Ecology and production of Nebalia sp. (Crustacea : Leptostraca) in a shallow-water seagrass community.

Abstract

Nebalia sp. is an abundant epifaunal crustacean in seagrass meadows at Seven Mile Beach, Western Australia, in water temperatures of 16-27ºC. Its maximum length is 6.0-6.4 mm; females generally reach maturity when 4 mm long and males when 5 mm long. They breed throughout the year, and juveniles comprised 94% of animals sampled (n = 880). Males comprised only 11% of mature animals in field samples, compared with 40% in field chambers and 67% in the stomachs of nocturnal fish predators. Abundance during the year reflected changes in growth rate (0.050-0.088 mm day^-1), mortality rate (0.020-0.069 day^-1) and life span (49-102 days). The annual production of Nebalia sp. in seagrass meadows was estimated at 5.8 g ash-free dry weight (AFDW) m^-2, with a corresponding P :B (production:biomass) ratio of 22.5. Predation is probably the main source of mortality at times of high density of Nebalia sp., and at least three significant fish predators on Nebalia sp. were found. Together with Nebalia sp., small crustaceans with high P:B ratios may have a significant role in secondary production in the seagrass beds at Seven Mile Beach.