A crab swarm at an ecological hotspot: patchiness and population density from AUV observations at a coastal, tropical seamount

Abstract

A research cruise to Hannibal Bank, a seamount and an ecological hotspot in the coastal eastern tropical Pacific Ocean off Panama, explored the zonation, biodiversity, and the ecological processes that contribute to the seamount’s elevated biomass. Here we describe the spatial structure of a benthic anomuran red crab population, using submarine video and autonomous underwater vehicle (AUV) photographs. High density aggregations and a swarm of red crabs were associated with a dense turbid layer 4–10 m above the bottom. The high density aggregations were constrained to 355–385 m water depth over the Northwest flank of the seamount, although the crabs also occurred at lower densities in shallower waters (∼280 m) and in another location of the seamount. The crab aggregations occurred in hypoxic water, with oxygen levels of 0.04 ml/l. Barcoding of Hannibal red crabs, and pelagic red crabs sampled in a mass stranding event in 2015 at a beach in San Diego, California, USA, revealed that the Panamanian and the Californian crabs are likely the same species, Pleuroncodes planipes, and these findings represent an extension of the southern endrange of this species. Measurements along a 1.6 km transect revealed three high density aggregations, with the highest density up to 78 crabs/m2, and that the crabs were patchily distributed. Crab density peaked in the middle of the patch, a density structure similar to that of swarming insects.

Feature discovery and visualization of robot mission data using convolutional autoencoders and Bayesian nonparametric topic models

“…The two models are visualized in Figure 1. We apply each model to image streams from two marine robot missions [25] and present experimental results.…”

Coastal marine ecosystem connectivity: pelagic ocean to kelp forest subsidies

“…, Pineda et al. ). Patches have been observed to span up to 6 km in nearshore waters of <80 m depth, though efforts to estimate patch size have not been comprehensive (Robinson et al.…”

“…Annual stranding is well documented in Mexico, but the species has a wide West coast distribution from Panama to Monterey Bay, California (Longhurst , Pineda et al. ). It is accepted that red crabs in their pelagic life phase move with warm water to California during El Niño years, though rarely have abundances or densities been measured in California waters (Table ).…”

“…Early life phases of red crabs exist in the plankton, followed by an adult life stage (age 2+) that is primarily benthic but includes migrations to the midwater, and a final ❖ www.esajournals.org 6 February 2019 ❖ Volume 10(2) ❖ Article e02602 entirely benthic adult phase (Boyd 1967, Aurioles-Gamboa 1992. Red crab densities can be extremely high in the pelagic environment and occur with a notoriously patchy distribution (Robinson et al 2004, Pineda et al 2016. Patches have been observed to span up to 6 km in nearshore waters of <80 m depth, though efforts to estimate patch size have not been comprehensive (Robinson et al 2004).…”

“…These swarms become especially conspicuous during annual stranding events to shallow water and intertidal beaches that occur in Bahia Magdalena (Baja California, Mexico) during the spring season (the end of crab's reproductive season), and that occasionally occur in southern and central California (Glynn 1961, Aurioles-Gamboa et al 1994, McClatchie et al 2016). Annual stranding is well documented in Mexico, but the species has a wide West coast distribution from Panama to Monterey Bay, California (Longhurst 1967, Pineda et al 2016. It is accepted that red crabs in their pelagic life phase move with warm water to California during El Niño years, though rarely have abundances or densities been measured in California waters (Table 2).…”