Non‐Linear Thresholds Characterize the Relationship Between Reef Fishes and Mangrove Habitat

A significant obstacle to evaluating the importance of mangrove habitat to coral reef fishes has been the difficulty of disentangling its effects from other subtidal/nearshore habitats or human population pressures. Florida\u27s seascape, unlike most others, has been extensively surveyed and mapped, and there are reliable estimates of human population density. Despite many studies that have correlated reef fish abundance with nearby mangrove habitat, some researchers continue to question the importance of mangroves to reef fishes. Previous studies that have investigated the mangrove–reef fish subsidy effect have applied methods that either compared averages or examined linear relationships; yet there is a body of literature that indicates that the effects of habitat are characterized by thresholds and limiting functions. Here, we employed a generalized additive model to investigate whether species richness of 106 mangrove‐associated reef fishes is related to thresholds in the extent of nearby mangrove forests along the Florida Keys Reef Tract. In addition, we used linear discriminant analyses (LDAs) to examine the relationships between the occurrence of 77 reef fish species and extent of Florida mangrove forests. We found that after accounting for confounding factors, at scales \u3c20 km2, species richness declines with decreasing mangrove extent, whereas richness increases with increasing mangrove extent at scales \u3e80 km2. Results of our LDA suggested that at least 49 reef fish species (64% of focal species) were associated with higher nearby mangrove forest extent. Our results indicate that of all habitat attributes considered, mangroves played the most substantial role in the diversity of nearby reef fish populations. These apparent thresholds (i.e., non‐linearities) in the extent of mangrove forests should be incorporated into fisheries critical habitat management and emphasize the need to consider non‐linear relationships between fishes and their habitat

Regional differences in an established population of invasive Indo-Pacific lionfish (Pterois volitans and P. miles) in south Florida

About nine years ago (circa 2009), Indo-Pacific lionfishes (Pterois volitans and P. miles) invaded the south Florida coral reef ecosystem. During the intervening period of time, there has been substantial research on their biology, life history, demography, and habitat preferences; however, little is known concerning their regional population status and trends in the region. Here, we use a large-scale fisheries independent reef fish visual survey to investigate lionfish population status among three south Florida regions: Dry Tortugas, Florida Keys, and southeast Florida. Density estimates (ind ha−1) have been relatively stable since 2012, and are lower than other areas reported in the western Atlantic and Caribbean Sea. Low, stable population densities in south Florida suggest there may be a natural mechanism for lionfish population control. In the Dry Tortugas, lionfish density in 2016 was significantly lower (0.6 ind ha−1 ± 0.15 SE) than the two other south Florida regions. The Dry Tortugas region has the highest percentage of marine protected areas, the lowest level of exploitation, and thus the highest densities of potential lionfish predators and competitors. In the Florida Keys and southeast Florida in 2016, lionfish densities were greater (5.4 ind ha−1 ± 1.0 SE and 9.0 ± 2.7 SE, respectively) than the Dry Tortugas. Fishing pressure on lionfish was higher in these two regions, but densities of several potential predators and competitors were substantially lower. Despite relatively low regional lionfish densities that can be attributed to some combination of fishing mortality and natural biocontrol, lionfish are still well established in the south Florida coral reef ecosystem, warranting continued concern

Comparative Use of a Caribbean Mesophotic Coral Ecosystem and Association with Fish Spawning Aggregations by Three Species of Shark

Understanding of species interactions within mesophotic coral ecosystems (MCEs; ~ 30–150 m) lags well behind that for shallow coral reefs. MCEs are often sites of fish spawning aggregations (FSAs) for a variety of species, including many groupers. Such reproductive fish aggregations represent temporal concentrations of potential prey that may be drivers of habitat use by predatory species, including sharks. We investigated movements of three species of sharks within a MCE and in relation to FSAs located on the shelf edge south of St. Thomas, United States Virgin Islands. Movements of 17 tiger (Galeocerdo cuvier), seven lemon (Negaprion brevirostris), and six Caribbean reef (Carcharhinus perezi) sharks tagged with acoustic transmitters were monitored within the MCE using an array of acoustic receivers spanning an area of 1,060 km2 over a five year period. Receivers were concentrated around prominent grouper FSAs to monitor movements of sharks in relation to these temporally transient aggregations. Over 130,000 detections of telemetered sharks were recorded, with four sharks tracked in excess of 3 years. All three shark species were present within the MCE over long periods of time and detected frequently at FSAs, but patterns of MCE use and orientation towards FSAs varied both spatially and temporally among species. Lemon sharks moved over a large expanse of the MCE, but concentrated their activities around FSAs during grouper spawning and were present within the MCE significantly more during grouper spawning season. Caribbean reef sharks were present within a restricted portion of the MCE for prolonged periods of time, but were also absent for long periods. Tiger sharks were detected throughout the extent of the acoustic array, with the MCE representing only portion of their habitat use, although a high degree of individual variation was observed. Our findings indicate that although patterns of use varied, all three species of sharks repeatedly utilized the MCE and as upper trophic level predators they are likely involved in a range of interactions with other members of MCEs

Rapid Invasion of Indo-Pacific Lionfishes (\u3cem\u3ePterois Volitans\u3c/em\u3e and \u3cem\u3ePterois Miles\u3c/em\u3e) in the Florida Keys, USA: Evidence from Multiple Pre- and Post-Invasion Data Sets

Over the past decade, Indo-Pacific lionfishes, Pterois volitans (Linnaeus, 1758) and Pterois miles (Bennett, 1828), venomous members of the scorpionfish family (Scorpaenidae), have invaded and spread throughout much of the tropical and subtropical northwestern Atlantic Ocean and Caribbean Sea. These species are generalist predators of fishes and invertebrates with the potential to disrupt the ecology of the invaded range. Lionfishes have been present in low numbers along the east coast of Florida since the 1980s, but were not reported in the Florida Keys until 2009. We document the appearance and rapid spread of lionfishes in the Florida Keys using multiple long-term data sets that include both pre- and post-invasion sampling. Our results are the first to quantify the invasion of lionfishes in a new area using multiple independent, ongoing monitoring data sets, two of which have explicit estimates of sampling effort. Between 2009 and 2011, lionfish frequency of occurrence, abundance, and biomass increased rapidly, increasing three- to six-fold between 2010 and 2011 alone. In addition, individuals were detected on a variety of reef and non-reef habitats throughout the Florida Keys. Because lionfish occurrence, abundance, and impacts are expected to continue to increase throughout the region, monitoring programs like those used in this study will be essential to document ecosystem changes that may result from this invasion

A quantitative assessment of the status of reef fish communities from a large-scale probability survey in southern Florida

Numerous reef fish monitoring programs worldwide produce the data necessary to describe the status and trends of coral reefs; however, quantitative description of status at ecosystem scales has been challenging. Our goal was to use southern Florida’s coral reefs as the template to complete a holistic, ecosystem-scale evaluation of reef fish community status using large-scale diver surveys that sampled across a spatial gradient of human urbanization, exploitation, and fishery protection. Key aspects of the analysis were: (i) identification of a low human impact reference area as the basis for quantifying resource condition; (ii) selection of indicator variables that helped discriminate two classes of impacts: habitat quality and fishing; (iii) application of estimation methods that facilitated distinguishing anthropogenic impacts from inherent productivity of different habitats; and (iv) use of a sustainability benchmark to gauge the resource condition of the reference area. The reference-centering analysis approach reduced reliance on qualitative judgements by an expert panel and outputted results on a scale that was informative and could be easily interpreted by a variety of audiences. Our findings identified habitat quality issues in the most urbanized region, southeast Florida, and pervasive fishing issues throughout the ecosystem, including the remote Dry Tortugas region

Temporal and spatial dynamics of Lutjanus cyanopterus (Pisces: Lutjanidae) and L. jocu spawning aggregations in the United States Virgin Islands

The Grammanik bank is a deep reef (35-40 m) located approximately 14 km south of St. Thomas USVI, on the southern edge of the Puerto Rico shelf. The relatively narrow 1.5 km long reef annually hosts spawning aggregations of several species of groupers, snappers and jacks. Until February of 2005, when temporary seasonal protection was offered by the Caribbean Fisheries Management Council, the bank was subject to moderate or heavy exploitation from fishers. Cubera snapper (Lutjanus cyanopterus) were observed aggregating on the Grammanik bank in relatively large numbers from 2003 to 2005 and dog snapper (L. jocu) aggregations were observed in 2005. The arrival and departure of these aggregations appeared to be seasonal and to revolve around the moon phase. Cubera snapper spawning seasonality coincided with that elsewhere in the Caribbean and off south Florida. Schools of up to 1000 fish of each species were observed as well as pre-spawning behavior and milt release. Aggregations of both species showed high site fidelity within seasons but cubera snapper aggregations sites moved between seasons. The authors recommend year-round closure of the Grammanik bank based on its importance as critical fish habitat and a multi-species aggregation area. Rev. Biol. Trop. 54 (Suppl. 3): 69-78. Epub 2007 Jan. 15.El banco Grammanik es un arrecife profundo (35-40 m) ubicado aproximadamente 14 km al Sur de St. Thomas (Islas Vírgenes EUA), en el límite sur de la plataforma de Puerto Rico. Este arrecife relativamente angosto y de 1.5 km de longitud, recibe anualmente agrupaciones de varias especies de meros, pargos y jureles, durante sus desoves. Fue objeto de explotación de moderada a alta por parte de los pescadores hasta febrero del 2005, cuando el Consejo de Pesca del Caribe le ofreció protección temporal. El pargo cubera (Lutjanus cyanopterus) fue observado en el banco Grammanik en agrupaciones numerosas entre el año 2003 y el 2005, a su vez, agrupaciones del pargo perro o pargo caucha (L. jocu) se observaron en el 2005. La llegada y partida de estos grupos parece ser estacional y estar relacionada con la fase lunar. El desove estacional del pargo cubera coincide con informes de otros sitios del Caribe y al Sur de la Florida, donde se observaron cardúmenes de hasta 1000 peces de cada especie, así como comportamientos previos al desove y liberación de esperma. Agrupaciones de ambas especies mostraron alta fidelidad al sitio en una misma estación, pero los sitios de agrupación del pargo cubera cambiaron entre estaciones. Los autores recomiendan el cierre del banco Gammanik durante todo el año, basados en su importancia como hábitat crítico para los peces y por ser un área de agrupación para múltiples especies

Reproductive Biology and Behavior Associated With a Spawning Aggregation of the Yellowfin Grouper \u3ci\u3eMycteroperca venenosa\u3c/i\u3e In the US Virgin Islands

The reproductive characteristics, movement patterns and courtship behaviors associated with a yellowfin grouper (Mycteroperca venenosa, Linnaeus, 1758) fish spawning aggregation (FSA) were assessed between 2004 and 2014. The FSA was located on the Grammanik Bank, a seasonally closed area on the edge of the Puerto Rico platform, south of St. Thomas, US Virgin Islands. Fish arrived at the FSA site around full moon and departed 10–12 days after full moon (dafm), during two or three consecutive months, from January to May each year. Males were significantly larger than females and preceded females at the spawning site. Courtship coloration and behaviors showed distinct patterns relative to lunar date and time of day. Spawning was observed for several days each month in 2008, 2009, 2011 and 2014, from 6 to 10 dafm. Female gonadosomatic index (GSI) values were highest from 4 to 7 dafm. Spawning, which began at sunset, consisted of 7 to 12 males following one female along the bottom before ascending 10–20 m, then rushing upward to release gametes. Histological analysis of ovaries indicated females spawned every 2–3 nights, although 11.6% were capable of spawning two consecutive nights. Total spawning population size of yellowfin grouper fluctuated from 600 to 1100 fish during the study period, but consistent annual population assessments using scuba were difficult to carry out due to ocean conditions. Based on size-frequency analysis and other metrics, the M. venenosa spawning population at the Grammanik bank appears to be stable at this time with existing regulations

The Ups and Downs of Coral Reef Fishes: The Genetic Characteristics of a Formerly Severely Overfished but Currently Recovering Nassau Grouper Fish Spawning Aggregation

The Nassau grouper (Epinephelus striatus) has sustained large declines across its distribution, including extirpation of many of its fish spawning aggregations (FSAs). Within US Virgin Islands (USVI) waters, Nassau grouper FSAs were overfished until their disappearance in the 1970s and 1980s. In the early 2000s, however, Nassau grouper were found gathering at Grammanik Bank, USVI, a mesophotic coral reef adjacent to one of the extinct aggregation sites, and regulatory protective measures were implemented to protect this fledgling FSA. The population genetic dynamics of this rapid FSA deterioration followed by protection-facilitated, incipient recovery are unknown. We addressed two objectives: (1) we explored which factors (i.e., local vs. external recruitment) might be key in shaping the USVI FSA recovery; and (2) we examined the consequences of severe past overfishing on this FSA’s current genetic status. We genotyped individuals (15 microsatellites) from the USVI FSA comprising three successive spawning years (2008–2010), as well as individuals from a much larger, presumably less impacted, Nassau grouper FSA in the Cayman Islands, to assess their comparative population dynamics. No population structure was detected between the USVI and Cayman FSAs (FST = −0.0004); however, a temporally waning, genetic bottleneck signal was detected in the USVI FSA. Parentage analysis failed to identify any parent–offspring matches between USVI FSA adults and nearby juveniles, and relatedness analysis showed low levels of genetic relatedness among USVI FSA individuals. Genetic diversity across USVI FSA temporal collections was relatively high, and no marked differences were found between the USVI and Cayman FSAs. These collective results suggest that external recruitment is an important driver of the USVI FSA recovery. Furthermore, despite an apparent genetic bottleneck, the genetic diversity of USVI Nassau grouper has not been severely compromised. Our findings also provide a baseline for future genetic monitoring of the nascent USVI aggregation