Evaluation of remote sensing techniques for monitoring giant kelp populations

Photographs and maps of the floating canopy of the giant kelp, Macrocystis pyrifera, provide an important data source to monitor nearshore water quality in southern California. Declines in water quality related to turbidity from coastal development, ocean discharges, and non-point source runoff have caused reductions in the areal extent of these kelp beds. Historically the kelp beds have been monitored by a variety of methods including small format infrared and color photography. New digital remote sensing instruments combined with geographical information system (GIS) databases offer an efficient method for collecting and analyzing data on changes in kelp bed size and location. SPOT satellite imagery has been found to provide adequate resolution for mapping the larger beds of giant kelp along the California coast. Beds smaller than 10 ha are not resolved well with SPOT imagery and need to be mapped with a resolution greater than the 20 m pixel size provided by the SPOT multispectral imagery. Imagery from a prototype of the Positive Systems ADAR system, an airplane mounted multispectral video sensor, provided a spatial resolution of 2.3 m in 4 spectral bands. ADAR imagery taken on 2 October 1991 of the San Onofre Kelp Bed in northern San Diego County showed 39% more kelp than small format color infrared photography made during the same time period.     

Recolonization and restoration of upper intertidal Fucus gardneri (Fucales,Phaeophyta) following the Exxon Valdez oil spill

The Exxon Valdez oil spill in March 1989 and subsequent cleanup caused injury to intertidal Fucus gardneri populations especially in the upper intertidal. A survey in 1994 in Prince William Sound, Alaska showed that the upper boundary of Fucus populations at oiled sites was still an average of 0.4 m lower than the upper boundary at unoiled sites.Restoration of severely damaged Fucus populations was started on a small-scale at a heavily oiled rocky site in Herring Bay, Prince William Sound. Experiments employed mats of biodegradable erosion control fabric to act as a substratum for Fucus germlings and to protect germlings from heat and desiccation stress. A series of plots was covered with mats made from a resilient coconut-fiber fabric in June 1993. Half of the mats were inoculated with Fucus zygotes. A series of uncovered control plots was also monitored. There was no enhancement of Fucus recruitment on the rock surfaces under the mats. Dense populations of Fucus developed on the surface of all of the mats by the summer of 1994. The natural rock surfaces in the control plots, both inoculated and not, were barren of macroscopic algal cover. By September 1994, the juvenile thalli on the mats were approximately 2 cm in length. Inoculating the mats had an effect only in the upper region of the intertidal. It is expected that the thalli will become fertile during the 1995 season. These thalli may serve as a source of embryos to enhance the recovery of new Fucus populations in this high intertidal area.     

CRITICAL IRRADIANCE LEVELS AND THE INTERACTIVE EFFECTS OF QUANTUM IRRADIANCE AND DOSE ON GAMETOGENESIS IN THE GIANT KELP,MACROCYSTIS PYRIFERA1

Gametophytes of Macrocystis pyrifera (L.) C. Ag. were cultured under a series of quantum irradiances in three photoperiod regimes. The quantum irradiances in each photoperiod were adjusted to provide equal daily irradiation dosages between photoperiods which allowed a critical examination of the interactions between quantum irradiance and quantum dose in determining gametophyte fertility. The lowest quantum irradiance which stimulated gametogenesis in more than 50% of the female gametophytes was 5 μE·m^?2·s^?1. The saturating irradiance was ca. 10 μE·m^?2·s^?1 at photoperiods of 12 h or greater. In terms of daily quantum dose, the lowest dose at which greater than 50% gametogenesis occurred was 0.2 E·m^?2·d^?1. However, this critical quantum dose was higher (0.4 E·m^?2·d^?1) when instantaneous irradiances were less than 5 μE·m^?2·s^?1. The saturation quantum dose was also affected by the rate at which the quantum dose was received and varied from 0.4 to 0.8 E·m^?2·d^?1. Gametophytes in all three photoperiods reached 100% fertility at quantum irradiances above 5 μE·m^?2·s^?1. Photoperiod effects were small and could be accounted for by quantum dosage effects.     

155 Mapping Floating Kelp Beds in Alaska With Remote Sensing

The commercial harvest of floating kelps has promise as a business opportunity that could be especially valuable for small communities in southeast Alaska. The giant kelp, Macrocystis, is harvested mainly for the commercial herring roe‐on‐kelp harvest in Alaska. In addition, in southeast Alaska the two other species of floating kelps, Nereocystis luetkeana and Alaria fistulosa, have been commercially harvested since 1992 for use as agrochemicals by the Alaska KelpCo. The continued existence of this company and others that may wish to harvest seaweeds on a commercial basis is threatened by the lack of a kelp harvest management system in Alaska. The objective of this research is to develop a reliable and cost effective method for estimating the aerial extent and the standing crop biomass of the floating kelps in SE Alaska. We are employing an aerial multispectral imaging system that can be flown at varying altitudes to achieve spatial resolutions ranging from 0.5 to 2 meters. We are investigating whether the three species have unique spectral or textural characteristics in the multispectral imagery that can be used to differentiate the populations. The end products for this project will be kelp resource maps that delineate the spatial extent and biomass of kelp populations within the beds and a methodology for assessing kelp beds with mixed species composition. These products will find use by resource managers such as the Alaska Department of Fish and Game and the Department of Natural Resources.     

A remote sensing approach to estimating harvestable kelp biomass

Regulations of the Alaska Department of Fish and Game require that all fisheries in the state have a harvest management plan. In southeast Alaska two species of floating kelps, Nereocystis luetkeana and Alaria fistulosa, have been commercially harvested since 1992 for use as agrochemicals by the Alaska Kelp Company. However, there is currently no harvest management plan for this fishery. The lack of a formalized management plan is one factor that has kept the kelp industry from expanding in the state. We have employed an aerial digital multispectral imaging system (DMSC) calibrated with ground truthing for performing such an assessment. The system can be flown at varying altitudes to achieve spatial resolutions ranging from 0.5 to 2 m. Rapid ground truthing techniques were developed using morphometric measurements to predict biomass. Analysis of the DMSC imagery showed that good correlations could be developed between the multispectral imagery and kelp biomass estimates collected at the ground-truth sites. Repeatable estimates of kelp bed area derived from the multispectral imagery could be made at varying tidal levels. However, broad scale maps of kelp biomass suitable for estimating harvest rates could not be made at different tide levels. Multispectral imagery suitable for this purpose must be collected at a standard tidal level.