Shallow Rocky Reefs Research Articles

Predation risk of the sea urchin Paracentrotus lividus juveniles in an overfished area reveal system stability mechanisms and restocking challenges.

Where sea urchin harvest has been so intense that populations have drastically regressed, concerns have arisen about the effectiveness of harvesting management. According to the theory of phase transition in shallow rocky reefs between vegetated and barren habitats, sea urchin recruitment, a key population structuring process, seems hampered by some stabilizing feedback despite an end to local human harvest of sea urchins. To shed a light on predation effects on sea urchin recruits, a 27-day field experiment was conducted using mega-predator exclusion cages (40x40x40 cm, 1 cm in mesh size) in barren and turf substrates. To facilitate this, 672 recruits (1.1 ± 0.02 cm in size) reared under control conditions were positioned in groups of 42 in each experimental unit (n = 4). Exclusion of mega-predators had a significant effect regardless the substrate, since a higher number of recruits was found under cages both in turf and barren. However, the results showed that in uncaged treatments the size of recruits that survived was larger in turf than in barren, as in the former substrate predation had reduced the abundance of the smallest recruits, highlighting that mega-predator presence affects differently the size of the recruits that had survived depending on the substrate. Overall, these results provide valuable information to address restocking actions of sea urchin populations in overharvested areas, where algal turfs are widespread, and assist studies on habitat stability mechanisms.

Estimating the extent of urchin barrens and kelp forest loss in northeastern Aotearoa, New Zealand

ABSTRACT On shallow rocky reefs in northeastern Aotearoa, New Zealand, urchin barrens are indicators of the ecosystem effects of overfishing reef predators. Yet, information on their extent and variability is lacking. We use aerial imagery to map the urchin barrens and kelp forests on reefs (<30 m depth) across seven locations, including two long-established marine reserves and a marine protected area that allows recreational fishing. Urchin barrens were present in all locations and were restricted to reefs <10–16 m deep. Urchin barrens covered 30% (7–49%) of shallow reefs in fished areas, with variation among and within locations likely related to the relative extent and topography of reefs and wave exposure. Within the marine reserves, barrens covered <2% of shallow reefs. Long-term comparison of historical imagery at two fished locations demonstrates that current areas of urchin barrens were historically dominated by kelp forests, but barrens have persisted since at least the early 2000s. We estimate ∼30 km2 of barrens exist across the region. This demonstrates the widespread nature of barrens, the potential long-term effectiveness of no-take marine protection in restoring urchin barrens, and the need for a multifaceted management approach to restore kelp forests and prevent further expansion of barrens.

ECOfast – An integrative ecological evaluation index for an ecosystem-based assessment of shallow rocky reefs

The degradation of marine ecosystems is a growing concern worldwide, emphasizing the need for efficient tools to assess their ecological status. Herein, a novel ecosystem-based ecological evaluation index of shallow rocky reefs is introduced and tested in the Aegean and Ionian Seas (NE Mediterranean). The index focuses on a specific set of pre-selected species, including habitat-forming, key, commercially important, and non-indigenous species, across a wide range of trophic levels (1.00–4.53). Data acquisition is conducted through rapid non-destructive SCUBA diving surveys to assess all macroscopic food web components (macroalgae, invertebrates, and fish). Two versions of the index, ECOfast and ECOfast-NIS, were developed, each applying a different approach to account for the impact of non-indigenous species. In our case study, the correlations between the two versions of the index and sea surface temperature, protection status, occurrence of carnivorous fish, and non-indigenous herbivores were assessed through generalized additive models (GAMs). The assessment assigned 93% (ECOfast) or 96% (ECOfast-NIS) of the sites to a moderate to bad ecological status, indicating an alarming situation in the shallow rocky reefs of the NE Mediterranean. Sites evaluated as poor or bad were characterized by extensive coverage of ephemeral macroalgae, absence or minimal presence of large indigenous carnivorous fish, and complete absence of one to three out of five invertebrate functional trophic groups. The community composition of macroalgae, herbivorous species, and carnivorous fishes differed between the 5 m and 15 m depth zones. Surface temperature and carnivorous fish occurrence were the most important tested predictors of the ecological status of shallow rocky reefs. The best GAMs showed that the ECOfast score declined with sea surface temperature and increased with the occurrence of carnivorous fish; ECOfast-NIS declined with sea surface temperature and the occurrence of non-indigenous fish and increased with the occurrence of carnivorous fish. The non-destructive and integrative nature of this approach, its speed of data acquisition and analysis, and its capacity to account for highly mobile predatory fish and non-indigenous species render the ECOfast index a novel, robust, and valuable tool for assessing the ecological status of shallow rocky reefs.

Assessment of macroalgal communities on shallow rocky reefs in the Aegean Sea indicates an impoverished ecological status

Mediterranean rocky reefs are undergoing regime shifts, from a structurally complex and diverse state dominated by canopy- forming macroalgae to a degraded one characterised by low-lying turf or encrusting macroalgal species, due to increased anthropogenic pressure and climate change. Using data gathered from 89 sites across the entire Aegean Sea, this study aims to provide the most comprehensive health status assessment of shallow rocky reefs in the area, based on macroalgal community structure. Overall, 2520 benthic images were collected through photoquadrat sampling at 0, 5 and, 15 m depth. Five macroalgal and seven invertebrate morphofunctional groups, along with four substrate categories, were considered for community structure description. Health status was assessed using the reef-EBQI and EEI-c indices. Results indicate turf as the most widespread macroalgal group (36.8% average area cover), followed by encrusting calcareous (16.6%), shrubby (12.7%), articulated calcareous (8.9%), and canopy-forming algae (3.7%). Bare rock also occupied a substantial surface area (9.0%) with highest cover (13.8%) at 5 m. The area cover of canopy-forming algae was particularly low, ranging from 10% at 0 m to 0.1% at 15 m depth, on average. All depths pooled, according to the reef-EBQI index, the ecological status of the Aegean Sea was estimated to be ‘Bad’, mainly due to the bad ecological status of the 5 and 15 m stations. At 0 m depth, the status of the Aegean Sea was ranked ‘Moderate’ according to the reef-EBQI index and ‘Good’ according to the EEI-c index. The results underline the importance of considering a wide depth range when assessing the health status of rocky reef communities.

Epilithic Bacterial Assemblages on Subtidal Rocky Reefs: Variation Among Alternative Habitats at Ambient and Enhanced Nutrient Levels.

Temperate rocky reefs often support mosaics of alternative habitats such as macroalgal forests, algal turfs and sea urchin barrens. Although the composition of epilithic microbial biofilms (EMBs) is recognized as a major determinant of macroalgal recruitment, their role in regulating the stability of alternative habitats on temperate rocky reefs remains unexplored. On shallow rocky reefs of the Island of Capraia (NW Mediterranean), we compared EMB structure among canopy stands formed by the fucoid Ericaria brachycarpa, algal turfs, and urchin barrens under ambient versus experimentally enhanced nutrient levels. The three habitats shared a core microbial community consisting of 21.6 and 25.3% of total ASVs under ambient and enhanced nutrient conditions, respectively. Although Gammaproteobacteria, Alphaproteobacteria and Flavobacteriia were the most abundant classes across habitats, multivariate analyses at the ASV level showed marked differences in EMB composition among habitats. Enhancing nutrient level had no significant effect on EMBs, although it increased their similarity between macroalgal canopy and turf habitats. At both ambient and enriched nutrient levels, ASVs mostly belonging to Proteobacteria and Bacteroidetes were more abundant in EMBs from macroalgal canopies than barrens. In contrast, ASVs belonging to the phylum of Proteobacteria and, in particular, to the families of Rhodobacteraceae and Flavobacteriaceae at ambient nutrient levels and of Rhodobacteraceae and Bacteriovoracaceae at enhanced nutrient levels were more abundant in turf than canopy habitats. Our results show that primary surfaces from alternative habitats that form mosaics on shallow rocky reefs in oligotrophic areas host distinct microbial communities that are, to some extent, resistant to moderate nutrient enhancement. Understanding the role of EMBs in generating reinforcing feedback under different nutrient loading regimes appears crucial to advance our understanding of the mechanisms underpinning the stability of habitats alternative to macroalgal forests as well as their role in regulating reverse shifts.

Fouling of a boat hull by the invasive zooxanthellate coral Oculina patagonica - could shipping be enhancing its unique large-scale spread?

The zooxanthellate coral Oculina patagonica (Scleractinia, Oculinidae) is an invasive species that was first recorded in the Mediterranean Sea in 1966 and currently has expanded its distribution across both the western and eastern Atlantic. Here, we reviewed data from multiple databases to compile historical distribution records of O. patagonica and analyze its spread. The chronological review highlights the unique spread of this zooxanthellate coral during the last two decades, expanding its distribution in multiple directions and establishing populations in disjunct regions separated by ~12,000 km, including most biogeographic regions within the temperate Mediterranean, the subtropical eastern Atlantic and the tropical Gulf of Mexico. The biogeographic distribution discontinuities documented in O. patagonica are difficult to explain by larval dispersion alone; therefore, other mechanisms may contribute to its large-scale spread pattern. This study provides the first observation of several O. patagonica colonies fouling the hull and metal crevices of a recreational boat in the western Mediterranean (37°N, 1°W). The presence of several mature O. patagonica colonies on a single ship, rather than a single coral colony rafting on natural or artificial floating substrates, could greatly increase its potential for spread, coupled with its ecological and biological traits adapted to rafting. We hypothesized that the travel of coral populations by shipping may act as a dispersal vector contributing to explaining the long-distance dispersal events and secondary introductions experienced by this invasive species. The broad spread of O. patagonica, which is able to drive phase shifts from macroalgae dominance to coral dominance, is consistent with the ongoing process of coral-mediated tropicalization of high-latitude shallow rocky reefs under current global change

Ecofast - an Integrative Ecological Evaluation Index for an Ecosystem-Based Assessment of Shallow Rocky Reefs

Ecofast - an Integrative Ecological Evaluation Index for an Ecosystem-Based Assessment of Shallow Rocky Reefs

Temporal consistency of a facilitation cascade on shallow rocky reefs

Facilitation cascades are increasingly recognized as key drivers of biodiversity in a variety of habitats, yet their temporal variability remains poorly investigated. On shallow subtidal rocky reefs, positive interactions between the canopy-forming species, Halopithys incurva, and its epiphyte, Jania rubens, enhance the abundance and diversity of the associated mobile invertebrate assemblage. By means of a field experiment manipulating the presence of J. rubens on H. incurva plants, we investigated whether the effects of this facilitation cascade varied over time scales of months. Despite seasonal fluctuations in its biomass, J. rubens enhanced total invertebrate abundance and species richness by 64% and 45%, respectively, throughout the experiment. Our results suggest that the presence of J. rubens, likely by providing novel microhabitats and increasing resource availability, sustains invertebrate biodiversity of shallow macroalgal forests consistently between warm and cold periods. Understanding the temporal dynamics of facilitation cascades and their mechanisms can help inform management strategies targeting biodiversity conservation and restoration under current and future climates.

Habitat type and environmental conditions influence the age and growth of a temperate marine damselfish

Life history parameters for fishes have generally been applied to species across their entire range, however, different ecological and environmental conditions and processes (e.g., sea surface temperature, habitat, primary productivity, fishing mortality, resource availability) influence life history patterns at smaller spatial scales. By focusing on a historically protected species, we determined how environmental and ecological factors shape patterns in growth and longevity, without the impact of fishing. The Garibaldi (Hypsypops rubicundus) is a territorial marine damselfish native to the shallow rocky reefs of southern California. Garibaldi were collected from five mainland locations and five Channel Islands throughout the Southern California Bight. Paired natural reef and artificial reef habitats (i.e., breakwaters and jetties) in each mainland location were sampled. Otolith-based ageing and biological data from these populations were used to assess how age and growth vary by location, reef type (natural/artificial), island or mainland, mean annual sea surface temperature, and/or sex. The annual formation of growth increments in otoliths was validated in-situ using tetracycline mark-recapture methods to confirm that increments are formed annually. Garibaldi grew significantly larger on artificial reefs than on natural reefs but tended to live longer on paired natural reefs. Regionally, growth and longevity followed mean annual sea surface temperature gradients, consistent with Bergmann’s rule. Garibaldi exhibited clear sexual size dimorphism; males grew larger, which is uncharacteristic for both damselfish and other marine fishes from the southern California. The Garibaldi collected for this study had a maximum age of 57 years, which makes this the longest lived damselfish species by two decades.

Mussels and canopy-forming algae as ecosystem engineers: their contribution to community organization in the rocky sublittoral

Understanding the influence of biogenic habitats on species assemblage structure and ecosystem productivity is crucial for successful conservation of natural systems. Brown algae, Fucus vesiculosus, and blue mussels, Mytilus trossulus, coexist on sheltered and moderately wave exposed shallow rocky reefs of the northern Baltic Proper. Here, they function as important biogenic structures for an abundant associated macroinvertebrate fauna. Despite their dominance and space sympatry, there is little understanding of how they differ in their role as provisioners of biodiversity in this system. While Fucus has been recognized as an important habitat provider for decades, the similar role of blue mussels has been seriously understudied in the northern Baltic Proper, leading to pressing knowledge gaps and an underestimation of their role for overall biodiversity. In this study, we compared macroinvertebrate species assemblages within 40 rocky reefs where Fucus and Mytilus co-occur in either intermixed or adjacent assemblages. We show that both habitats represent a species rich and abundant community that are comparable regarding diversity. However, abundance and biomass of the associated community is much higher in the Mytilus habitat in relation to the Fucus habitat, implying a far higher secondary production in the former habitat. Recognizing key habitats and understanding how they differ in their ability to support biodiversity and ecosystem productivity is necessary for predicting community responses to human pressures, including an altered climate, and for implementing efficient mitigation actions to minimize loss of biodiversity.

Kelp Patch-Specific Characteristics Limit Detection Capability of Rapid Survey Method for Determining Canopy Biomass Using an Unmanned Aerial Vehicle

Kelp forests dominate autotrophic biomass and primary productivity of approximately 30,000 to 60,000 km of shallow temperate and Arctic rocky reef coastline globally and contribute significantly to carbon cycling in the coastal ocean. Rapid biomass turnover is driven by very high growth rates and seasonal environmental drivers. As a result, kelp biomass varies greatly with time, space, and by species. In the northeast Pacific region, bull kelp (Nereocystis leutkeana) and giant kelp (Macrocystis pyrifera) form extensive floating surface canopies with a distinct spectral signature compared to the surrounding water. Studies have shown that remote sensing is advantageous for deriving large-scale estimates of floating surface canopy biomass, which comprises more than 90% of bull and giant kelp standing stock. However, development and validation of remotely derived kelp canopy biomass is lacking because existing approaches are time intensive and costly. This study attempted to close that gap by developing a rapid survey design utilizing diver and unmanned aerial vehicle (UAV) imagery across six sites in northern and central California. Kelp sporophytes were collected and measured for morphometric characteristics and genera-specific allometry to canopy biomass. Kelp density was measured using in situ diver surveys and coupled with UAV imagery to quantify kelp canopy biomass at a range of ground sampling distances. We successfully estimated kelp canopy biomass from UAV imagery at 33% (2/6) of the survey sites, but consistently determining canopy biomass via this approach was challenged by both survey design and kelp patch-specific spatial characteristics. The morphologies of bull kelp in Monterey were significantly different than other regions measured, but further work should be conducted to fully characterize differences in canopy biomass at the regional and sub-regional scale. We use this opportunity to suggest survey design strategies that will increase the success of future methodological development of UAV biomass retrieval. We also recommend developing long-term, annual genera-specific monitoring programs across the northeast Pacific region and beyond to validate remote sensing derived biomass estimates beyond the small number of existing well-characterized sites.

New octocoral records for the Ecuadorian Tropical Eastern Pacific

ABSTRACT The genus Muricea, a highly speciose gorgonian coral group in the Tropical Eastern Pacific (TEP), is commonly found on shallow rocky reefs including Machalilla National Park (MNP), El Pelado Marine Reserve (REMAPE) and Galápagos Marine Reserve (GMR). Here, we report the presence of M. hebes, M. echinata and M. robusta, which have been not previously reported at the REMAPE area and along the Ecuadorian region. These new records for Muricea hebes (Verril, 1864) in Ecuador broaden the known geographical distribution of these species across the tempered waters of California and Mexico, and the Tropical Eastern Pacific, belonging to Panama and Ecuador. Muricea robusta (Verril, 1864) was previously recorded in Mexico and Colombia, whereas M. echinata (Verril, 1866) was only found in Panama. This report contributes to increasing the knowledge of marine diversity in Ecuador, and broadens the previously recorded geographic distribution of the genus Muricea throughout the TEP.

Rocky reef biodiversity survey: Punta Pardelas, Argentina.

BackgroundTemperate rocky reefs in the SW Atlantic are productive areas that support highly diverse communities of invertebrates, algae and fishes. Rocky outcrops form complex structures which offer a diversity of microhabitats that lead to a great variety of co-existing species. Subtidal biodiversity within the Natural Protected Area Península Valdés is largely unexplored and studies are mainly limited to fish. A total of 560 high definition photoquadrats from seven rocky reefs (1-25 m depth) at Punta Pardelas were obtained during March 2019. In total, 4491 occurrences were recorded and identified to phyla (n = 2), superclasses (n = 1), classes (n = 5), subclasses (n = 2), orders (n = 2), families (n = 1), subfamilies (n = 1), genera (n = 10) and species (n = 43) levels. This dataset was developed to provide a baseline inventory of Punta Pardelas inside the Natural Protected Area, that was only partially reported more than 50 years ago. Such data represent the first step towards monitoring these less-accessible ecosystems.New informationMost of the available information about Atlantic Patagonian marine biodiversity is related to rocky intertidal communities or rocky reef fish communities. Despite having more than 4000 km of coastline, in the last 20 years only four studies have focused on subtidal benthic communities from shallow rocky reefs in Argentina (Genzano et al. 2011, Rechimont et al. 2013, Bravo et al. 2015, Bravo et al. 2020a). However, none of them described the epi-benthic community of different surface orientations on the rocky reefs. This dataset includes several surface orientations (i.e. horizontal, vertical, overhang and cave floor) and their microhabitats. We found almost double the number of taxa previously reported for the area. Through stratified sampling of different surface orientations, we recorded species that are often overlooked and thus registered as part of the existing biodiversity. For example, overhang surfaces in our study showed a unique assemblage and a great diversity of sponges. This work will be valuable as baseline information that is currently out of date in Nuevo Gulf rocky reefs.

Dominance of Scorpaena maderensis among scorpaenids of littoral rocky reefs in Corsica (NW Mediterranean): Further evidence of Mediterranean Sea warming.

The population of Scorpaenidae was investigated in the Nature Reserve of Scàndula (Corsica, France, NW Mediterranean). While absent from Corsica a few decades ago, the Madeira rockfish Scorpaena maderensis is now the most abundant scorpaenid species in shallow rocky reef areas, far outnumbering Scorpaena notata and Scorpaena porcus. Considered as a subtropical species of Atlantic origin, the northward progression of the thermophilic S. maderensis and its dominance in Corsican waters is further evidence of the ongoing warming of the Mediterranean Sea.

Marine diversity in the biosphere reserve of the most oceanic island in the Gulf of California: San Pedro Mártir.

San Pedro Mártir island is of high biological, ecological, and fishery importance and was declared a biosphere reserve in 2002. This island is the most oceanic in the Gulf of California, and information on its rocky reefs is scarce. The present study aimed to generate the first list of conspicuous invertebrate and fish species based on in situ observations and to examine the community structure of the shallow rocky reefs of the reserve. In addition, we estimated the ecological indicators of richness, abundance, Shannon diversity, and Pielou evenness to evaluate the conservation status of the biosphere reserve. Data were collected annually from 2007 to 2017 through 2,192 underwater SCUBA transects. A total of 35 species of invertebrates and 73 species of fish were recorded. Most of the species are widely distributed along the eastern Pacific. Overall, 64% of the species found in this study are commercially important, and 11 species have been listed as protected. The abundance of commercially important invertebrate species (i.e., the sea cucumber Isostichopusfuscus and the spiny oyster Spondyluslimbatus) is decreasing, while commercially important fish species have maintained their abundance with periods of increase. The ecological indicators and the abundance and size of the commercial species indicate that the reserve is in good condition while meeting its conservation objectives.

A multi-locus approach to elucidating the evolutionary history of the clingfish Tomicodon petersii (Gobiesocidae) in the Tropical Eastern Pacific

Marine species that are widely distributed in the Tropical Eastern Pacific (TEP) has served as a model for studying biogeographic patterns resulting from the effects of intraregional habitat discontinuities and oceanographic processes on the diversification and evolution of cryptobenthic reef fishes. Tomicodon petersii, a clingfish (Gobiesocidae) endemic to the TEP, is found on very shallow rocky reefs from central Mexico to northern Peru, and in the Cocos and Galapagos islands. We evaluated the effect of likely biogeographic barriers in different parts of the TEP on the diversification process of this species. We used one mitochondrial and three nuclear DNA markers from 112 individuals collected across the distribution range of T. petersii. Our phylogenetic results showed the samples constituted a monophyletic group, with three well-supported, allopatric subgroups: in the Mexican province, the Panamic province (from El Salvador to Ecuador), and the Galapagos Islands. The split between the Mexican and more southerly clades was estimated to occur at the end of the Miocene ca. 5.74 Mya, and the subsequent cladogenetic event separating the Galapagos population from the Panamic population at the junction of the Pliocene and Pleistocene, ca. 2.85 Mya. The species tree, Bayesian species delimitation tests (BPP), STACEY, and substantial genetic distances separating these three populations indicate that these three independent evolutionary units likely include two unnamed species. The cladogenetic events that promoted the formation of those genetically differentiated groups are consistent with disruptive effects on gene flow of habitat discontinuities and oceanographic processes along the mainland shoreline in the TEP and of ocean-island isolation, in conjunction with the species intrinsic life-history characteristics.

The Three-Dimensional Structure of Mediterranean Shallow Rocky Reefs: Use of Photogrammetry-Based Descriptors to Assess Its Influence on Associated Teleost Assemblages

In the Mediterranean Sea, shallow rocky reefs and the associated three-dimensional (3D) structure support rich and abundant communities; they are therefore of functional importance, in particular for the renewal of fish stocks. However, these habitats and their functions are likely to be altered by anthropogenic pressures inducing habitat transformations. It is therefore necessary to assess their 3D structure, their transformations and relationship to communities, especially for management and conservation purposes. In this article we aimed (i) to compare two methods that quantify the metrics of the 3D structure (rugosity) of shallow rocky reefs (chain-and-tape method and photogrammetry), and (ii) to quantify the possible links between this habitat structure and the fish assemblages. We found that photogrammetry and the chain-and-tape method yielded a similar estimate of rugosity, but photogrammetry was the most efficient method in terms of measurement quality and time (when considering in-water acquisition). This method also displayed the best repeatability. The 3D habitat descriptors (mean surface rugosity, variation of surface rugosity, and depth) differed significantly between the studied sites and were therefore included as covariables. Total fish abundance and species richness increased with higher mean surface rugosity. In addition, the composition of fish assemblages was significantly influenced by surface rugosity, although this effect was modulated by depth. When focusing on specific taxa, neither density patterns nor size class distributions displayed clear patterns in relation to rugosity metrics. However, this study demonstrated that spatial variability of teleost fish assemblages can be explained by habitat rugosity which probably increases the number of shelters and food resources, and therefore improves chances of survival. In addition, our study has shown that photogrammetry is an appropriate method to assess 3D structure metrics in a temperate rocky reef.

Using qualitative data to classify reef fishes into dietary guilds

AbstractClassification of species into dietary guilds that consume similar food resources can provide a useful framework for understanding ecosystem function. Traditionally, species were assigned to guilds qualitatively rather than quantitatively, largely due to a lack of detailed data on the diets of many species. More recently, detailed dietary data are collected and analysed quantitatively to produce a classification, but the collection of such data is intensive and usually limits a study to a small number of species. Here, we show that quantitative classifications can be built from qualitative data sourced from natural history texts and expert knowledge for well‐known fauna. We collected available data on the presence or absence of nine broad food item categories in the diets of 158 species of fish observed on New Zealand’s shallow rocky reefs. These data were analysed using multivariate statistical methods pioneered by K. R. Clarke and colleagues for use with site‐by‐species ecological survey data. In particular, we adapted a taxonomic dissimilarity measure to take into account a natural hierarchy of the food items, so that, for example, the diets of two species that consume different types of invertebrates were considered more similar to each other than those of, say, invertivores vs piscivores, or carnivores vs herbivores. Our analysis produced five distinct dietary guilds: Herbivore (9 species), Omnivore (11), Invertivore (80), Macro‐carnivore (52) and Piscivore (6). We suggest that invertivores, which made up around half of the species, are likely underrepresented in many studies due to the exclusion of smaller species. The approach of collecting broadly available qualitative data and applying modern multivariate quantitative methods to produce more inclusive dietary classifications may be usefully applied to other well‐known taxonomic groups for which detailed data are scarce.

Triennial migration and philopatry in the critically endangered soupfin shark Galeorhinus galeus

Abstract Globally, one quarter of shark and ray species are threatened with extinction due to overfishing. Effective conservation and management can facilitate population recoveries. However, these efforts depend on robust data on movement patterns and stock structure, which are lacking for many threatened species, including the Critically Endangered soupfin shark Galeorhinus galeus, a circumglobal coastal‐pelagic species. Using passive acoustic telemetry, we continuously tracked 34 mature female soupfin sharks, surgically implanted with coded acoustic transmitters, for 7 years via 337 underwater acoustic receivers stationed along the west coast of North America. These sharks and an additional six were also externally fitted with spaghetti identification tags. Our tagging site was a shallow rocky reef off La Jolla (San Diego County), California, USA, where adult females were observed to aggregate every summer. Tagged soupfin sharks were highly migratory along the west coast of North America, between Washington, USA and Baja California Sur, Mexico. However, every 3 years, they returned to waters off La Jolla, California, where they underwent gestation. This is the first conclusive evidence of triennial migration and philopatry (‘home‐loving’) in any animal, which is apparently driven by this species’ unusual triennial reproductive cycle. Females of other shark and ray species with triennial reproductive cycles are also likely to exhibit triennial cycles of migration and philopatry. At least six (15%) of our tagged soupfin sharks were killed in commercial gillnets in Mexico. Policy implications. Identifying multiennial migratory cycles in mature female sharks can reveal hidden stock structure in the form of discrete breeding cohorts, which are spatially and temporally segregated as they cycle through different reproductive phases. Accounting for this complexity may improve the performance of spatially structured stock assessment models, particularly when fishery removals are spatially heterogeneous, as well as inform the spatiotemporal design of fishery‐independent surveys. In the United States, the soupfin shark is neither actively managed nor recognized as a Highly Migratory Species; however, given the highly migratory behaviour we report, this designation should be revisited by the US Pacific Fishery Management Council. Finally, given the extensive fishery removals in Mexico, any future management must be internationally cooperative.

The neglected role of omnivore fish in the overgrazing of Mediterranean rocky reefs

Sea urchins are considered the most important grazers in Mediterranean shallow sublittoral rocky reef ecosystems, but fish can also have an important role in overgrazing and the reduction of habitat complexity. In this study, the trophic behavior of fish was recorded when provided access to experimental surfaces with increased macroalgal biomass and associated benthic fauna, created by herbivore exclusion cages. After a sufficient period for substantial algal growth, the cages were removed and the activity of fish on these surfaces was recorded for 3 h by an automated photographic camera system. Control surfaces with no restriction on grazers were defined on similar substrates for comparison. To quantify the effects of fish feeding activity on macroalgal coverage, photographic samples were taken immediately after the opening of the cages and after each 3 h recording. The response of fish when the cages were removed was immediate and intense. Feeding activity by 13 different fish species was recorded in total, of which the most frequent were the omnivores Diplodus vulgaris, Coris julis and Thalassoma pavo, and to a lesser extent the herbivore Sarpa salpa. The coverage of erect algae was substantially decreased on the experimental surfaces due to fish feeding activity. The algae were either directly consumed by the fish or cut off when the fish were feeding on macroinvertebrates. We conclude that in addition to grazing by herbivores, fish of higher trophic levels can also significantly affect macroalgal assemblages and restrict the recovery of erect algae in overgrazed reefs where prey is scarce.