Seagrass beds provide habitat for crabs, shrimps and fish in two estuaries on the South Island of New Zealand

Abstract

O_LISeagrasses are marine angiosperms that potentially provide habitat for crabs, shrimps and fish. However, these types of data are lacking for the seagrass species (Zostera muelleri/rimur[e]hia) that inhabit intertidal estuaries on the South Island of New Zealand. C_LIO_LIAbundances of crabs, shrimps and fish were therefore quantified from 361 non-destructive seine tows done in seagrass beds and bare mudflats in Duvauchelle bay and two sites in the Avon-Heathcote/Ihutai estuary between October 2019 and February 2020. C_LIO_LIA total of 2549 crabs, 5824 shrimps and 1149 fish (75% were juvenile flounders) were identified and counted in the seine-net and immediately released back in healthy condition to the exact location from where they were caught. C_LIO_LIOnly few seagrass leaves were caught in the net and these leaves may have been previously uprooted drift fragments. The instant catch-and-release methodology therefore leaves, literally, nothing but a footprint. C_LIO_LIMore fish taxa, including two species of pipefish, were found in seagrass beds in Duvauchelle bay than in the Avon-Heathcote estuary. Fish (minus juvenile flounders) were also more abundant in these seagrass beds. Furthermore, juvenile flounders and shrimps were more abundant in Duvauchelle bay compared to the Avon-Heathcote estuary, but were found in similar abundances in seagrass beds and on bare flats. C_LIO_LIIt is possible that more fish were found in Duvauchelle seagrass beds because these beds have adjacent deeper areas, and may have high connectivity to seagrass beds in nearby bays. This hypothesis should be tested by sampling more seagrass beds in different types of estuaries and bays. C_LIO_LIBy contrast, crabs were more abundant in the Avon-Heathcote estuary, where spider crabs were most abundant in the seagrass beds, but other crabs were found in similar abundances in seagrass beds and bare habitat. We hypothesize that crab abundances were higher in the Avon-Heathcote estuary because of lower fish predation pressure and/or larger populations of prey like mollusc and polychaetes. C_LIO_LIOur results suggests that (a) superficially similar Zostera beds in relatively close proximity can provide very different habitat values for fish and crustaceans, (b) seagrass beds with higher diversity and abundances of fish may be prioritized in conservation and management (assuming other important ecosystem functions are similar between beds), and (c) that pipefish may be useful indicator organisms, representing healthy, extensive, dense and connected seagrass beds. C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=177 SRC="FIGDIR/small/120055v1_ufig1.gif" ALT="Figure 1"> View larger version (111K): org.highwire.dtl.DTLVardef@1c21731org.highwire.dtl.DTLVardef@180c521org.highwire.dtl.DTLVardef@10e2875org.highwire.dtl.DTLVardef@824c21_HPS_FORMAT_FIGEXP M_FIG C_FIG