Microphytobenthic communities of subtidal locations in New Zealand: Taxonomy, biomass, production, and food‐web implications

Abstract

Diatom mats dominated by large sig‐moid, raphid species of the genus Gyrosigma (Naviculaceae) and, in some instances, the tube‐former, Berkeleya rutilans (Naviculaceae) were observed in the semi‐enclosed coastal waters (depths 6–20 m) of Tory Channel, Marlborough Sounds, New Zealand. The latter species, not previously observed in New Zealand, is generally associated with intertidal environments where light intensities are relatively higher than subtidal locations. Its presence imparted a filamentous nature to the mat that may play a role in maintaining the integrity of the sediment/water interface. Sediment chlorophyll a concentrations ranged from c. 20 to 200 mg m‐2. Microphytobenthic (MPB) contributions to the total (benthic + planktonic) chlorophyll a equated to 92, 89, and 84% at depths of 8, 16, and 20 m, respectively. Oxygen production in intact cores often exceeded consumption (e.g., by up to 2.5 mmol m‐2h‐1) under near‐m situ conditions of light (8–30 μmol m‐2 s‐1). The feeding strategies of major components of the benthic macroinvertebrate fauna were used to identify possible pathways for utilisation of MPB production. MPB communities of more exposed subtidal locations in Tasman Bay were generally less dense and comprised of different species dominated by Pleurosigma amara and/or Paralia marina. We conclude that microalgal communities inhabiting the soft sediments in these regions can provide an important contribution to the benthic food web.