Mesoscale oceanographic features drive divergent patterns in connectivity for co‐occurring estuarine portunid crabs

Abstract

Larval dispersal and connectivity have important implications for fisheries management, especially for species with life cycles influenced by ocean boundary currents.Giant Mud Crab (Scylla serrata) and Blue Swimmer Crab (Portunus armatus) are two estuarine portunid crabs (Family: Portunidae) that support significant commercial and recreational harvest in eastern Australia. Giant Mud Crab migrate to coastal waters to spawn, and while Blue Swimmer Crab spawn primarily within estuaries they occasionally migrate to coastal waters to spawn, followed by larval dispersal in the East Australian Current (EAC). Here, we coupled a high-resolution oceanographic model with a Lagrangian particle tracking framework to simulate larval dispersal and determine the extent of population connectivity in this region. Our simulations indicate broad-scale connectivity ($40-400 km), characterised by high inter-estuary connectivity. Overall, our results suggest a north-to-south source-sink structure for both species, with contributions of particles from the north ranging from 51% to 99%.Recruitment to a given estuary is dependent on the proximity of mesoscale oceanographic features of the EAC. Most notably, the EAC separation acts as a barrier to recruitment between spawning and settlement to the north/south of this region. This significantly limits interjurisdictional connectivity for these species, especially Blue Swimmer Crab, likely due to a shorter pelagic larval duration than Giant Mud Crab.Our results provide evidence to inform the assessment and management of these species.

Patterns in abundance, size and space‐use of Giant Mud Crab (Scylla serrata) in a temperate marine protected area

“…In temperate estuaries of eastern Australia, larger portunid crabs produce more eggs per batch (e.g., Blue Swimmer Crab, Portunus armatus ; Nolan et al, 2021) which suggests that no‐take zones may enhance reproductive output in Port Stephens, especially given that crab space‐use was constrained to an area much smaller than no‐take zones (meaning crabs were unlikely to leave these areas during routine behaviours; Table 1). If this is the case, protection in Port Stephens may enhance larval supply within the estuary (i.e., self‐recruitment) and estuaries to the south (e.g., Hunter River, Hawkesbury River), given the northward coastal migration of mature females (Hewitt, Niella, et al, 2022) and the predominantly southward flow of the East Australian Current (Hewitt, Schilling, et al, 2022). This interpretation is contingent on two assumptions.…”

“…Stephens may enhance larval supply within the estuary (i.e., selfrecruitment) and estuaries to the south (e.g., Hunter River, Hawkesbury River), given the northward coastal migration of mature females (Hewitt, Niella, et al, 2022) and the predominantly southward flow of the East Australian Current (Hewitt, Schilling, et al, 2022). This interpretation is contingent on two assumptions.…”

A warming western boundary current increases the prevalence of commercially disruptive parasites in broadbill swordfish

“…Key outstanding gaps to improve a mechanistic understanding of progression from infection to jellymeat include resolving infection dynamics, such as understanding the (i) life cycle of the parasite, (ii) swordfish immune response and susceptibility to infection at different life stages, (iii) movement ecology and spawning dynamics of swordfish in the ETBF and (iv) distribution of both the actinospore and myxospore stages of the parasite. Once these have been resolved, coupled epidemiological–oceanographic models may yield promise for understanding the dispersal characteristics of spores throughout the fishery and potential infection hotspots, since physical ocean models have already been developed for the ETBF region and applied to fish and crustacean larval transport dynamics (Hewitt et al, 2022; Kerry & Roughan, 2020; Schilling et al, 2022; Wijeratne et al, 2018). Mechanistic, process‐based models that quantify relationships between climate and pathogen dynamics—integrating field and experimental data—have already yielded promising results in other host–pathogen systems in terms of understanding physiological, demographic and evolutionary responses to climate change (Jiranek et al, 2023; Rohr et al, 2011).…”

Crabs ride the tide: incoming tides promote foraging of Giant Mud Crab (Scylla serrata)

“…Conversely, at greater temporal scales (e.g., seasonal) differences in movement have been observed. For example, mature female Giant Mud Crab typically migrate to oceanic waters to spawn [39,40,53], facilitating the broad-scale dispersal of larvae [104] which may explain the detection of a tagged female ~ 150 km north of our array in the coastal ocean. While males are typically thought to remain within estuaries, there have been a few examples of broad-scale migrations reported [41].…”