Digestive gland inclusion bodies in queen conch (Lobatus gigas) are non-parasitic

Limiting factors for queen conch (Lobatus gigas) reproduction: A simulation-based evaluation

Queen conch are among the most economically, socially, and culturally important fishery resources in the Caribbean. Despite a multitude of fisheries management measures enacted across the region, populations are depleted and failing to recover. It is believed that queen conch are highly susceptible to depensatory processes, impacting reproductive success and contributing to the lack of recovery. We developed a model of reproductive dynamics to evaluate how variations in biological factors such as population density, movement speeds, rest periods between mating events, scent tracking, visual perception of conspecifics, sexual facilitation, and barriers to movement affect reproductive success and overall reproductive output. We compared simulation results to empirical observations of mating and spawning frequencies from conch populations in the central Bahamas and Florida Keys. Our results confirm that low probability of mate finding associated with decreased population density is the primary driver behind observed breeding behavior in the field, but is insufficient to explain observed trends. Specifically, sexual facilitation coupled with differences in movement speeds and ability to perceive conspecifics may explain the observed lack of mating at low densities and differences between mating frequencies in the central Bahamas and Florida Keys, respectively. Our simulations suggest that effective management strategies for queen conch should aim to protect high-density reproductive aggregations and critical breeding habitats.

Laccase and catecholoxidase activities contribute to innate immunity in slipper limpets, Crepidula fornicata

The slipper limpet Crepidula fornicata is an invasive, non-native, marine species found throughout the coastal waters of southern England and Wales, UK. These limpets are considered to blight commercial shellfish banks, notably oysters, yet little is known about their disease-carrying capacity or their immunobiology. To address the latter, we isolated haemolymph (blood) from limpets and tested for the presence of the immune-enzyme phenoloxidase. Invertebrate phenoloxidases produce melanic polymers from simple phenolic substrates, which are deployed in the presence of pathogens because of their potent microbicidal and microbiostatic properties. We used a series of established substrates (e.g., tyrosine, hydroquinone) and inhibitors (e.g., 4-hexylresorcinol, benzoic acid) to target three distinct enzymes: laccase (para-diphenoloxidase), catecholoxidase (ortho-diphenoloxidase) and tyrosinase (monophenoloxidase). We confirmed laccase and catecholoxidase activities and characterised their kinetic properties across temperature and pH gradients (5-70 °C and 5-10, respectively). Crucially, we demonstrated that products derived from such laccase and catecholoxidase activities reduced significantly the numbers of colony-forming units of both Gram-positive and Gram-negative bacteria in vitro. We further screened limpet tissues for signs of melanin using wax histology, and found cells replete with eumelanin-like pigments and lipofuscin in the digestive gland, connective tissues, barrier epithelia and gills. Our data represent the first account of enzyme-based antibacterial defences, notably laccase, in C. fornicata.