Larval Connectivity and the International Management of Fisheries

Predicting the oceanic dispersal of planktonic larvae that connect scattered marine animal populations is difficult, yet crucial for management of species whose movements transcend international boundaries. Using multi-scale biophysical modeling techniques coupled with empirical estimates of larval behavior and gamete production, we predict and empirically verify spatio-temporal patterns of larval supply and describe the Caribbean-wide pattern of larval connectivity for the Caribbean spiny lobster (Panulirus argus), an iconic coral reef species whose commercial value approaches $1 billion USD annually. Our results provide long sought information needed for international cooperation in the management of marine resources by identifying lobster larval connectivity and dispersal pathways throughout the Caribbean. Moreover, we outline how large-scale fishery management could explicitly recognize metapopulation structure by considering larval transport dynamics and pelagic larval sanctuaries

The Spatial Context of “Winning” in MPA Network Design: Location Matters

(First paragraph) Chollett et al. (2017) make the case that a local network of marine protected areas (MPAs) enhances fisheries for Caribbean spiny lobster (Panulirus argus) off the coast of Honduras. However, their simulation focused on one ecoregion where self-recruitment is predicted to be among the highest in the Caribbean (Cowen, Paris, & Srinivasan, 2006). The shallow banks and scattered cays of the Honduran-Nicaraguan Rise, separating the Cayman and Colombian basins, create an obstacle to the powerful southern Caribbean jet (Richardson, 2005), fostering an ideal location for topographically steered eddies and larval retention. Local management,whether based on traditional techniques or MPAs, is indeed likely to be successful in sustaining the lobster population in that region. But the authors go too far in promoting local management based on a best-case scenario where the population is largely self recruiting, and they downplay the need for international cooperation in managing one of the most economically important species in the Caribbean (Kough, Paris, & Butler IV, 2013)

Tiger sharks support the characterization of the world’s largest seagrass ecosystem

Seagrass conservation is critical for mitigating climate change due to the large stocks of carbon they sequester in the seafloor. However, effective conservation and its potential to provide nature-based solutions to climate change is hindered by major uncertainties regarding seagrass extent and distribution. Here, we describe the characterization of the world’s largest seagrass ecosystem, located in The Bahamas. We integrate existing spatial estimates with an updated empirical remote sensing product and perform extensive ground-truthing of seafloor with 2,542 diver surveys across remote sensing tiles. We also leverage seafloor assessments and movement data obtained from instrument-equipped tiger sharks, which have strong fidelity to seagrass ecosystems, to augment and further validate predictions. We report a consensus area of at least 66,000 km and up to 92,000 km of seagrass habitat across The Bahamas Banks. Sediment core analysis of stored organic carbon further confirmed the global relevance of the blue carbon stock in this ecosystem. Data from tiger sharks proved important in supporting mapping and ground-truthing remote sensing estimates. This work provides evidence of major knowledge gaps in the ocean ecosystem, the benefits in partnering with marine animals to address these gaps, and underscores support for rapid protection of oceanic carbon sinks

Increasing the Depth of Current Understanding: Sensitivity Testing of Deep-Sea Larval Dispersal Models for Ecologists

Larval dispersal is an important ecological process of great interest to conservation and the establishment of marine protected areas. Increasing numbers of studies are turning to biophysical models to simulate dispersal patterns, including in the deep-sea, but for many ecologists unassisted by a physical oceanographer, a model can present as a black box. Sensitivity testing offers a means to test the models' abilities and limitations and is a starting point for all modelling efforts. The aim of this study is to illustrate a sensitivity testing process for the unassisted ecologist, through a deep-sea case study example, and demonstrate how sensitivity testing can be used to determine optimal model settings, assess model adequacy, and inform ecological interpretation of model outputs. Five input parameters are tested (timestep of particle simulator (TS), horizontal (HS) and vertical separation (VS) of release points, release frequency (RF), and temporal range (TR) of simulations) using a commonly employed pairing of models. The procedures used are relevant to all marine larval dispersal models. It is shown how the results of these tests can inform the future set up and interpretation of ecological studies in this area. For example, an optimal arrangement of release locations spanning a release area could be deduced; the increased depth range spanned in deep-sea studies may necessitate the stratification of dispersal simulations with different numbers of release locations at different depths; no fewer than 52 releases per year should be used unless biologically informed; three years of simulations chosen based on climatic extremes may provide results with 90% similarity to five years of simulation; and this model setup is not appropriate for simulating rare dispersal events. A step-by-step process, summarising advice on the sensitivity testing procedure, is provided to inform all future unassisted ecologists looking to run a larval dispersal simulation

Population Connectivity and Larval Dispersal of Caribbean Spiny Lobster

Studies of movement, fundamental to most life on earth, become complicated in the ocean. Many marine organisms have a complex lifecycle with a larval phase, giving them vast dispersal potential from powerful ocean currents while obscuring direct observation by virtue of their minute size. These research challenges are beginning to be circumvented through biophysical modeling of larval transport. Modeling simulates the potential pathways of larvae, but not fine-scale spatial movements. Despite their small size, larvae actively participate in their dispersive journey, detecting and responding to environmental cues. Orientation behavior has a great impact on a larva’s survival and journey, and links dispersal and settlement. A thorough examination of larval movement encompasses two scales: investigating small-scale orientation behavior in situ and broad dispersal through modeling. Comprehensive studies spanning a range of spatial scales are rare, thus there is a knowledge gap between modeling dispersal and studying behavioral ecology. This dissertation bridges the gap by addressing both scales of movement for the Caribbean spiny lobster, Panulirus argus, and asking: what are the consequences of larval lobster movement? Caribbean larval movement and connectivity were explored using Lagrangian stochastic modeling of larval dispersal. The first focus was on how variation in modeled biological traits impacted connectivity networks, to provide a template for setting up and evaluating future models of larval dispersal. Any linkage of modeled larvae between two habitat sites was defined as a connection. Connections were rare in time, associated with mesoscale features in both time and space, and vertical migration behavior increased the stability of connections. Next a dispersal model was parameterized, validated with observed average monthly settlement at multiple sites, and used to determine the probabilistic larval connectivity of lobster; translating connectivity into fisheries management strategy. The majority of larval exchanges cross international boundaries, and management scenarios focused on international exchange yielded the most settlement potential. However, self-recruitment still dominated in some areas. Management scenarios focused on preserving connectivity from self-recruitment caused a near universal increase in modeled larval settlement across the Caribbean. Simulations including behavior and realistic spawning biology performed best when compared with empirical data. Modeled pelagic nurseries were identified that entrained lobster larvae across age classes, and may be important features for conservation. Previous studies suggest that as a larva moves towards appropriate settlement habitat, it is exposed to environmental cues including sound, odor, pressure, and light. If, when, and how a settling larva integrates this information to influence its journey remains a mystery. The Drifting In Situ Chamber (DISC) allows glimpses into this process; while imbedded in the ocean current it simultaneously observes the environment, and quantifies the orientation behavior of larvae. This study deployed this new instrumentation in a novel manner, investigating the orientation behavior preceding settlement of postlarval lobsters in situ and nocturnally for the first time. Postlarvae oriented differently relative to the tide. During ebb tide postlarvae oriented using partial compensation into the current and towards the shore, potentially facilitating transport towards settlement habitat. Postlarvae may orient using the wind while at the surface, using a seabreeze as a compass to swim towards settlement habitat. Investigating the specific movement patterns during settlement and the far-flung dispersal of a species throughout its range gives this study a comprehensive examination of marine larval movement ecology over multiple spaciotemporal scales. The dynamics of spiny lobster dispersal throughout the Caribbean are necessary information for managing an internationally important fishery. Understanding the cues that guide the postlarvae of lobster, and likely a broad range of other species, into settlement habitat is important to better conserve nursery habitats.</p

The influence of spawning periodicity on population connectivity

Many coral reef populations exist as discrete habitat patches linked through larval dispersal into a larger network. On these reefs, organisms spawn periodically and release propagules over a range of frequencies. Biophysical models of larval transport examine marine networks, yet particle release frequency needs careful consideration. We describe the time between sequential spawning events as the release interval and define any linkage of modeled larvae between two habitat sites as a connection. We investigate how changing the release interval affects the connectivity networks of three Caribbean species with low- to high-dispersal potential and swimming behavior. We find that spawning periodicity controls the number and persistence of network connections. Further, larval vertical movement behavior stabilizes the network, significantly increasing connections and connection persistence. This work demonstrates the impact of release interval on connectivity networks and underscores including larval behavior with realistic spawning periodicity in biophysical models of larval transport

First evidence of fish larvae producing sounds

The acoustic ecology of marine fishes has traditionally focused on adults, while overlooking the early life-history stages. Here, we document the first acoustic recordings of pre-settlement stage grey snapper larvae ( Lutjanus griseus ). Through a combination of in situ and unprovoked laboratory recordings, we found that L. griseus larvae are acoustically active during the night, producing ‘knock’ and ‘growl’ sounds that are spectrally and temporally similar to those of adults. While the exact function and physiological mechanisms of sound production in fish larvae are unknown, we suggest that these sounds may enable snapper larvae to maintain group cohesion at night when visual cues are reduced

Dates and locations of Callinectes blue crab samples from the coastal Atlantic waters of north and south America, Gulf of Mexico and Caribbean from Massachusetts to Uruguay from 2017 through 2019

Dataset: blue crab samplesDates and locations of Callinectes blue crab samples from the coastal Atlantic waters of north and south America, Gulf of Mexico and Caribbean from Massachusetts to Uruguay from 2017 through 2019. Crab populations sampled using methods available to collaborating scientists, managers, and fishermen, as listed in the table. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/785930NSF Division of Ocean Sciences (NSF OCE) OCE-1658466, NSF Division of Ocean Sciences (NSF OCE) OCE-1658396, NSF Division of Ocean Sciences (NSF OCE) OCE-165838