Energetics and Nutrient Cycling

The food webs of sandy beaches and their surf zones are examined through a quantitative consideration of energy flow and nutrient cycling. Major food sources are identified and then food webs evaluated in terms of biomass, production, consumption, and energy flow, beginning with primary food sources and ending with top predators. Three distinct food webs are considered in detail: macrofauna, interstitial fauna, and the microbial loop in surf waters. Clear differences are demonstrated between different beach types: reflective beaches function as interfaces, whereas dissipative beaches function as complex ecosystems. Nutrient cycling is also considered, both in terms of sources of inorganic nutrients and the relative importance of the three food webs in generating nutrients. Stable isotope analysis shows variations in food web structure and diet of consumers with changes in the physical environment and shifts in food supply. Terrestrial subsidies may have more importance than originally thought. Conceptual models are presented of the changes in relative importance in all these elements across the spectrum of beach types.