Light Limitation within Southern New Zealand Kelp Forest Communities

Abstract

Light is the fundamental driver of primary productivity in the marine environment. Reduced light availability has the potential to alter the distribution, community composition, and productivity of key benthic primary producers, potentially reducing habitat and energy provision to coastal food webs. We compared the underwater light environment of macroalgal dominated shallow subtidal rocky reef habitats on a coastline modified by human activities with a coastline of forested catchments. Key metrics describing the availability of photosynthetically active radiation (PAR) were determined over 295 days and were related to macroalgal depth distribution, community composition, and standing biomass patterns, which were recorded seasonally. Light attenuation was more than twice as high in shallow subtidal zones along the modified coast. Macroalgal biomass was 2–5 times greater within forested sites, and even in shallow water (2m) a significant difference in biomass was observed. Long-term light dose provided the best explanation for differences in observed biomass between modified and forested coasts, with light availability over the study period differing by 60 and 90 mol photons m−2 at 2 and 10 metres, respectively. Higher biomass on the forested coast was driven by the presence of larger individuals rather than species diversity or density. This study suggests that commonly used metrics such as species diversity and density are not as sensitive as direct measures of biomass when detecting the effects of light limitation within macroalgal communities.

Variation of fucoid community metabolism during the tidal cycle: Insights from in situ measurements of seasonal carbon fluxes during emersion and immersion

“…The large changes in GCP measured during the underwater incubation series are consistent with the fluctuation in underwater light availability. However, it would be interesting to reproduce such measurements on different seasons, as underwater light regimes might display substantial seasonal changes (Anthony et al ; Desmond et al ). GCP appears therefore to be a highly fluctuating process when underwater, due to the continuous and rapid changes in light intensity caused by ebbing and rising tides, as suggested by Dring and Lüning ().…”

A kelp with integrity: Macrocystis pyrifera prioritises tissue maintenance in response to nitrogen fertilisation

“…The HOBO sensors recorded light intensity in units of lux and it was necessary to convert these data to photosynthetically active radiation values. Calibration was achieved through simultaneous recording using the HOBO logger and a LI-COR underwater quantum sensor and then appropriate calibration, the full methods of which are described in Desmond et al (2015), who share the same field site as this study. Seawater NO 3 − concentrations were measured five times (once before fertilisation and four times during).…”

Geographic distance, water circulation and environmental conditions shape the biodiversity of Mediterranean rocky coasts

“…Higher concentrations of CDOM dominate the absorption of both visible and blue spectrum UV light in the water column, potentially limiting photosynthetically available radiation to the sublittoral benthos. Modification of the underwater light regime can impact biomass and species richness of macroalgae (Desmond et al 2015), which act as foundation species, providing habitat and hosting complex ecosystem processes to a suite of associated species.…”