Temporal variation in food limitation in larvae of the sand dollar Dendraster excentricus

Rates of development of the feeding larvae of marine invertebrates may often be limited by inadequate food, extending the length of the larval period and increasing overall larval mortality. A better understanding of the frequency and importance of this phenomenon requires knowledge of the food concentration below which larvae are limited, and above which they are not, as well as estimates of how strongly food supply affects length of the planktonic period. We addressed these issues using larvae of the sand dollar Dendraster excentricus as a model and chl a concentration as a metric of food abundance. We reared larvae in natural seawater collected from coastal southern California (USA), as well as in reduced and supplemented food treatments created from this natural seawater, 6 times from 2017 to 2019 to take advantage of temporal variation in chl a concentration. Larvae showed morphological responses indicative of low food in nature in only 1 of 6 experiments and showed delayed time to 50% metamorphic competence in 2 of 6 experiments. Larvae appeared to be food limited below chl a concentrations of similar to 2.4-3.0 mu g l(-1), but developed at maximal rates at higher food concentrations. Low natural food supplies delayed time to 50% competence by up to 1.25 d. An 11 yr record of chl a concentration in waters of coastal southern California suggests that larvae of D. excentricus are likely food limited in developmental rate throughout much of the year except for late winter to late spring.

Automated summary

Experimental findings demonstrate that sand dollar larvae are constrained by food limitation, with slower developmental rates observed at low food concentrations but maximized rates at higher levels. Variations in chlorophyll a concentration throughout the year impact larval development rates.