The importance of vegetative habitat in influencing distribution patterns, species interactions, and biodiversity is well documented in marine ecosystems, yet most previous studies on macroalgal–fish relationships have focused on influences of density and identity of macroalgae, often ignoring how the unique physical structure provided by each alga contributes to patterns. We tested whether the distribution, abundance, and biomass of rocky reef fishes could be predicted as well or better by measures of physical structure of macroalgae than by species identity and abundance. Divers visually sampled fishes and macroalgae at seven sites spread over several km at Santa Catalina Island, California, over a 1-year period, to examine how the distribution patterns of fishes related to spatiotemporal differences in the macroalgal assemblage. We found that variation in the composition, density, and diversity of the fish assemblage was equally or better explained by macroalgal structure (total surface area and height) than by macroalgal species density. In contrast, biomass and vertical distribution of fishes were better predicted by macroalgal species identity and density than by macroalgal physical structure. Of the macroalgal attributes, surface area was the best predictor of fish abundance and multivariate assemblage structure (species and their densities). However, much of the spatiotemporal variation in the fish assemblage was not explained by macroalgae, indicating that even in habitats visually dominated by macroalgae, macrophytes are only one of many factors that drive spatiotemporal variation in community structure. Our results suggest that quantifying the physical structure provided by marine macroalgae can be more useful than macroalgal species identity in predicting some aspects of fish assemblage structure.

California abalone Haliotis spp., listed as species of concern, have been slow to recover, after 22 years of fishery closure, or are not recovering at all because of low-density populations and recruitment failure. It is not known if there is successful recruitment in populations in the wild in Southern California. This work examines, for the first time, whether newly settled abalones (<3 mm) are present in the wild at Santa Catalina Island to determine if recruitment is occurring. Natural cobbles with crustose coralline algae cover were sampled for recently settled abalones at two sites and at three depths over the reproductive season of green and pink abalone. A total of 128 abalone recruits (Haliotis spp.) were found over a cumulative rock surface area of 7.47 m(2), on 325 cobbles, for a total recruitment density of 17.14 recruits per m2. Abalone recruits ranged in size from 220 to 2,120 mm, with an average recruit size of 490 +/- 20 mm (mean +/- SE, n = 124). Recruitment was similar across depths (2-4, 6-8, and 10-12 m) but differed between the two study sites, and was highest in June and September. Genetic work is needed to confirm species identification of the new recruits; however, they were most likely green abalone which would be consistent with the signs of green abalone recovery at the island. This work quantifies abalone settlement in Southern California, confirming successful recruitment. These methods can aid future restoration efforts empowering managers and restoration practitioners to monitor and quantify recruitment dynamics for abalones in California.

Most fishing methods are inherently size-selective, and many fisheries have minimum size limits, resulting in removal of the largest, most fecund size-classes of harvested species. Some modeling and correlative studies suggest protogynous (female-to-male sex changing) fishes may be particularly strongly impacted by removal of large individuals, but controlled experiments are necessary to test this expectation. By manipulating the density and size structure of populations of the blackeye goby (Rhinogobiops nicholsii) in the field via size-selective removals, this experiment aimed to identify the effects of size-selective harvesting on the (1) growth, (2) maturation, (3) sex change, and (4) reproductive output of a protogynous hermaphroditic reef fish that uses exogenous cues for sex change. Removals of ~ 25% of fish established in populations on standardized artificial reefs simulated a pulse of fishing mortality with minimum size limits, slot size limits, and maximum size limits, which are used in some fisheries. Size-selective removals had no statistically significant effects on the growth, maturation, sex change, or reproduction in blackeye gobies, indicating that this protogynous species is resilient to moderately intense size-selective removals. Some trends consistent with predicted effects of size-selective removals were present, but we had low power to detect some effects. Specifically, the rate of maturation was highest in the slot size limit treatment, and the rate of sex change was highest where large fish had been removed. Regardless of simulated fishing type, populations in all treatments exhibited similar size- and sex-structure by the end of the experiment, nearly two months after population structure had been manipulated. These results suggest that sequentially hermaphroditic fishes with exogenous cues for sex change may be able to quickly replace individuals with high reproductive value after experiencing moderately intense size-selective harvesting. However, experiments incorporating additional sex-changing species, particularly with different modes of reproduction and cues for sex change, as well as higher fishing intensities or longer durations of fishing are still necessary to reconcile differences in results reported herein and those from modeling and correlative studies.

Increasing abundance of arborescent octocorals (often referred to as gorgonians) on Caribbean reefs raises the question of whether habitat structure provided by octocorals can mediate a transition between coral- and algal- dominated states by increasing fish abundance and herbivory. This study tested the hypotheses that feeding rates and densities of demersal reef fishes are affected by the habitat structure provided by dense octocoral communities. Surveys of fishes on coral reefs in St John, US Virgin Islands, found 1.7-fold higher densities, and 2.4-fold higher feeding rates within versus outside of dense octocoral canopies. This difference, however, was only seen at sites with octocoral densities > 8 colonies m−2. Furthemore, the proximity of octocoral colonies to fish had an effect on the grazing rate of key herbivores (surgeonfishes and parrotfishes), with a 53% higher feeding rate (1.90 ± 0.11 bites min−1 m−2) near octocorals (< 20 or 30 cm, depending on the site) versus farther from them (1.24 ± 0.09 bites min−1 m−2). Finally, within the canopy of dense octocoral communities (17 colonies m−2), reef fishes fed at a rate that was 2.2-fold higher within the community than at the edge of the community that faced an adjacent sand patch. Fish abundance, however, was not uniformly higher within versus at the edge of the octocoral community, as ecotone specialists such as gobiids, blennioids, ostraciids, holocentrids, labrids, and pomacentrids were 1.3—2.3 times more abundant at the edge. In contrast, other taxa of demersal fishes, notably herbivores, were twice as abundant within octocoral communities than at the edges. Together, these results reveal an association between habitat structure created by octocorals on shallow reefs and increased feeding rates of demersal fishes (including those of herbivores). The potential of octocorals to increase herbivory that could mediate stony coral recovery is therefore worthy of further study.

Easter et al. used population models to analyze the expected pattern of recovery of sex-changing fish populations inside marine protected areas (MPAs). Many fishes begin life female and then change to male when older. In these female-first (protogynous) species, harvest tends to selectively remove males, shifting sex ratios and impairing reproduction. Setting expectations for population recovery inside MPAs requires understanding how quickly sex ratios (and reproduction) rebound. Easter et al. show that whether sex-changing populations recover faster or slower than non-sex-changing species depends on how many males a population needs for successful reproduction. This quantity can be estimated using field experiments. These photographs illustrate the article “Influence of protogynous sex change on recovery of fish populations within marine protected areas” by E. E. Easter, M. S. Adreani, S. L. Hamilton, M. S. Steele, S. Pang, and J. W. White published in Ecological Applications. https://doi.org/10.1002/eap.2070

Resource managers often outline discrete goals when implementing marine protected areas (MPAs), such as increases in organism abundance, biomass, or body size, to evaluate MPA success and thus inform future management decisions. Understanding which biological indicators are most sensitive to protection is essential for adaptive management, and while density is a commonly used metric to monitor MPAs, previous work has pointed to a lack of reliability of this metric to effectively evaluate MPAs, particularly during initial stages of protection. To determine which biological indicators of MPA success were evident 5 yr after protection began, we examined the differences in populations inside vs. outside MPAs for 3 fishes targeted by anglers—kelp bass Paralabrax clathratus, barred sand bass P. nebulifer, and California sheephead Semicossyphus pulcher—and 4 non-targeted species. We used stereo-video to determine the average body size, biomass, and density of each species in 7 MPAs in Southern California that were paired with nearby non-MPA sites. Responses of targeted species were detectable after 5 yr of protection in some MPAs. In most but not all MPAs, individuals were larger compared to outside MPAs for kelp bass and California sheephead. Biomass and density of targeted species appeared to be less sensitive to MPA effects. As expected, non-targeted species did not show evidence of MPA effects. Similar to past studies, our findings indicate that the choice of response variable and species studied may influence the perceived efficacy of MPAs, and we emphasize that increases in length may be a particularly sensitive indicator of effective protection.

Marine protected areas (MPAs) are increasingly implemented as a conservation tool worldwide. In many cases, they are managed adaptively: the abundance of target species is monitored, and observations are compared to some model-based expectation for the trajectory of population recovery to ensure that the MPA is achieving its goals. Most previous analyses of the transient (short-term) response of populations to the cessation of fishing inside MPAs have dealt only with gonochore (fixed-sex) species. However, many important fishery species are protogynous hermaphrodites (female-to-male sex-changing). Because size-selective harvest will predominantly target males in these species, harvesting not only reduces abundance but also skews the sex ratio toward females. Thus the response to MPA implementation will involve changes in both survival and sex ratio, and ultimately reproductive output. We used an age-structured model of a generic sex-changing fish population to compare transient population dynamics after MPA implementation to those of an otherwise similar gonochore population and examine how different features of sex-changing life history affect those dynamics. We examined both demographically open (most larval recruitment comes from outside the MPA) and demographically closed (most larval recruitment is locally produced) dynamics. Under both scenarios, population recovery of protogynous species takes longer when fishing was more intense pre-MPA (as in gonochores), but also depends heavily on the mating function, the degree to which the sex ratio affects reproduction. If few males are needed and reproduction is not affected by a highly female-biased sex ratio, then population recovery is much faster; if males are a limiting resource, then increases in abundance after MPA implementation are much slower than for gonochores. Unfortunately, the mating function is largely unknown for fishes. In general, we expect that most protogynous species with haremic mating systems will be in the first category (few males needed), though there is at least one example of a fish species (though not a sex-changing species) for which males are limiting. Thus a better understanding of the importance of male fish to population dynamics is needed for the adaptive management of MPAs.

Biological invasions can dramatically affect the ecology of invaded regions, and globally have resulted in economic damages that total billions of dollars annually. In recent years, an invasive alga, Sargassum horneri, has become established and spread along the coast of southern California (USA). Using field observations and a field experiment, we explored how this non-native alga influences the structure of fish assemblages on temperate reefs in southern California where S. horneri has become prolific. Fish and algal assemblages were quantified along transects on rocky reefs at depths of 3 and 6 m at 6-8 study sites spanning 5 km on 4 occasions over 1.5 yr. Spatiotemporal variation in the fish assemblage was not strongly correlated with the abundance of invasive S. horneri over this period, although it became less variable as native giant kelp Macrocystis pyrifera disappeared from the study sites due to a warm-water event, during which the invasive S. horneri became more dominant. An experiment removing a total of 4.25 t of S. horneri from 6 × 6 m plots (n = 14) revealed that the invasive alga did not affect fish abundance, species richness, species diversity (H’), or multivariate assemblage structure over a 5 mo period. Overall, we found little evidence of negative effects of S. horneri on fishes even though it drastically changed the underwater landscape. Nevertheless, we advise cautionary management actions to limit the movement of this invasive alga because its effects on other community members, such as other algal species, may be detrimental, and longer-term effects on fishes might develop.

To test life-history theory that body size and sex should influence how animals allocate time to foraging versus reproductive activities, we measured the effects of size and sex on courting success and foraging behaviour of black surfperch Embiotoca jacksoni off Santa Catalina Island, southern California. Observations of focal fish were made while snorkelling, during which the length of each fish (estimated to the nearest cm), total duration of courting encounters and foraging rates were recorded. We made observations during and outside the mating season. Courtship occurred only between pairs and its duration increased with the size of both the male and female. Although males would court females that were smaller or larger than themselves, pairs that were closely matched in size had long courting sessions, whereas those that differed considerably in size courted only briefly. Small fish foraged more than larger fish, both during and outside the mating season. Males and females foraged at similar rates outside of the mating season, but during the mating season males reduced their foraging rates to less than half that seen outside of the mating season, whereas females continued to forage at the same rate. This decrease in foraging rate of males during the mating season was seen in all sizes of males but was proportionally greatest in the largest males. These observations indicate that males trade off time spent on foraging for time spent courting during the mating season, whereas females do not.

Marine protected areas (MPAs) can be effective tools for marine resource management. However, despite evidence of the positive effects of MPAs, such as increases in body sizes of organisms targeted by fisheries, there is often heterogeneity in biological outcomes among them. Because fishing can drastically impact fish populations, the goal of this study was to determine if the levels of exploitation prior to protection could predict variation in the magnitude of MPA effects. Using a diver-operated stereo-video camera system, we compared sizes of fishes targeted by anglers within seven MPAs spanning the Southern California Bight to nearby comparison areas (non-MPAs). We used fine-scale data on pre-closure fishing pressure to test responses of fishes to protection along a gradient of exploitation. Fish size responded to protection in proportion to pre-closure fishing pressure, with MPAs in areas with high pre-closure fishing having greater responses in average lengths and size distributions than those in areas with low fishing pressure. This response was evident in species heavily targeted by recreational fishing, but not in species that were not targeted in fisheries. Synthesis and applications. Pre-closure fishing pressure of an area can impact the efficacy of MPAs, and, when available, should be considered when predicting and evaluating MPA performance. Prioritizing heavily exploited areas for protection when implementing spatial management tools could maximize ecological outcomes.

The reproductive and acoustic behaviours of Gulf grouper Mycteroperca jordani were studied at a spawning aggregation site in the southern Gulf of California, México. In May 2015-2017, divers located and surveyed a spawning aggregation site within Cabo Pulmo National Park. Adult M. jordani conformed to a lek mating system in which large males formed territories over sand adjacent to a rocky reef that were spatially segregated from smaller females outside of courtship and spawning periods. Females moved into male territories during evening hours to spawn. Male courtship behaviours targeted a single female, included head shakes and burst rises and preceded pair spawning prior to sunset. Males and females displayed three shared colour phases, but four phases were sex-specific. During evening hours, courtship and spawning, both sexes exhibited sexual dichromatism concurrent with reproductive behaviours. The pair-spawning mating system and observations of bimodal size distributions by sex support previous claims of protogyny in the species. Males produced sounds during territorial patrols, courtship and spawning rushes, which corroborated the importance of acoustic communication within the behavioural repertoire associated with spawning. Long-term acoustic monitoring revealed increases in total sounds detected day-1 from March through June with diel increases (e.g., evenings) that may be indicative of the spawning season. Observations of spawning on 12 consecutive evenings in May 2017 coupled with extended periods of sound production suggest that spawning does not follow a lunar rhythm. This first description of the mating system and sounds of the endangered M. jordani facilitates future development of seasonal and areal protections to restore and manage the species.

Macroalgae are key foundation species in temperate reef systems in part because their structure can transform the physical composition of the reef landscape. Previous assessments of the effects of algae on fishes have mostly focused on effects of changes in the density and identity of algae and often ignore how the unique structure provided by each alga contributes to such patterns. We performed a series of experiments and surveys to test the relative importance of algal size versus identity on the abundance, species richness, and behavior of fishes. In experiments, fish abundance and species richness did not differ among algal species but varied among sizes of algae. Fishes engaged in resting/refuging behavior were more abundant near tall than short algae, but the abundance of fishes engaged in feeding did not differ among sizes or species of algae. Field surveys of macroalgae occurring naturally on reefs detected similar patterns: fish abundance and richness were positively related to algal size, though there was considerable variation that was not explained by algal size. Differences in the fish community among algal species indicated that certain algae (e.g. Macrocystis pyrifera) were more important than others in providing habitat for fishes due to their size. Moreover, the influence of an invasive alga, Sargassum horneri, on the fish community appeared to be predictable based on its size. These results reveal that the importance of macroalgae as structural habitat for fishes may be more related to size than to species.

Some invasive species have devastating ecological impacts on native species, whereas others have little effect. The macroalga Sargassum horneri recently invaded the waters of California (USA) and Mexico, and in some places has largely replaced an important native macroalga, the giant kelp Macrocystis pyrifera. To explore the potential impacts of the invasive alga on populations of an ecologically and economically important fish, the kelp bass Paralabrax clathratus, we tested whether recruitment of kelp bass onto macroalgae differed between the invasive S. horneri and native M. pyrifera. Field surveys by scuba divers on naturally occurring S. horneri and M pyrifera at Santa Catalina Island revealed that kelp bass recruits were -30 times more abundant on individual M. pyrifera than on individual S. horneri. To assess the cause of this pattern, we conducted a field experiment in which plots containing 3 treatments (M. pyrifera only, S. horneri only, and M. pyrifera and S. horneri together) were isolated over a sandy bottom, which limited post-settlement movement of recently settled kelp bass among macroalgae. Kelp bass recruitment was similar for the 2 treatments containing M. pyrifera, but no recruits were observed on S. horneri, regardless of whether the alga was alone or paired with M. pyrifera. Additionally, we found a strong spatial gradient in recruitment among the experimental plots that was explained by the abundance of larger, cannibalistic conspecifics. This study presents the first evidence that invasive S. horneri may negatively impact an important reef fish.

Herbivore distribution can impact community structure and ecosystem function. On coral reefs, herbivores are thought to play an important role in promoting coral dominance, but how they are distributed relative to algae is not well known. Here, we evaluated whether the distribution, behavior, and condition of herbivorous fishes correlated with algal resource availability at six sites in the back reef environment of Moorea, French Polynesia. Specifically, we tested the hypotheses that increased algal turf availability would coincide with (1) increased biomass, (2) altered foraging behavior, and (3) increased energy reserves of herbivorous fishes. Fish biomass and algal cover were visually estimated along underwater transects; behavior of herbivorous fishes was quantified by observations of focal individuals; fish were collected to assess their condition; and algal turf production rates were measured on standardized tiles. The best predictor of herbivorous fish biomass was algal turf production, with fish biomass increasing with algal production. Biomass of herbivorous fishes was also negatively related to sea urchin density, suggesting competition for limited resources. Regression models including both algal turf production and urchin density explained 94 % of the variation in herbivorous fish biomass among sites spread over ~20 km. Behavioral observations of the parrotfish Chlorurus sordidus revealed that foraging area increased as algal turf cover decreased. Additionally, energy reserves increased with algal turf production, but declined with herbivorous fish density, implying that algal turf is a limited resource for this species. Our findings support the hypothesis that herbivorous fishes can spatially track algal resources on coral reefs.

The blackeye goby is a protogynous reef fish common to the northeastern Pacific Ocean. While this ubiquitous species has been the focus of numerous studies, there are several aspects of its reproductive ecology that are unknown. By directly quantifying reproduction from digital photographs of blackeye goby nests in the field, this study aimed to determine whether reproductive patterns were linked to 1) lunar phase or 2) ambient water temperature; and 3) whether the behavior of gobies changed when a nearby conspecific had eggs in his nest. At Santa Catalina Island, California, twenty 2.25-m2 artificial reefs were established and stocked with similar numbers and size-distributions of blackeye gobies during the summers of 2012 and 2013. Photographs of nests were taken weekly for ∼3 months each summer. Through analysis of photographs, incubation time was found to be more than 7 days but less than 14 days. Nests, each guarded by one male, contained an average of 8664 eggs, in an area of 43.8 cm2, with 215 eggs cm−2. Blackeye gobies laid eggs during all lunar phases and the number of eggs produced was not related to lunar phase. Reproductive output, however, was negatively correlated with water temperature, with populations on reefs that experienced cooler temperatures producing more eggs. The presence of eggs in a nest had little effect on behavior of blackeye gobies on that reef. Additional observations made outside of summer months indicated that blackeye gobies can reproduce year-round in southern California. These results suggest a reproductive strategy aimed at maximizing total reproductive output by spreading the risk of reproductive failure throughout the year rather than optimizing the timing of reproduction.

Variations in abiotic conditions across large latitudinal gradients can strongly influence the early life history of coastal marine organisms. We investigated the effects of temperature and latitude on the larval traits of 2 estuarine fish species. The arrow goby Clevelandia ios and the endangered tidewater goby Eucyclogobius newberryi were studied in 18 estuaries along the coast of California, spanning similar to 8 degrees of latitude. These 2 species were selected because of their dissimilar preferences for estuary type: the arrow goby prefers cooler, fully tidal systems, whereas the tidewater goby prefers warmer lagoons that experience some degree of seasonal isolation from the ocean. Recently settled individuals were collected from July to October 2011, and temperatures within each estuary were recorded to determine how temperature affected larval duration, settlement, and growth rates. Temperatures were more variable among estuaries inhabited by the tidewater goby (10 degrees C range) than among those inhabited by the arrow goby (5 degrees C range). Larval traits of both species differed among sites, but more so for the tidewater goby, a difference that was tied to the greater differences in temperatures among sites in the seasonally closed estuaries it inhabited. In both species, fish that experienced warmer temperatures had shorter larval durations and faster growth rates and were smaller at settlement. Since the length of the larval period has been related to survival and dispersal distance, future variations in temperature due to climate change could have predictable influences on population density and connectivity in estuarine species.

Artificial reefs are used to enhance populations of marine organisms, but relatively few studies have quantitatively evaluated which attributes of reef structure are most critical in determining whether assemblages of organisms on artificial reefs are similar to those on natural reefs. Using five pairs of artificial and natural reefs that spanned 225 km in the Southern California Bight, we evaluated how well fish assemblages on artificial reefs mimicked those on natural reefs and which attributes of reefs best predicted assemblage structure. Along underwater visual transects, we quantified fish species richness, density, and size structure, as well as substrate structure (rugosity and cover of substrate types), giant kelp density, and invertebrate density. Artificial reefs that were more similar in physical structure to natural reefs (low relief, low rugosity, and composed of small-to medium-sized boulders) supported fish assemblages that were similar to those on natural reefs. Fish species richness was not significantly different between artificial and natural reefs, but density and biomass tended to be higher on average on artificial reefs, body size was slightly smaller, and assemblage structure differed between the two reef types. Generally, artificial reefs extended higher off the seabed, were made of larger boulders, had higher rugosity, harboured more invertebrates, and supported less giant kelp. At both the within-reef (transect) and whole-reef scales, fish density and biomass were positively correlated with complex substrate structure, positively correlated with invertebrate density, and negatively correlated with giant kelp abundance, which was sparse or absent on most artificial reefs. Our results indicate that artificial reefs can support fish assemblages that are similar to those found on natural reefs if they are constructed to match the physical characteristics of natural reefs, or they can be made to exceed natural reefs in some regards at the expense of other biological attributes.

The early life history of the federally endangered Tidewater Goby (Eucyclogobius newberryi) and its sister species the Arrow Goby (Clevelandia ios) has been poorly documented to date. Both are endemic to estuarine habitats throughout the California coast, however, habitat use differs between these two species. The Arrow Goby is commonly found in fully marine tidal bays and mudflats. The Tidewater Goby, however, prefers lagoons with some degree of seasonal isolation from the sea. Here, we used otoliths to examine the larval duration, size at settlement, and growth rates of newly settled gobies collected from 18 estuaries in California. The Tidewater Goby had a larval duration that was ∼2 days shorter than the Arrow Goby (23.95 vs. 26.11 days, respectively), but a larger size at settlement based on back-calculated size (12.38 vs. 10.00 mm SL) due to a faster larval growth rate (2.86 vs. 2.60 µm/day−1). There are several reasons that could explain these differences in larval traits, such as differences in temperature or food resources between the two estuary types, or the faster, annual life cycle of the Tidewater Goby relative to the Arrow Goby.

Larval traits in reef fishes influence their probability of surviving after settling, but few studies have explored the extent to which selective mortality varies from site to site. We examined the effects of larval traits on the survival of Chromis viridis at 2 sites in Moorea, French Polynesia. We compared average traits of recently settled fish with those of 1 mo old survivors from the same cohort. At both study sites, there was selection for larger size at settlement. A commonly used statistical approach that does not account for correlations among larval traits (ANOVA) indicated that selection on planktonic larval duration (PLD) and larval growth rate was inconsistent between the 2 sites, with selection for PLD at one site and larval growth rate at the other. Larval growth rate and PLD, however, were strongly correlated, such that faster-growing larvae settled at younger ages at both sites. Selection gradient analysis, which accounts for correlations among larval traits, revealed that selection for longer PLD and faster larval growth rates occurred at both study sites but was stronger at one site than the other. We detected no significant differences in habitat characteristics or predator assemblages between the 2 sites. Our findings highlight the need to statistically control for correlations among larval traits when measuring selection, as well as the need to explore spatial variation in selection on larval traits.