Extended parental care, where parents provide for fully developed juveniles, is an uncommon reproductive strategy in the marine environment. The reproductive biology of three amphipod species that engage in extended parental care was examined in Lowes Cove in the Damariscotta River Estuary, Maine, USA.

The amphipod habitat at and just below MLW was characterized by dense microphytobenthos populations, large numbers of decapod predators during the summer and fall, and macrofauna organisms that predominantly feed below the sediment surface. In fall and spring, females of the filter-feeding species Leptocheirus pinguis hosted several consecutive broods in their burrows. Large numbers of juveniles were born in spring/early summer, without subsequent increase in abundance, probably due to subadult emigration during summer and fall. Females of the deposit-feeding Casco bigelowi produced a single brood in September/October, and hosted growing offspring in their burrows until December/January. Throughout the year, high percentages (60-100%) of female Dyopedos monacanthus were reproductive, but only during winter/early spring did large females occur in the population and successfully produce great numbers of offspring, causing a large increase in D. monacanthus abundance.

D. monacanthus provided care for their offspring for about 15 days, L. pinguis for about 50 days and C. bigelowi for about 100 days. Experimental studies showed that extended parental care improves the survival chances of small juveniles of all three amphipods by protecting them from predation. C. bigelowi, the species with the longest duration of extended parental care, was highly infested with gill parasites Cothurnia sp. Juveniles of highly infested females were also infested while juveniles of 'clean' females were not, indicating that parasite transmission can be a consequence of extended parental care.

Juvenile amphipods gain important advantages from extended parental care but availability of resources such as space (and possibly food) limits the potential for long duration of parental care. Estuarine soft-bottoms in the shallow subtidal with high stocks of microphytobenthos guarantee a continual food supply but increasing space requirements of parent-offspring groups become problematic for soft-sediment dwelling amphipods due to the low stability of large burrow systems.