Coral Gardens Reef, Belize: An \u3ci\u3eAcropora\u3c/i\u3e spp. Refugium under Threat in a Warming World

Live coral cover has declined precipitously on Caribbean reefs in recent decades. Acropora cervicornis coral has been particularly decimated, and few Western Atlantic Acropora spp. refugia remain. Coral Gardens, Belize, was identified in 2020 as a long-term refugium for this species. This study assesses changes in live A. cervicornis coral abundance over time at Coral Gardens to monitor the stability of A. cervicornis corals, and to explore potential threats to this important refugium. Live coral cover was documented annually from 2012– 2019 along five permanent transects. In situ sea-surface temperature data were collected at Coral Gardens throughout the study period and compared with calibrated satellite data to calculate Maximum Monthly Mean (MMM) temperatures and Degree Heating Weeks (DHW). Data on bathymetry, sediment, substrate, herbivore abundance, and macroalgal abundance were collected in 2014 and 2019 to assess potential threats to Coral Gardens. Live coral cover declined at all five transect sites over the study period. The greatest loss of live coral occurred between 2016 and 2017, coincident with the earliest and highest maxi- mum average temperatures recorded at the study site, and the passage of a hurricane in 2016. Structural storm damage was not observed at Coral Gardens, though live coral cover declined after the passage of the storm. Uranium-thorium (230Th) dating of 26 dead in situ fragments of A. cervicornis collected in 2015 from Coral Gardens revealed no correlation between coral mortality and tropical storms and hurricanes in the recent past. Our data suggest that several other common drivers for coral decline (i.e. herbivory, predation, sedimentation, pH) may likely be ruled out for Coral Gardens. At the end of the study period, Coral Gardens satisfied most criteria for refugium status. However, the early onset, higher mean, and longer duration of above-average temperatures, as well as intermittent temperature anomalies likely played a critical role in the stability of this refugium. We suggest that temperature stress in 2016 and perhaps 2015 may have increased coral tissue vulnerability at Coral Gardens to a passing hurricane, threatening the status of this unique refugium

Development of movement models to assess the spatial dynamics of marine fish populations

A simulation model is constructed which considers the population dynamics of bonefish, Albula vulpes, in a spatio-temporally articulated seascape using biological and physical environmental data describing Biscayne Bay. A sub-model of behavioral movement of bonefish in response to environmental cues is employed to describe the dynamic distribution of individual bonefish cohorts relative to features of their habitat. This sub-model is developed from a generalized framework based upon principles of kinesis behavior described herein. The function and performance of the movement model in acquisition of spatial resources for growth is analyzed with respect their subsequent influence on bonefish stock dynamics predicted in simulation. Two other movement behaviors are inserted in simulation for comparison of results: (1) random walk; and (2) a model of restricted-area search behavior. Simulations are designed to test the null hypothesis that population dynamics are not significantly influenced by the assumptions of the behavioral movement sub-model. The results of simulations are compared to elucidate the effect behavioral assumptions of movement and their practical application in simulation may have on stock dynamic simulations incorporating the spatial interactions of fish and habitat. It is demonstrated that implicit differences in a priori assumptions of behavioral movement can significantly affect stock dynamics predicted in simulation. The implications of simulation results on existing hypotheses of bonefish biology and stock dynamics are considered, which lead to recommendations for further coordinated efforts in both modeling and empirical studies. It is concluded that assumptions dictating movement behavior can significantly influence the population dynamics predicted in simulation, yet support of assumptions can be difficult to demonstrate from empirical data. It is submitted that a minimalist approach be adopted with respect to cognitive mechanisms in the design of behavioral movement models for incorporation into simulations of fish population dynamics

Geologic Analyses for Evaluating Watershed Heterogeneity: Implications for Otolith Chemistry Studies

Abstract: Studies using otolith chemistry to distinguish fish stocks in fresh waters have suggested that spatial heterogeneity in basin geology determines the scale of stock discrimination possible with this approach. However, no studies have illustrated an association between spatial variation in fish otolith chemistry and watershed geology. We consider this relationship in the context of a recent study describing within-and between-river variation in trace element chemistry of otoliths from YOY smallmouth bass (Micropterus dolomieu) from the Maury and James rivers (Virginia). Cluster analysis of multivariate geologic data for discrete river segment basins illustrates a phenomenological association between geologic heterogeneity and our ability to discriminate spatial groupings of fish from their otolith chemistry. This analysis provides two significant results: 1) a starting point for considering the mechanistic relationship between watershed geology and fish otolith chemistry; and, 2) a framework for assessing basin heterogeneity prior to designing studies that use otolith chemistry to distinguish fish stocks in river-tributary networks. The latter can be used a priori to determine the efficacy of otolith chemistry comparisons and to guide sample collection over large spatial areas. In approximately the last decade, significant advances were made in analysis of fish "hard parts" (e.g., bones, scales, and spines) as records of water chemistry in areas inhabited by fish during their lifetimes Our objective in this paper is to determine if differences in basin geology correspond with successful discrimination of fish origins in a recent study of otolith chemistry in riverine smallmouth bass (Micropterus dolomieu) populations. Trace element concentrations were used to successfully discriminate natal origins of age-0 smallmouth bass spawned in the James River or its tributary Maury River. The analysis was further able to differentiate among fish collected from different segments of the Maury River based on otolith chemistry. Here we compare the spatial resolution of fish origin discrimination in this previous study (summarized below for context) with patterns of land attribute variation across the study area as a first-order attempt to illustrate an association between otolith chemistry and basin geology. Using readily available spatial data analyzed in a GIS, we present a framework for characterizing geology of river segment basins and for quantifying dissimilarity among basins in the study area. We then use cluster analysis to group segment basins with similar geologic compositions, and compare results of clustering with our ability to distinguish fish origins among basins by otolith chemistry. We discuss our results in the context of applying these methods to guide experimental design and collection effort in future studies of otolith chemistry in river systems. Study Area and Otolith Chemistry Study The James River is a large (fifth order) river that runs from the Ridge and Valley physiographic province through the Coastal Plain. The Maury River is a smaller (fourth order) river that originates in the Ridge and Valley and terminates in the James River at the edge of the Blue Ridge province. The James River and its 13

Behavioral Assumptions in Models of Fish Movement and Their Influence on Population Dynamics

This study investigates the movement and growth of cohorts in a coastal fish stock by simulating animal responses to spatial heterogeneity of biotic and abiotic conditions in a dynamic marine landscape. A coastal bay is modeled using spatial and temporal data on prey distribution, benthic habitat, depth, and salinity. Prey abundance and salinity vary daily through an annual cycle to create a spatiotemporally dynamic environment with seasonal fluctuations in the quality and distribution of habitats favoring growth. Three movement behaviors—random walk, kinesis, and gradient response via restricted‐area search—simulate fish cohort movements in relation to environmental characteristics. A bioenergetic growth model is used to describe somatic growth by comparing spatiotemporally variable prey consumption rates and metabolic requirements. This facilitates evaluation of the way in which movement behavior influences the ability of cohorts to locate and occupy favorable habitats in a heterogeneous environment. Random movement behavior proved inefficient for locating preferable habitats and resulted in the lowest cohort growth trajectory and stock biomass per recruit. Kinesis and restricted‐area search behaviors resulted in similar spatial distributions and characteristics of stock biomass when cohorts were initially distributed at random. However, the results from the restricted‐area search simulations were highly sensitive to the initial positions of cohorts. The restricted‐area search simulations also resulted in high variation in growth rates among cohorts, reflecting complex interactions between behavioral mechanisms and the structure of local heterogeneity. The results show that movement models reflecting similar density patterns can differ in their influence on cohort growth and mortality. In particular, the presence of local optima can bias the results of movement models employing directional responses to a gradient structure. These results underscore the importance of sound theoretical assumptions in movement model construction and suggest that minimalism be adopted in the absence of empirical support for behavioral assumptions concerning animal responses to environmental cues

Schooling and migration of large pelagic fishes relative to environmental cues

A kinesis model driven by high‐resolution sea surface temperature maps is used to simulate Atlantic bluefin tuna movements in the Gulf of Maine during summer months. Simulations showed that individuals concentrated in areas of thermal preference. Results are compared to empirical distribution maps of bluefin tuna schools determined from aerial overflights of the stock during the same time periods. Simulations and empirical observations showed similar bluefin tuna distributions along fronts, although interannual variations in temperature ranges occupied suggest that additional foraging factors are involved. Performance of the model is further tested by simulating the relatively large‐scale annual north–south migrations of bluefin tuna that followed a preferred thermal regime. Despite the model’s relatively simple structure, results suggest that kinesis is an effective mechanism for describing movements of large pelagic fish in the expansive ocean environment