Spatial and temporal patterns of decapod larvae in the Strait of Georgia, British Columbia

The abundance and dispersal of meroplankton play a fundamental role in determining spatial and temporal patterns of benthic organisms in marine systems. Field studies that quantify abundance patterns are heavily dependent on, and often limited by, proper identification resources. In the present study, diagnostic features of laboratory reared Glebocarcinus oregonensis zoeae were described to facilitate identification of cancrid zoeae in the Salish Sea. The larval community was then described from two surveys spanning the Strait of Georgia that were conducted in consecutive spring seasons in 2009 and 2010. Interannual variability in larval abundance, diversity (Shannon index), and similarity between revisited stations was quantified to compare assemblages between years. Finally, the species- and stage-specific abundance and horizontal distribution of three cancrid species including Cancer productus, G. oregonensis, and Metacarcinus magister, were described from surveys conducted in consecutive spring and summer seasons in 2010.

The zoeae of G. oregonensis exhibited much shorter and acutely angled lateral exospines on the telson and much longer posterolateral abdominal spines than other local cancrid species. Other morphological features used to identify G. oregonensis in previous studies were found to be misleading. In both years the reptantian decapod larval community consisted of at least 10 families but was dominated by cancrid larvae (approximately 80 % of total larval abundance). Although the relative abundance of the different families was generally consistent with reproductive potential and timing, overall measures of larval abundance, diversity, and similarity between samples were significantly different between years. Large variation in total abundance, possibly caused by heavy mortality in 2009 or increased reproductive output in 2010, could result in a large variation in the year class strength of adult crab populations. Spatial patterns of both total larval abundance and diversity also contrasted between years, and although they were sometimes moderately correlated with environmental variables, these correlations were found not to be consistent enough to function as good predictors of total larval abundance (all species and stages combined). Larvae of C. productus were apparently released later than those of G. oregonensis and M. magister. Larval distributions of these cancrid species did not change dramatically from stage to stage, indicating that transport did not occur rapidly. The distribution of larvae and environmental variables indicated the potential for nearshore retention and/or alongshore larval transport within the central Strait's eastern margin and cross-strait transport in the southern region. Fresh water input from the Fraser River appeared to play an important role in shaping larval distributions, especially for M. magister.