Newly hatched lobster larvae live in the upper waters of the sea. They molt several times into an adult-looking postlarval stage, settle to the sea bottom, and become tiny juveniles that must hide in sheltered burrows. Along the southern two-thirds of coastal Maine, many of these juveniles settle in the lower intertidal rockweed zone. There are rare, anecdotal reports of this behaviour in Maine waters adjacent to New Brunswick and in Charlotte County. However, the extent of juvenile lobster utilization of the extensive rockweed regions in southern New Brunswickis unknown. Because of the vital importance of lobsters and rockweed to the economy of southern New Brunswick, the Huntsman Marine Science Centre recently undertook a study to establish whether the intertidal rockweed regions in southern New Brunswick provide nursery habitat for juvenile lobsters. Funding for the study was provided by New Brunswick’s Wildlife Trust Fund (Department of Natural Resources and Energy, NB Wildlife Council) and Total Development Fund (Department of Agriculture, Aquaculture and Fisheries). Sampling sites were coordinated with Acadian Seaplants Limited.
Sampling sites included locations inside and outside Passamaquoddy Bay, including two sites known for presence of recently settled juvenile lobsters in subtidal waters near shore. Varied environments were examined to compare to observations in Maine. The timeframe was August to October, which includes the predicted period of highest juvenile lobster abundance. During the lowest ebb tides, systematic methods plus intensive spot checking were employed throughout the intertidal zone.
Despite the abundance of apparently suitable habitat for intertidal juvenile lobsters in southern New Brunswick, no juvenile lobsters were observed. Tiny to adult green crabs were present to abundant at all sites. Observations of the smallest green crabs indicate that the smallest of lobsters would have been noted had they been present. Thus, though intertidal juvenile lobsters are a common occurrence in Maine southward, apparently they occur only rarely on New Brunswick’s Fundy shore. Their absence was not linked to wave exposure or inner versus outer coast location. Since settled postlarvae and juveniles remain in their burrows for one to two years, in southern New Brunswick, intertidal individuals would be exposed to potentially lethal temperatures on winter ebb tides. This may explain the virtual absence of 1+ year olds in southern New Brunswick intertidal waters during ebb tide, but does not explain the absence of newly settled postlarvae when temperatures appear to be suitable. Green crabs were present to abundant in this and other studies. Intertidal green crab predation may limit survival of recently settled and young lobsters, but their common subtidalco-occurrencein New Brunswick and intertidal co-occurrence further south contradicts this limitation.
Juvenile lobster presence in the subtidal zone near shore is well known in this region. Also, in another study, juvenile and adult lobsters moved into the intertidal zone of Hardwood Island, Passamaquoddy Bay, on the flood tide where we commonly caught them in experimental fish traps. In a future study, flood tide use of the intertidal zone by lobsters of all sizes will be examined. Such information is necessary to evaluate potential unanticipated threats to lobsters in our waters such as rockweed harvesting and shoreline modification.