) were observed significantly more often on video than caught in traps, and only 2 species out of 40 (5%)—black sea bass Centropristis striata and bank sea bass C.ocyurus—were caught significantly more often in traps than observed on video. Moreover, site-specific species richness was approximately 3-4 times higher on average for video compared to traps. We also used a generalized additive model to show that the ratio of trap-caught species to video-observed species was higher in shallower waters off North and South Carolina, especially when water clarity was low. Results demonstrate that video can be an efficient gear to sample most reef fishes around the world but may provide even greater benefits when paired with traditional sampling gears like traps to leverage the strengths of each gear for estimating relative abundance and species richness with more certainty.

A decade implementing ecosystem approach to fisheries management improves diversity of taxa and traits within a marine protected area in the UK

AbstractAimEcosystem Approach to Fisheries Management has highlighted the importance of studying ecosystem functions and services, and the biological traits that drive them. Yet, ecosystem services and the associated benefits that they provide are rarely the motive for creating marine protected area (MPA). Therefore, many MPA monitoring projects do not explicitly study these functions and services or the underlying biological traits linked to them.LocationLyme Bay MPA, located in the SW of England, was established in 2008 to protect the reef biodiversity across a 206‐km2 area, which includes rocky reef habitats, pebbly sand and soft muddy sediments. Mobile demersal fishing was excluded across the whole site to allow the recovery of the reef habitats.MethodsUsing a combination of towed underwater video and Baited Remote Underwater Video Systems changes in diversity (taxonomic and trait), and traits affected by mobile demersal fishing were assessed in Lyme Bay MPA over 10 years.ResultsThere was a consistent increase in the number of taxa and the trait diversity they provide within the MPA as well as an increase in functional redundancy, which may increase community resilience to perturbations. Outside of the MPA there was an increase in the abundance of mobile species, while the MPA showed an increase in filter feeders.Main conclusionsThe MPA showed a trend towards more diverse and potentially resilient rocky reef habitats. This study constitutes a novel MPA assessment using multiple sampling methods to encompass a wide range of taxa. It also reinforces the importance of effective MPA monitoring, which has demonstrated changes in trait diversity and trait composition driven by changes in taxonomic diversity.

High-resolution marine heatwave mapping in Australasian waters using Himawari-8 SST and SSTAARS data

Marine heatwaves (MHWs) have significant ecological and economic impact at local and regional scales. Consequently, there is a pressing need to map the fine-scale temporal and spatial patterns of MHWs, for both historical and near real-time events. Satellite remote sensing of Sea Surface Temperature (SST) provides fundamental data for the mapping of MHWs. This study used high-resolution Himawari-8 SST and the Sea Surface Temperature Atlas of the Australian Regional Seas (SSTAARS) data, which have a spatial resolution of ~2 km, to map recent and near real-time MHW events in waters around Australasia. The high-resolution MHWs mapping identified two broad areas of MHW hotspots that occurred between August 2015 and February 2019. The Tropical Warm Pool region (including the Great Barrier Reef and part of the Coral Sea) was affected by strong and prolonged MHW conditions for the greater part of 2016. The unusually strong 2015–16 El Niño event was believed to be the primary underlying driver for the MHWs, and the air-sea heat flux was likely the key local process controlling the heat budget. The south-east of the study area (including Australia's south-east coast, the Tasman Sea and New Zealand's east coast) suffered severe MHWs in 2015–16, 2017–18 and 2018–19. The 2015–16 summer Bass Strait and East Tasmania MHW event was likely due to the anomalous heat transported by the East Australia Current. The air-sea heat flux, however, was likely an important local driver for the MHW events in the Tasman Sea during the 2016 autumn, the 2017–18 summer and the 2018–19 summer. The anomalous heat flux into ocean was attributed to potential underlying climate drivers including ENSO teleconnections, positive SAM and their interaction. This mapping has not only enhanced our understanding of the spatio-temporal characteristics of several previously documented MHWs, but also identified and mapped several previously undocumented MHWs. Two case studies in the Beagle Marine Park located in north-eastern Bass Strait and the Elizabeth and Middleton Reefs situated ~550 km east of the Australian coast within the Lord Howe Marine Park proved the value of Himawari-8 SST and SSTAARS data in mapping fine details of MHWs in a small area, which could not be captured by the broad-scale DOISST data. During the 2017–18 summer event, the case studies revealed much stronger MHW influence in the shallow waters east of the Beagle Marine Park where most of the important rocky reef habitats exist. During the same event, the case studies also confirmed more severe MHW impact on the Elizabeth Reef than the Middleton Reef which resulted in bleaching to selective coral species on the Elizabeth Reef. The near-real time MHWs mapping showed that both the GBR and the Coral Sea marine parks were experiencing MHW conditions in early March 2020, with most affected areas having strong MHW class.

Habitat type and complexity drive fish assemblages in a tropical seascape.

Inshore marine seascapes support a diversity of interconnected habitats and are an important focus for biodiversity conservation. This study examines the importance of habitat attributes to fish assemblages across a mosaic of inshore habitats: coral reefs, rocky reefs, macroalgae beds and sand/rubble beds. Fishes and benthic habitats were surveyed at 34 sites around continental islands of the central Great Barrier Reef using baited remote underwater video stations (BRUVS). Species richness was influenced foremost by habitat type and also by structural complexity within habitat types. The most speciose assemblages occurred in coral and rocky reef habitats with high structural complexity, provided by the presence of coral bommies/overhangs, boulders and rock crevices. Nonetheless, macroalgae and sand/rubble beds also supported unique species, and therefore contributed to the overall richness of fish assemblages in the seascape. Most trophic groups had positive associations with complexity, which was the most important predictor for abundance of piscivorous fishes and mobile planktivores. There was significant differentiation of fish assemblages among habitats, with the notable exception of coral and rocky reefs. Species assemblages overlapped substantially between coral and rocky reefs, which had 60% common species, despite coral cover being lower on rocky reefs. This suggests that, for many species, rocky and coral substrates can provide equivalent habitat structure, emphasizing the importance of complexity in providing habitat refuges, and highlighting the contribution of rocky reefs to habitat provision within tropical seascapes. The results of this study support an emerging recognition of the collective value of habitat mosaics in inshore marine ecosystems.

Spatial ecology of hawksbill sea turtles (Eretmochelys imbricata) in foraging habitats of the Gulf of California, Mexico

Understanding movement patterns and habitat preferences of endangered species during their most vulnerable life stages is a key step to developing effective conservation strategies that prevent extinctions. Hawksbills (Eretmochelys imbricata) are among the most-imperiled sea turtles and are generally thought to associate with very specific coral and rocky reef habitats. However, in the Eastern Pacific, hawksbills have also been found to have a strong association with mangrove estuaries. Eastern Pacific hawksbills constitute one of the most endangered sea turtle populations globally, and the Gulf of California, Mexico, was recently identified as a potentially important foraging region. Here we analyzed movement patterns of 12 individuals equipped with Argos-linked GPS transmitters. We calculated home ranges using kernel density estimations and found that hawksbills were highly restricted in their movements, spending months to years in areas ranging from 0.05 to 17 km2. Mean sizes of 50% and 95% kernel utilization distributions were 0.72 km2 and 3.8 km2, respectively. Also, 85.6% of hawksbill locations were associated within, or in close proximity to, mangrove estuaries, further highlighting the importance of these fragile ecosystems for hawksbill conservation. The fine-scale resident behavior of hawksbill turtles in foraging grounds presents a unique conservation opportunity while also underscoring the need to identify these sites and work with local communities to protect them.