Residency and reproductive patterns of the green porcelain crab, Petrolisthes armatus, on an intertidal oyster reef in its non-native range

Abstract

The green porcelain crab Petrolisthes armatus is an abundant invader on intertidal oyster reefs along the southeastern coast of the United States. Its range expansion appears to be thermally limited and is predicted to shift poleward as water temperatures rise. Little is known about how P. armatus' seasonal residency patterns affect its reproductive potential near its northern range limit. To study these factors, P. armatus was collected every two weeks over a 20-month period (April 2017 to November 2018) on an intertidal oyster reef within its non-native range in Charleston, SC. Crab abundance, size, sex, and ovigery status were recorded. In addition, a laboratory experiment was conducted to determine the time elapsed between broods for large vs. small adult females. Petrolisthes armatus abundances varied seasonally and were highest in the summers of both years. Adults were collected in April after a mild winter (2017), indicating overwintering occurred, but after a harsh winter (2018), no crabs were collected on the reef the following spring, with adults first collected in July. Peak ovigery rates reached 95% of adult female crabs in some summer months. Juvenile recruits matured and contributed to the reproductive population 6–8 weeks after first being collected in the intertidal oyster habitat. In the laboratory experiment, the median time between broods was 6 days (range 2–22 days). Females were observed with new broods immediately post-molt and also several days following their molt, suggesting mating occurs for females in intermolt and post-molt states. Study results indicate that overwintering success affects the timing of the start of the reproductive season, its duration, and total annual brood production. The laboratory observations suggest rapid sequential brood production occurs for this species in the non-native range. Brood production rates and evidence that females mate in intermolt and post-molt states are new information for this species and are consistent with previous observations of high reproductive output in the non-native range. Further poleward range expansion seems likely, in part due to high reproductive output and rapid recovery following harsh winters.