The interplay between mangroves and saltmarshes at the temperate to subtropical transition in Florida results in dramatic changes to the appearance of the coastal landscape. In the 1980s, freezes killed entire mangrove forests dominated by black mangroves, Avicennia germinans (L.). Following the freezes, saltmarshes dominated by smooth cordgrass, Spartina alterniflora Loisel, revegetated the intertidal zone. After a decade of mild winters, however, mangroves are beginning to reclaim the area. The rate of mangrove expansion was determined by comparing aerial photography (change from 1995 to 1999), and from monitoring transects (over a 3 year period) on three of the Cedar Keys, Florida (Lat. 29°08¢). The rate of mangrove expansion varied among islands, and the mechanism of expansion ranged from propaguletrapping by saltmarshes along the edges of mangrove clumps to widespread dispersal and growth of existing or newly imported propagules. A freeze occurred during the study, which may have set back mangrove expansion by defoliating mangrove trees and resetting mangrove reproduction. Mangrove expansion was projected to take 20-30 years for complete seedling cover. Given the possibility of global climate change and its potential influence on the distribution of coastal vegetation, the timeframes and implications to coastal wetland ecosystems involved in this regular interplay will provide valuable baseline information for future studies.

Understanding how endangered marine species rely on coastal habitats is vital for population recovery planning. The smalltooth sawfish (Pristis pectinata) is one of several critically endangered sawfishes worldwide known to use estuaries and rivers during their early life history. In a Florida estuary designated as critical habitat by the USA government, juveniles were monitored to characterise seasonality, recruitment, and habitat use. Stretched total length ranged from 671 to 2172 mm (n = 137, mean = 1248 mm). Sawfish were captured year round. Captures of neonates with embryonic rostral sheaths allowed refinement of the size at birth (671–812 mm) and confirmed a protracted timing of parturition (November–July), which peaked between April and May. Although sampling occurred throughout the estuary, five locations had the greatest catch rates. Most juvenile sawfish had an affinity for water <1 m deep, water >30°C, dissolved oxygen >6 mg L–1, and salinity between 18 and 30. Greater catch rates for sawfish >1 year old were associated with shoreline habitats with overhanging vegetation such as mangroves. These results detail habitat use within a recognised nursery that can be used for conservation of the first endangered marine fish species in the USA.

No abstract

Tropicalization is a term used to describe the transformation of temperate ecosystems by poleward-moving tropical organisms in response to warming temperatures. In North America, decreases in the frequency and intensity of extreme winter cold events are expected to allow the poleward range expansion of many cold-sensitive tropical organisms, sometimes at the expense of temperate organisms. Although ecologists have long noted the critical ecological role of winter cold temperature extremes in tropicaltemperate transition zones, the ecological effects of extreme cold events have been understudied, and the influence of warming winter temperatures has too often been left out of climate change vulnerability assessments. Here, we examine the influence of extreme cold events on the northward range limits of a diverse group of tropical organisms, including terrestrial plants, coastal wetland plants, coastal fishes, sea turtles, terrestrial reptiles, amphibians, manatees, and insects. For these organisms, extreme This article has been contributed to by US Government employees and their work is in the public domain in the USA.